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neutron stars (nss) which could contain exotic degrees of freedom in the core and the self-bound quark stars (qss) made purely of absolutely stable deconfined quark matter are still two main candidates for the compact objects observed in pulsars and gravitational wave (gw) events in binary star mergers. we perform a bayesian model-agnostic inference of the properties of nss and qss by combining multi-messenger data of gw170817, gw190425, psr j0030+0451, psr j0740+6620, psr j1614-2230, psr j0348+0432 as well as ab initio calculations from perturbative quantum chromodynamics and chiral effective field theory. we find the ns scenario is strongly favored against the qs scenario with a bayes factor of ns over qs $\mathcal{b}^\text{ns}_\text{qs} = 11.5$. in addition, the peak of the squared sound velocity $c_s^2 \sim 0.5c^2$ around $3.5$ times nuclear saturation density $n_0$ observed in the ns case disappears in the qs case which suggests that the $c_s^2$ first increases and then saturates at $c_s^2 \sim 0.5c^2$ above $\sim 4n_0$. the sound velocity and trace anomaly are found to approach the conformal limit in the core of heavy nss with mass $m \gtrsim 2m_{\odot}$, but not in the core of qss. | neutron star vs quark star in the multimessenger era |
we present new measurements of the flux power-spectrum p(k) of the z < 0.5 h i lyman-α forest spanning scales k ∼ 0.001-0.1 s km^{-1}. these results were derived from 65 far-ultraviolet quasar spectra (resolution r ∼ 18 000) observed with the cosmic origin spectrograph (cos) on board the hubble space telescope. the analysis required careful masking of all contaminating, coincident absorption from h i and metal-line transitions of the galactic interstellar medium and intervening absorbers as well as proper treatment of the complex cos line-spread function. from the p(k) measurements, we estimate the h i photoionization rate (γ _{h i}) in the z < 0.5 intergalactic medium. our results confirm most of the previous γ _{h i} estimates. we conclude that previous concerns of a photon underproduction crisis are now resolved by demonstrating that the measured γ _{h i} can be accounted for by ultraviolet emission from quasars alone. in a companion paper, we will present constraints on the thermal state of the z < 0.5 intergalactic medium from the p(k) measurements presented here. | the power spectrum of the lyman-α forest at z < 0.5 |
we present a new method to study the contribution of faint sources to the ultraviolet background using the 1d correlation of metal absorbers with the intergalactic medium transmission in a quasi-stellar object (qso) sightline. we take advantage of a sample of 25 high signal-to-noise ratio qso spectra to retrieve 150 triply-ionized carbon (c iv) absorbers at 4.5 ≲ z ≲ 6.2, of which 37 systems whose expected h i absorption lie in the lyman-α forest. we derive improved constraints on the cosmic density of c iv at 4.3 < z < 6.2 and infer from abundance matching that c iv absorbers trace muv ≲ -16 galaxies. correlation with the lyman-α forest of the qsos indicates that these objects are surrounded by a highly opaque region at r ≲ 5 cmpc h-1 followed by an excess of transmission at r ≳ 10 cmpc h-1 detected at 2.7σ. this is in contrast to equivalent measurements at lower redshifts where only the opaque trough is detected. we interpret this excess as a statistical enhancement of the local photoionization rate due to clustered faint galaxies around the c iv absorbers. using the analytical framework described in paper i of this series, we derive a constraint on the average product of the escape fraction and the lyman continuum photon production efficiency of the galaxy population clustered around the c iv absorbers, log < f_{esc}ξ _{ion}> /[erg^{-1 hz}] = 25.01^{+0.30}_{-0.19}. this implies that faint galaxies beyond the reach of current facilities may have harder radiation fields and/or larger escape fractions than currently detected objects at the end of the reionization epoch. | the role of galaxies and agns in reionizing the igm - ii. metal-tracing the faint sources of reionization at 5 ≲ z ≲ 6 |
in the standard active galactic nucleus (agn) reverberation-mapping model, variations in broad-line region (blr) fluxes are predicted from optical continuum variability (taken as a proxy for the ionizing continuum) convolved with a response function that depends on the geometry. however, it has long been known that blr variability can deviate from these predictions. we analyse both extensive long-term hβ and continuum monitoring of ngc 5548 and a large sample of high-quality hβ light curves of other agns to investigate the frequency and characteristics of the anomalous responses of the blr. we find that anomalies are very common and probably occur in every object. onsets can be on a time-scale only slightly longer than the light-crossing time and durations are of the order of the characteristic time-scale of variability of the optical continuum to several times longer. anomalies are larger when ngc 5548 is in a low state, but otherwise there is no correlation with continuum variability. there is abundant evidence for the optical continuum of agns varying independently of the higher-energy continua and this is sufficient to explain the anomalous responses of the total blr flux. there are good reasons for believing that the frequent lack of correlation between spectral regions is due to anisotropic and non-axisymmetric emission. rapid changes in line profiles and velocity-dependent lags are consistent with this. motion of compact absorbing clouds across the line of sight is another possible cause of anomalies. the prevalence of anomalies should be considered when planning reverberation-mapping campaigns. | anomalous broad-line region responses to continuum variability in active galactic nuclei - i. hβ variability |
i study the location of the γ-ray emission in blazar jets by creating a compton-scattering approximation that is valid for all anisotropic radiation fields in the thomson through klein-nishina regimes, is highly accurate, and can speed up numerical calculations by up to a factor of ∼10. i apply this approximation to synchrotron self-compton, external compton scattering of photons from the accretion disk, broad line region (blr), and dust torus. i use a stratified blr model and include detailed compton-scattering calculations of a spherical and flattened blr. i create two dust torus models, one where the torus is an annulus and one where it is an extended disk. i present detailed calculations of the photoabsorption optical depth using my detailed blr and dust torus models, including the full angle dependence. i apply these calculations to the emission from a relativistically moving blob traveling through these radiation fields. the ratio of γ-ray to optical flux produces a predictable pattern that could help locate the γ-ray emission region. i show that the bright flare from 3c 454.3 in 2010 november detected by the fermi large area telescope is unlikely to originate from a single blob inside the blr. this is because it moves outside the blr in a time shorter than the flare duration, although emission by multiple blobs inside the blr is possible. also, γ-rays are unlikely to originate from outside of the blr, due to the scattering of photons from an extended dust torus, since the cooling timescale would be too long to explain the observed short variability. | external compton scattering in blazar jets and the location of the gamma-ray emitting region |
context. the vera rubin observatory will provide an unprecedented set of time-dependent observations of the sky. the planned legacy survey of space and time (lsst), operating for ten years, will provide dense light curves for thousands of active galactic nuclei (agn) in deep drilling fields (ddfs) and less dense light curves for millions of agn from the main survey (ms).aims: we model the prospects for measuring the time delays for the agn emission lines with respect to the continuum, using these data.methods: we modeled the artificial light curves using the timmer-könig algorithm. we used the exemplary cadence to sample them (one for the ms and one for the ddf), we supplement light curves with the expected contamination by the strong emission lines (hβ, mg ii, and civ, as well as with fe ii pseudo-continuum and the starlight). we chose suitable photometric bands that are appropriate for the redshift and compared the assumed line time-delay with the recovered time delay for 100 statistical realizations of the light curves.results: we show that time delays for emission lines can be well measured from the main survey for the bright tail of the quasar distribution (about 15% of all sources) with an accuracy within 1σ error. for the ddf, the results for fainter quasars are also reliable when the entire ten years of data are used. there are also some prospects to measure the time delays for the faintest quasars at the lowest redshifts from the first two years of data, and possibly even from the first season. the entire quasar population will allow us to obtain results of apparently high accuracy, but in our simulations, we see a systematic offset between the assumed and recovered time delay that depends on the redshift and source luminosity. this offset will not disappear even in the case of large statistics. this problem might affect the slope of the radius-luminosity relation and cosmological applications of quasars if no simulations are performed that correct for these effects. on behalf of the lsst-agn science collaboration. | expectations for time-delay measurements in active galactic nuclei with the vera rubin observatory |
