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we present initial results from the cosmic ultraviolet baryon survey (cubs). cubs is designed to map diffuse baryonic structures at redshift z ≲ 1 using absorption-line spectroscopy of 15 uv-bright qsos with matching deep galaxy survey data. cubs qsos are selected based on their nuv brightness to avoid biases against the presence of intervening lyman limit systems (llss) at zabs < 1. we report five new llss of $\log \, n({\mathrm{ h} \,{\small i}})/{{\rm cm^{-2}}}\gtrsim 17.2$ over a total redshift survey path-length of $\delta \, z_{\mathrm{ ll}}=9.3$ , and a number density of $n(z)=0.43_{-0.18}^{+0.26}$ . considering all absorbers with $\log \, n({{\mathrm{ h} \,{\small i}}})/{{\rm cm^{-2}}}\gt 16.5$ leads to $n(z)=1.08_{-0.25}^{+0.31}$ at zabs < 1. all llss exhibit a multicomponent structure and associated metal transitions from multiple ionization states such as c ii, c iii, mg ii, si ii, si iii, and o vi absorption. differential chemical enrichment levels as well as ionization states are directly observed across individual components in three llss. we present deep galaxy survey data obtained using the vlt-muse integral field spectrograph and the magellan telescopes, reaching sensitivities necessary for detecting galaxies fainter than $0.1\, l_*$ at d ≲ 300 physical kpc (pkpc) in all five fields. a diverse range of galaxy properties is seen around these llss, from a low-mass dwarf galaxy pair, a co-rotating gaseous halo/disc, a star-forming galaxy, a massive quiescent galaxy, to a galaxy group. the closest galaxies have projected distances ranging from d = 15 to 72 pkpc and intrinsic luminosities from ${\approx} 0.01\, l_*$ to ${\approx} 3\, l_*$ . our study shows that llss originate in a variety of galaxy environments and trace gaseous structures with a broad range of metallicities. | the cosmic ultraviolet baryon survey (cubs) - i. overview and the diverse environments of lyman limit systems at z < 1 |
we present basic data and modeling for a survey of the cool, photoionized circumgalactic medium (cgm) of low-redshift galaxies using far-uv qso absorption-line probes. this survey consists of “targeted” and “serendipitous” cgm subsamples, originally described in stocke et al. (paper i). the targeted subsample probes low-luminosity, late-type galaxies at z< 0.02 with small impact parameters (< ρ > =71 kpc), and the serendipitous subsample probes higher luminosity galaxies at z≲ 0.2 with larger impact parameters (< ρ > =222 kpc). hubble space telescope and fuse uv spectroscopy of the absorbers and basic data for the associated galaxies, derived from ground-based imaging and spectroscopy, are presented. we find broad agreement with the cos-halos results, but our sample shows no evidence for changing ionization parameter or hydrogen density with distance from the cgm host galaxy, probably because the cos-halos survey probes the cgm at smaller impact parameters. we find at least two passive galaxies with h i and metal-line absorption, confirming the intriguing cos-halos result that galaxies sometimes have cool gas halos despite no on-going star formation. using a new methodology for fitting h i absorption complexes, we confirm the cgm cool gas mass of paper i, but this value is significantly smaller than that found by the cos-halos survey. we trace much of this difference to the specific values of the low-z metagalactic ionization rate assumed. after accounting for this difference, a best-value for the cgm cool gas mass is found by combining the results of both surveys to obtain {log}(m/{m}⊙ )=10.5+/- 0.3, or ∼30% of the total baryon reservoir of an l≥slant {l}* , star-forming galaxy. based on observations with the nasa/esa hubble space telescope, obtained at the space telescope science institute, which is operated by aura, inc., under nasa contract nas 5-26555. | characterizing the circumgalactic medium of nearby galaxies with hst/cos and hst/stis absorption-line spectroscopy. ii. methods and models |
the recent measurement of an ionising mean free path $\lambda_{\text{mfp}}<1$ pmpc at $z=6$ challenges our understanding of the small-scale structure of the intergalactic medium (igm) at the end of reionisation. we introduce a new method to constrain \mfp at $z=6$ by using lower limits on the individual free paths of ionisation around quasars. lyman-limit absorbers with a density sufficient to halt ionising photons produce strong absorption in the 6 lowest-energy lyman transitions, in the absence of which a robust lower limit can be placed on the individual free path. applying this method to a set of $26$ quasars at $5.5<z<6.5$, we find that $80\%$ of bright quasars ($m_{1450}<-26.5$) require individual free paths larger than $2$ pmpc. we model the relation between opacity $\kappa$ and photo-ionisation rate $\gamma$ via the parameter $\xi$ such that $\kappa\propto\gamma^{-\xi}$, and pose joint limits on \mfp and $\xi$. for the nominal value of $\xi=2/3$, we constrain $\lambda_{\text{mfp}}>0.31 \ (0.18)$ pmpc at $2\sigma \ (3\sigma)$: a much tighter lower bound than obtained through traditional stacking methods. our constraints get significantly stronger for lower values of $\xi$. new constraints on \mfp and $\xi$ are crucial to our understanding of the reionisation-era igm. | constraints on the mean free path of ionising photons at $z\\sim6$ using limits on individual free paths |
outflows driven by active galactic nuclei (agns) are often invoked as agents of the long-sought agn feedback. yet, characterizing and quantifying the impact on their host galaxies has been challenging. we present gemini multi-object spectrograph integral field unit data of six local (z \lt 0.1) and luminous (l{}[{{o}{{iii}}]}\gt {10}42 erg s-1) type 2 agns. in the first of a series of papers, we investigate the kinematics and constrain the size of the outflows. the ionized gas kinematics can be described as a superposition of a gravitational component that follows the stellar motion and an outflow-driven component that shows large velocity (up to 600 km s-1) and large velocity dispersion (up to 800 km s-1). using the spatially resolved measurements of the gas, we kinematically measure the size of the outflow, which is found to be between 1.3 and 2.1 kpc. owing to the lack of a detailed kinematic analysis, previous outflow studies likely overestimate their size by up to more than a factor of two, depending on how the size is estimated and whether the [o iii] or hα emission line is used. the relatively small size of the outflows for all six of our objects casts doubts on their potency as a mechanism for negative agn feedback. | unraveling the complex structure of agn-driven outflows. i. kinematics and sizes |
we present a self-consistent prediction from a large-scale cosmological simulation for the population of “wandering” supermassive black holes (smbhs) of mass greater than 106 m ⊙ on long-lived, kpc-scale orbits within milky way (mw)-mass galaxies. we extract a sample of mw-mass halos from the romulus25 cosmological simulation, which is uniquely able to capture the orbital evolution of smbhs during and following galaxy mergers. we predict that such halos, regardless of recent merger history or morphology, host an average of 5.1 ± 3.3 smbhs, including their central black hole, within 10 kpc from the galactic center and an average of 12.2 ± 8.4 smbhs total within their virial radius, not counting those in satellite halos. wandering smbhs exist within their host galaxies for several gyr, often accreted by their host halo in the early universe. we find, with >4σ significance, that wandering smbhs are preferentially found outside of galactic disks. | wandering supermassive black holes in milky-way-mass halos |
we present an x-ray point-source catalogue from the xmm-large scale structure (xmm-lss) survey region, one of the xmm-spitzer extragalactic representative volume survey (xmm-servs) fields. we target the xmm-lss region with 1.3 ms of new xmm-newton ao-15 observations, transforming the archival x-ray coverage in this region into a 5.3 deg2 contiguous field with uniform x-ray coverage totaling 2.7 ms of flare-filtered exposure, with a 46 ks median pn exposure time. we provide an x-ray catalogue of 5242 sources detected in the soft (0.5-2 kev), hard (2-10 kev), and/or full (0.5-10 kev) bands with a 1 per cent expected spurious fraction determined from simulations. a total of 2381 new x-ray sources are detected compared to previous source catalogues in the same area. our survey has flux limits of 1.7 × 10-15, 1.3 × 10-14, and 6.5 × 10-15 erg cm-2 s-1 over 90 per cent of its area in the soft, hard, and full bands, respectively, which is comparable to those of the xmm-cosmos survey. we identify multiwavelength counterpart candidates for 99.9 per cent of the x-ray sources, of which 93 per cent are considered as reliable based on their matching likelihood ratios. the reliabilities of these high-likelihood-ratio counterparts are further confirmed to be ≈97 per cent reliable based on deep chandra coverage over ≈5 per cent of the xmm-lss region. results of multiwavelength identifications are also included in the source catalogue, along with basic optical-to-infrared photometry and spectroscopic redshifts from publicly available surveys. we compute photometric redshifts for x-ray sources in 4.5 deg2 of our field where forced-aperture multiband photometry is available; >70 per cent of the x-ray sources in this subfield have either spectroscopic or high-quality photometric redshifts. | the xmm-servs survey: new xmm-newton point-source catalogue for the xmm-lss field |
a supramassive, strongly magnetized millisecond neutron star (ns) has been proposed to be the candidate central engine of at least some short gamma-ray bursts (sgrbs), based on the "internal plateau" commonly observed in the early x-ray afterglow. while a previous analysis shows a qualitative consistency between this suggestion and the swift sgrb data, the distribution of observed break time tb is much narrower than the distribution of the collapse time of supramassive nss for the several ns equations-of-state (eoss) investigated. in this paper, we study four recently constructed "unified" ns eoss (bcpm, bsk20, bsk21, and shen) as well as three developed strange quark star (qs) eoss within the new confinement density-dependent mass (cddm) model, labelled as ciddm, cddm1, and cddm2. all the eoss chosen here satisfy the recent observational constraints of the two massive pulsars of which the masses are precisely measured. we construct sequences of rigidly rotating ns/qs configurations with increasing spinning frequency f , from nonrotating (f =0 ) to the keplerian frequency (f =fk), and provide convenient analytical parametrizations of the results. assuming that the cosmological ns-ns merger systems have the same mass distribution as the galactic ns-ns systems, we demonstrate that all except the bcpm ns eos can reproduce the current 22% supramassive ns/qs fraction constraint as derived from the sgrb data. we simultaneously simulate the observed quantities (the break time tb, the break time luminosity lb, and the total energy in the electromagnetic channel etotal) of sgrbs and find that, while equally well reproducing other observational constraints, qs eoss predict a much narrower tb distribution than that of the ns eoss, better matching the data. we therefore suggest that the postmerger product of ns-ns mergers might be fast-rotating supramassive qss rather than nss. | internal x-ray plateau in short grbs: signature of supramassive fast-rotating quark stars? |
the observational evidence that super-massive black holes (m• ∼ 109-10 m⊙) are already in place less than 1 gyr after the big bang poses stringent time constraints on the growth efficiency of their seeds. among proposed possibilities, the formation of massive (∼103-6 m⊙) seeds and/or the occurrence of super-eddington (dot{m}>dot{m}_{edd}) accretion episodes may contribute to the solution of this problem. in this work, using a set of astrophysically motivated initial conditions, we analytically and numerically investigate the accretion flow on to high-redshift (z ∼ 10) black holes to understand the physical requirements favouring rapid and efficient growth. our model identifies a `feeding-dominated' accretion regime and a `feedback-limited' one, the latter being characterized by intermittent (duty cycles d ≲ 0.5) and inefficient growth, with recurring outflow episodes. we find that low-mass seeds (≲103-4 m⊙) evolve in the feedback-limited regime, while more massive seeds (≳105-6 m⊙) grow very rapidly as they are found in the feeding-dominated regime. in addition to the standard accretion model with a fixed matter-energy conversion factor (ɛ = 0.1), we have also explored slim disc models, appropriate for super-eddington accretion, where radiation is trapped in the disc and the radiative efficiency is reduced (ɛ ≲ 0.04), which may ensure a continuous growth with dot{m} ≫ dot{m}_{edd} (up to {∼ } 300 dot{m}_{edd} in our simulations). under these conditions, outflows play a negligible role and a black hole can accrete 80-100 per cent of the gas mass of the host halo (∼107 m⊙) in ∼10 myr, while in feedback-limited systems we predict that black holes can accrete only up to ∼15 per cent of the available mass. | the growth efficiency of high-redshift black holes |
we report on the acceleration properties of 329 features in 95 blazar jets from the mojave very long baseline array program. nearly half the features and three-quarters of the jets show significant changes in speed and/or direction. in general, apparent speed changes are distinctly larger than changes in direction, indicating that changes in the lorentz factors of jet features dominate the observed speed changes rather than bends along the line of sight. observed accelerations tend to increase the speed of features near the jet base, <~ 10-20 pc projected, and decrease their speed at longer distances. the range of apparent speeds at a fixed distance in an individual jet can span a factor of a few, indicating that shock properties and geometry may influence the apparent motions; however, we suggest that the broad trend of jet features increasing their speed near the origin is due to an overall acceleration of the jet flow out to deprojected distances of the order of 102 pc, beyond which the flow begins to decelerate or remains nearly constant in speed. we estimate intrinsic rates of change of the lorentz factors in the galaxy frame of the order of \dot{γ }/γ ≃ 10-3 to 10-2 yr-1, which can lead to total lorentz factor changes of a factor of a few on the length scales observed here. finally, we also find evidence for jet collimation at projected distances of <~ 10 pc in the form of the non-radial motion and bending accelerations that tend to better align features with the inner jet. | mojave. xii. acceleration and collimation of blazar jets on parsec scales |
observations show a prevalence of high-redshift galaxies with large stellar masses and predominantly passive stellar populations. a variety of processes have been suggested that could reduce the star formation in such galaxies to observed levels, including quasar mode feedback, virial shock heating, or galactic winds driven by stellar feedback. however, the main quenching mechanisms have yet to be identified. here we study the origin of star formation quenching using argo, a cosmological, hydrodynamical zoom-in simulation that follows the evolution of a massive galaxy at z ≥ 2. this simulation adopts the same subgrid recipes of the eris simulations, which have been shown to form realistic disc galaxies, and, in one version, adopts also a mass and spatial resolution identical to eris. the resulting galaxy has properties consistent with those of observed, massive (m* ∼ 1011 m⊙) galaxies at z ∼ 2 and with abundance matching predictions. our models do not include active galactic nuclei (agn) feedback indicating that supermassive black holes likely play a subordinate role in determining masses and sizes of massive galaxies at high-z. the specific star formation rate (ssfr) of the simulated galaxy matches the observed m*-ssfr relation at early times. this period of smooth stellar mass growth comes to a sudden halt at z = 3.5 when the ssfr drops by almost an order of magnitude within a few hundred myr. the suppression is initiated by a levelling off and a subsequent reduction of the cool gas accretion rate on to the galaxy, and not by feedback processes. this `cosmological starvation' occurs as the parent dark matter halo switches from a fast collapsing mode to a slow accretion mode. additional mechanisms, such as perhaps radio mode feedback from an agn, are needed to quench any residual star formation of the galaxy and to maintain a low ssfr until the present time. | the argo simulation - i. quenching of massive galaxies at high redshift as a result of cosmological starvation |
we confirm two new local massive relic galaxies, i.e. untouched survivors of the early universe massive population: mrk 1216 and pgc 032873. both show early and peaked formation events within very short time-scales (<1 gyr) and thus old mean mass-weighted ages (∼13 gyr). their star formation histories remain virtually unchanged out to several effective radii, even when considering the steeper initial-mass-function values inferred out to ∼3 effective radii. their morphologies, kinematics and density profiles are like those found in the z > 2 massive population, setting them apart from the typical z ∼ 0 massive early-type galaxies. we find that there seems to exist a degree of relic that is related to how far into the path, to become one of these typical z ∼ 0 massive galaxies, the compact relic has moved. this path is partly dictated by the environment the galaxy lives in. for galaxies in rich environments, such as the previously reported relic galaxy ngc 1277, the most extreme properties (e.g. sizes, short formation time-scales, larger supermassive black holes) are expected, while lower density environments will have galaxies with delayed and/or extended star formations, slightly larger sizes and not that extreme black hole masses. the confirmation of three relic galaxies up to a distance of 106 mpc, implies a lower limit in the number density of these red nuggets in the local universe of 6 × 10-7 mpc3, which is within the theoretical expectations. | two new confirmed massive relic galaxies: red nuggets in the present-day universe |
we examine the distribution of radio emission from ~42 000 quasars from the sloan digital sky survey, as measured in the lofar two-metre sky survey (lotss). we present a model of the radio luminosity distribution of the quasars that assumes that every quasar displays a superposition of two sources of radio emission: active galactic nuclei (jets) and star formation. our two-component model provides an excellent match to the observed radio flux density distributions across a wide range of redshifts and quasar optical luminosities; this suggests that the jet-launching mechanism operates in all quasars but with different powering efficiency. the wide distribution of jet powers allows for a smooth transition between the 'radio-quiet' and 'radio-loud' quasar regimes, without need for any explicit bimodality. the best-fitting model parameters indicate that the star formation rate of quasar host galaxies correlates strongly with quasar luminosity and also increases with redshift at least out to z ~ 2. for a model where star formation rate scales as $l_{\rm bol}^{\alpha } (1+z)^{\beta }$, we find α = 0.47 ± 0.01 and β = 1.61 ± 0.05, in agreement with far-infrared studies. quasars contribute ≈0.15 per cent of the cosmic star formation rate density at z = 0.5, rising to 0.4 per cent by z ~ 2. the typical radio jet power is seen to increase with both increasing optical luminosity and black hole mass independently, but does not vary with redshift, suggesting intrinsic properties govern the production of the radio jets. we discuss the implications of these results for the triggering of quasar activity and the launching of jets. | the radio loudness of sdss quasars from the lofar two-metre sky survey: ubiquitous jet activity and constraints on star formation |
in this paper, we use the latest observations of quasars covering the redshift range of 0.04 <z <5.1 to investigate a series of chaplygin gas models as candidates for unified dark matter and dark energy. based on different combinations of available standard candle and standard ruler data, we put constraints on the generalized chaplygin gas (gcg), modified chaplygin gas (mcg), new generalized chaplygin gas (ngcg) and viscous generalized chaplygin gas (vgcg) models. moreover, we apply jensen-shannon divergence (jsd), statefinder diagnostics, and the deviance information criterion (dic) to distinguish these cg models, based on the statistical results derived from markov chain monte carlo method. the results show that (1) the standard ruler data could provide more stringent constraints on the cosmological parameters of different cg models considered in this analysis. interestingly, the matter density parameter ωm and hubble constant h0 derived from the available data are well consistent with those from the planck 2018 results; (2) based on the statistical criteria jsd, our findings demonstrate the well consistency between chaplygin gas and the concordance λ cdm model. however, in the framework of statefinder diagnostics, the gcg and ngcg models cannot be distinguished from λ cdm, while mcg and vgcg models show significant deviation from λ cdm in the present epoch; (3) according to the the statistical criteria dic, we show that the mcg and vgcg models have substantial observational support from high-redshift quasars, whereas the gcg and ngcg models miss out on the less observational support category but can not be ruled out. | revisiting chaplygin gas cosmologies with the recent observations of high-redshift quasars |