we study the structure of quark stars (qss) adopting homogeneously confined matter inside the star with a 3-flavor neutral charge and a fixed strange quark mass ms. we explore the internal structure, and the physical properties of specific classes of qss in the recently proposed energy-momentum squared gravity (emsg). also, we obtain the mass-radius (m- r) and mass-central energy density (m-ρc) relations for qs using the qcd motivated eos. the maximum mass for qss in emsg is investigated depending on the presence and absence of the free parameter α. furthermore, the stability of stars is determined by the condition dm/dρc > 0 . we observe that consideration of the emsg has specific contributions to the structure of qss. | the mass-radius relation for quark stars in energy-momentum squared gravity |
the size of the dust torus in active galactic nuclei (agns) and their high-luminosity counterparts, quasars, can be inferred from the time delay between uv/optical accretion disk continuum variability and the response in the mid-infrared (mir) torus emission. this dust reverberation mapping (rm) technique has been successfully applied to ∼70 z ≲ 0.3 agns and quasars. here we present first results of our dust rm program for distant quasars covered in the sloan digital sky survey stripe 82 region combining ∼20 yr ground-based optical light curves with 10 yr mir light curves from the wise satellite. we measure a high-fidelity lag between w1 band (3.4 μm) and g band for 587 quasars over 0.3 ≲ z ≲ 2 ( $\left\langle z\right\rangle \sim 0.8$ ) and two orders of magnitude in quasar luminosity. they tightly follow (intrinsic scatter ∼0.17 dex in lag) the ir lag-luminosity relation observed for z < 0.3 agns, revealing a remarkable size-luminosity relation for the dust torus over more than four decades in agn luminosity, with little dependence on additional quasar properties such as eddington ratio and variability amplitude. this study motivates further investigations in the utility of dust rm for cosmology and strongly endorses a compelling science case for the combined 10 yr vera c. rubin observatory legacy survey of space and time (optical) and 5 yr nancy grace roman space telescope 2 μm light curves in a deep survey for low-redshift agn dust rm with much lower luminosities and shorter, measurable ir lags. the compiled optical and mir light curves for 7384 quasars in our parent sample are made public with this work. | dust reverberation mapping in distant quasars from optical and mid-infrared imaging surveys |
the correlation between neutral hydrogen (h i) in the intergalactic medium (igm) and galaxies attracts great interest. we select four fields that include several coherently strong lyα absorption systems at z ∼ 2.2 detected using background quasars from the whole sdss/(e) baryon oscillation spectroscopic survey (boss) database. deep narrowband and g-band imaging are performed using the hyper suprime-cam on the subaru telescope. we select 2642 lyα emitter (lae) candidates at z = 2.177 ± 0.023 down to the lyα luminosity of llyα ≈ 2 × 1042 erg s-1 to construct the galaxy overdensity maps, covering an effective area of 5.39 deg2. combining the sample with the lyα absorption estimated from 64 (e) boss quasar spectra, we find a moderate to strong correlation between the lae overdensity δlae and the effective optical depth τlos in lines of sight, with p value = 0.09% or <0.01% when the field containing a significant quasar overdensity is included or excluded. cross-correlation analysis also clearly suggests that up to 4 ± 1 pmpc, laes tend to cluster in regions rich in h i gas, as indicated by the high τlos, and avoid the low τlos regions where the h i gas is deficient. by averaging the τlos as a function of the projected distance (d) to laes, we find a 30% excess signal at 2σ level at d < 200 pkpc, indicating the dense h i in the circumgalactic medium, and a tentative excess at 400 < d < 600 pkpc in the igm regime, corroborating the cross-correlation signal detected at about 0.5 pmpc. these statistical analyses suggest that galaxy-igm h i correlations exist on scales ranging from several hundred pkpc to several pmpc at z ∼ 2.2. | statistical correlation between the distribution of lyα emitters and intergalactic medium h i at z ∼ 2.2 mapped by the subaru/hyper suprime-cam |
the masses of supermassive black holes at the centres of local galaxies appear to be tightly correlated with the mass and velocity dispersions of their galactic hosts. however, the local mbh-mstar relation inferred from dynamically measured inactive black holes is up to an order-of-magnitude higher than some estimates from active black holes, and recent work suggests that this discrepancy arises from selection bias on the sample of dynamical black hole mass measurements. in this work, we combine x-ray measurements of the mean black hole accretion luminosity as a function of stellar mass and redshift with empirical models of galaxy stellar mass growth, integrating over time to predict the evolving mbh-mstar relation. the implied relation is nearly independent of redshift, indicating that stellar and black hole masses grow, on average, at similar rates. matching the de-biased local mbh-mstar relation requires a mean radiative efficiency ɛ ≳ 0.15, in line with theoretical expectations for accretion on to spinning black holes. however, matching the `raw' observed relation for inactive black holes requires ɛ ∼ 0.02, far below theoretical expectations. this result provides independent evidence for selection bias in dynamically estimated black hole masses, a conclusion that is robust to uncertainties in bolometric corrections, obscured active black hole fractions, and kinetic accretion efficiency. for our fiducial assumptions, they favour moderate-to-rapid spins of typical supermassive black holes, to achieve ɛ ∼ 0.12-0.20. our approach has similarities to the classic soltan analysis, but by using galaxy-based data instead of integrated quantities we are able to focus on regimes where observational uncertainties are minimized. | probing black hole accretion tracks, scaling relations, and radiative efficiencies from stacked x-ray active galactic nuclei |
observational studies are increasingly finding evidence against major mergers being the dominant mechanism responsible for triggering an active galactic nucleus (agn). after studying the connection between major mergers and agns with the highest eddington ratios at z = 2, we here expand our analysis to $z\lt 0.2$ , exploring the same agn parameter space. using eso vlt/fors2 $b-$ , $v-$ , and color images, we examine the morphologies of 17 galaxies hosting agns with eddington ratios ${\lambda }_{\mathrm{edd}}\gt 0.3$ , and 25 mass- and redshift-matched control galaxies. to match the appearance of the two samples, we add synthetic point sources to the inactive comparison galaxies. the combined sample of agn and inactive galaxies was independently ranked by 19 experts with respect to the degree of morphological distortion. we combine the resulting individual rankings into multiple overall rankings, from which we derive the respective major merger fractions of the two samples. with a best estimate of fm,agn = 0.41 ± 0.12 for the agn host galaxies and fm,ina = 0.08 ± 0.06 for the inactive galaxies, our results imply that our agn host galaxies have a significantly higher merger rate, regardless of the observed wavelength or applied methodology. we conclude that although major mergers are an essential mechanism to trigger local high eddington ratio agns at $z\lt 0.2$ , the origin of $\gtrsim 50 \% $ of this specific agn subpopulation still remains unclear. | a significant excess in major merger rate for agns with the highest eddington ratios at z < 0.2 |
dirac, in 1937, proposed the potential variation of coupling constants derived from his large numbers hypothesis. efforts have continued since then to constrain their variation by various methods, including astrophysical and cosmological observations. we briefly discuss several methods used for the purpose while focusing primarily on the use of supernovae type 1a, quasars, and gamma-ray bursts as cosmological probes for determining cosmological distances. supernovae type ia (sneia) are considered the best standard candles since their intrinsic luminosity can be determined precisely from their light curves. however, they have only been observed up to about redshift z=2.3, mostly at z≤1.5. quasars are the brightest non-transient cosmic sources in the universe. they have been observed up to z=7.5. certain types of quasars can be calibrated well enough for their use as standard candles but with a higher degree of uncertainty in their intrinsic luminosity than sneia. gamma-ray bursts (grbs) are even brighter than quasars, and they have been observed up to z=9.4. they are sources of highly transient radiation lasting from tens of milliseconds to several minutes and, in rare cases, a few hours. however, they are even more challenging to calibrate as standard candles than quasars. both quasars and grbs use sneia for distance calibration. what if the standard candles' intrinsic luminosities are affected when the coupling constants become dynamic and depend on measured distances? assuming it to be constant at all cosmic distances leads to the wrong constraint on the data-fitted model parameters. this paper uses our earlier finding that the speed of light c, the gravitational constant g, the planck constant h, and the boltzmann constant k vary in such a way that their variation is interrelated as g~c3~h3~k3/2 with g˙/g=3c˙/c=3h˙/h=1.5k˙/k =3.90±0.04×10‑10 yr‑1 and corroborates it with sneia, quasars, and grbs observational data. additionally, we show that this covarying coupling constant model may be better than the standard λcdm model for using quasars and grbs as standard candles and predict that the mass of the grbs scales with z as 1+z1/3‑1. noether's symmetry on the coupling constants is now transferred effectively to the constant in the function relating to their variation. | constraining coupling constants' variation with supernovae, quasars, and grbs |