context. positions and proper motions of gaia sources are expressed in a reference frame that ideally should be non-rotating relative to distant extragalactic objects, coincident with the international celestial reference system (icrs), and consistent across all magnitudes. for sources fainter than 16th magnitude, this is achieved through gaia's direct observations of quasars. at brighter magnitudes, it is difficult to validate the quality of the reference frame because comparison data are scarce.aims: the aim of this paper is to examine the use of very long baseline interferometry (vlbi) observations of radio stars to determine the spin and orientation of the bright reference frame of current and future gaia data releases.methods: simultaneous estimation of the six spin and orientation parameters makes optimal use of vlbi data and makes it possible to include even single-epoch vlbi observations in the solution. the method is applied to gaia data release 2 (dr2) using published vlbi data for 41 radio stars.results: the vlbi data for the best-fitting 26 sources indicate that the bright reference frame of gaia dr2 rotates relative to the faint quasars at a rate of about 0.1 mas yr-1, which is significant at the 2σ level. this supports a similar conclusion based on a comparison with stellar positions in the hipparcos frame. the accuracy is currently limited because only a few radio sources are included in the solution, by uncertainties in the gaia dr2 proper motions, and by issues related to the astrophysical nature of the radio stars.conclusions: while the origin of the indicated rotation is understood and can be avoided in future data releases, it remains important to validate the bright reference frame of gaia by independent observations. this can be achieved using vlbi astrometry, which may require re-observing the old sample of radio stars as well as measuring new objects. the unique historical value of positional measurements is stressed and vlbi observers are urged to ensure that relevant positional information is preserved for the future. | the gaia reference frame for bright sources examined using vlbi observations of radio stars |
we present a systematic investigation of physical conditions and elemental abundances in four optically thick lyman-limit systems (llss) at z = 0.36-0.6 discovered within the cosmic ultraviolet baryon survey (cubs). because intervening llss at z < 1 suppress far-uv (ultraviolet) light from background qsos, an unbiased search of these absorbers requires a near-uv-selected qso sample, as achieved by cubs. cubs llss exhibit multicomponent kinematic structure and a complex mix of multiphase gas, with associated metal transitions from multiple ionization states such as c ii, c iii, n iii, mg ii, si ii, si iii, o ii, o iii, o vi, and fe ii absorption that span several hundred km s-1 in line-of-sight velocity. specifically, higher column density components (log n(h i)/cm-2≳ 16) in all four absorbers comprise dynamically cool gas with $\langle t \rangle =(2\pm 1) \times 10^4\,$k and modest non-thermal broadening of $\langle b_\mathrm{nt} \rangle =5\pm 3\,$km s-1. the high quality of the qso absorption spectra allows us to infer the physical conditions of the gas, using a detailed ionization modelling that takes into account the resolved component structures of h i and metal transitions. the range of inferred gas densities indicates that these absorbers consist of spatially compact clouds with a median line-of-sight thickness of $160^{+140}_{-50}$ pc. while obtaining robust metallicity constraints for the low density, highly ionized phase remains challenging due to the uncertain $n\mathrm{(h\, {\small i})}$, we demonstrate that the cool-phase gas in llss has a median metallicity of $\mathrm{[\alpha /h]_{1/2}}=-0.7^{+0.1}_{-0.2}$, with a 16-84 percentile range of [α/h] = (-1.3, -0.1). furthermore, the wide range of inferred elemental abundance ratios ([c/α], [n/α], and [fe/α]) indicate a diversity of chemical enrichment histories. combining the absorption data with deep galaxy survey data characterizing the galaxy environment of these absorbers, we discuss the physical connection between star-forming regions in galaxies and diffuse gas associated with optically thick absorption systems in the z < 1 circumgalactic medium. | the cosmic ultraviolet baryon survey (cubs) - iii. physical properties and elemental abundances of lyman-limit systems at z < 1 |
context. the damped random walk (drw) stochastic process is nowadays frequently used to model aperiodic light curves of active galactic nuclei (agns). a number of correlations between the drw model parameters, the signal decorrelation timescale and amplitude, and the physical agn parameters, such as the black hole mass or luminosity, have been reported.aims: we are interested in whether or not it is plausible to correctly measure the drw parameters from a typical ground-based survey, and, in particular, in how accurate the recovered drw parameters are compared to the input ones.methods: by means of monte carlo simulations of agn light curves, we studied the impact of the light curve length, the source magnitude (the photometric properties of a survey), cadence, and additional light (e.g., from a host galaxy) on the drw model parameters.results: the most significant finding is that currently existing surveys are going to return unconstrained drw decorrelation timescales, because typical rest-frame data do not probe long enough timescales or the white noise part of the power spectral density for drw. the experiment length must be at least ten times longer than the true drw decorrelation timescale, being presumably in the vicinity of one year, thus meaning the necessity for agn light curves measuring a minimum of 10 years (rest-frame). the drw timescales for sufficiently long light curves are typically weakly biased, and the exact bias depends on the fitting method and used priors. the drw amplitude is mostly affected by the photometric noise (the source magnitude or the signal-to-noise ratio), cadence, and the agn host light.conclusions: because the drw parameters appear to be incorrectly determined from typically existing data, the reported correlations of the drw variability and physical agn parameters from other works seem unlikely to be correct. in particular, the anti-correlation of the drw decorrelation timescale with redshift is a manifestation of the survey length being too short. application of drw to modeling typical agn optical light curves is questioned. | limitations on the recovery of the true agn variability parameters using damped random walk modeling |
the radio galaxy 0402+379 is believed to host a supermassive black hole binary (smbhb). the two compact-core sources are separated by a projected distance of 7.3 pc, making it the most (spatially) compact resolved smbhb known. we present new multi-frequency vlbi observations of 0402+379 at 5, 8, 15, and 22 ghz and combine them with previous observations spanning 12 years. a strong frequency-dependent core shift is evident, which we use to infer magnetic fields near the jet base. after correcting for these shifts we detect significant relative motion of the two cores at β =v/c=0.0054+/- 0.0003 at {pa}=-34\buildrel{\circ}\over{.} 4. with some assumptions about the orbit, we use this measurement to constrain the orbital period p≈ 3× {10}4 yr and smbhb mass m≈ 15× {10}9 {m}⊙ . while additional observations are needed to confirm this motion and obtain a precise orbit, this is apparently the first black hole system resolved as a visual binary. | constraining the orbit of the supermassive black hole binary 0402+379 |
we present time-delay measurements for the new quadruple imaged quasar des j0408-5354, the first quadruple imaged quasar found in the dark energy survey (des). our result is made possible by implementing a new observational strategy using almost daily observations with the mpia 2.2 m telescope at la silla observatory and deep exposures reaching a signal-to-noise ratio of about 1000 per quasar image. this data qualityallows us to catch small photometric variations (a few mmag rms) of the quasar, acting on temporal scales much shorter than microlensing, and hence making the time delay measurement very robust against microlensing. in only seven months we very accurately measured one of the time delays in des j0408-5354: δt(ab) = -112.1 ± 2.1 days (1.8%) using only the mpia 2.2 m data. in combination with data taken with the 1.2 m euler swiss telescope, we also measured two delays involving the d component of the system δt(ad) = -155.5 ± 12.8 days (8.2%) and δt(bd) = -42.4 ± 17.6 days (41%), where all the error bars include systematics. turning these time delays into cosmological constraints will require deep hubble space telescope (hst) imaging or ground-based adaptive optics (ao), and information on the velocity field of the lensing galaxy. lightcurves are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/609/a71 | cosmograil: the cosmological monitoring of gravitational lenses. xvi. time delays for the quadruply imaged quasar des j0408-5354 with high-cadence photometric monitoring |
motivated by the claimed detection of a large population of faint active galactic nuclei (agns) at high redshift, recent studies have proposed models in which agns contribute significantly to the z > 4 h i ionizing background. in some models, agns are even the chief sources of reionization. if proved true, these models would make necessary a complete revision to the standard view that galaxies dominated the high-redshift ionizing background. it has been suggested that agn-dominated models can better account for two recent observations that appear to be in conflict with the standard view: (1) large opacity variations in the z ∼ 5.5 h i ly α forest, and (2) slow evolution in the mean opacity of the he ii ly α forest. large spatial fluctuations in the ionizing background from the brightness and rarity of agns may account for the former, while the earlier onset of he ii reionization in these models may account for the latter. here we show that models in which agn emissions source ≳50 per cent of the ionizing background generally provide a better fit to the observed h i ly α forest opacity variations compared to standard galaxy-dominated models. however, we argue that these agn-dominated models are in tension with constraints on the thermal history of the intergalactic medium (igm). under standard assumptions about the spectra of agns, we show that the earlier onset of he ii reionization heats up the igm well above recent temperature measurements. we further argue that the slower evolution of the mean opacity of the he ii ly α forest relative to simulations may reflect deficiencies in current simulations rather than favour agn-dominated models as has been suggested. | on the contribution of active galactic nuclei to the high-redshift metagalactic ionizing background |
research over the past decade has shown diminishing evidence for major galaxy mergers being a dominant mechanism for the growth of supermassive black holes (bhs) in galaxies and the triggering of optically or x-ray-selected active galactic nuclei (agns). for the first time we test whether such a connection exists at least in the most “plausible” part of parameter space: the highest specific accretion rate broad-line agns at the peak epoch of bh activity around z = 2. to that end we analyze two samples—21 agns with l/l edd > 0.7 and 92 stellar mass- and redshift-matched inactive galaxies—observed with hst/wfc3. we remove the agn point sources from their host galaxies and avoid bias in visual classification by adding and then subtracting mock point sources to and from the comparison galaxies, producing matched residual structures for both sets. the resulting samples are joined and visually ranked according to distortion strength by 10 experts. the ensuing individual rankings are combined into a consensus sequence and from this we derive the merger fractions for both samples. with the merger fractions f m,agn = 0.24 ± 0.09 for the agn host galaxy sample and f m,ina = 0.19 ± 0.04 for the inactive galaxies, we find no significant difference between the samples. this finding is consistent with previous studies for different agn populations, and we conclude that even bh growth at the highest specific accretion rates and at the peak of cosmic agn activity is not predominantly caused by major mergers. | major mergers are not the dominant trigger for high-accretion agns at z ∼ 2 |
we compare cosmological hydrodynamical simulations combined with the homogeneous metagalactic uv background (uvb) of haardt & madau (hereafter hm2012) to observations of the lyman α forest that are sensitive to the thermal and ionization state of the intergalactic medium (igm). the transition from optically thick to thin photoheating predicted by the simple one-zone, radiative transfer model implemented by hm2012 predicts a thermal history that is in remarkably good agreement with the observed rise of the igm temperature at z ∼ 3 if we account for the expected evolution of the volume filling factor of he iii. our simulations indicate that there may be, however, some tension between the observed peak in the temperature evolution and the rather slow evolution of the he ii opacities suggested by recent hubble space telescope/cosmic origins spectrograph measurements. the hm2012 uvb also underpredicts the metagalactic hydrogen photoionization rate required by our simulations to match the observed opacity of the forest at z > 4 and z < 2. | the photoheating of the intergalactic medium in synthesis models of the uv background |
this paper presents a survey of x-ray-selected active galactic nuclei (agns) with optical spectroscopic follow-up in a ∼ 18 deg2 area of the equatorial xmm-xxl north field. a sample of 8445 point-like x-ray sources detected by xmm-newton above a limiting flux of f_{0.5-10 kev} > 10^{-15} erg cm^{-2} s^{-1} was matched to optical (sloan digital sky survey, sdss) and infrared (ir; wise) counterparts. we followed up 3042 sources brighter than r = 22.5 mag with the sdss baryon oscillation spectroscopic survey (boss) spectrograph. the spectra yielded a reliable redshift measurement for 2578 agns in the redshift range z = 0.02-5.0, with 0.5-2 kev luminosities ranging from 1039-1046 erg s- 1. this is currently the largest published spectroscopic sample of x-ray-selected agns in a contiguous area. the boss spectra of agn candidates show a distribution of optical line widths which is clearly bimodal, allowing an efficient separation between broad- and narrow-emission line agns. the former dominate our sample (70 per cent) due to the relatively bright x-ray flux limit and the optical boss magnitude limit. we classify the narrow-emission line objects (22 per cent of the full sample) using standard optical emission line diagnostics: the majority have line ratios indicating the dominant source of ionization is the agn. a small number (8 per cent of the full sample) exhibit the typical narrow line ratios of star-forming galaxies, or only have absorption lines in their spectra. we term the latter two classes `elusive' agn, which would not be easy to identify correctly without their x-ray emission. we also compare x-ray (xmm-newton), optical colour (sdss) and and ir (wise) agn selections in this field. x-ray observations reveal, by far, the largest number of agn. the overlap between the selections, which is a strong function of the imaging depth in a given band, is also remarkably small. we show using spectral stacking that a large fraction of the x-ray agns would not be selectable via optical or ir colours due to host galaxy contamination. a substantial fraction of agn may therefore be missed by these longer wavelength selection methods. | a spectroscopic survey of x-ray-selected agns in the northern xmm-xxl field |
we report results of a spectroscopic campaign carried out at the 10 m gran telescopio canarias for a sample of 22 bl lac objects detected (or candidates) at tev energies, aiming to determine or constrain their redshift. this is of fundamental importance for the interpretation of their emission models and for population studies and is also mandatory for studying the interaction of high-energy photons with the extragalactic background light using tev sources. optical spectra with high signal-to-noise ratios in the range 4250-10000 å were obtained to search for faint emission or absorption lines from both the host galaxy and the nucleus. we determine a new redshift for pks 1424+240 (z = 0.604) and a tentative one for 1es 0033+595 (z = 0.467). we are able to set new spectroscopic redshift lower limits for three other sources on the basis of mg ii and ca ii intervening absorption features: bzb j1243+3627 (z > 0.483), bzb j1540+8155 (z > 0.672), and bzb 0j2323+4210 (z > 0.267). we confirm previous redshift estimates for four blazars: s3 0218+357 (z = 0.944), 1es 1215+303 (z = 0.129), w comae (z = 0.102), and ms 1221.8+2452 (z = 0.218). for the remaining targets, in seven cases (s2 0109+22, 3c 66a, ver j0521+211, s4 0954+65, bzb j1120+4214, s3 1227+25, bzb j2323+4210), we do not validate the proposed redshift. finally, for all sources of still-unknown redshift, we set a lower limit based on the minimum equivalent width of absorption features expected from the host galaxy. | on the redshift of tev bl lac objects |
binary supermassive black holes (bsbhs) are expected to be a generic byproduct from hierarchical galaxy formation. the final coalescence of bsbhs is thought to be the loudest gravitational wave (gw) siren, yet no confirmed bsbh is known in the gw-dominated regime. while periodic quasars have been proposed as bsbh candidates, the physical origin of the periodicity has been largely uncertain. here, we report discovery of a periodicity (p = 1607 ± 7 d) at 99.95 per cent significance (with a global p value of ~10-3 accounting for the look elsewhere effect) in the optical light curves of a redshift 1.53 quasar, sdss j025214.67-002813.7. combining archival sloan digital sky survey data with new, sensitive imaging from the dark energy survey, the total ~20-yr time baseline spans ~4.6 cycles of the observed 4.4-yr (rest frame 1.7-yr) periodicity. the light curves are best fit by a bursty model predicted by hydrodynamic simulations of circumbinary accretion discs. the periodicity is likely caused by accretion rate modulation by a milli-parsec bsbh emitting gws, dynamically coupled to the circumbinary accretion disc. a bursty hydrodynamic variability model is statistically preferred over a smooth, sinusoidal model expected from relativistic doppler boost, a kinematic effect proposed for pg1302-102. furthermore, the frequency dependence of the variability amplitudes disfavours doppler boost, lending independent support to the circumbinary accretion variability hypothesis. given our detection rate of one bsbh candidate from circumbinary accretion variability out of 625 quasars, it suggests that future large, sensitive synoptic surveys such as the vera c. rubin observatory legacy survey of space and time may be able to detect hundreds to thousands of candidate bsbhs from circumbinary accretion with direct implications for laser interferometer space antenna. | discovery of a candidate binary supermassive black hole in a periodic quasar from circumbinary accretion variability |
we report the detection (>4σ) of a quasi-periodic oscillation (qpo) in the gamma-ray light curve of 3c 454.3 along with a simultaneous marginal qpo detection (>2.4σ) in the optical light curves. periodic flux modulations were detected in both of these wavebands with a dominant period of ~47 d. the gamma-ray qpo lasted for over 450 d (from mjd 56800 to 57250), resulting in over nine observed cycles which is among the highest number of periods ever detected in a blazar light curve. the optical light curve was not well sampled for almost half of the gamma-ray qpo span due to the daytime transit of the source, which could explain the lower significance of the optical qpo. autoregressive integrated moving average (arima) modelling of the light curve revealed a significant, exponentially decaying, trend in the light curve during the qpo, along with the 47 d periodicity. we explore several physical models to explain the origin of this transient quasi-periodic modulation and the overall trend in the observed flux with a month-like period. these scenarios include a binary black hole system, a hotspot orbiting close to the innermost stable circular orbit of the supermassive black hole, and precessing jets. we conclude that the most likely scenario involves a region of enhanced emission moving helically inside a curved jet. the helical motion gives rise to the qpo and the curvature (~0.05○ pc-1) of the jet is responsible for the observed trend in the light curve. | multiwaveband quasi-periodic oscillation in the blazar 3c 454.3 |