hot dust-obscured galaxies (dogs) are hyperluminous (l8-1000 μm > 1013 l⊙) infrared galaxies with extremely high (up to hundreds of k) dust temperatures. the sources powering both their extremely high luminosities and dust temperatures are thought to be deeply buried and rapidly accreting supermassive black holes (smbhs). hot dogs could therefore represent a key evolutionary phase in which the smbh growth peaks. x-ray observations can be used to study their obscuration levels and luminosities. in this work, we present the x-ray properties of the 20 most luminous (lbol ≳ 1014 l⊙) known hot dogs at z = 2-4.6. five of them are covered by long-exposure (10-70 ks) chandra and xmm-newton observations, with three being x-ray detected, and we study their individual properties. one of these sources (w0116-0505) is a compton-thick candidate, with column density nh = (1.0-1.5) × 1024 cm-2 derived from x-ray spectral fitting. the remaining 15 hot dogs have been targeted by a chandra snapshot (3.1 ks) survey. none of these 15 are individually detected; therefore, we applied a stacking analysis to investigate their average emission. from hardness ratio analysis, we constrained the average obscuring column density and intrinsic luminosity to be log nh (cm-2) > 23.5 and lx ≳ 1044 erg s-1, which are consistent with results for individually detected sources. we also investigated the lx-l6 μm and lx-lbol relations, finding hints that hot dogs are typically x-ray weaker than expected, although larger samples of luminous obscured quasi-stellar objects are needed to derive solid conclusions. | heavy x-ray obscuration in the most luminous galaxies discovered by wise |
the scaling relations between supermassive black holes and their host galaxy properties are of fundamental importance in the context black hole-host galaxy co-evolution throughout cosmic time. in this work, we use a novel algorithm that identifies smooth trends in complex data sets and apply it to a sample of 2000 type 1 active galactic nuclei (agns) spectra. we detect a sequence in emission line shapes and strengths which reveals a correlation between the narrow l([o iii])/l(h β) line ratio and the width of the broad h α. this scaling relation ties the kinematics of the gas clouds in the broad line region to the ionization state of the narrow line region, connecting the properties of gas clouds kiloparsecs away from the black hole to material gravitationally bound to it on sub-parsec scales. this relation can be used to estimate black hole masses from narrow emission lines only. it therefore enables black hole mass estimation for obscured type 2 agns and allows us to explore the connection between black holes and host galaxy properties for thousands of objects, well beyond the local universe. using this technique, we present the mbh-σ and mbh-m* scaling relations for a sample of about 10 000 type 2 agns from sloan digital sky survey. these relations are remarkably consistent with those observed for type 1 agns, suggesting that this new method may perform as reliably as the classical estimate used in non-obscured type 1 agns. these findings open a new window for studies of black hole-host galaxy co-evolution throughout cosmic time. | black hole mass estimation for active galactic nuclei from a new angle |
early-type galaxies (etgs) frequently show emission from warm ionized gas. these low-ionization emission regions (liers) were originally attributed to a central, low-luminosity active galactic nucleus. however, the recent discovery of spatially extended lier emission suggests ionization by both a central source and an extended component that follows a stellar-like radial distribution. for passively evolving galaxies with old stellar populations, hot post-asymptotic giant branch (agb) stars are the only viable extended source of ionizing photons. in this work, we present the first prediction of lier-like emission from post-agb stars that is based on fully self-consistent models of stellar evolution and photoionization. we show that models where post-agb stars are the dominant source of ionizing photons reproduce the signatures of nebular emission observed in etgs, including lier-like emission line ratios in standard optical diagnostic diagrams and {{h}}α equivalent widths of the order of 0.1-3 {{\mathringa }}. we test the sensitivity of lier-like emission to the details of post-agb models, including the mass loss efficiency and convective mixing efficiency, and show that line strengths are relatively insensitive to variations in post-agb timescale. finally, we examine the uv-optical colors of the models and the stellar populations responsible for the uv excess observed in some etgs. we find that allowing as little as 3% of the horizontal branch population to be uniformly distributed to very high temperatures (30,000 k) produces realistic uv colors for old, quiescent etgs. | self-consistent predictions for lier-like emission lines from post-agb stars |
numerous observations indicate that galaxies need a continuous gas supply to fuel star formation and explain the star formation history. however, direct observational evidence of gas accretion remains rare. using the eagle cosmological hydrodynamic simulation suite, we study cold gas accretion onto galaxies and the observational signatures of the cold gas kinematics. for eagle galaxies at z = 0.27, we find that cold gas accretes onto galaxies anisotropically with typical inflow speeds between 20 and 60 km s-1. most of these galaxies have comparable mass inflow rates and star formation rates, implying that the cold inflowing gas plausibly accounts for sustaining the star-forming activities of the galaxies. as motivation for future work to compare the cold gas kinematics with measurements from quasar sightline observations, we select an eagle galaxy with an extended cold gas disk, and we probe the cold gas using mock quasar sightlines. we demonstrate that by viewing the disk edge on, sightlines at azimuthal angles below 10° and impact parameters out to 60 pkpc can detect cold gas that corotates with the galaxy disk. this example suggests that cold gas disks extending beyond the optical disks possibly explain the sightline observations that detect corotating cold gas near galaxy major axes. | how gas accretion feeds galactic disks |
we report on a spectroscopic program to search for dual quasars using subaru hyper suprime-cam (hsc) images of sdss quasars, which represent an important stage during galaxy mergers. using subaru/focas and gemini-n/gmos, we identify three new physically associated quasar pairs having projected separations less than 20 kpc, out of 26 observed candidates. these include the discovery of the highest-redshift (z = 3.1) quasar pair with a separation <10 kpc. based on the sample acquired to date, the success rate of identifying physically associated dual quasars is 19% when excluding stars based on their hsc colors. using the full sample of six spectroscopically confirmed dual quasars, including three previously published, we find that the black holes in these systems have black hole masses (m bh ~ 108-9 m ⊙), bolometric luminosities (log l bol ~ 44.5-47.5 erg s-1) and eddington ratios (0.01-0.3) similar to single sdss quasars. we measure the stellar mass of their host galaxies based on 2d image decomposition of the five-band (grizy) optical emission and assess the mass relation between supermassive black holes (smbhs) and their hosts. dual smbhs appear to have elevated masses relative to their host galaxies. thus, mergers may not necessarily align such systems onto the local mass relation, as suggested by the horizon-agn simulation. this study suggests that dual luminous quasars are triggered by mergers prior to the final coalescence of the two smbhs, resulting in early mass growth of the black holes relative to their host galaxies. | optical spectroscopy of dual quasar candidates from the subaru hsc-ssp program |