we study the frequently used assumption in multi-messenger astrophysics that the gamma-ray and neutrino fluxes are directly connected because they are assumed to be produced by the same photohadronic production chain. an interesting candidate source for this test is the flat-spectrum radio quasar pks b1424-418, which recently called attention to a potential correlation between an icecube pev neutrino event and its burst phase. we simulate both the multi-waveband photon and the neutrino emission from this source using a self-consistent radiation model. we demonstrate that a simple hadronic model cannot adequately describe the spectral energy distribution for this source, but a lepto-hadronic model with a subdominant hadronic component can reproduce the multi-waveband photon spectrum observed during various activity phases of the blazar. as a conclusion, up to about 0.3 neutrino events may coincide with the burst, which implies that the leptonic contribution dominates in the relevant energy band. we also demonstrate that the time-wise correlation between the neutrino event and burst phase is weak. | on the direct correlation between gamma-rays and pev neutrinos from blazars |
ratios of different ions of the same element encode ionization information independently from relative abundances in quasar absorption line systems, crucial for understanding the multiphase nature and origin of absorbing gas, particularly at z > 6 where h i cannot be observed. observational considerations have limited such studies to a small number of sightlines, with most surveys at z > 6 focused upon the statistical properties of individual ions such as mg ii or c iv. here we compare high- and low-ionization absorption within 69 intervening systems at z > 5, including 16 systems at z > 6, from magellan/fire spectra of 47 quasars together with a keck/high resolution echelle spectrometer (hires) spectrum of the “ultraluminous” z = 6.3 quasar sdssj010013.02+280225.8. the highest redshift absorbers increasingly exhibit low-ionization species alone, consistent with previous single-ion surveys that show the frequency of mg ii is unchanging with redshift, while c iv absorption drops markedly toward z = 6. we detect no c iv or si iv in half of all metal-line absorbers at z > 5.7, with stacks not revealing any slightly weaker c iv just below our detection threshold, and most of the other half have {n}{{c}{{ii}}}> {n}{{c}{{iv}}}. in contrast, only 20% of absorbers at 5.0-5.7 lack high-ionization gas, and a search of 25 hires sightlines at z ∼ 3 yielded zero such examples. we infer that these low-ionization high-redshift absorption systems may be analogous to metal-poor damped lyα systems (∼1% of the absorber population at z ∼ 3), based on incidence rates and absolute and relative column densities. simple photoionization models suggest that circumgalactic matter at redshift six has systematically lower chemical abundances and experiences a softer ionizing background relative to redshift three. | heavy element absorption systems at 5.0 < z < 6.8: metal-poor neutral gas and a diminishing signature of highly ionized circumgalactic matter |
active galactic nuclei can be copious extragalactic emitters of mev-gev-tev γ rays, a phenomenon linked to the presence of relativistic jets powered by a super-massive black hole in the center of the host galaxy. most of γ-ray emitting active galactic nuclei, with more than 1500 known at gev energies, and more than 60 at tev energies, are called ;blazars;. the standard blazar paradigm features a jet of relativistic magnetized plasma ejected from the neighborhood of a spinning and accreting super-massive black hole, close to the observer direction. two classes of blazars are distinguished from observations: the flat-spectrum radio-quasar class (fsrq) is characterized by strong external radiation fields, emission of broad optical lines, and dust tori. the bl lac class (from the name of one of its members, bl lacertae) corresponds to weaker advection-dominated flows with γ-ray spectra dominated by the inverse compton effect on synchrotron photons. this paradigm has been very successful for modeling the broadband spectral energy distributions of blazars. however, many fundamental issues remain, including the role of hadronic processes and the rapid variability of a few fsrqs and several bl lac objects whose synchrotron spectrum peaks at uv or x-ray frequencies. a class of γ-ray-emitting radio galaxies, which are thought to be the misaligned counterparts of blazars, has emerged from the results of the fermi-large area telescope and of ground-based cherenkov telescopes. soft γ-ray emission has been detected from a few nearby seyfert galaxies, though it is not clear whether those γ rays originate from the nucleus. blazars and their misaligned counterparts make up most of the ≳100 mev extragalactic γ-ray background (egb), and are suspected of being the sources of ultra-high energy cosmic rays. the future ;cherenkov telescope array;, in synergy with the fermi-large area telescope and a wide range of telescopes in space and on the ground, will write the next chapter of blazar physics. | active galactic nuclei at gamma-ray energies |
we calibrate here cosmological radiative transfer simulations with aton/ramses with a range of measurements of the ly α opacity from quasi-stellar objects (qso) absorption spectra. we find the ly α opacity to be very sensitive to the exact timing of hydrogen reionization. models reproducing the measured evolution of the mean photoionization rate and average mean free path reach overlap at z ∼ 7 and predict an accelerated evolution of the ly α opacity at z > 6 consistent with the rapidly evolving luminosity function of ly α emitters in this redshift range. similar to `optically thin' simulations our full radiative transfer simulations fail, however, to reproduce the high-opacity tail of the ly α opacity pdf (probability distribution function) at z > 5. we argue that this is due to spatial uv fluctuations in the post-overlap phase of reionization on substantially larger scales than predicted by our source model, where the ionizing emissivity is dominated by large numbers of sub-l* galaxies. we further argue that this suggests a significant contribution to the ionizing uv background by much rarer bright sources at high redshift. | calibrating cosmological radiative transfer simulations with ly α forest data: evidence for large spatial uv background fluctuations at z ∼ 5.6-5.8 due to rare bright sources |
we present the first discoveries from a survey of z ≳ 6 quasars using imaging data from the decam legacy survey (decals) in the optical, the ukirt deep infrared sky survey (ukidss) and a preliminary version of the ukirt hemisphere survey (uhs) in the near-ir, and allwise in the mid-ir. decals will image 9000 deg2 of sky down to z ab ∼ 23.0, and ukidss and uhs will map the northern sky at 0 < decl. < +60°, reaching j vega ∼ 19.6 (5-σ). the combination of these data sets allows us to discover quasars at redshift z ≳ 7 and to conduct a complete census of the faint quasar population at z ≳ 6. in this paper, we report on the selection method of our search, and on the initial discoveries of two new, faint z ≳ 6 quasars and one new z = 6.63 quasar in our pilot spectroscopic observations. the two new z ∼ 6 quasars are at z = 6.07 and z = 6.17 with absolute magnitudes at rest-frame wavelength 1450 å being m 1450 = -25.83 and m 1450 = -25.76, respectively. these discoveries suggest that we can find quasars close to or fainter than the break magnitude of the quasar luminosity function (qlf) at z ≳ 6. the new z = 6.63 quasar has an absolute magnitude of m 1450 = -25.95. this demonstrates the potential of using the combined decals and ukidss/uhs data sets to find z ≳ 7 quasars. extrapolating from previous qlf measurements, we predict that these combined data sets will yield ∼200 z ∼ 6 quasars to z ab < 21.5, ∼1000 z ∼ 6 quasars to z ab < 23, and ∼30 quasars at z > 6.5 to j vega < 19.5. | first discoveries of z > 6 quasars with the decam legacy survey and ukirt hemisphere survey |
high-redshift quasars are important tracers of structure and evolution in the early universe. however, they are very rare and difficult to find when using color selection because of contamination from late-type dwarfs. high-redshift quasar surveys based on only optical colors suffer from incompleteness and low identification efficiency, especially at z≳ 4.5. we have developed a new method to select 4.7≲ z≲ 5.4 quasars with both high efficiency and completeness by combining optical and mid-ir wide-field infrared survey explorer (wise) photometric data, and are conducting a luminous z∼ 5 quasar survey in the whole sloan digital sky survey (sdss) footprint. we have spectroscopically observed 99 out of 110 candidates with z-band magnitudes brighter than 19.5, and 64 (64.6%) of them are quasars with redshifts of 4.4≲ z≲ 5.5 and absolute magnitudes of -29≲ {m}1450≲ -26.4. in addition, we also observed 14 fainter candidates selected with the same criteria and identified 8 (57.1%) of them as quasars with 4.7\lt z\lt 5.4. among 72 newly identified quasars, 12 of them are at 5.2\lt z\lt 5.7, which leads to an increase of ∼36% of the number of known quasars at this redshift range. more importantly, our identifications doubled the number of quasars with {m}1450\lt -27.5 at z\gt 4.5, which will set strong constraints on the bright end of the quasar luminosity function. we also expand our method to select quasars at z ≳ 5.7. in this paper we report the discovery of four new luminous z ≳ 5.7 quasars based on sdss-wise selection. | a survey of luminous high-redshift quasars with sdss and wise. i. target selection and optical spectroscopy |
radio-loud quasars (rlqs) are more x-ray luminous than predicted by the x-ray-optical/uv relation (i.e. $l_\mathrm{x}\propto l_\mathrm{uv}^\gamma$) for radio-quiet quasars (rqqs). the excess x-ray emission depends on the radio-loudness parameter (r) and radio spectral slope (αr). we construct a uniform sample of 729 optically selected rlqs with high fractions of x-ray detections and αr measurements. we find that steep-spectrum radio quasars (ssrqs; αr ≤ -0.5) follow a quantitatively similar $l_\mathrm{x}\propto l_\mathrm{uv}^{\gamma }$ relation as that for rqqs, suggesting a common coronal origin for the x-ray emission of both ssrqs and rqqs. however, the corresponding intercept of ssrqs is larger than that for rqqs and increases with r, suggesting a connection between the radio jets and the configuration of the accretion flow. flat-spectrum radio quasars (fsrqs; αr > -0.5) are generally more x-ray luminous than ssrqs at given luv and r, likely involving more physical processes. the emergent picture is different from that commonly assumed where the excess x-ray emission of rlqs is attributed to the jets. we thus perform model selection to compare critically these different interpretations, which prefers the coronal scenario with a corona-jet connection. a distinct jet component is likely important for only a small portion of fsrqs. the corona-jet, disc-corona, and disc-jet connections of rlqs are likely driven by independent physical processes. furthermore, the corona-jet connection implies that small-scale processes in the vicinity of supermassive black holes, probably associated with the magnetic flux/topology instead of black hole spin, are controlling the radio-loudness of quasars. | the lx-luv-lradio relation and corona-disc-jet connection in optically selected radio-loud quasars |
we used 3.1 million spectroscopically labelled sources from the sloan digital sky survey (sdss) to train an optimised random forest classifier using photometry from the sdss and the widefield infrared survey explorer. we applied this machine learning model to 111 million previously unlabelled sources from the sdss photometric catalogue which did not have existing spectroscopic observations. our new catalogue contains 50.4 million galaxies, 2.1 million quasars, and 58.8 million stars. we provide individual classification probabilities for each source, with 6.7 million galaxies (13%), 0.33 million quasars (15%), and 41.3 million stars (70%) having classification probabilities greater than 0.99; and 35.1 million galaxies (70%), 0.72 million quasars (34%), and 54.7 million stars (93%) having classification probabilities greater than 0.9. precision, recall, and f1 score were determined as a function of selected features and magnitude error. we investigate the effect of class imbalance on our machine learning model and discuss the implications of transfer learning for populations of sources at fainter magnitudes than the training set. we used a non-linear dimension reduction technique, uniform manifold approximation and projection, in unsupervised, semi-supervised, and fully-supervised schemes to visualise the separation of galaxies, quasars, and stars in a two-dimensional space. when applying this algorithm to the 111 million sources without spectra, it is in strong agreement with the class labels applied by our random forest model. | identifying galaxies, quasars, and stars with machine learning: a new catalogue of classifications for 111 million sdss sources without spectra |
the broad mg ii line in quasars has distinct variability properties compared with broad balmer lines: it is less variable and usually does not display a “breathing” mode, the increase in the average cloud distance when luminosity increases. we demonstrate that these variability properties of mg ii can be reasonably well explained by simple locally optimally emitting cloud (loc) photoionization models, confirming earlier photoionization results. in the fiducial loc model, the mg ii-emitting gas is on average more distant from the ionizing source than the hα/hβ gas and responds with a lower amplitude to continuum variations. if the broad-line region (blr) is truncated at a physical radius of ∼0.3 pc (for a 108.5 m ⊙ bh accreting at eddington ratio of 0.1), most of the mg ii flux will always be emitted near this outer boundary and hence will not display breathing. these results indicate that reverberation mapping results on broad mg ii, while generally more difficult to obtain owing to the lower line responsivity, can still be used to infer the mg ii blr size and hence black hole mass. but it is possible that mg ii does not have a well-defined intrinsic blr size-luminosity relation for individual quasars, even though a global one for the general population may still exist. the dramatic changes in broad hα/hβ emission in the observationally rare changing-look quasars are fully consistent with photoionization responses to extreme continuum variability, and the loc model provides natural explanations for the persistence of broad mg ii in changing-look quasars defined on hα/hβ and the rare population of broad mg ii emitters in the spectra of massive inactive galaxies. | understanding broad mg ii variability in quasars with photoionization: implications for reverberation mapping and changing-look quasars |
powerful radio galaxies exist as either compact or extended sources, with the extended sources traditionally classified by their radio morphologies as fanaroff-riley (fr) type i and ii sources. fri/frii and compact radio galaxies have also been classified by their optical spectra into two different types: high excitation (herg; quasar-mode) and low excitation (lerg; jet-mode). we present a catalogue of visual morphologies for a complete sample of >1000 1.4-ghz-selected extended radio sources from the sloan digital sky survey. we study the environment and host galaxy properties of fri/frii and compact sources, classified into herg/lerg types, in order to separate and distinguish the factors that drive the radio morphological variations from those responsible for the spectral properties. comparing fri lergs with frii lergs at fixed stellar mass and radio luminosity, we show that fris typically reside in richer environments and are hosted by smaller galaxies with higher mass surface density; this is consistent with extrinsic effects of jet disruption driving the fanaroff-riley (fr) dichotomy. using matched samples of hergs and lergs, we show that herg host galaxies are more frequently star forming, with more evidence for disc-like structure than lergs, in accordance with currently favoured models of fundamentally different fuelling mechanisms. comparing fri/frii lergs with compact lergs, we find the primary difference is that compact objects typically harbour less massive black holes. this suggests that lower mass black holes may be less efficient at launching stable radio jets, or do so for shorter times. finally, we investigate rarer sub-classes: wide-angle-tailed, head-tail, fr-hybrid and double-double sources. | the nuclear properties and extended morphologies of powerful radio galaxies: the roles of host galaxy and environment |
we construct a supervised classifier based on gaussian mixture models to probabilistically classify objects in gaia data release 2 (gdr2) using only photometric and astrometric data in that release. the model is trained empirically to classify objects into three classes - star, quasar, galaxy - for g ≥ 14.5 mag down to the gaia magnitude limit of g = 21.0 mag. galaxies and quasars are identified for the training set by a cross-match to objects with spectroscopic classifications from the sloan digital sky survey. stars are defined directly from gdr2. when allowing for the expectation that quasars are 500 times rarer than stars, and galaxies 7500 times rarer than stars (the class imbalance problem), samples classified with a threshold probability of 0.5 are predicted to have purities of 0.43 for quasars and 0.28 for galaxies, and completenesses of 0.58 and 0.72, respectively. the purities can be increased up to 0.60 by adopting a higher threshold. not accounting for this expected low frequency of extragalactic objects (the class prior) would give both erroneously optimistic performance predictions and severely impure samples. applying our model to all 1.20 billion objects in gdr2 with the required features, we classify 2.3 million objects as quasars and 0.37 million objects as galaxies (with individual probabilities above 0.5). the small number of galaxies is due to the strong bias of the satellite detection algorithm and on-ground data selection against extended objects. we infer the true number of quasars and galaxies - as these classes are defined by our training set - to be 690 000 and 110 000, respectively (±50 per cent). the aim of this work is to see how well extragalactic objects can be classified using only gdr2 data. better classifications should be possible with the low resolution spectroscopy (bp/rp) planned for gdr3. | quasar and galaxy classification in gaia data release 2 |
we present a systematic x-ray and multiwavelength study of a sample of 47 active galactic nuclei (agns) with reverberation mapping measurements. this sample includes 21 super-eddington accreting agns and 26 sub-eddington accreting agns. using high-state observations with simultaneous x-ray and uv/optical measurements, we investigate whether super-eddington accreting agns exhibit different accretion disk-corona connections compared to sub-eddington accreting agns. we find tight correlations between the x-ray-to-uv/optical spectral slope parameter (αox) and the monochromatic luminosity at 2500 å (l2500å) for both the super- and sub-eddington subsamples. the best-fit αox-l2500å relations are consistent overall, indicating that super-eddington accreting agns are not particularly x-ray weak in general compared to sub-eddington accreting agns. we find dependences of αox on both the eddington ratio (lbol/ledd) and black hole mass (mbh) parameters for our full sample. a multivariate linear regression analysis yields ${\alpha }_{\mathrm{ox}}=-0.13\mathrm{log}({l}_{\mathrm{bol}}/{l}_{\mathrm{edd}})-0.10\mathrm{log}{m}_{\mathrm{bh}}-0.69$ <!-- --> , with a scatter similar to that of the αox-l2500å relation. the hard (rest-frame >2 kev) x-ray photon index (γ) is strongly correlated with lbol/ledd for the full sample and the super-eddington subsample, but these two parameters are not significantly correlated for the sub-eddington subsample. a fraction of super-eddington accreting agns show strong x-ray variability, probably due to small-scale gas absorption, and we highlight the importance of employing high-state (intrinsic) x-ray radiation to study the accretion disk-corona connections in agns. | on the observational difference between the accretion disk-corona connections among super- and sub-eddington accreting active galactic nuclei |
quasar absorption systems encode a wealth of information about the abundances, ionization structure, and physical conditions in intergalactic and circumgalactic media. simple (often single-phase) photoionization models are frequently used to decode such data. using five discrete absorbers from the cos absorption survey of baryon harbors (casbah) that exhibit a wide range of detected ions (e.g. mg ii, s ii - s vi, o ii - o vi, ne viii), we show several examples where single-phase ionization models cannot reproduce the full set of measured column densities. to explore models that can self-consistently explain the measurements and kinematic alignment of disparate ions, we develop a bayesian multiphase ionization modelling framework that characterizes discrete phases by their unique physical conditions and also investigates variations in the shape of the uv flux field, metallicity, and relative abundances. our models require at least two (but favour three) distinct ionization phases ranging from t ≈ 104 k photoionized gas to warm-hot phases at t ≲ 105.8 k. for some ions, an apparently single absorption 'component' includes contributions from more than one phase, and up to 30 per cent of the h i is not from the lowest ionization phase. if we assume that all of the phases are photoionized, we cannot find solutions in thermal pressure equilibrium. by introducing hotter, collisionally ionized phases, however, we can achieve balanced pressures. the best models indicate moderate metallicities, often with subsolar n/α, and, in two cases, ionizing flux fields that are softer and brighter than the fiducial haardt & madau uv background model. | the cos absorption survey of baryon harbors: unveiling the physical conditions of circumgalactic gas through multiphase bayesian ionization modelling |
the concurrent growth of supermassive black holes (smbhs) and their host galaxies remains to be fully explored, especially at high redshift. while often understood as a consequence of self-regulation via agn feedback, it can also be explained by alternative smbh accretion models. here, we expand on previous work by studying the growth of smbhs with the help of a large suite of cosmological zoom-in simulations (massivefire) that are part of the feedback in realistic environments (fire) project. the growth of smbhs is modelled in post-processing with different black hole accretion models, placements, and merger treatments, and validated by comparing to on-the-fly calculations. scaling relations predicted by the gravitational torque-driven accretion (gtda) model agree with observations at low redshift without the need for agn feedback, in contrast to models in which the accretion rate depends strongly on smbh mass. at high redshift, we find deviations from the local scaling relations in line with previous theoretical results. in particular, smbhs are undermassive, presumably due to stellar feedback, but start to grow efficiently once their host galaxies reach m* ~ 1010m⊙. we analyse and explain these findings in the context of a simple analytic model. finally, we show that the predicted scaling relations depend sensitively on the smbh location and the efficiency of smbh merging, particularly in low-mass systems. these findings highlight the relevance of understanding the evolution of smbh-galaxy scaling relations to predict the rate of gravitational wave signals from smbh mergers across cosmic history. | black hole-galaxy scaling relations in fire: the importance of black hole location and mergers |
high-redshift quasars (z > 5) that also shine brightly at radio wavelengths are unique signposts of supermassive black hole activity in the early universe. however, bright radio sources at z ≥ 5 are extremely rare and therefore we have started a campaign to search for new high-z quasars by combining an optical dropout selection driven by the g, r, and z bands from the dark energy spectroscopic instrument (desi) legacy imaging surveys with low-frequency radio observations from the lofar two-metre sky survey (lotss). currently, lotss covers a large fraction of the northern sky (∼5720 deg2) to such a depth (median noise level ∼83 μjy beam−1) that about 30% of the general quasar population is detected − which is a factor of 5-10 more than previous large sky radio surveys such as nvss and first, respectively. in this paper, we present the discovery of 20 new quasars (and the independent confirmation of four) between 4.9 ≤ z ≤ 6.6. out of the 24 quasars, 21 satisfy the traditional radio-loudness criterion of r = f5 ghz/f4400 å > 10, with the full sample spanning r ∼ 6-1000, thereby more than doubling the sample of known radio-loud quasars at z ≥ 5. our radio detection requirement strongly decreases the contamination of stellar sources and allows one to select these quasars in a broad redshift range. despite selecting our quasar candidates using fewer and less conservative colour restrictions, both the optical and near-infrared colours, lyα emission line properties, and dust reddening, e(b − v), measurements of our quasar sample do not deviate from the known radio-quiet quasar population, suggesting similar optical quasar properties of the radio-loud and radio-quiet quasar population at high-z. our campaign demonstrates the potential for discovering new high-z quasar populations through next generation radio continuum surveys. full table 3 is only available at the cds via anonymous ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/j/a+a/668/a27 based on observations obtained with the hobby-eberly telescope (het), which is a joint project of the university of texas at austin, pennsylvania state university, ludwig-maximillians-universitaet muenchen, and georg-august universitaet goettingen. the het is named in honor of its principal benefactors, william p. hobby and robert e. eberly. | discovery of 24 radio-bright quasars at 4.9 ≤ z ≤ 6.6 using low-frequency radio observations |
peculiar motion of the solar system, determined from the dipole anisotropy in the cosmic microwave background radiation (cmbr), has given a velocity 370 km s-1 along ra = 168°, dec. = -7°. subsequent peculiar motion determinations from the number counts, sky brightness, or redshift dipoles observed in large samples of distant radio galaxies and quasars yielded peculiar velocities 2 to 10 times larger than cmbr, though in all cases the directions matched with the cmbr dipole. here, we introduce a novel technique for determining the peculiar motion from the magnitude-redshift (mb-z) hubble diagram of type ia supernovae (sn ia), one of the best standard candles available. we find a peculiar velocity 1.6 ± 0.5 × 103 km s-1, larger than the cmbr value roughly by a factor of four, along ra = 173° ± 12°, dec. = 10° ± 9°, the direction being within $\stackrel{\lt }{_{\sim }}2\sigma$ of the cmbr dipole. since a genuine solar motion would not depend upon the method or the data set employed, large discrepancies seen among various dipole amplitudes could imply that these dipoles, including the cmbr one, might not pertain to observer's peculiar motion. however, a common direction for various dipoles might indicate a preferred direction in the universe, implying an intrinsic anisotropy, in violation of the cosmological principle, a cornerstone of the modern cosmology. | peculiar motion of solar system from the hubble diagram of supernovae ia and its implications for cosmology |
the recent advanced ligo/virgo detections of gravitational waves (gws) from stellar binary black hole (bbh) mergers, in particular gw190521, which is potentially associated with a quasar, have stimulated renewed interest in active galactic nuclei as factories of merging bbhs. compact objects evolving from massive stars are unavoidably enshrouded by a massive envelope to form accretion-modified stars (amss) in the dense gaseous environment of a supermassive black hole (smbh) accretion disk. we show that most amss form binaries due to gravitational interaction with each other during radial migration in the smbh disk, forming bbhs inside the ams. when a bbh is born, its orbit is initially governed by the tidal torque of the smbh. bondi accretion onto a bbh at a hyper-eddington rate naturally develops and then controls the evolution of its orbits. we find that bondi accretion leads to efficient removal of the orbital angular momentum of the binary, whose final merger produces a gw burst. meanwhile, the blandford-znajek mechanism pumps the spin energy of the merged bh to produce an electromagnetic counterpart (emc). moreover, hyper-eddington accretion onto the bbh develops powerful outflows and triggers a bondi explosion, which manifests itself as an emc of the gw burst, depending on the viscosity of the accretion flow. thermal emission from the bondi sphere appears as one of the emcs. the bbhs radiate gws with frequencies of ~102 hz, which are accessible to ligo. | accretion-modified stars in accretion disks of active galactic nuclei: gravitational-wave bursts and electromagnetic counterparts from merging stellar black hole binaries |
recent analyses of the planck data and quasars at high redshifts have suggested possible deviations from the flat λ cold dark matter model (λcdm), where λ is the cosmological constant. here we use machine learning methods to investigate any possible deviations from λcdm at both low and high redshifts by using the latest cosmological data. specifically, we apply the genetic algorithms to explore the nature of dark energy (de) in a model independent fashion by reconstructing its equation of state w(z), the growth index of matter density perturbations γ(z), the linear de anisotropic stress ηde(z) and the adiabatic sound speed cs,de2(z) of de perturbations. we find a ~ 2σ deviation of w(z) from -1 at high redshifts, the adiabatic sound speed is negative at the ~ 2.5σ level at z = 0.1 and a ~ 2σ deviation of the anisotropic stress from unity at low redshifts and ~ 4σ at high redshifts. these results hint towards either the presence of an non-adiabatic component in the de sound speed or the presence of de anisotropic stress, thus hinting at possible deviations from the λcdm model. | hints of dark energy anisotropic stress using machine learning |
we have designed, developed, and applied a convolutional neural network (cnn) architecture using multi-task learning to search for and characterize strong h i lyα absorption in quasar spectra. without any explicit modelling of the quasar continuum or application of the predicted line profile for lyα from quantum mechanics, our algorithm predicts the presence of strong h i absorption and estimates the corresponding redshift zabs and h i column density n_{h i}, with emphasis on damped lyα systems (dlas, absorbers with n_{h i}≥ 2 × 10^{20} cm^{-2}). we tuned the cnn model using a custom training set of dlas injected into dla-free quasar spectra from the sloan digital sky survey (sdss), data release 5 (dr5). testing on a held-back validation set demonstrates a high incidence of dlas recovered by the algorithm (97.4 per cent as dlas and 99 per cent as an h i absorber with n_{h i}> 10^{19.5} cm^{-2}) and excellent estimates for zabs and n_{h i}. similar results are obtained against a human-generated survey of the sdss dr5 data set. the algorithm yields a low incidence of false positives and negatives but is challenged by overlapping dlas and/or very high n_{h i} systems. we have applied this cnn model to the quasar spectra of sdss dr7 and the baryon oscillation spectroscopic survey (data release 12) and provide catalogues of 4913 and 50 969 dlas, respectively (including 1659 and 9230 high-confidence dlas that were previously unpublished). this work validates the application of deep learning techniques to astronomical spectra for both classification and quantitative measurements. | deep learning of quasar spectra to discover and characterize damped lyα systems |
measuring the proximity effect and the damping wing of intergalactic neutral hydrogen in quasar spectra during the epoch of reionization requires an estimate of the intrinsic continuum at rest-frame wavelengths of λ rest ∼ 1200-1260 å. in contrast to previous works which used composite spectra with matched spectral properties or explored correlations between parameters of broad emission lines, we opted for a nonparametric predictive approach based on principal component analysis (pca) to predict the intrinsic spectrum from the spectral properties at redder (i.e., unabsorbed) wavelengths. we decomposed a sample of 12764 spectra of z ∼ 2-2.5 quasars from the sloan digital sky survey (sdss)/baryon oscillation spectroscopic survey (boss) into 10 red-side (1280 å < λ rest < 2900 å) and 6 blue-side (1180 å < λ rest < 1280 å) pca basis spectra, and constructed a projection matrix to predict the blue-side coefficients from a fit to the red-side spectrum. we found that our method predicts the blue-side continuum with ∼6%-12% precision and ≲1% bias by testing on the full training set sample. we then computed predictions for the blue-side continua of the two quasars currently known at z > 7: ulas j1120+0641 (z = 7.09) and ulas j1342+0928 (z = 7.54). both of these quasars are known to exhibit extreme emission line properties, so we individually calibrated the uncertainty in the continuum predictions from similar quasars in the training set, finding comparable precision but moderately higher bias than the predictions for the training set as a whole, although they may face additional systematic uncertainties due to calibration artifacts present in near-infrared echelle spectra. we find that both z > 7 quasars, and in particular ulas j1342+0928, show signs of damping wing-like absorption at wavelengths redward of lyα. | predicting quasar continua near lyα with principal component analysis |
context. the physical characteristics of the material closest to supermassive black holes (smbhs) are primarily studied through x-ray observations. however, the origins of the main x-ray components such as the soft x-ray excess, the fe kα line complex, and the hard x-ray excess are still hotly debated. this is particularly problematic for active galactic nuclei (agn) showing a significant intrinsic absorption, either warm or neutral, which can severely distort the observed continuum. therefore, agn with no (or very weak) intrinsic absorption along the line of sight, so-called "bare agn", are the best targets to directly probe matter very close to the smbh.aims: we perform an x-ray spectral analysis of the brightest and cleanest bare agn known so far, ark 120, in order to determine the process(es) at work in the vicinity of the smbh.methods: we present spectral analyses of data from an extensive campaign observing ark 120 in x-rays with xmm-newton (4 × 120 ks, 2014 march 18-24), and nustar (65.5 ks, 2014 march 22).results: during this very deep x-ray campaign, the source was caught in a high-flux state similar to the earlier 2003 xmm-newton observation, and about twice as bright as the lower-flux observation in 2013. the spectral analysis confirms the "softer when brighter" behavior of ark 120. the four xmm-newton/pn spectra are characterized by the presence of a prominent soft x-ray excess and a significant fe kα complex. the continuum is very similar above about 3 kev, while significant variability is present for the soft x-ray excess. we find that relativistic reflection from a constant-density, flat accretion disk cannot simultaneously produce the soft excess, broad fe kα complex, and hard x-ray excess. instead, comptonization reproduces the broadband (0.3-79 kev) continuum well, together with a contribution from a mildly relativistic disk reflection spectrum.conclusions: during this 2014 observational campaign, the soft x-ray spectrum of ark 120 below ~0.5 kev was found to be dominated by comptonization of seed photons from the disk by a warm (kte ~ 0.5 kev), optically-thick corona (τ ~ 9). above this energy, the x-ray spectrum becomes dominated by comptonization from electrons in a hot optically thin corona, while the broad fe kα line and the mild compton hump result from reflection off the disk at several tens of gravitational radii. | a deep x-ray view of the bare agn ark 120. iv. xmm-newton and nustar spectra dominated by two temperature (warm, hot) comptonization processes |
we have utilized high-resolution optical hubble space telescope images and deep, ground-based near-infrared images to examine the host galaxies of 37 active galactic nuclei (agns) with reverberation-based black hole masses. using two-dimensional image decompositions, we have separated the host galaxy from the bright central agn, allowing a re-examination of the {m}bh}{--}{l}bulge} and {m}bh}{--}{l}galaxy} relationships and the {m}bh}{--}{m}bulge} and {m}bh}{--}{m}stars} relationships using v-h color to constrain the stellar mass-to-light ratio. we find clear correlations for all of these scaling relationships, and the best-fit correlations are generally in good agreement with the sample of early-type galaxies with m bh from dynamical modeling and the sample of megamasers. we also find good agreement with the expectations from the illustris simulations, although the agreement with other simulations is less clear because of the different black hole mass ranges that are probed. {m}bh}{--}{l}bulge} is found to have the least scatter, and is therefore the best predictor of m bh among the relationships examined here. large photometric surveys that rely on automated analysis and forego bulge-to-disk decompositions will achieve more accurate m bh predictions if they rely on {m}bh}{--}{m}stars} rather than {m}bh}{--}{l}galaxy}. finally, we have examined m bh/m stars and find a clear trend with black hole mass but not galaxy mass. this trend is also exhibited by galaxies with m bh from dynamical modeling and megamaser galaxies, as well as simulated galaxies from illustris, rising from ∼0.01% at 106 m ⊙ to ∼1.0% at 1010 m ⊙. this scaling should be taken into account when comparing galaxy samples that are not matched in m bh. | black hole-galaxy scaling relationships for active galactic nuclei with reverberation masses |
we present the ultraviolet (uv) spectroscopic evolution of a tidal disruption event (tde) for the first time. after the discovery of the nearby tde iptf16fnl, we obtained a series of observations with the space telescope imaging spectrograph (stis) onboard the hubble space telescope (hst). the dominant emission features closely resemble those seen in the uv spectra of the tde asassn-14li and are also similar to those of n-rich quasars. there is evolution in the shape and central wavelength of the dominant emission features over the course of our observations, such that at early times the lines tend to be broad and redshifted, while at later times they are narrower and peak near the wavelengths of their atomic transitions. like asassn-14li, but unlike n-rich quasars, iptf16fnl shows neither mg ii 2798 å nor c iii] 1909 å emission features. we also present optical photometry and spectroscopy, which suggest that the complex he ii profiles observed in the optical spectra of many tdes are in part due to the presence of n iii and c iii wolf-rayet features, which can potentially serve as probes of the far-uv when space-based observations are not possible. finally, we use swift x-ray telescope and ultraviolet/optical telescope (uvot) observations to place strong limits on the x-ray emission and determine the characteristic temperature, radius and luminosity of the emitting material. we find that iptf16fnl is subluminous and evolves more rapidly than other optically discovered tdes. | the ultraviolet spectroscopic evolution of the low-luminosity tidal disruption event iptf16fnl |
we have analysed the differences in positions of 9081 matched sources between the gaia data release 2 (dr2) and very long baseline interferometry (vlbi) catalogues. the median position uncertainty of matched sources in the vlbi catalogue is a factor of two larger than the median position uncertainty in gaia dr2. there are 9 per cent matched sources with statistically significant offsets between both catalogues. we found that the reported positional errors should be rescaled by a factor of 1.3 for vlbi and 1.06 for gaia and, in addition, the gaia errors should be multiplied by the square root of chi squared per degree of freedom in order to best fit the normalized position differences to the rayleigh distribution. we have established that the major contributor to statistically significant position offsets is the presence of optical jets. among the sources for which the jet direction was determined, the position offsets are parallel to the jet directions for 62 per cent of the outliers. among the matched sources with significant proper motion, the fraction of objects with proper motion directions parallel to jets is a factor of three greater than on average. such sources have systematically higher chi squared per degree of freedom. we explain these proper motions as a manifestation of the source position jitter caused by flares, which we predicted earlier. therefore, the assumption that quasars are fixed points, and thus that differential proper motions determined with respect to quasar photocentres can be regarded as absolute proper motions, should be treated with great caution. | a quantitative analysis of systematic differences in the positions and proper motions of gaia dr2 with respect to vlbi |