active galactic nuclei (agn) produce copious amounts of x-rays through the corona, the region of hot gas that lies close to the accretion disk. the temperature of the corona can be accurately determined by the cut-off signature in the x-ray spectrum. owing to the high temperatures in the corona, observations well above 10 kev are necessary. here, we explore the nustar observations of 118 seyfert 1 agn selected using gehrels/swift. we modelled the spectrum using a single power-law with an exponential cut-off modified by neutral and ionised absorption as well as a reflection component. we found secure spectral cut-off estimates in 62 sources, while for the remaining ones, we derived only the lower limits. the resulting mean value is 103 kev, with a skewed distribution towards large energies with a large dispersion. when we consider the lower limits using survival analysis techniques, the mean cut-off energy becomes significantly larger, that is, about 200 kev. because of various limitations (e.g., limited spectral passband, photon statistics, model degeneracies), we performed extensive simulations to explore the underlying spectral cut-off distribution. we find that an intrinsic spectral cut-off distribution, which has a maxwell-boltzmann shape with a mean value in the range of 160-200 kev, can reproduce the observations sufficiently well. finally, our spectral analysis places very stringent constraints on both the photon index (γ = 1.77 ± 0.01) as well as on the reflection component (r = 0.69 ± 0.04) of the seyfert 1 population. from the values of the spectral cut-off and the photon-index, we deduce that the mean optical depth of the agn corona is approximately τe = 1.82 ± 0.14 and its mean temperature is approximately kte = 65 ± 10 kev. | distribution of the coronal temperature in seyfert 1 galaxies |
so far large and different data sets revealed the accelerated expansion rate of the universe, which is usually explained in terms of dark energy. the nature of dark energy is not yet known, and several models have been introduced: a non zero cosmological constant, a potential energy of some scalar field, effects related to the non homogeneous distribution of matter, or effects due to alternative theories of gravity. recently, a tension with the flat {\lambda}cdm model has been discovered using a high-redshift hubble diagram of supernovae, quasars, and gamma-ray bursts. here we use the union2 type ia supernovae (snia) and gamma ray bursts (grb) hubble diagram, and a set of direct measurements of the hubble parameter to explore different dark energy models. we use the chevallier-polarski- linder (cpl) parametrization of the dark energy equation of state (eos), a minimally coupled quintessence scalar field, and, finally, we consider models with dark energy at early times (ede). we perform a statistical analysis based on the markov chain monte carlo (mcmc) method, and explore the probability distributions of the cosmological parameters for each of the competing models. we apply the akaike information criterion (aic) to compare these models: our analysis indicates that an evolving dark energy, described by a scalar field with exponential potential seems to be favoured by observational data. | prospects of high redshift constraints on dark energy models with the ep- eiso correlation in long gamma ray bursts |
strong gravitationally lensed quasars provide a powerful means to study galaxy evolution and cosmology. we use chitah, which is an algorithm used to hunt for new lens systems, particularly lensed quasars, in the hyper suprime-cam subaru strategic program (hsc ssp) s16a. we present 46 lens candidates, of which 3 are previously known. we select four high-grade candidates from chitah for spectroscopic follow-up observations, and include two additional lenses found by yattalens, an algorithm used to classify lensed galaxies. we obtain x-shooter spectra of these six promising candidates for lens confirmation and redshift measurements. we report new spectroscopic redshift measurements for both the lens and source galaxies in four lens systems. we apply the lens modeling software glee to model our six x-shooter lenses uniformly. through our analysis of the hsc images, we find that hscj022622-042522, hscj115252+004733, and hscj141136-010216 have point-like lensed images, and that the lens light distribution is well aligned with the lens mass distribution within 6 deg. we estimate the fluxes of the lensed source emission lines using x-shooter spectra, and use line ratio as a diagnostic on the baldwin-phillips-terlevich (bpt) diagram. as a result, we find that hscj022622-042522 has a probable quasar source based on the upper limit of the [n ii] flux intensity. we also measure the fwhm of lyα emission of hscj141136-010216 to be ∼233 km s-1, showing that it is a probable lyman-α emitter. | survey of gravitationally lensed objects in hsc imaging (sugohi). iv. lensed quasar search in the hsc survey |
the final fate of gravitational collapse of massive stars has been a subject of interest for a long time since such a collapse may lead to black holes and naked singularities alike. since, the formation of naked singularities is forbidden by the cosmic censorship conjecture, exploring their observational differences from black holes may be a possible avenue to search for these exotic objects. the simplest possible naked singularity spacetime emerges from the einstein massless scalar field theory with the advantage that it smoothly translates to the schwarzschild solution by the variation of the scalar charge. this background, known as the janis-newman-winicour spacetime is the subject of interest in this work. we explore electromagnetic observations around this metric which involves investigating the characteristics of black hole accretion and shadow. we compute the shadow radius in this spacetime and compare it with the image of m87*, recently released by the event horizon telescope collaboration. similarly, we derive the expression for the luminosity from the accretion disk and compare it with the observed optical luminosity of eleven palomar green quasars. our analysis indicates that the shadow of m87* and the quasar optical data consistently favor the schwarzschild background over the janis-newman-winicour spacetime. the implications of this result are discussed. | imprints of the janis-newman-winicour spacetime on observations related to shadow and accretion |
our ancestors, such as cro-magnon, always looked up at the stars and wished to understand the mysteries of the universe, but their view of the universe was probably quite simple: the stars are inlaid on the inner surface of the sky, and they are very small. however, now we know that stars and galaxies are actually extremely huge, and they look small because they are too far away from us. this indicates that the measurement of cosmological distance is always very important in the study of the universe. due to the expansion of the cosmos, the stars we see are actually what they used to be. the wavelength of light emitted from a star becomes longer due to the expansion of the universe, which is called "redshift of light". the larger the redshift, the older is the star. if we can measure both the distances and redshifts of stars (luminous objects), we can then establish a relationship between distance and redshift, from which the information of cosmic expansion history can be obtained. actually, the measurement of the expansion history of the universe can answer the fundamental questions about the cosmos, such as its age, geometry, composition, and so forth. | a novel method of measuring cosmological distances using broad-line regions of quasars |
the relation between the mass of the supermassive black hole (smbh) in the center of galaxies and their bulge mass or central velocity dispersion is well known. this suggests a coevolution between the smbhs and their galaxy hosts. our aim is to study this relation, specifically, for radio loud galaxies, and as a function of redshift z. we selected a sample of 42 radio galaxies and active galactic nuclei (agn) with broad emission lines and spectroscopic redshifts between z = 0.3 − 4 by cross-matching the low radio frequency sources from very large array (vla) first with spectroscopically confirmed galaxies from wide-field surveys, including sloan digital sky survey (sdss) dr14 ugriz and dark energy survey (des) dr2 grzy in the optical, wield infrared survey explorer (wise), and the galaxy and mass assembly (gama) spectroscopic survey. we characterized the stellar mass (m⋆), star formation, and black hole properties (mass of the central smbh, eddington ratio η, and jet power, qjet). the relation between smbh mass, m⋆, η, and z is placed into context by comparing them with scaling relations (mbh-m⋆, mbh/m⋆-z, mbh-qjet, and qjet-η) from the literature. on the basis of a multiwavelength spectral energy distribution modeling, our radio sources are broadly consistent with being on the star-forming main sequence. they have sub-eddington accretion rates, η ≃ 1% on average, as typically found in type i agn, while higher accretion rates favor more powerful jets to be launched by the central engine. we find overmassive smbhs in (17 ± 5)% of our radio sources, similarly to previous studies on nearby early-type galaxies. altogether, an evolutionary scenario in which radio-mode agn feedback regulates the accretion onto the smbhs and the stellar mass assembly of the radio sources is discussed, which may explain the observed phenomenology. this pilot study represents a benchmark for future studies using wide-field surveys such as those with euclid and the vera rubin observatory. tables a.1 and a.2 are also 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/672/a164 | black hole and galaxy co-evolution in radio-loud active galactic nuclei at z ∼ 0.3-4 |