we present the results of a model-independent investigation of the rest-frame uv spectra from a comprehensive sample of 394 quasars in the redshift range 1.5 ≤ z ≤ 7.5. we fit the main broad emission lines (bels) in the rest-frame range 1280 å ≤ λ ≤ 3000 å (o i, c ii, si iv, c iii], c iv, and mg ii) with a lightly supervised spline fitting technique. redshifts are derived from the peaks of each fitted bel and used to compute relative velocity shifts. we show that our method gives unbiased velocity shifts and is insensitive to spectral resolution and instrumental parameters. it is found that the average blueshift of the c iv line with respect to several low-ionization lines in luminosity-matched samples does not significantly evolve over 1.5 ≤ z ≤ 6. however, the average blueshift increases significantly by a factor of ∼2.5 at z ≳ 6. we propose that this redshift evolution can be explained by c iv winds launched perpendicularly to an accretion disc with increased torus opacity at high redshift, coupled with a potential orientation-driven selection bias. our results open new exciting avenues of investigation into young quasars in the reionization epoch. | new constraints on quasar evolution: broad-line velocity shifts over 1.5 ≲ z ≲ 7.5 |
we resolve the host galaxies of seven gravitationally lensed quasars at redshift 1.5-2.8 using observations with the atacama large (sub)millimetre array. using a visibility plane lens modelling technique, we create pixellated reconstructions of the dust morphology, and co line morphology and kinematics. we find that the quasar hosts in our sample can be distinguished into two types: (1) galaxies characterized by clumpy, extended dust distributions (reff ∼ 2 kpc) and mean star formation rate (sfr) surface densities comparable to sub-mm-selected dusty star-forming galaxies (σsfr ∼ 3 m⊙ yr-1 kpc-2 ) and (2) galaxies that have sizes in dust emission similar to coeval passive galaxies and compact starbursts (reff ∼ 0.5 kpc), with high mean sfr surface densities (σsfr = 400-4500 m⊙ yr-1 kpc-2 ) that may be eddington-limited or super-eddington. the small sizes of some quasar hosts suggest that we observe them at a stage in their transformation into compact spheroids via dissipative contraction, where a high density of dynamically unstable gas leads to efficient star formation and black hole accretion. for the one system where we probe the bulk of the gas reservoir, we find a gas fraction of just 0.06 ± 0.04 and a depletion time-scale of 50 ± 40 myr, suggesting it is transitioning into quiescence. in general, we expect that the extreme level of star formation in the compact quasar host galaxies will rapidly exhaust their gas reservoirs and could quench with or without help from active galactic nucleus feedback. | the rocky road to quiescence: compaction and quenching of quasar host galaxies at z ∼ 2 |
we present the effective-field theory (eft-)based cosmological full-shape analysis of the anisotropic power spectrum of eboss quasars at the effective redshift zeff=1.48 . we perform extensive tests of our pipeline on simulations, paying particular attention to the modeling of observational systematics, such as redshift smearing, fiber collisions, and the radial integral constraint. assuming the minimal λ cold dark matter model, and fixing the primordial power spectrum tilt and the physical baryon density, we find the hubble constant h0=(66.7 ±3.2 ) km s-1 mpc-1 , the matter density fraction ωm=0.32 ±0.03 , and the late-time mass fluctuation amplitude σ8=0.95 ±0.08 . these measurements are fully consistent with the planck cosmic microwave background results. our eboss quasar s8 posterior, 0.98 ±0.11 , does not exhibit the so-called s8 tension. our work paves the way for systematic full-shape analyses of quasar samples from future surveys like desi. | cosmological constraints from the power spectrum of eboss quasars |
general relativity reproduces main current cosmological observations, assuming the validity of the cosmic distance duality relation (cddr) at all scales and epochs. however, cddr is poorly tested in the redshift interval between the farthest observed type ia supernovae and that of the cosmic microwave background. we present a new idea of testing the validity of cddr, through the multiple measurements of high-redshift quasars. luminosity distances are derived from the relation between the uv and x-ray luminosities of quasars, while angular diameter distances are obtained from the compact structure in radio quasars. this will create a valuable opportunity where two different cosmological distances from the same kind of objects at high redshifts are compared. our constraints are more stringent than other currently available results based on different observational data and show no evidence for the deviation from cddr at z ∼ 3. such an accurate model-independent test of fundamental cosmological principles can become a milestone in precision cosmology. | multiple measurements of quasars acting as standard probes: exploring the cosmic distance duality relation at higher redshift |
we derive predictions from state-of-the-art cosmological galaxy simulations for the spatial distribution of the hot circumgalactic medium (cgm, [0.1-1]r200c) through its emission lines in the x-ray soft band ([0.3-1.3] kev). in particular, we compare illustristng, eagle, and simba and focus on galaxies with stellar mass $10^{10-11.6}\, \rm {m}_{\odot }$ at z = 0. the three simulation models return significantly different surface brightness radial profiles of prominent emission lines from ionized metals such as o vii(f), o viii, and fe xvii as a function of galaxy mass. likewise, the three simulations predict varying azimuthal distributions of line emission with respect to the galactic stellar planes, with illustristng predicting the strongest angular modulation of cgm physical properties at radial range ${{\gtrsim}0.3{-}0.5\, r_{200c}}$. this anisotropic signal is more prominent for higher energy lines, where it can manifest as x-ray erosita-like bubbles. despite different models of stellar and supermassive black hole (smbh) feedback, the three simulations consistently predict a dichotomy between star-forming and quiescent galaxies at the milky way and andromeda mass range, where the former are x-ray brighter than the latter. this is a signature of smbh-driven outflows, which are responsible for quenching star formation. finally, we explore the prospect of testing these predictions with a microcalorimeter-based x-ray mission concept with a large field of view. such a mission would probe the extended hot cgm via soft x-ray line emission, determine the physical properties of the cgm, including temperature, from the measurement of line ratios, and provide critical constraints on the efficiency and impact of smbh feedback on the cgm. | x-ray metal line emission from the hot circumgalactic medium: probing the effects of supermassive black hole feedback |
understanding the growth of the supermassive black holes (smbh) powering luminous quasars, their co-evolution with host galaxies, and impact on the surrounding intergalactic medium (igm) depends sensitively on the duration of quasar accretion episodes. unfortunately, this time-scale, known as the quasar lifetime, tq, is still uncertain by orders of magnitude ($t_{\rm q} \simeq 0.01\, {\rm myr} - 1\, {\rm gyr}$). however, the extent of the he ii ly α proximity zones in the absorption spectra of zqso ~ 3-4 quasars constitutes a unique probe, providing sensitivity to lifetimes up to ~30 myr. our recent analysis of 22 archival hubble space telescope he ii proximity zone spectra reveals a surprisingly broad range of emission time-scales, indicating that some quasars turned on ≲1 myr ago, whereas others have been shining for ≳30 myr. determining the underlying quasar lifetime distribution (qld) from proximity zone measurements is a challenging task owing to: (1) the limited sensitivity of individual measurements; (2) random sampling of the quasar light curves; (3) density fluctuations in the quasar environment; and (4) the inhomogeneous ionization state of he ii in a reionizing igm. we combine a seminumerical he ii reionization model, hydrodynamical simulations post-processed with ionizing radiative transfer, and a novel statistical framework to infer the qld from an ensemble of proximity zone measurements. assuming a lognormal qld, we infer a mean $\langle {\rm log}_{10}(t_{\rm q} / {\rm myr})\rangle = 0.22^{+0.22}_{-0.25}$ and standard deviation $\sigma _{{\rm log}_{10}t_{\rm q}} = 0.80^{+0.37}_{-0.27}$. our results allow us to estimate the probability of detecting very young quasars with tq ≤ 0.1 myr from their proximity zone sizes yielding $p ({\le}0.1\, {\rm myr}) = 0.19^{+0.11}_{-0.09}$, which is broadly consistent with recent determination at z ~ 6. | the first measurement of the quasar lifetime distribution |
we present a novel, few-body computational framework designed to shed light on the likelihood of forming intermediate-mass (im) and supermassive (sm) black holes (bhs) in nuclear star clusters (nscs) through successive bh mergers, initiated with a single bh seed. using observationally motivated nsc profiles, we find that the probability of an ${\sim }100\hbox{-}\mathrm{m}_\odot$ bh to grow beyond ${\sim }1000 \, \mathrm{m}_\odot$ through successive mergers ranges from ${\sim }0.1~{{\ \rm per\ cent}}$ in low-density, low-mass clusters to nearly 90 per cent in high-mass, high-density clusters. however, in the most massive nscs, the growth time-scale can be very long ($\gtrsim 1\,$ gyr); vice versa, while growth is least likely in less massive nscs, it is faster there, requiring as little as ${\sim }0.1\,$gyr. the increased gravitational focusing in systems with lower velocity dispersions is the primary contributor to this behaviour. we find that there is a simple '7-strikes-and-you're-in' rule governing the growth of bhs: our results suggest that if the seed survives 7-10 successive mergers without being ejected (primarily through gravitational wave recoil kicks), the growing bh will most likely remain in the cluster and will then undergo runaway, continuous growth all the way to the formation of an smbh (under the simplifying assumption adopted here of a fixed background nsc). furthermore, we find that rapid mergers enforce a dynamically mediated 'mass gap' between about ${50\!-\!300 \, \mathrm{m}_\odot }$ in an nsc. | growing black holes through successive mergers in galactic nuclei - i. methods and first results |
aims: modelling the low-ionisation lines (lils) in active galactic nuclei (agns) still faces problems in explaining the observed equivalent widths (ews) when realistic covering factors are used and the distance of the broad-line region (blr) from the centre is assumed to be consistent with the reverberation mapping measurements. we re-emphasise this problem and suggest that the blr `sees' a different continuum from that seen by a distant observer. this change in the continuum reflected in the change in the net bolometric luminosity from the agn is then able to resolve the above problem.methods: we carefully examine the optical fe ii and near-infrared (nir) ca ii triplet (cat) emission strengths with respect to hβ emission using the photoionisation code cloudy and a range of physical parameters. prominent among these parameters are (a) the ionisation parameter (u), (b) the local blr cloud density (nh), (c) the metal content in the blr cloud, and (d) the cloud column density. using an incident continuum for i zw 1 -a prototypical type-1 narrow-line seyfert galaxy- our basic setup is able to recover the line ratios for the optical fe ii (i.e. rfeii) and for the nir cat (i.e. rcat) in agreement with the observed estimates. nevertheless, the pairs of (u,nh) that reproduce the conforming line ratios do not relate to agreeable line ews. we therefore propose a way to mitigate this issue. the lil region of the blr cloud does not see the same continuum emitted by the accretion disc as that seen by a distant observer; rather it sees a filtered version of the original continuum which brings the radial sizes into agreement with the reverberation mapped estimates for the extension of the blr. this is achieved by scaling the radial distance of the emitting regions from the central continuum source using the photoionisation method in correspondence with the reverberation mapping estimates for i zw 1. taking inspiration from past studies, we suggest that this collimation of the incident continuum can be explained by the anisotropic emission from the accretion disc, which modifies the spectral energy distribution such that the blr receives a much cooler continuum with a reduced number of line-ionising photons, allowing reconciliation in the modelling with the line ews.results: (1) the assumption of the filtered continuum as the source of blr irradiation recovers realistic ews for the lil species, such as the hβ, fe ii, and cat. however, our study finds that to account for the adequate rfeii (fe ii/hβ flux ratio) emission, the blr needs to be selectively overabundant in iron. on the other hand, the rcat (cat/hβ flux ratio) emission spans a broader range from solar to super-solar metallicities. in all these models, the blr cloud density is found to be consistent with our conclusions from prior studies, that is, nh ∼ 1012 cm−3 is required for the sufficient emission of fe ii and cat. (2) we extend our modelling to test and confirm the co-dependence between metallicity and cloud column density for these two ionic species (fe ii and cat), further allowing us to constrain the physical parameter space for the emission of these lils. adopting the estimates from line ratios that diagnose the metallicity in these gas-rich media -which suggest super-solar values (≳5−10 z⊙)-, we arrive at cloud columns that are of the order of 1024 cm−2. (3) finally, we test the effect of inclusion of a micro-turbulent velocity within the blr cloud and find that the fe ii emission is positively affected. an interesting result obtained here is the reduction in the value of the metallicity by up to a factor of ten for the rfeii cases when the microturbulence is invoked, suggesting that microturbulence can act as an apparent metallicity controller for the fe ii. on the contrary, the rcat cases are relatively unaffected by the inclusion of microturbulence. | the cafe project: optical fe ii and near-infrared ca ii triplet emission in active galaxies: simulated ews and the co-dependence of cloud size and metal content |
we study the genesis and evolution of supermassive black hole (smbh) seeds through different formation channels, from popiii remnants to massive seeds, modelled within the l-galaxies semi-analytic code. we run the model on the millennium-ii simulation (mr-ii) merger trees, as their halo-mass resolution ($m_{\rm vir,res} \sim 10^7\, \mathrm{m}_\odot \, h^{-1}$) allows to study in a cosmological volume ($l_{\rm box}=100\, \mathrm{mpc}\, h^{-1}$) the evolution of atomic-cooling haloes ($t_{\rm vir} \gtrsim 10^4\, \mathrm{k}$) where intermediate-mass and heavy seeds are expected to form. we track the formation of these seeds according to spatial variations of the chemical and radiative feedback of star formation. not being able to resolve the first mini-haloes ($t_{\rm vir} \sim 10^3\, \mathrm{k}$), we inherit evolved popiii remnants in a sub-grid fashion, using the results of the gqd model. we also include the formation of heavy seeds in gas-rich massive mergers, which are very rare in the mr-ii volume. the descendants of light seeds numerically prevail among our smbhs population at all masses and z. heavier seeds form in dense environments where close neighbours provide the required uv illumination. overall, our model produces a z = 0 smbhs population whose statistical properties meet current constraints. we find that the bh occupation fraction highly depends on the seeding efficiency and that the scaling relation between bh and stellar mass, in the dwarf-mass regime, is flatter than in the high-mass range. finally, a fraction of bhs hosted in local dwarf galaxies never grow since they form at z > 6. | multiflavour smbh seeding and evolution in cosmological environments |
the physical properties of galactic winds are one of the keys to understand galaxy formation and evolution. these properties can be constrained thanks to background quasar lines of sight (los) passing near star-forming galaxies (sfgs). we present the first results of the muse gas flow and wind survey obtained from two quasar fields, which have eight mg ii absorbers of which three have rest equivalent width greater than 0.8 å. with the new multi unit spectroscopic explorer (muse) spectrograph on the very large telescope (vlt), we detect six (75%) mg ii host galaxy candidates within a radius of 30″ from the quasar los. out of these six galaxy-quasar pairs, from geometrical argument, one is likely probing galactic outflows, where two are classified as “ambiguous,” two are likely probing extended gaseous disks and one pair seems to be a merger. we focus on the wind-pair and constrain the outflow using a high-resolution quasar spectra from the ultraviolet and visual echelle spectrograph. assuming the metal absorption to be due to ga;s flowing out of the detected galaxy through a cone along the minor axis, we find outflow velocities in the order of ≈150 {km} {{{s}}}-1 (i.e., smaller than the escape velocity) with a loading factor, η ={\dot{m}}{out}/{{sfr}}, of ≈0.7. we see evidence for an open conical flow, with a low-density inner core. in the future, muse will provide us with about 80 multiple galaxy-quasar pairs in two dozen fields. based on observations made at the eso telescopes under programs 094.a-0211(b) and 293.a-5038(a). | muse gas flow and wind (megaflow). i. first muse results on background quasars |
the completed extended baryon oscillation spectroscopic survey (eboss) catalogues contain redshifts of 344 080 quasars at 0.8 < z < 2.2, 174 816 luminous red galaxies between 0.6 < z < 1.0, and 173 736 emission-line galaxies over 0.6 < z < 1.1 in order to constrain the expansion history of the universe and the growth rate of structure through clustering measurements. mechanical limitations of the fibre-fed spectrograph on the sloan telescope prevent two fibres being placed closer than 62 arcsec in a single pass of the instrument. these 'fibre collisions' strongly correlate with the intrinsic clustering of targets and can bias measurements of the two-point correlation function resulting in a systematic error on the inferred values of the cosmological parameters. we combine the new techniques of pairwise-inverse probability and the angular upweighting (pip+ang) to correct the clustering measurements for the effect of fibre collisions. using mock catalogues, we show that our corrections provide unbiased measurements, within data precision, of both the projected $\rm {\mathit{ w}_p}\left(\mathit{ r}_p\right)$ and the redshift-space multipole ξ(ℓ = 0, 2, 4)(s) correlation functions down to $0.1\, h^{-1}{\rm mpc}$, regardless of the tracer type. we apply the corrections to the eboss dr16 catalogues. we find that, on scales $s\gtrsim 20\, h^{-1}{\rm mpc}$ for ξℓ, as used to make baryon acoustic oscillation and large-scale redshift-space distortion measurements, approximate methods such as nearest-neighbour upweighting are sufficiently accurate given the statistical errors of the data. using the pip method, for the first time for a spectroscopic program of the sloan digital sky survey, we are able to successfully access the one-halo term in the clustering measurements down to $\sim 0.1\, h^{-1}{\rm mpc}$ scales. our results will therefore allow studies that use the small-scale clustering to strengthen the constraints on both cosmological parameters and the halo occupation distribution models. | the completed sdss-iv extended baryon oscillation spectroscopic survey: pairwise-inverse probability and angular correction for fibre collisions in clustering measurements |
the australian dark energy survey (ozdes) is a five-year, 100-night, spectroscopic survey on the anglo-australian telescope, whose primary aim is to measure redshifts of approximately 2500 type ia supernovae host galaxies over the redshift range 0.1 < z < 1.2, and derive reverberation-mapped black hole masses for approximately 500 active galactic nuclei and quasars over 0.3 < z < 4.5. this treasure trove of data forms a major part of the spectroscopic follow-up for the dark energy survey for which we are also targeting cluster galaxies, radio galaxies, strong lenses, and unidentified transients, as well as measuring luminous red galaxies and emission line galaxies to help calibrate photometric redshifts. here, we present an overview of the ozdes programme and our first-year results. between 2012 december and 2013 december, we observed over 10 000 objects and measured more than 6 000 redshifts. our strategy of retargeting faint objects across many observing runs has allowed us to measure redshifts for galaxies as faint as mr = 25 mag. we outline our target selection and observing strategy, quantify the redshift success rate for different types of targets, and discuss the implications for our main science goals. finally, we highlight a few interesting objects as examples of the fortuitous yet not totally unexpected discoveries that can come from such a large spectroscopic survey. | ozdes multifibre spectroscopy for the dark energy survey: first-year operation and results |