about 70 luminous quasars discovered at z > 6.5 are strongly biased toward the bright end, thus not providing a comprehensive view of quasar abundance beyond the cosmic dawn. we present the predicted results of the roman/rubin high-redshift quasar survey, yielding 3 times more, 2-4 mag deeper quasar samples, probing high-redshift quasars across a broad range of luminosities, especially faint quasars at l bol ~ 1010 l ⊙ or m 1450 ~ -22, which are currently poorly explored. we include high-z quasars, galactic dwarfs, and low-z compact galaxies with similar colors as quasar candidates. we create mock catalogs based on population models to evaluate selection completeness and efficiency. we utilize the classical color dropout method in the z and y bands to select primary quasar candidates, followed up with the bayesian selection method to identify quasars. we show that overall selection completeness >80% and efficiency ~10% at 6.5 < z < 9, with 180 quasars at z > 6.5, 20 at z > 7.5, and 2 at z > 8.5. the quasar yields depend sensitively on the assumed quasar luminosity shape and redshift evolution. brown dwarf rejection through proper motion up to 50% can be made for stars brighter than 25 mag, low-z galaxies dominate at fainter magnitude. our results show that roman/rubin are able to discover a statistical sample of the earliest and faintest quasars in the universe. the new valuable data sets are worth follow-up studies with jwst and extremely large telescopes to determine the quasar luminosity function faint end slope and constraint the supermassive black holes growth in the early universe. | predicting the yields of z > 6.5 quasar surveys in the era of roman and rubin |
the flat spectrum radio quasar (fsrq) pks 1510−089 is known for its complex multiwavelength behaviour and it is one of only a few fsrqs detected in very-high-energy (vhe, e > 100 gev) γ rays. the vhe γ-ray observations with h.e.s.s. and magic in late may and early june 2016 resulted in the detection of an unprecedented flare, which revealed, for the first time, vhe γ-ray intranight variability for this source. while a common variability timescale of 1.5 h has been found, there is a significant deviation near the end of the flare, with a timescale of ∼20 min marking the cessation of the event. the peak flux is nearly two orders of magnitude above the low-level emission. for the first time, a curvature was detected in the vhe γ-ray spectrum of pks 1510-089, which can be fully explained by the absorption on the part of the extragalactic background light. optical r-band observations with atom revealed a counterpart of the γ-ray flare, even though the detailed flux evolution differs from the vhe γ-ray light curve. interestingly, a steep flux decrease was observed at the same time as the cessation of the vhe γ-ray flare. in the high-energy (he, e > 100 mev) γ-ray band, only a moderate flux increase was observed with fermi-lat, while the he γ-ray spectrum significantly hardens up to a photon index of 1.6. a search for broad-line region (blr) absorption features in the γ-ray spectrum indicates that the emission region is located outside of the blr. radio very-long-baseline interferometry observations reveal a fast-moving knot interacting with a standing jet feature around the time of the flare. as the standing feature is located ∼50 pc from the black hole, the emission region of the flare may have been located at a significant distance from the black hole. if this is indeed a true correlation, the vhe γ rays must have been produced far down in the jet, where turbulent plasma crosses a standing shock. | h.e.s.s. and magic observations of a sudden cessation of a very-high-energy γ-ray flare in pks 1510−089 in may 2016 |
we utilize recent nustar observations (co-added depth ≈55-120 ks) of pg 1001+054, pg 1254+047, and phl 1811 to constrain their hard x-ray (≳5 kev) weakness and spectral shapes and thus to investigate the nature of their extreme x-ray weakness. these quasars showed very weak soft x-ray emission, and they were proposed to be intrinsically x-ray weak, with the x-ray coronae producing weak continuum emission relative to their optical/uv emission. however, the new observations suggest an alternative explanation. the nustar 3-24 kev spectral shapes for pg 1001+054 and phl 1811 are likely flat (effective power-law photon indices ${{\rm{\gamma }}}_{\mathrm{eff}}={1.0}_{-0.6}^{+0.5}$ and ${{\rm{\gamma }}}_{\mathrm{eff}}={1.4}_{-0.7}^{+0.8}$ , respectively), while the shape is nominal for pg 1254+047 (γeff = 1.8 ± 0.3). pg 1001+054 and phl 1811 are significantly weak at hard x-ray energies (by factors of ≈26-74 at rest-frame 8 kev) compared to the expectations from their optical/uv emission, while pg 1254+047 is only hard x-ray weak by a factor of ≈3. we suggest that x-ray obscuration is present in all three quasars. we propose that, as an alternative to the intrinsic x-ray weakness + x-ray obscuration scenario, the soft and hard x-ray weakness of these quasars can be uniformly explained under an obscuration-only scenario. this model provides adequate descriptions of the multiepoch soft and hard x-ray data of these quasars, with variable column density and leaked fraction of the partial covering absorber. we suggest that the absorber is the clumpy dust-free wind launched from the accretion disk. these quasars probably have super-eddington accretion rates that drive powerful and high-density winds. | nustar observations of intrinsically x-ray weak quasar candidates: an obscuration-only scenario |
tension between cosmic microwave background-based and distance ladder-based determinations of the hubble constant h 0 motivates the pursuit of independent methods that are not subject to the same systematic effects. a promising alternative, proposed by refsdal in 1964, relies on the inverse scaling of h 0 with the delay between the arrival times of at least two images of a strongly lensed variable source such as a quasar. to date, refsdal's method has mostly been applied to quasars lensed by individual galaxies rather than by galaxy clusters. using the three quasars strongly lensed by galaxy clusters (sdss j1004+4112, sdss j1029+2623, and sdss j2222+2745) that have both multiband hubble space telescope data and published time delay measurements, we derive h 0, accounting for the systematic and statistical sources of uncertainty. while a single time delay measurement does not yield a well-constrained h 0 value, analyzing the systems together tightens the constraint. combining the six time delays measured in the three cluster-lensed quasars gives h 0 = 74.1 ± 8.0 km s-1 mpc-1. to reach 1% uncertainty in h 0, we estimate that a sample size of order of 620 time delay measurements of similar quality as those from sdss j1004+4112, sdss j1029+2623, and sdss j2222+2745 would be needed. improving the lens modeling uncertainties by a factor of two and a half may reduce the needed sample size to 100 time delays, potentially reachable in the next decade. | hubble constant measurement from three large-separation quasars strongly lensed by galaxy clusters |
context. sdss j2222+2745, at z = 0.489, is one of the few currently known lens clusters with multiple images (six) of a background (z = 2.801) quasar with measured time delays between two image pairs (with a sub-percent relative error for the longer time delay). systems of this kind can be exploited as alternative cosmological probes through high-precision and accurate strong lensing models.aims: we present recent observations from the multi unit spectroscopic explorer (muse) on the very large telescope (vlt) and new total mass models of the core of the galaxy cluster sdss j2222+2745.methods: we combine archival multi-band, high-resolution imaging from the hubble space telescope (hst) with our vlt/muse spectroscopic data to securely identify 34 cluster members and 12 multiple images from 3 background sources. we also measure the stellar velocity dispersions of 13 cluster galaxies, down to hst f160w = 21 mag, enabling an independent estimate of the contribution of the sub-halo mass component to the lens total mass. by leveraging the new spectroscopic dataset, we build improved strong lensing models.results: the projected total mass distribution of the lens cluster is best modelled with a single large-scale mass component, a galaxy-scale component, anchored by the vlt/muse kinematic information, and an external shear component. the best-fit strong lensing model yields a root mean square separation between the model-predicted and observed positions of the multiple images of 0″.29. when analysing the impact of systematic uncertainties, stemming from modelling assumptions and used observables, we find that the resulting projected total mass profile, the relative weight of the sub-halo mass component, and the critical lines are consistent, within the statistical uncertainties. the predicted magnification and time-delay values are, instead, more sensitive to the local details of the lens total mass distribution, and vary significantly among lens models that are similarly good at reproducing the observed multiple image positions. in particular, the model-predicted time delays can differ by a factor of up to ∼1.5.conclusions: sdss j2222+2745 is a promising lens cluster for cosmological applications. however, due to its complex morphology, the relatively low number of secure `point-like' multiple images, and current model degeneracies, it becomes clear that additional information (from the observed surface brightness distribution of lensed sources and the measured time delays) needs to be included in the modelling for accurate and precise cosmological measurements. the full vlt/muse secure spectroscopic catalogue presented in this work is made publicly available. | new strong lensing modelling of sdss j2222+2745 enhanced with vlt/muse spectroscopy |
the origin of jets is one of the most important issues concerning active galactic nuclei, yet it has remained obscure. in this work, we made use of information from emission lines, spectral energy distributions, and fermi-lat γ-ray emission to construct a blazar sample that contains 667 sources. we note that jet power originations are different for bl lacertae objects (bl lacs) and flat-spectrum radio quasars (fsrqs). the correlation between jet power p jet and the normalized disk luminosity l disk/l edd shows a slope of -1.77 for bl lacs and a slope of 1.16 for fsrqs. the results seem to suggest that bl lac jets are powered by extracting black hole (bh) rotation energy, while fsrq jets are mostly powered by accretion disks. meanwhile, we find the accretion ratio $\dot{m}/{\dot{m}}_{\mathrm{edd}}$ increases with the normalized γ-ray luminosity. based on this, we propose a dividing line, $\mathrm{log}({l}_{\mathrm{blr}}/{l}_{\mathrm{edd}})=0.25\ \mathrm{log}({l}_{\gamma }/{l}_{\mathrm{edd}})-2.23$ , to separate fsrqs and bl lacs in the diagram of l blr/l edd against lγ /l edd using a machine-learning method; the method gives an accuracy of 84.5%. in addition, we propose an empirical formula, ${m}_{\mathrm{bh}}/{m}_{\odot }\simeq {l}_{\gamma }^{0.65}/21.46$ , to estimate bh mass based on a strong correlation between γ-ray luminosity and bh mass. strong γ-ray emission is typical in blazars, and the emission is always boosted by a doppler-beaming effect. in this work, we generate a new method to estimate a lower limit of doppler factor δ and give δ bl lac = 7.94 and δ fsrq = 11.55. | the relativistic jet and central engine of fermi blazars |
observations of z ≳ 6 quasars provide information on the early phases of the most massive black holes (mbhs) and galaxies. current observations at sub-mm wavelengths trace cold and warm gases, and future observations will extend information to other gas phases and the stellar properties. the goal of this study is to examine the gas life cycle in a z ≳ 6 quasar: from accretion from the halo to the galaxy and all the way into the mbh, to how star formation and the mbh itself affect the gas properties. using a very high resolution cosmological zoom-in simulation of a z = 7 quasar, including state-of-the-art non-equilibrium chemistry, mbh formation, growth, and feedback, we investigate the distribution of the different gas phases in the interstellar medium across cosmic time. we assess the morphological evolution of the quasar host using different tracers (star- or gas-based) and the thermodynamic distribution of the mbh accretion-driven outflows, finding that obscuration in the disc is mainly due to molecular gas, with the atomic component contributing at larger scales and/or above/below the disc plane. moreover, our results also show that molecular outflows, if present, are more likely the result of gas being lifted near the mbh than production within the wind because of thermal instabilities. finally, we also discuss how different gas phases can be employed to dynamically constrain the mbh mass, and argue that resolutions below ~100 pc yield unreliable estimates because of the strong contribution of the nuclear stellar component to the potential at larger scales. | high-redshift quasars and their host galaxies - ii. multiphase gas and stellar kinematics |
water vapor (h2o) is one of the brightest molecular emitters after carbon monoxide (co) in galaxies with high infrared (ir) luminosity, allowing us to investigate the warm and dense phase of the interstellar medium (ism) where star formation occurs. however, due to the complexity of its radiative spectrum, h2o is not frequently exploited as an ism tracer in distant galaxies. therefore, h2o studies of the warm and dense gas at high-z remain largely unexplored. in this work, we present observations conducted with the northern extended millimeter array (noema) toward three z > 6 ir-bright quasars j2310+1855, j1148+5251, and j0439+1634 targeted in their multiple para- and ortho-h2o transitions (312 − 303, 111 − 000, 220 − 211, and 422 − 413), as well as their far-ir (fir) dust continuum. by combining our data with previous measurements from the literature, we estimated the dust masses and temperatures, continuum optical depths, ir luminosities, and star formation rates (sfr) from the fir continuum. we modeled the h2o lines using the molpop-cep radiative transfer code, finding that water vapor lines in our quasar host galaxies are primarily excited in the warm, dense (with a gas kinetic temperature and density of tkin = 50 k, nh2 ∼ 104.5 − 105 cm−3) molecular medium with a water vapor column density of nh2o ∼ 2 × 1017 − 3 × 1018 cm−3. high-j h2o lines are mainly radiatively pumped by the intense optically-thin far-ir radiation field associated with a warm dust component at temperatures of tdust ∼ 80 − 190 k that account for < 5 − 10% of the total dust mass. in the case of j2310+1855, our analysis points to a relatively high value of the continuum optical depth at 100 μm (τ100 ∼ 1). our results are in agreement with expectations based on the h2o spectral line energy distribution of local and high-z ultra-luminous ir galaxies and active galactic nuclei (agn). the analysis of the boltzmann diagrams highlights the interplay between collisions and ir pumping in populating the high h2o energy levels and it allows us to directly compare the excitation conditions in the targeted quasar host galaxies. in addition, the observations enable us to sample the high-luminosity part of the h2o-total-ir (tir) luminosity relations (lh2o − ltir). overall, our results point to supralinear trends that suggest h2o-tir relations are likely driven by ir pumping, rather than the mere co-spatiality between the fir continuum- and line-emitting regions. the observed lh2o/ltir ratios in our z > 6 quasars do not show any strong deviations with respect to those measured in star-forming galaxies and agn at lower redshifts. this supports the notion that h2o can be likely used to trace the star formation activity buried deep within the dense molecular clouds. the reduced spectra and images reported in figs. 2 and 3 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/667/a9 | unveiling the warm and dense ism in z > 6 quasar host galaxies via water vapor emission |
we study the impact of active galactic nuclei (agns) on the co spectral line energy distribution (sled) of high-z galaxies. in particular, we want to assess if the co sled can be used as a probe of agn activity. to this purpose, we develop a semi-analytical model that takes into account the radiative transfer and the clumpy structure of giant molecular clouds where the co lines are excited, their distribution in the galaxy disc, and the torus obscuration of the agn radiation. we study the joint effect on the co sled excitation of (i) the x-ray luminosity from the agns (lx), (ii) the size of the molecular disc, (iii) the inclination angle (ω) of the torus with respect to the molecular disc, and (iv) the giant molecular cloud (gmc) mean density. we also discuss the possibility of an enhanced cosmic ray ionization rate (crir). we find that the x-ray-dominated region (xdr) generated by the agns in every case enhances the co sled for j > 5, with increasing excitation of high-j co lines for increasing x-ray luminosity. because high-z galaxies are compact, the xdr typically encloses the whole disc, thus its effect can be more important with respect to lower redshift objects. the impact of the xdr can be disentangled from an enhanced crir either if l_ x > 10^{44} erg s^{-1}, or if ω ≥ 60°. we finally provide predictions on the co(7-6)/[c ii] and co(17-16)/[c ii] ratios as a function of lx, which can be relevant for alma follow-up of galaxies and quasars previously detected in [c ii]. | impact of x-rays on co emission from high-z galaxies |
various unification schemes interpret the complex phenomenology of quasars and luminous active galactic nuclei (agn) in terms of a simple picture involving a central black hole, an accretion disc and an associated outflow. here, we continue our tests of this paradigm by comparing quasar spectra to synthetic spectra of biconical disc wind models, produced with our state-of-the-art monte carlo radiative transfer code. previously, we have shown that we could produce synthetic spectra resembling those of observed broad absorption line (bal) quasars, but only if the x-ray luminosity was limited to 1043 erg s-1. here, we introduce a simple treatment of clumping, and find that a filling factor of ∼0.01 moderates the ionization state sufficiently for bal features to form in the rest-frame uv at more realistic x-ray luminosities. our fiducial model shows good agreement with agn x-ray properties and the wind produces strong line emission in, e.g., lyα and c iv 1550 å at low inclinations. at high inclinations, the spectra possess prominent lobal features. despite these successes, we cannot reproduce all emission lines seen in quasar spectra with the correct equivalent-width ratios, and we find an angular dependence of emission line equivalent width despite the similarities in the observed emission line properties of bal and non-bal quasars. overall, our work suggests that biconical winds can reproduce much of the qualitative behaviour expected from a unified model, but we cannot yet provide quantitative matches with quasar properties at all viewing angles. whether disc winds can successfully unify quasars is therefore still an open question. | testing quasar unification: radiative transfer in clumpy winds |