we introduce a new method for determining the influence of galaxies and active galactic nuclei (agn) on the intergalactic medium (igm) at high redshift and illustrate its potential via a first application to the field of the z = 6.42 qso j1148+5251. correlating spatial positions lyman break galaxies (lbgs) with the lyman alpha forest seen in the spectrum of a background qso, we provide a statistical measure of the typical escape fraction of lyman continuum photons. using keck deimos spectroscopy to locate seven colour-selected lbgs in the range 5.3 ≲ z ≲ 6.4 we examine the spatial correlation between this sample and lyα/lyβ transmission fluctuations in a keck esi spectrum of the qso. interpreting the statistical h i proximity effect as arising from faint galaxies clustered around the lbgs, we translate the observed mean lyα transmitted flux into a constraint on the mean escape fraction ⟨fesc⟩ ⩾ 0.08 at z ≃ 6. we also report individual transverse h i proximity effect for a z = 6.177 luminous lbg via a lyβ transmission spike and two broad lyα transmission spikes around the z = 5.701 agn. we discuss the origin of such associations which suggest that while faint galaxies are primarily driving reionization, luminous galaxies and agn may provide important contributions to the uv background or thermal fluctuations of the igm at z ≃ 6. although a limited sample, our results demonstrate the potential of making progress using this method in resolving one of the most challenging aspects of the contribution of galaxies and agn to cosmic reionization. | the role of galaxies and agn in reionizing the igm - i. keck spectroscopy of 5 < z < 7 galaxies in the qso field j1148+5251 |
we study h i and metal-line absorption around z ≈ 2 star-forming galaxies by comparing an analysis of data from the keck baryonic structure survey to mock spectra generated from the evolution and assembly of galaxies and their environments (eagle) cosmological, hydrodynamical simulations. we extract sightlines from the simulations and compare the properties of the absorption by h i, c iv, and si iv around simulated and observed galaxies using pixel optical depths. we mimic the resolution, pixel size, and signal-to-noise ratio of the observations, as well as the distributions of impact parameters and galaxy redshift errors. we find that the eagle reference model is in excellent agreement with the observations. in particular, the simulation reproduces the high metal-line optical depths found at small galactocentric distances, the optical depth enhancements out to impact parameters of 2 proper mpc, and the prominent redshift-space distortions which we find are due to peculiar velocities rather than redshift errors. the agreement is best for halo masses ~1012.0 m⊙, for which the observed and simulated stellar masses also agree most closely. we examine the median ion mass-weighted radial gas velocities around the galaxies, and find that most of the gas is infalling, with the infall velocity depending on halo rather than stellar mass. from this, we conclude that the observed redshift-space distortions are predominantly caused by infall rather than outflows. | a comparison of observed and simulated absorption from h i, c iv, and si iv around z ≈ 2 star-forming galaxies suggests redshift-space distortions are due to inflows |
a new estimation of the isotropic diffuse γ -ray background (igrb) observed by the large area telescope (lat) on board the fermi gamma-ray space telescope (fermi) has been presented for 50 months of data, in the energy range 100 mev-820 gev and for different modelings of the galactic foreground. we attempt here the interpretation of the fermi-lat igrb data in terms of the γ -ray unresolved emission from different extragalactic populations. we find very good fits to the experimental igrb, obtained with theoretical predictions for the emission from active galactic nuclei and star-forming galaxies. in addition, we probe a possible emission coming from the annihilation of weakly interacting dark matter (dm) particles in the halo of our galaxy. we set stringent limits on its annihilation cross section into γ rays, which are about the thermal relic value for a wide range of dm masses. we also identify regions in the dm mass and annihilation cross section parameter space which can significantly improve the fit to the igrb data. our analysis is conducted within the different igrb data sets obtained from different models for the galactic emission, which is shown to add a significant ambiguity on the igrb interpretation. | composition of the fermi-lat isotropic gamma-ray background intensity: emission from extragalactic point sources and dark matter annihilations |
we present two catalogues of active galactic nucleus (agn) candidates selected from the latest data of two all-sky surveys - data release 2 of the gaia mission and the unwise catalogue of the wide-field infrared survey explorer (wise). we train a random forest classifier to predict the probability of each source in the gaia-unwise joint sample being an agn, prf, based on gaia astrometric and photometric measurements and unwise photometry. the two catalogues, which we designate c75 and r85, are constructed by applying different prf threshold cuts to achieve an overall completeness of 75 per cent (≈90 per cent at gaiag ≤ 20 mag) and reliability of 85 per cent, respectively. the c75 (r85) catalogue contains 2734 464 (2182 193) agn candidates across the effective 36 000 deg2 sky, of which ≈0.91 (0.52) million are new discoveries. photometric redshifts of the agn candidates are derived by a random forest regressor using gaia and wise magnitudes and colours. the estimated overall photometric redshift accuracy is 0.11. cross-matching the agn candidates with a sample of known bright cluster galaxies, we identify a high-probability strongly lensed agn candidate system, sdss j1326+4806, with a large image separation of 21{^''.}06. all the agn candidates in our catalogues will have ∼5-yr long light curves from gaia by the end of the mission, and thus will be a great resource for agn variability studies. our agn catalogues will also be helpful in agn target selections for future spectroscopic surveys, especially those in the southern hemisphere. the c75 catalogue can be downloaded at https://www.ast.cam.ac.uk/ ypshu/agn_catalogues.html. | catalogues of active galactic nuclei from gaia and unwise data |
we carry out a series of deep karl g. jansky very large array (vla) s-band observations of a sample of 21 quasars at z ∼ 6. the new observations expand the searches of radio continuum emission to the optically faint quasar population at the highest redshift with rest-frame $4400\,\mathring{\rm a} $ luminosities down to $3\times {10}^{11}\ {l}_{\odot }$ . we report the detections of two new radio-loud quasars: cfhqs j2242+0334 (hereafter j2242+0334) at z = 5.88 and cfhqs j0227-0605 (hereafter j0227-0605) at z = 6.20, detected with 3 ghz flux densities of $87.0\pm 6.3\ \mu \mathrm{jy}$ and $55.4\pm 6.7\ \mu \mathrm{jy}$ , respectively. their radio loudnesses are estimated to be 54.9 ± 4.7 and 16.5 ± 3.2, respectively. to better constrain the radio-loud fraction (rlf), we combine the new measurements with the archival vla l-band data as well as available data from the literature, considering the upper limits for non-detections and possible selection effects. the final derived rlf is 9.4 ± 5.7% for the optically selected quasars at z ∼ 6. we also compare the rlf to that of the quasar samples at low redshift and check the rlf in different quasar luminosity bins. the rlf for the optically faint objects is still poorly constrained due to the limited sample size. our results show no evidence of significant quasar rlf evolution with redshift. there is also no clear trend of rlf evolution with quasar uv/optical luminosity due to the limited sample size of optically faint objects with deep radio observations. | constraining the quasar radio-loud fraction at z ∼ 6 with deep radio observations |
the high redshift lyman-α forest, in particular the gunn-peterson trough, is the most unambiguous signature of the neutral to ionized transition of the intergalactic medium (igm) taking place during the epoch of reionization. recent studies have shown that reproducing the observed lyman-α opacity distributions after overlap required a non-monotonous evolution of cosmic emissivity: rising, peaking at z ~ 6, and then decreasing onwards to z = 4. such an evolution is puzzling considering galaxy buildup and the cosmic star formation rate are still continously on the rise at these epochs. here, we use new ramses-cudaton simulations to show that such a peaked evolution may occur naturally in a fully coupled radiation-hydrodynamical framework. in our fiducial run, cosmic emissivity at z > 6 is dominated by a low mass (${\rm m_{dm}}\lt 2 \times 10^9 \rm \,m_{\odot }$), high escape fraction halo population, driving reionization, up to overlap. approaching z = 6, this population is radiatively suppressed due to the rising ionizing uv background, and its emissivity drops. in the meantime, the high mass halo population builds up and its emissivity rises, but not fast enough to compensate the dimming of the low mass haloes, because of low escape fractions. the combined ionizing emissivity of these two populations therefore naturally results in a rise and fall of the cosmic emissivity, from z = 12 to z = 4, with a peak at z ~ 6. an alternative run, which features higher escape fractions for the high mass haloes and later suppression at low mass, leads to overshooting the ionizing rate, over-ionizing the igm and therefore too low lyman-α opacities. | lyman-alpha opacities at z = 4-6 require low mass, radiatively-suppressed galaxies to drive cosmic reionization |
we study the physical properties of a homogeneous sample of 157 optically thick absorption line systems at redshifts ∼1.8-4.4, selected from a high-dispersion spectroscopic survey of lyman limit systems (llss). by means of multiple ionization models and bayesian techniques, we derive the posterior probability distribution functions for the density, metallicity, temperature and dust content of the absorbing gas. we find that z > 2 llss are highly ionized with ionization parameters between -3 ≲ log u ≲ -2, depending on the h i column density. llss are characterized by low temperatures (t < 5 × 104k) and reside in dust-poor environments. between z ∼ 2.5-3.5, ∼80 per cent of the llss have physical densities between nh ∼ 10- 3.5-10- 2 cm- 3 for the assumed uv background, but we caution that a degeneracy between the ionization parameter and the intensity of the radiation field prevents robust inference on the density and sizes of llss. conversely, metallicity estimates are less sensitive to the assumptions behind ionization corrections. llss at z > 2 are characterized by a broad unimodal distribution over > 4 orders of magnitude, with a peak at log z/z⊙ ∼ -2. llss are metal poor, significantly less enriched than dlas, with ∼70 per cent of the metallicity pdf below log z/z⊙ ≤ -1.5. the median metallicity of super llss with log n_{h i}≥ 19 rapidly evolves with redshift, with a 10-fold increase between z ∼ 2.1-3.6 (∼1.5 gyr). based on this sample, we find that llss at z = 2.5-3.5 account for ∼15 per cent of all the metals produced by uv-selected galaxies. the implications for theories of cold gas accretion and metal ejection from galaxies are also discussed. | the physical properties of z > 2 lyman limit systems: new constraints for feedback and accretion models |
outbursts from gamma-ray quasars provide insights on the relativistic jets of active galactic nuclei and constraints on the diffuse radiation fields that fill the universe. the detection of significant emission above 100 gev from a distant quasar would show that some of the radiated gamma-rays escape pair-production interactions with low-energy photons, be it the extragalactic background light (ebl), or the radiation near the supermassive black hole lying at the jet’s base. veritas detected gamma-ray emission up to ∼200 gev from pks 1441+25 (z = 0.939) during 2015 april, a period of high activity across all wavelengths. this observation of pks 1441+25 suggests that the emission region is located thousands of schwarzschild radii away from the black hole. the gamma-ray detection also sets a stringent upper limit on the near-ultraviolet to near-infrared ebl intensity, suggesting that galaxy surveys have resolved most, if not all, of the sources of the ebl at these wavelengths. | gamma-rays from the quasar pks 1441+25: story of an escape |
context. the reionisation of the universe is a process that is thought to have ended around z ~ 6, as inferred from spectroscopy of distant bright background sources, such as quasars (qso) and gamma-ray burst (grb) afterglows. furthermore, spectroscopy of a grb afterglow provides insight in its host galaxy, which is often too dim and distant to study otherwise.aims: for the swift grb 130606a at z = 5.913 we have obtained a high s/n spectrum covering the full optical and near-ir wavelength region at intermediate spectral resolution with vlt/x-shooter. we aim to measure the degree of ionisation of the intergalactic medium (igm) between z = 5.02-5.84 and to study the chemical abundance pattern and dust content of its host galaxy.methods: we estimated the uv continuum of the grb afterglow using a power-law extrapolation, then measured the flux decrement due to absorption at lyα,β, and γ wavelength regions. furthermore, we fitted the shape of the red damping wing of lyα. the hydrogen and metal absorption lines formed in the host galaxy were fitted with voigt profiles to obtain column densities. we investigated whether ionisation corrections needed to be applied.results: our measurements of the lyα-forest optical depth are consistent with previous measurements of qsos, but have a much smaller uncertainty. the analysis of the red damping wing yields a neutral fraction xh i< 0.05 (3σ). we obtain column density measurements of h, al, si, and fe; for c, o, s and ni we obtain limits. the ionisation due to the grb is estimated to be negligible (corrections <0.03 dex), but larger corrections may apply due to the pre-existing radiation field (up to 0.4 dex based on sub-dla studies). assuming that [ si/fe ] = +0.79 ± 0.13 is due to dust depletion, the dust-to-metal ratio is similar to the galactic value.conclusions: our measurements confirm that the universe is already predominantly ionised over the redshift range probed in this work, but was slightly more neutral at z> 5.6. grbs are useful probes of the ionisation state of the igm in the early universe, but because of internal scatter we need a larger statistical sample to draw robust conclusions. the high [si/fe] in the host can be due to dust depletion, α-element enhancement, or a combination of both. the very high value of [ al/fe ] = 2.40 ± 0.78 might be due to a proton capture process and is probably connected to the stellar population history. we estimate the host metallicity to be -1.7 < [ m/h ] < -0.9 (2%-13% of solar). based on observations carried out under prog. id 091.c-0934(c) with the x-shooter spectrograph installed at the cassegrain focus of the very large telescope (vlt), unit 2 - kueyen, operated by the european southern observatory (eso) on cerro paranal, chile. partly based on observations made with the nordic optical telescope, operated on the island of la palma jointly by denmark, finland, iceland, norway, and sweden, in the spanish observatorio del roque de los muchachos of the instituto de astrofísica de canarias. partly based on observations made with the italian telescopio nazionale galileo (tng) operated on the island of la palma by the fundación galileo galilei of the inaf (istituto nazionale di astrofisica) at the spanish observatorio del roque de los muchachos of the instituto de astrofísica de canarias, under programme a26tac_63.appendix a is available in electronic form at http://www.aanda.orgthe reduced spectrum (fits file) is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/580/a139 | vlt/x-shooter spectroscopy of the afterglow of the swift grb 130606a. chemical abundances and reionisation at z ~ 6 |
radio-loud active galactic nuclei at z∼ 2-4 are typically located in dense environments and their host galaxies are among the most massive systems at those redshifts, providing key insights for galaxy evolution. finding radio-loud quasars at the highest accessible redshifts (z∼ 6) is important to the study of their properties and environments at even earlier cosmic time. they could also serve as background sources for radio surveys intended to study the intergalactic medium beyond the epoch of reionization in hi 21 cm absorption. currently, only five radio-loud (r={{f}ν ,5 ghz}/{{f}ν ,4400 \overset{\circa }}\gt 10) quasars are known at z∼ 6. in this paper we search for 5.5≲ z≲ 7.2 quasars by cross-matching the optical panoramic survey telescope & rapid response system 1 and radio faint images of the radio sky at twenty cm surveys. the radio information allows identification of quasars missed by typical color-based selections. while we find no good 6.4≲ z≲ 7.2 quasar candidates at the sensitivities of these surveys, we discover two new radio-loud quasars at z∼ 6. furthermore, we identify two additional z∼ 6 radio-loud quasars that were not previously known to be radio-loud, nearly doubling the current z∼ 6 sample. we show the importance of having infrared photometry for z\gt 5.5 quasars to robustly classify them as radio-quiet or radio-loud. based on this, we reclassify the quasar j0203+0012 (z = 5.72), previously considered radio-loud, to be radio-quiet. using the available data in the literature, we constrain the radio-loud fraction of quasars at z∼ 6, using the kaplan-meier estimator, to be 8.1-3.2+5.0%. this result is consistent with there being no evolution of the radio-loud fraction with redshift, in contrast to what has been suggested by some studies at lower redshifts. | constraining the radio-loud fraction of quasars at z > 5.5 |
observations of high-redshift quasars at z > 6 indicate that they harbour supermassive black holes (smbhs) of a billion solar masses. the direct collapse scenario has emerged as the most plausible way to assemble smbhs. the nurseries for the direct collapse black holes are massive primordial haloes illuminated with an intense uv flux emitted by population ii (pop ii) stars. in this study, we compute the critical value of such a flux (j_{21}^crit) for realistic spectra of pop ii stars through three-dimensional cosmological simulations. we derive the dependence of j_{21}^crit on the radiation spectra, on variations from halo to halo, and on the impact of x-ray ionization. our findings show that the value of j_{21}^crit is a few times 104 and only weakly depends on the adopted radiation spectra in the range between trad = 2 × 104and105 k. for three simulated haloes of a few times 107 m⊙, j_{21}^crit varies from 2 × 104 to 5 × 104. the impact of x-ray ionization is almost negligible and within the expected scatter of j_{21}^crit for background fluxes of jx, 21 ≤ 0.1. the computed estimates of j_{21}^crit have profound implications for the quasar abundance at z = 10 as it lowers the number density of black holes forming through an isothermal direct collapse by a few orders of magnitude below the observed black hole density. however, the sites with moderate amounts of h2 cooling may still form massive objects sufficient to be compatible with observations. | how realistic uv spectra and x-rays suppress the abundance of direct collapse black holes |
we use time-domain optical spectroscopy to distinguish between broad emission lines powered by accreting black holes (bhs) and stellar processes (i.e., supernovae) for 16 galaxies identified as active galactic nucleus (agn) candidates by reines et al (2013). our study is primarily focused on those objects with narrow emission line ratios dominated by star formation, for which the origin of the broad hα emission was unclear. based on follow-up spectroscopy, we find that the broad hα emission has faded or was ambiguous for all of the star-forming objects (14/16), over baselines ranging from 5-14 years, suggesting a transient stellar process was responsible for the broad emission in previous sloan digital sky survey observations. for the two objects in our follow-up sample with narrow-line agn signatures (rgg 9 and rgg 119), we find persistent broad hα emission consistent with an agn origin. additionally, we use high spectral resolution observations to measure stellar velocity dispersions for 15 objects in the reines et al. (2013) sample, all with narrow-line ratios indicating the presence of an agn. stellar masses range from ∼ 5× {10}8 to 3× {10}9 m ⊙, and we measure {σ }*in the range of 28{--}71 {km} {{{s}}}-1. these {σ }*correspond to some of the lowest-mass galaxies with optical signatures of agn activity. we show that rgg 119, the one object that has both a measured {σ }*and persistent broad hα emission, falls near the extrapolation of the {\text{}}{m}{bh}-{σ }\starrelation to the low-mass end. | multi-epoch spectroscopy of dwarf galaxies with agn signatures: identifying sources with persistent broad hα emission |