in order to study the circumgalactic medium (cgm) of galaxies we develop an automated pipeline to estimate the optical continuum of quasars and detect intervening metal absorption line systems with a matched kernel convolution technique and adaptive s/n criteria. we process ~ one million quasars in the latest data release 16 (dr16) of the sloan digital sky survey (sdss) and compile a large sample of ~ 160 000 mg ii absorbers, together with ~ 70 000 fe ii systems, in the redshift range 0.35 < zabs < 2.3. combining these with the sdss dr16 spectroscopy of ~1.1 million luminous red galaxies (lrgs) and ~200 000 emission line galaxies (elgs), we investigate the nature of cold gas absorption at 0.5 < z < 1. these large samples allow us to characterize the scale dependence of mg ii with greater accuracy than in previous work. we find that there is a strong enhancement of mg ii absorption within ~50 kpc of elgs, and the covering fraction within 0.5rvir of elgs is 2-5 times higher than for lrgs. beyond 50 kpc, there is a sharp decline in mg ii for both kinds of galaxies, indicating a transition to the regime where the cgm is tightly linked with the dark matter halo. the mg ii-covering fraction correlates strongly with stellar mass for lrgs, but weakly for elgs, where covering fractions increase with star formation rate. our analysis implies that cool circumgalactic gas has a different physical origin for star-forming versus quiescent galaxies. | characterizing the abundance, properties, and kinematics of the cool circumgalactic medium of galaxies in absorption with sdss dr16 |
we present the results of a pilot hubble space telescope (hst) imaging study of the host galaxies of ten quasars from the sloan digital sky survey reverberation mapping (sdss-rm) project. probing more than an order of magnitude in black hole (bh) and stellar masses, our sample is the first statistical sample to study the bh-host correlations beyond z > 0.3 with reliable bh masses from reverberation mapping rather than from single-epoch spectroscopy. we perform image decomposition in two hst bands (uvis-f606w and ir-f110w) to measure host colors and estimate stellar masses using empirical relations between broadband colors and the mass-to-light ratio. the stellar masses of our targets are mostly dominated by a bulge component. the bh masses and stellar masses of our sample broadly follow the same correlations found for local rm active galactic nuclei and quiescent bulge-dominant galaxies, with no strong evidence of evolution in the ${m}_{\mathrm{bh}}\mbox{--}{m}_{* ,\mathrm{bulge}}$ relation to z ∼ 0.6. we further compare the host light fraction from hst imaging decomposition to that estimated from spectral decomposition. we find a good correlation between the host fractions derived with both methods. however, the host fraction derived from spectral decomposition is systematically smaller than that from imaging decomposition by ∼30%, indicating different systematics in both approaches. this study paves the way for upcoming more ambitious host galaxy studies of quasars with direct rm-based bh masses at high redshift. | the sloan digital sky survey reverberation mapping project: the mbh-host relations at 0.2 ≲ z ≲ 0.6 from reverberation mapping and hubble space telescope imaging |
the active galactic nucleus (agn) re j1034+396 displays the most significant x-ray quasi-periodic oscillation (qpo) detected so far. we perform a detailed spectral-timing analysis of our recent simultaneous xmm-newton, nustar, and swift observations. we present the energy dependence of the qpo's frequency, rms, coherence, and phase lag, and model them together with the time-averaged spectra. our study shows that four components are required to fit all the spectra. these components include an inner disc component (diskbb), two warm corona components (comptt-1 and comptt-2), and a hot corona component (nthcomp). we find that diskbb, comptt-2 (the hotter but less luminous component), and nthcomp all contain the qpo signal, while comptt-1 only exhibits stochastic variability. by fitting the lag spectrum, we find that the qpo in diskbb leads comptt-2 by 679 s, and comptt-2 leads nthcomp by 180 s. by only varying the normalizations, these components can also produce good fits to the time-averaged and variability spectra obtained from previous observations when qpos were present and absent. our multiwavelength study shows that the detectability of the qpo does not depend on the contemporaneous mass accretion rate. we do not detect a significant iron k α emission line, or any significant reflection hump. finally, we show that the rms and lag spectra in the latest observation are very similar to the 67-hz qpo observed in the micro-quasar grs 1915+105. these new results support the physical analogy between these two sources. we speculate that the qpo in both sources is due to the expansion/contraction of the vertical structure in the inner disc. | re-observing the nls1 galaxy re j1034+396 - ii. new insights on the soft x-ray excess, qpo, and the analogy with grs 1915+105 |
gaia used a large sample of photometrically selected active galactic nuclei (agns) and quasars to remove the residual spin of its global proper motion system in order to achieve a maximally inertial reference frame. a small fraction of these reference objects have statistically significant astrometric proper motions in gaia edr3. we compile a source sample of 105,593 high-fidelity agns with accurate spectroscopically determined redshifts above 0.5 from the sdss and normalized proper motions below 4. the rate of genuinely perturbed proper motions is at least 0.17%. a smaller high completeness sample of 152 quasars with excess proper motions at a confidence level of 0.9995 is examined in detail. pan-starrs images and gaia-resolved pairs reveal that 29% of the sample are either double sources or gravitationally lensed quasars. an anderson-darling test on parameters of a smaller high-reliability sample and their statistical controls reveals 17 significant factors that favor multiplicity and multi-source structure as the main cause of perturbed astrometry. using a nearest-neighbor distance statistical analysis and counts of close companions in gaia on a much larger initial sample of agns, an excess of closely separated sources in gaia is detected. at least 0.33% of all optical quasars are genuinely double or multiply imaged. we provide a list of 44 candidate double or multiple agns and four previously known gravitational lenses. many proper motion quasars may be more closely separated, unresolved doubles exhibiting the variability imposed motion effect, and a smaller fraction may be chance alignments with foreground stars causing weak gravitational lensing. | quasars with proper motions and the link to double and multiple agns |
context. thanks to the cross-identification between the gaia edr3 (e-data release 3) catalogue and the quasars' compiled catalogue lqac-5 (large quasar astrometric catalogue-5), accurate astrometric parameters as well as photometric measurements were available for a set of 416 113 quasars.aims: after analysing the astrometric and photometric properties of these quasars,we concentrate our study on objects characterized by significant proper motion, which contradicts the postulate that they are fixed in the celestial sphere.methods: we derived statistical properties of the positions, parallaxes, and proper motions of the quasars cross-matched with gaia edr3. we carried out a specific investigation of quasars with a proper motion larger than 10 mas yr−1, and used colour-colour diagrams in mid-infrared to discriminate these quasars from stellar contamination. we discuss, in detail, a few cases where the abnormal proper motion could be caused by misidentifications.results: we note that 43% of lqac-5 quasars were not detected by gaia edr3, mainly because of the cut-off magnitude at g = 21. the comparison between r(g) (gaia) and r (sdss) shows a normal distribution. the normalized distributions of parallaxes and proper motions are identical to that of the gaia crf2, as well as the distribution of the gbp − grp colour index. we have identified 937 lqac-5 objects (0.27% of the sample) with gaia edr3 proper motion which is significant at the 5σ level. we have clearly shown that below z = 0.35, the integrated magnitude g(r) obtained from sdss spectra is smaller than g (gaia), leading to the statement that the quasars are generally resolved under this threshold, which should lead to a bad determination of proper motion. moreover, to discriminate quasars from stellar contamination, we have plotted them in a mid-infrared colour-colour diagram. finally, we have made a final selection of 41 objects with μ > 10 mas yr−1, satisfying drastic constraints, which makes them potential candidates for considering their proper motion as real.conclusions: in this paper we carried out a complete analysis of the quasars of the lqac-5 which were cross-identified with gaia edr3 ; this serves as an alternative and complementary study with respect to gaia crf2, involving a different population of quasars. we selected a set of 41 quasars with a proper motion exceeding 10 mas yr−1, which can be considered as very high for objects which are a priori fixed in the celestial sphere. full table a.1 is 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/660/a16 | quasars with large proper motions: a selection from the lqac-5 catalogue combined with gaia edr3. focusing on astrometric and photometric properties |