we present the results of a dust-reverberation survey of quasars at redshifts z < 0.6. we found a delayed response of the k-band flux variation after the optical flux variation in 25 out of 31 targets, and obtained the lag time between them for 22 targets. combined with the results for nearby seyfert galaxies, we provide the largest homogeneous collection of k-band dust-reverberation data for 36 type 1 active galactic nuclei (agns). this doubles the sample and includes the most distant agn and the largest lag so far measured. we estimated the optical luminosity of the agn component of each target using three different methods: spectral decomposition, the flux-variation-gradient method, and image decomposition. we found a strong correlation between the reverberation radius for the innermost dust torus and the optical luminosity over a range of approximately four orders of magnitude in luminosity, as is already known for seyfert galaxies. we estimated the luminosity distances of the agns based on their dust-reverberation lags, and found that the data in the redshift-distance diagram are consistent with the current standard estimates of the cosmological parameters. we also present the radius-luminosity relations for isotropic luminosity indicators such as the hard x-ray (14-195 kev), [o iv] 25.89 μm, and mid-infrared (12 μm) continuum luminosities, which are applicable to obscured agns. | reverberation measurements of the inner radii of the dust tori in quasars |
we explore whether an independent determination of the distance−redshift relation, and hence cosmological model parameters, can be obtained from the apparent correlations between two different wave-band luminosities or fluxes, as has been claimed in recent works using the x-ray and ultraviolet luminosities and fluxes of quasars. we show that such an independent determination is possible only if the correlation between luminosities is obtained independently of the cosmological model and measured fluxes and redshifts, for example, based on sound theoretical models or unrelated observations. in particular, we show that if the correlation is determined empirically for two luminosities obtained from fluxes and redshifts, then the method suffers from circularity. in the case where the observed correlation between fluxes in very narrow redshift bins is used as a proxy for the luminosity correlation, we show that one is dealing with a pure tautology with no information on distances and cosmological model. we argue that the problem arises because of the incomplete treatment of the correlation, and we use numerical methods with a joint x-ray and ultraviolet quasar data set to demonstrate this shortcoming. | can the distance−redshift relation be determined from correlations between luminosities? |
we present a new x-ray spectroscopic study of 22 luminous (2 × 1045 ≲ lbol/erg s−1 ≲ 2 × 1046) active galactic nuclei (agns) at intermediate redshifts (0.1 ≲ z ≲ 0.4), as part of the supermassive black hole winds in the x-rays (subways) sample, mostly composed of quasars and type 1 agns. here, 17 targets were observed with xmm-newton in 2019-2020, and the remaining 5 are from previous observations. the aim of this large campaign (1.45 ms duration) is to characterise the various manifestations of winds in the x-rays driven from supermassive black holes in agns. in this paper we focus on the search for and characterisation of ultra-fast outflows (ufos), which are typically detected through blueshifted absorption troughs in the fe k band (e > 7 kev). by following monte carlo procedures, we confirm the detection of absorption lines corresponding to highly ionised iron (e.g. fe xxv hα and fe xxvi lyα) in 7 out of 22 sources at the ≳95% confidence level (for each individual line). the global combined probability of such absorption features in the sample is > 99.9%. the subways campaign, based on xmm-newton, extends to higher luminosities and redshifts than previous local studies on seyferts. we find a ufo detection fraction of ∼30% of the total sample, which is in agreement with previous findings. this work independently provides further support for the existence of highly ionised matter propagating at mildly relativistic speeds (≳0.1c) in a considerable fraction of agns over a broad range of luminosities, which is believed to play a key role in the self-regulated agn feeding-feedback cycle, as also supported by hydrodynamical multi-phase simulations. | supermassive black hole winds in x-rays: subways. i. ultra-fast outflows in quasars beyond the local universe |
the james webb space telescope (jwst) will open a new window into the most distant universe and unveil the early growth of supermassive black holes (bhs) in the first galaxies. in preparation for deep jwst imaging surveys, it is crucial to understand the color selection of high-redshift accreting seed bhs. we model the spectral energy distribution of super-eddington accreting bhs with millions of solar masses in metal-poor galaxies at z ≳ 8, applying postprocess line transfer calculations to radiation hydrodynamical simulation results. exposures of 10 ks with the nircam and miri broadband filters are sufficient to detect the radiation flux from the seed bhs with bolometric luminosities of l bol ≃ 1045 erg s-1. while the continuum colors are similar to those of typical low-z quasars, strong hα line emission with a rest-frame equivalent width ewrest ≃ 1300 å is so prominent that the line flux affects the broadband colors significantly. the unique colors, for instance, f356w - f560w ≳ 1 at 7 < z < 8 and f444w - f770w ≳ 1 at 9 < z < 12, provide robust criteria for photometric selection of rapidly growing seed bhs. moreover, nirspec observations of low-ionization emission lines can test whether the bh is fed via a dense accretion disk at super-eddington rates. | the age of discovery with the james webb space telescope: excavating the spectral signatures of the first massive black holes |
we use measurements of 59/58 quasars (qsos), over a redshift range 0.0041 ≤ z ≤ 1.686, to do a comparative study of the radius-luminosity (r - l) and x-ray-uv luminosity (lx - luv) relations and the implication of these relations for cosmological parameter estimation. by simultaneously determining r - l or lx - luv relation parameters and cosmological parameters in six different cosmological models, we find that both r - l and lx - luv relations are standardizable but provide only weak cosmological parameter constraints, with lx - luv relation data favouring larger current non-relativistic matter density parameter ωm0 values than r - l relation data and most other available data. we derive lx - luv and r - l luminosity distances for each of the sources in the six cosmological models and find that lx - luv relation luminosity distances are shorter than r - l relation luminosity distances as well as standard flat λcdm model luminosity distances. this explains why lx - luv relation qso data favour larger ωm0 values than do r - l relation qso data or most other cosmological measurements. while our sample size is small and only spans a small z range, these results indicate that more work is needed to determine whether the lx - luv relation can be used as a cosmological probe. | quasar uv/x-ray relation luminosity distances are shorter than reverberation-measured radius-luminosity relation luminosity distances |
the cosmological principle (cp) is part of the foundation that underpins the standard model of the universe. in the era of precision cosmology, when stress tests of the standard model are uncovering various tensions and possible anomalies, it is critical to check the viability of this principle. a key test is the consistency between the kinematic dipoles of the cosmic microwave background and of the large-scale matter distribution. results using radio continuum and quasar samples indicate a rough agreement in the directions of the two dipoles, but a larger than expected amplitude of the matter dipole. the resulting tension with the radiation dipole has been estimated at ~5σ for some cases, suggesting a potential new cosmological tension and a possible violation of the cp. however, the standard formalism for predicting the dipole in the two-dimensional projection of sources overlooks possible evolution effects in the luminosity function. in fact, radial information from the luminosity function is necessary for a correct projection of the three-dimensional source distribution. using a variety of current models of the quasar luminosity function, we show that neglecting redshift evolution can significantly overestimate the relative velocity amplitude. while the models we investigate are consistent with each other and with current data, the dipole derived from these, which depends on derivatives of the luminosity function, can disagree by more than 3σ. this theoretical systematic bias needs to be resolved before robust conclusions can be made about a new cosmic tension. | theoretical systematics in testing the cosmological principle with the kinematic quasar dipole |
the active galactic nucleus (agn) phenomenon results from a supermassive black hole accreting its surrounding gaseous and dusty material. the infrared (ir) regime provides most of the information to characterize the dusty structures that bridge from the galaxy to the black hole, providing clues to the black hole growth and host galaxy evolution. over the past several decades, with the commissioning of various ground, airborne and space ir observing facilities, our interpretations of the agn circumnuclear structures have advanced significantly through an improved understanding of how their dust emission changes as a function of wavelength and how the heating of the dusty structures responds to variations in the energy released from the central engine. in this review, we summarize the current observational knowledge of the agn ir broad-band spectral energy distributions (seds) and the ir time variability behavior covering large ranges of agn luminosity and redshift, and discuss some first-order insights into the obscuring structures and host galaxy ir properties that can be obtained by integrating the relevant observations into a coherent picture. | infrared spectral energy distribution and variability of active galactic nuclei: clues to the structure of circumnuclear material |
we have conducted an extensive x-ray spectral variability study of a sample of 20 compton-thin type ii galaxies using broadband spectra from xmm-newton, chandra, and suzaku. the aim is to study the variability of the neutral intrinsic x-ray obscuration along the line of sight and investigate the properties and location of the dominant component of the x-ray-obscuring gas. the observations are sensitive to absorption columns of ${n}_{{\rm{h}}}$ ∼ 1020.5-24 cm-2 of fully and partially covering neutral and/or lowly ionized gas on timescales spanning days to well over a decade. we detected variability in the column density of the full-covering absorber in 7/20 sources, on timescales of months to years, indicating a component of compact-scale x-ray-obscuring gas lying along the line of sight of each of these objects. our results imply that torus models incorporating clouds or over-dense regions should account for line-of-sight column densities as low as ∼a few ×1021 cm-2. however, 13/20 sources yielded no detection of significant variability in the full-covering obscurer, with upper limits of δnh spanning 1021-23 cm-2. the dominant absorbing media in these systems could be distant, such as kiloparsec-scale dusty structures associated with the host galaxy, or a homogeneous medium along the line of sight. thus, we find that overall, strong variability in full-covering obscurers is not highly prevalent in compton-thin type iis, at least for our sample, in contrast to previous results in the literature. finally, 11/20 sources required a partial-covering, obscuring component in all or some of their observations, consistent with clumpy near-compton-thick compact-scale gas. | the variable and non-variable x-ray absorbers in compton-thin type ii active galactic nuclei |
every star-forming galaxy has a halo of metal-enriched gas that extends out to at least 100 kiloparsecs, as revealed by the absorption lines that this gas imprints on the spectra of background quasars. however, quasars are sparse and typically probe only one narrow beam of emission through the intervening galaxy. close quasar pairs and gravitationally lensed quasars have been used to circumvent this inherently one-dimensional technique, but these objects are rare and the structure of the circumgalactic medium remains poorly constrained. as a result, our understanding of the physical processes that drive the recycling of baryons across the lifetime of a galaxy is limited. here we report integral-field (tomographic) spectroscopy of an extended background source—a bright, giant gravitational arc. we can thus coherently map the spatial and kinematic distribution of mg ɪɪ absorption—a standard tracer of enriched gas—in an intervening galaxy system at redshift 0.98 (around 8 billion years ago). our gravitational-arc tomography unveils a clumpy medium in which the absorption strength decreases with increasing distance from the galaxy system, in good agreement with results for quasars. furthermore, we find strong evidence that the gas is not distributed isotropically. interestingly, we detect little kinematic variation over a projected area of approximately 600 square kiloparsecs, with all line-of-sight velocities confined to within a few tens of kilometres per second of each other. these results suggest that the detected absorption originates from entrained recycled material, rather than in a galactic outflow. | a clumpy and anisotropic galaxy halo at redshift 1 from gravitational-arc tomography |
aims: our goal is to study molecular gas properties in nuclei and large scale outflows/winds from active galactic nuclei (agns) and starburst galaxies.methods: we obtained high resolution (0.̋25 to 0.̋90) observations of hcn and hco+j = 3 → 2 of the ultraluminous qso galaxy mrk 231 with the iram plateau de bure interferometer (pdbi).results: we find luminous hcn and hco+j = 3 → 2 emission in the main disk and we detect compact (r ≲ 0''̣1 (90 pc)) vibrationally excited hcn j = 3 → 2ν2 = 1f emission centred on the nucleus. the velocity field of the vibrationally excited hcn is strongly inclined (position angle pa = 155°) compared to the east-west rotation of the main disk. the nuclear (r ≲ 0.̋1) molecular mass is estimated to 8 × 108 m⊙ with an average n(h2) of 1.2 × 1024 cm-2. prominent, spatially extended (≳350 pc) line wings are found for hcn j = 3 → 2 with velocities up to ± 750 km s-1. line ratios indicate that the emission is emerging in dense gas n = 104-5 × 105 cm-3 of elevated hcn abundance x(hcn) = 10-8-10-6. the highest x(hcn) also allows for the emission to originate in gas of more moderate density. we tentatively detect nuclear emission from the reactive ion hoc+ with hco+/hoc+ = 10-20.conclusions: the hcn ν2 = 1f line emission is consistent with the notion of a hot, dusty, warped inner disk of mrk 231 where the ν2 = 1f line is excited by bright mid-ir 14 μm continuum. we estimate the vibrational temperature tvib to 200-400 k. based on relative source sizes we propose that 50% of the main hcn emission may have its excitation affected by the radiation field through ir pumping of the vibrational ground state. the hcn emission in the line wings, however, is more extended and thus likely not strongly affected by ir pumping. our results reveal that dense clouds survive (and/or are formed) in the agn outflow on scales of at least several hundred pc before evaporating or collapsing. the elevated hcn abundance in the outflow is consistent with warm chemistry possibly related to shocks and/or x-ray irradiated gas. an upper limit to the mass and momentum flux is 4 × 108 m⊙ and 12lagn/c, respectively, and we discuss possible driving mechanisms for the dense outflow. based on observations carried out with the iram plateau de bure interferometer. iram is supported by insu/cnrs (france), mpg (germany) and ign (spain).the reduced data cubes are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/574/a85 | high resolution observations of hcn and hco+j = 3-2 in the disk and outflow of mrk 231. detection of vibrationally excited hcn in the warped nucleus |
ultra-light dark matter (uldm) refers to a class of theories, including ultra-light axions, in which particles with mass $m_{\psi } \lt 10^{-20}\, \rm {ev}$ comprise a significant fraction of the dark matter. a galactic scale de broglie wavelength distinguishes these theories from cold dark matter (cdm), suppressing the overall abundance of structure on sub-galactic scales, and producing wave-like interference phenomena in the density profiles of haloes. with the aim of constraining the particle mass, we analyse the flux ratios in a sample of 11 quadruple-image strong gravitational lenses. we account for the suppression of the halo mass function and concentration-mass relation predicted by uldm theories, and the wave-like fluctuations in the host halo density profile, calibrating the model for the wave interference against numerical simulations of galactic-scale haloes. we show that the granular structure of halo density profiles, in particular, the amplitude of the fluctuations, significantly impacts image flux ratios, and therefore inferences on the particle mass derived from these data. we infer relative likelihoods of cdm to uldm of 8:1, 7:1, 6:1, and 4:1 for particle masses $\log _{10}(m_\psi /\rm {ev})\in [-22.5,-22.25], [-22.25,-22.0],[-22.0,-21.75], [-21.75,-21.5]$, respectively. repeating the analysis and omitting fluctuations associated with the wave interference effects, we obtain relative likelihoods of cdm to uldm with a particle mass in the same ranges of 98:1, 48:1, 26:1, and 18:1, highlighting the significant perturbation to image flux ratios associated with the fluctuations. nevertheless, our results disfavour the lightest particle masses with $m_{\psi } \lt 10^{-21.5}\, \rm {ev}$, adding to mounting pressure on ultra-light axions as a viable dark matter candidate. | quantum fluctuations masquerade as haloes: bounds on ultra-light dark matter from quadruply imaged quasars |
the non-linear relation between the x-ray and ultraviolet (uv) luminosity in quasars has been used to derive quasar distances and to build a hubble diagram at redshifts up to z ∼ 7. this cosmological application is based on the assumption of independence of the relation on redshift and luminosity. we want to test the reliability of this hypothesis by studying the spectroscopic properties of high-redshift quasars in the x-ray and uv bands. we performed a one-by-one analysis of a sample of 130 quasars at z > 2.5 with high-quality x-ray and uv spectroscopic observations. we found that not only does the x-ray to uv correlation still hold at these redshifts, but its intrinsic dispersion is as low as 0.12 dex (previous works reached 0.20-0.22 dex). for a sample of quasars at z ∼ 3 with particularly high-quality observations, the dispersion further drops to 0.09 dex, a value entirely accountable for by intrinsic variability and source geometry effects. the composite spectra of these quasars, in both the x-rays and the uv, do not show any difference with respect to the average spectra of quasars at lower redshifts. the absence of any spectral difference between high- and low-z quasars and the tightness of the x-ray to uv relation suggests that no evolutionary effects are present in the relation. therefore, it can be safely employed to derive quasar distances. under this assumption, we obtain a measurement for the luminosity distance at z ∼ 3 with 15% uncertainty, and in a 4σ tension with the concordance model. data to build figs. 1 and 2 are only available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/663/l7 | quasars as high-redshift standard candles |
the idea that dark matter can be made of intermediate-mass primordial black holes (pbhs) in the 10 m ⊙ ≲ m ≲ 200 m ⊙ range has recently been reconsidered, particularly in the light of the detection of gravitational waves by the ligo experiment. the existence of even a small fraction of dark matter in black holes should nevertheless result in noticeable quasar gravitational microlensing. quasar microlensing is sensitive to any type of compact objects in the lens galaxy, to their abundance, and to their mass. we have analyzed optical and x-ray microlensing data from 24 gravitationally lensed quasars to estimate the abundance of compact objects in a very wide range of masses. we conclude that the fraction of mass in black holes or any type of compact objects is negligible outside of the 0.05 m ⊙ ≲ m ≲ 0.45 m ⊙ mass range and that it amounts to 20% ± 5% of the total matter, in agreement with the expected masses and abundances of the stellar component. consequently, the existence of a significant population of intermediate-mass pbhs appears to be inconsistent with current microlensing observations. therefore, primordial massive black holes are a very unlikely source of the gravitational radiation detected by ligo. | limits on the mass and abundance of primordial black holes from quasar gravitational microlensing |
the most robust way for determining the distance of quasar absorption outflows is the use of troughs from ionic excited states. the column density ratio between the excited and resonance states yields the outflow number density. combined with a knowledge of the outflow’s ionization parameter, a distance from the central source (r) can be determined. here we report results from two surveys targeting outflows that show troughs from s iv. one survey includes 1091 sdss and boss quasar spectra, and the other includes higher-quality spectra of 13 quasars observed with the very large telescope. our s iv samples include 38 broad absorption line (bal) outflows and four mini-bal outflows. the s iv is formed in the same physical region of the outflow as the canonical outflow-identifying species c iv. our results show that s iv absorption is only detected in 25% of c iv bal outflows. the smaller detection fraction is due to the higher total column density (n h) needed to detect s iv absorption. since r empirically anticorrelates with n h, the results of these surveys can be extrapolated to c iv quasar outflows with lower n h as well. we find that at least 50% of quasar outflows are at distances larger than 100 pc from the central source, and at least 12% are at distances larger than 1000 pc. these results have profound implications for the study of the origin and acceleration mechanism of quasar outflows and their effects on the host galaxy. | evidence that 50% of balqso outflows are situated at least 100 pc from the central source |
we present atacama large millimeter/submillimeter array band 8 observations of the [o iii] 88 μm line and the underlying thermal infrared continuum emission in the z = 6.08 quasar cfhqs j2100-1715 and its dust-obscured starburst companion galaxy (projected distance: ∼60 kpc). each galaxy hosts dust-obscured star formation at rates >100 m ⊙ yr-1, but only the quasar shows evidence for an accreting 109 m ⊙ black hole. therefore we can compare the properties of the interstellar medium in distinct galactic environments in two physically associated objects, ∼1 gyr after the big bang. bright [o iii] 88 μm emission from ionized gas is detected in both systems; the positions and linewidths are consistent with earlier [c ii] measurements, indicating that both lines trace the same gravitational potential on galactic scales. the [o iii] 88 μm/far-infrared (fir) luminosity ratios in both sources fall in the upper range observed in local luminous infrared galaxies of similar dust temperature, although the ratio of the quasar is smaller than in the companion. this suggests that gas ionization by the quasar (expected to lead to strong optical [o iii] 5008 å emission) does not dominantly determine the quasar’s fir [o iii] 88 μm luminosity. both the inferred number of photons needed for the creation of o++ and the typical line ratios can be accounted for without invoking extreme (top-heavy) stellar initial mass functions in the starbursts of both sources. | no evidence for enhanced [o iii] 88 μm emission in a z ∼ 6 quasar compared to its companion starbursting galaxy |
direct-collapse black holes (dcbhs) of mass $\sim 10^4$-$10^5 {m}_\odot$ that form in hi-cooling halos in the early universe are promising progenitors of the $\gtrsim 10^9 {m}_\odot$ supermassive black holes that fuel observed $z \gtrsim 7$ quasars. efficient accretion of the surrounding gas onto such dcbh seeds may render them sufficiently bright for detection with the jwst up to $z\approx 20$. additionally, the very steep and red spectral slope predicted across the $\approx 1$-5 $\mu$m wavelength range of the jwst/nirspec instrument during their initial growth phase should make them photometrically identifiable up to very high redshifts. in this work, we present a search for such dcbh candidates across the 34 arcmin$^{2}$ in the first two spokes of the jwst cycle-1 pearls survey of the north ecliptic pole time-domain field covering eight nircam filters down to a maximum depth of $\sim$ 29 ab mag. we identify two objects with spectral energy distributions consistent with the pacucci et al. (2016) dcbh models. however, we also note that even with data in eight nircam filters, objects of this type remain degenerate with dusty galaxies and obscured active galactic nuclei over a wide range of redshifts. follow-up spectroscopy would be required to pin down the nature of these objects. based on our sample of dcbh candidates and assumptions on the typical duration of the dcbh steep-slope state, we set a conservative upper limit of $\lesssim 5\times 10^{-4}$ comoving mpc$^{-3}$ (cmpc$^{-3}$) on the comoving density of host halos capable of hosting dcbhs with spectral energy distributions similar to the pacucci et al. (2016) models at $z\approx 6$-14. | a search for high-redshift direct-collapse black hole candidates in the pearls north ecliptic pole field |
we report 6 yr monitoring of distant bright quasar cts c30.10 (z = 0.90052) with the southern african large telescope. we measured the rest-frame time lag of {562}-68+116 days between the continuum variations and the response of the mg ii emission line, using six different methods. this time delay, combined with other available measurements of mg ii line delay, mostly for lower-redshift sources, shows that the mg ii line reverberation implies a radius-luminosity relation very similar to the one based on a more frequently studied hβ line. | time delay measurement of mg ii line in cts c30.10 with salt |
we separately assess elemental abundances in active galactic nuclei's (agns) broad and narrow emission line regions (blr and nlr), based on a critical assessment of published results together with new photoionization models. we find (1) he/h enhancements in some agn, exceeding what can be explained by normal chemical evolution and confirm, (2) super-solar α abundance, though to a lesser degree than previously reported. we also reaffirm, (3) an n/o ratio consistent with secondary production, (4) solar or slightly sub-solar fe abundance, and (5) red-shift independent metallicity, in contrast with galactic chemical evolution. we interpret (6) the larger metallicity in the blr than nrl in terms of an in situ stellar evolution and pollution in agn discs (sepad) model. we attribute (a) the redshift independence to the heavy element pollutants being disposed into the disc and accreted onto the central supermassive black hole (smbh), (b) the limited he excess to the accretion-wind metabolism of a top-heavy population of evolving massive main sequence stars, (c) the super-solar cno enrichment to the nuclear synthesis during their post-main-sequence evolution, (d) the large n/o to the byproduct of multiple stellar generations, and (e) the mg, si, and fe to the ejecta of type ii supernovae in the disc. these results provide supporting evidence for (f) ongoing self-regulated star formation, (g) adequate stellar luminosity to maintain marginal gravitational stability, (h) prolific production of seeds, and (i) dense coexistence of subsequently grown residual black hole populations in agn discs. | metal enrichment due to embedded stars in agn discs |
context. the precise determination of the present-day expansion rate of the universe, expressed through the hubble constant h0, is one of the most pressing challenges in modern cosmology. assuming flat λcdm, h0 inference at high redshift using cosmic microwave background data from planck disagrees at the 4.4σ level with measurements based on the local distance ladder made up of parallaxes, cepheids, and type ia supernovae (sne ia), often referred to as hubble tension. independent cosmological-model-insensitive ways to infer h0 are of critical importance.aims: we apply an inverse distance ladder approach, combining strong-lensing time-delay distance measurements with sn ia data. by themselves, sne ia are merely good indicators of relative distance, but by anchoring them to strong gravitational lenses we can obtain an h0 measurement that is relatively insensitive to other cosmological parameters.methods: a cosmological parameter estimate was performed for different cosmological background models, both for strong-lensing data alone and for the combined lensing + sne ia data sets.results: the cosmological-model dependence of strong-lensing h0 measurements is significantly mitigated through the inverse distance ladder. in combination with sn ia data, the inferred h0 consistently lies around 73-74 km s-1 mpc-1, regardless of the assumed cosmological background model. our results agree closely with those from the local distance ladder, but there is a > 2σ tension with planck results, and a ∼1.5σ discrepancy with results from an inverse distance ladder including planck, baryon acoustic oscillations, and sne ia. future strong-lensing distance measurements will reduce the uncertainties in h0 from our inverse distance ladder. | the hubble constant determined through an inverse distance ladder including quasar time delays and type ia supernovae |
galight is a python-based open-source package that can be used to perform two-dimensional model fitting of optical and near-infrared images to characterize the light distribution of galaxies with components including a disk, bulge, bar, and quasar. the decomposition of stellar components has been demonstrated in published studies of inactive galaxies and quasar host galaxies observed by the hubble space telescope and subaru's hyper suprime-cam. galight utilizes the image modeling capabilities of lenstronomy while redesigning the user interface for the analysis of large samples of extragalactic sources. the package is user-friendly with some automatic features such as determining the cutout size of the modeling frame, searching for psf-stars in field-of-view, estimating the noise map of the data, identifying all the objects to set the initial model, and associated parameters to fit them simultaneously. these features minimize the manpower and allow the automatic fitting tasks. the software is distributed under the mit license. the source code, installation guidelines, and example notebooks code can be found at https://galight.readthedocs.io/en/latest/ | galaxy shapes of light (galight): a 2d modeling of galaxy images |
negative feedback from accreting supermassive black holes is considered crucial in suppressing star formation and quenching massive galaxies. however, several models and observations suggest that black hole feedback may have a positive effect, triggering star formation by compressing interstellar medium gas to higher densities. we investigate the dual role of black hole feedback using cosmological hydrodynamic simulations from the feedback in realistic environment (fire) project, incorporating a novel implementation of hyper-refined accretion-disc winds. focusing on a massive, star-forming galaxy at z ~ 2 ($m_{\rm halo} \sim 10^{12.5}\, {\rm m}_{\odot }$), we demonstrate that strong quasar winds with a kinetic power of ~1046 erg s-1, persisting for over 20 myr, drive the formation of a central gas cavity and significantly reduce the surface density of star formation across the galaxy's disc. the suppression of star formation primarily occurs by limiting the availability of gas for star formation rather than by evacuating the pre-existing star-forming gas reservoir (preventive feedback dominates over ejective feedback). despite the overall negative impact of quasar winds, we identify several potential indicators of local positive feedback, including (1) the spatial anticorrelation between wind-dominated regions and star-forming clumps, (2) higher local star formation efficiency in compressed gas at the edge of the cavity, and (3) increased contribution of outflowing material to local star formation. moreover, stars formed under the influence of quasar winds tend to be located at larger radial distances. our findings suggest that both positive and negative agn feedback can coexist within galaxies, although the local positive triggering of star formation has a minor influence on global galaxy growth. | local positive feedback in the overall negative: the impact of quasar winds on star formation in the fire cosmological simulations |
announcing the final release, v8, of the milliquas (million quasars) quasar catalogue which presents all published quasars to 30 june 2023, including quasars from the first releases of the dark energy spectroscopic instrument (desi) and the sdss-dr18 black hole mapper. its totals are 907,144 type-i qsos/agn and 66,026 high-confidence (~99% likelihood) radio/x-ray associated quasar candidates. type-ii and bl lac type objects are also included, bringing the total count to 1,021,800. gaia-edr3 astrometry is given for most objects. the catalogue is available on nasa heasarc and cds and on its home page. | the million quasars (milliquas) catalogue, v8 |
the origin of ultracompact dwarfs (ucds), a class of compact stellar systems discovered two decades ago, still remains a matter of debate. recent discoveries of central supermassive black holes in ucds likely inherited from their massive progenitor galaxies provide support for the tidal stripping hypothesis. at the same time, on statistical grounds, some massive ucds might be representatives of the high luminosity tail of the globular cluster luminosity function. here we present a detection of a 3.3^{+1.4}_{-1.2}× 10^6 m_{⊙} black hole (1σ uncertainty) in the centre of the ucd3 galaxy in the fornax cluster, which corresponds to 4 per cent of its stellar mass. we performed isotropic jeans dynamical modelling of ucd3 using internal kinematics derived from adaptive optics-assisted observations with the sinfoni spectrograph and seeing limited data collected with the flames spectrograph at the eso vlt. we rule out the zero black hole mass at the 3σ confidence level when adopting a mass-to-light ratio inferred from stellar populations. this is the fourth supermassive black hole found in a ucd and the first one in the fornax cluster. similarly to other known ucds that harbour black holes, ucd3 hosts metal rich stars enhanced in α-elements that support the tidal stripping of a massive progenitor as its likely formation scenario. we estimate that up to 80 per cent of luminous ucds in galaxy clusters host central black holes. this fraction should be lower for ucds in groups, because their progenitors are more likely to be dwarf galaxies, which do not usually host black holes massive enough to be detected. | a 3.5 million solar masses black hole in the centre of the ultracompact dwarf galaxy fornax ucd3 |
the direct collapse model for the formation of massive black holes has gained increased support as it provides a natural explanation for the appearance of bright quasars already less than a billion years from the big bang. in this paper we review a recent scenario for direct collapse that relies on multi-scale gas inflows initiated by the major merger of massive gas-rich galaxies at z > 6, where gas has already achieved solar composition. hydrodynamical simulations undertaken to explore our scenario show that supermassive, gravitationally bound compact gaseous disks weighing a billion solar masses, only a few pc in size, form in the nuclei of merger remnants in less than 105 yr. these could later produce a supermassive protostar or supermassive star at their center via various mechanisms. moreover, we present a new analytical model, based on angular momentum transport in mass-loaded gravitoturbulent disks. this naturally predicts that a nuclear disk accreting at rates exceeding yr-1, as seen in the simulations, is stable against fragmentation irrespective of its metallicity. this is at variance with conventional direct collapse scenarios, which require the suppression of gas cooling in metal-free protogalaxies for gas collapse to take place. such high accretion rates reflect the high free-fall velocities in massive halos appearing only at z < 10, and occur naturally as a result of the efficient angular momentum loss provided by the merger dynamics. we discuss the implications of our scenario on the observed population of high-z quasars and on its evolution to lower redshifts using a semi-analytical galaxy formation model. finally, we consider the intriguing possibility that the secondary gas inflows in the unstable disks might drive gas to collapse into a supermassive black hole directly via the general relativistic radial instability. such dark collapse route could generate gravitational wave emission detectable via the future laser interferometer space antenna (lisa). | the route to massive black hole formation via merger-driven direct collapse: a review |
the dynamics of the broad line region (blr) in active galaxies is an open question; direct observational constraints suggest a predominantly keplerian motion, with possible traces of inflow or outflow. in this paper we study in detail the physically motivated blr model of czerny & hryniewicz based on the radiation pressure acting on dust at the surface layers of the accretion disk (ad). we consider here a nonhydrodynamical approach to the dynamics of the dusty cloud under the influence of radiation coming from the entire ad. we use here a realistic description of the dust opacity, and we introduce two simple geometrical models of the local shielding of the dusty cloud. we show that the radiation pressure acting on dusty clouds is strong enough to lead to dynamical outflow from the ad surface, so the blr has a dynamical character of a (mostly failed) outflow. the dynamics strongly depends on the eddington ratio of the source. large eddington ratio sources show a complex velocity field and large vertical velocities with respect to the ad surface, while for lower eddington ratio sources vertical velocities are small and most of the emission originates close to the ad surface. cloud dynamics thus determines the 3d geometry of the blr. | the picture of blr in 2.5d frado: dynamics and geometry |
we discuss a novel window to probe the origin of our universe via the mass functions of primordial black holes (pbhs). the mass functions of pbhs are simply estimated using the conventional press-schechter formalism for two paradigms of cosmic origin, including inflationary $\lambda$cdm and bounce cosmology. the standard inflationary $\lambda$cdm model cannot generate an appreciable number of massive pbhs; however, non-trivial inflation models with blue-tilted power spectra at small scales and matter bounce cosmology provide formation mechanisms for heavy pbhs, which in turn, may seed the observed supermassive black holes (smbhs). by fitting the smbh mass functions at high redshift ($z \sim 6$) derived from sloan digital sky survey (sdss) and canada-france high-z quasar survey (cfhqs) quasars, for two paradigms of cosmic origin, we derive constraints on the pbh density fraction $f_{\mathrm{pbh}}$ at $z \sim 6$ and the characteristic mass $m_{\star}$, with the prior assumption that all smbhs stem from pbhs. we demonstrate that this newly proposed procedure, relying on astronomical measurements that utilize deep-field surveys of smbhs at high redshift, can be used to constrain models of cosmic origin. additionally, although not the main focus of this paper, we evolve the mass function from $z\sim6$ to $z\sim0$ through an assumption of $3\times 10^8$-year eddington's accretion, and give a rough estimation of $f_{\mathrm{pbh}}$ at $z \sim 0$. | primordial black hole mass functions as a probe of cosmic origin |
if $z > 6$ quasars reside in rare, massive haloes, $\lambda$cdm cosmology predicts they should be surrounded by an anomalously high number of bright companion galaxies. in this paper, i show that these companion galaxies should also move unusually fast. using a new suite of cosmological, `zoom-in' hydrodynamic simulations, i here present predictions for the velocity distribution of quasar companion galaxies and its variation with quasar host halo mass at $z \, = \, 6$. satellites accelerate as they approach the quasar host galaxy, producing a line-of-sight velocity profile that broadens as the distance to the quasar host galaxy decreases. this increase in velocity dispersion is particularly pronounced if the host halo mass is $\gtrsim 5 \times 10^{12} \, \rm m_\odot$. in this case, typical line-of-sight speeds rise to $\approx 500 \, \rm km \, s^{-1}$ at projected radii $\sim 10 \, \rm kpc$. for about $10\%$ of satellites, they should exceed $800 \, \rm km \, s^{-1}$, with $\approx 5\%$ of companions reaching line-of-sight speeds $\sim 1000 \, \rm km \, s^{-1}$. for lower host halo masses $\approx 5 \times 10^{11} - 10^{12} \, \rm m_\odot$, the velocity profile of companion galaxies is significantly flatter. in this case, typical line-of-sight velocities are $\approx 250 \, \rm km \, s^{-1}$ and do not exceed $\approx 500 \, \rm km \, s^{-1}$. a comparison with existing alma, jwst and muse line-of-sight velocity measurements reveals that observed $z > 6$ quasar companions closely follow the velocity distribution expected for a host halo with mass $\gtrsim 5 \times 10^{12} \, \rm m_\odot$, ruling out a light host halo. finally, through an estimate of uv and [oiii] luminosity functions, i show that the velocity distribution more reliably discriminates between halo mass than companion number counts, which are strongly affected by cosmic variance. | the host dark matter haloes of the first quasars |
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