with the distance sum rule in the friedmann-lemaître-robertson-walker metric, model-independent constraints on both the hubble constant h0 and spatial curvature ${{\rm{\omega }}}_{k}$ can be obtained using strong lensing time-delay data and type ia supernovae (sne ia) luminosity distances. this method is limited by the relatively low redshifts of sne ia, however. here, we propose using quasars as distance indicators, extending the coverage to encompass the redshift range of strong lensing systems. we provide a novel and improved method of determining h0 and ${{\rm{\omega }}}_{k}$ simultaneously. by applying this technique to the time-delay measurements of seven strong lensing systems and the known ultraviolet versus x-ray luminosity correlation of quasars, we constrain the possible values of both h0 and ${{\rm{\omega }}}_{k}$ , and find that ${h}_{0}={75.3}_{-2.9}^{+3.0}$ km ${{\rm{s}}}^{-1}\,{\mathrm{mpc}}^{-1}$ and ${{\rm{\omega }}}_{k}=-{0.01}_{-0.17}^{+0.18}$ . the measured ${{\rm{\omega }}}_{k}$ is consistent with zero spatial curvature, indicating that there is no significant deviation from a flat universe. if we use flatness as a prior, we infer that ${h}_{0}={75.3}_{-1.9}^{+1.9}$ km ${{\rm{s}}}^{-1}\,{\mathrm{mpc}}^{-1}$ , representing a precision of 2.5%. if we further combine these data with the 1048 current pantheon sne ia, our model-independent constraints can be further improved to ${h}_{0}={75.3}_{-2.9}^{+3.0}$ km ${{\rm{s}}}^{-1}\,{\mathrm{mpc}}^{-1}$ and ${{\rm{\omega }}}_{k}={0.05}_{-0.14}^{+0.16}$ . in every case, we find that the hubble constant measured with this technique is strongly consistent with the value (∼74 km ${{\rm{s}}}^{-1}\,{\mathrm{mpc}}^{-1}$ ) measured using the local distance ladder, as opposed to the value optimized by planck. | cosmology-independent estimate of the hubble constant and spatial curvature using time-delay lenses and quasars |
context. when can an active galactic nucleus (agn) be considered radio loud (rl)? following the established view of the agns inner workings, an agn is rl if associated with relativistic ejections emitting a radio synchrotron spectrum (i.e., it is a "jetted" agn). in this paper we exploit the agn main sequence that offers a powerful tool to contextualize radio properties.aims: if large samples of optically-selected quasars are considered, agns are identified as rl if their kellermann's radio loudness ratio rk > 10. our aims are to characterize the optical properties of different classes based on radio loudness within the main sequence and to test whether the condition rk > 10 is sufficient for the identification of rl agns, since the origin of relatively strong radio emission may not be necessarily due to relativistic ejection.methods: a sample of 355 quasars was selected by cross-correlating the very large array faint images of the radio sky at twenty-centimeters survey (first) with the twelfth release of the sloan digital sky survey quasar catalog published in 2017. we classified the optical spectra according to their spectral types along the main sequence of quasars. for each spectral type, we distinguished compact and extended morphology (providing a first-based atlas of radio maps in the latter case), and three classes of radio loudness: detected ( specific flux ratio in the g band and at 1.4 ghz, r'k < 10), intermediate (10 ≤ r'k < 70), and rl (r'k ≥ 70).results: the analysis revealed systematic differences between radio-detected (i.e., radio-quiet), radio-intermediate, and rl classes in each spectral type along the main sequence. we show that spectral bins that contain the extreme population a sources have radio power compatible with emission by mechanisms ultimately due to star formation processes. rl sources of population b are characteristically jetted. their broad hβ profiles can be interpreted as due to a binary broad-line region. we suggest that rl population b sources should be preferential targets for the search of black hole binaries, and present a sample of binary black hole agn candidates.conclusions: the validity of the kellermann's criterion may be dependent on the source location along the quasar main sequence. the consideration of the main sequence trends allowed us to distinguish between sources whose radio emission mechanisms is jetted from the ones where the mechanism is likely to be fundamentally different. tables a.1-a.3 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/cat/j/a+a/630/a110 | radio loudness along the quasar main sequence |
the masses of supermassive black holes (bhs) in broad-line active galactic nuclei (agns) can be measured through reverberation mapping, but this method currently cannot be applied to very large samples or to high-redshift agns. as a practical alternative, one can devise empirical scaling relations, based on the correlation between broad-line region size and agn luminosity and the relation between bh mass and bulge stellar velocity dispersion, to estimate the virial masses of bhs from single-epoch spectroscopy. we present a revised calibration of the bh mass estimator for the commonly used hβ emission line. our new calibration takes into account the recent determination of the virial coefficient for pseudo and classical bulges. | a revised calibration of the virial mass estimator for black holes in active galaxies based on single-epoch hβ spectra |
the spectroscopy of background qso sightlines passing close to foreground galaxies is a potent technique for studying the circumgalactic medium (cgm). however, qsos are effectively point sources, limiting their potential to constrain the size of circumgalactic gaseous structures. here we present the first large keck/low-resolution imaging spectrometer (lris) and very large telescope (vlt)/focal reducer/low-dispersion spectrograph 2 (fors2) spectroscopic survey of bright ({b}{ab}< 22.3) background galaxies whose lines of sight probe mg ii λ λ 2796,2803 absorption from the cgm around close projected foreground galaxies at transverse distances 10 {kpc}< {r}\perp< 150 {kpc}. our sample of 72 projected pairs, drawn from the prism multi-object survey, includes 48 background galaxies that do not host bright active galactic nuclei, and both star-forming and quiescent foreground galaxies with stellar masses of 9.0< {log}{m}* /{m}⊙ < 11.2 at redshifts of 0.35< {z}{{f}/{{g}}}< 0.8. we detect mg ii absorption associated with these foreground galaxies with equivalent widths of 0.25 \mathring{{a}} < {w}2796< 2.6 \mathring{{a}} at > 2σ significance in 20 individual background sightlines passing within {r}\perp < 50 {kpc} and place 2σ upper limits on w 2796 of ≲ 0.5 \mathring{{a}} in an additional 11 close sightlines. within {r}\perp < 50 {kpc}, w 2796 is anticorrelated with r ⊥, consistent with analyses of mg ii absorption detected along background qso sightlines. subsamples of these foreground hosts divided at {log}{m}* /{m}⊙ =9.9 exhibit statistically inconsistent w 2796 distributions at 30 {kpc}< {r}\perp < 50 {kpc}, with the higher-m * galaxies yielding a larger median w 2796 by 0.9 \mathring{{a}} . finally, we demonstrate that foreground galaxies with similar stellar masses exhibit the same median w 2796 at a given r ⊥ to within < 0.2 \mathring{{a}} toward both background galaxies and toward qso sightlines drawn from the literature. analysis of these data sets constraining the spatial coherence scale of circumgalactic mg ii absorption is presented in a companion paper. | galaxies probing galaxies in primus. i. sample, spectroscopy, and characteristics of the z\\sim 0.5 mg ii-absorbing circumgalactic medium |
we study the relation between the metallicity of quasar broad line region (blr) and black hole (bh) mass (10^{7.5}{-}10^{10} m_{⊙}) and quasar bolometric luminosity (10^{44.6}{-}10^{48} { erg s^{-1}}) using a sample of ∼130 000 quasars at 2.25 ≤ z ≤ 5.25 from sloan digital sky survey data release 12 (dr12). we generate composite spectra by stacking individual spectra in the same bh mass (bolometric luminosity) and redshift bins and then estimate the metallicity of quasar blr using metallicity-sensitive broad emission-line flux ratios based on the photoionization models. we find a significant correlation between quasar blr metallicity and bh mass (bolometric luminosity) but no correlation between quasar blr metallicity and redshift. we also compare the metallicity of quasar blr and that of host galaxies inferred from the mass-metallicity relation of star-forming galaxy at z ∼ 2.3 and 3.5. we find quasar blr metallicity is 0.3 ∼ 1.0 dex higher than their host galaxies. this discrepancy cannot be interpreted by the uncertainty due to different metallicity diagnostic methods, mass-metallicity relation of galaxy, metallicity gradient in quasar host galaxies, bh mass estimation, the effect of different spectral energy distribution models, and a few other potential sources of uncertainties. we propose a possibility that the high metallicity in quasar blr might be caused by metal enrichment from massive star formation in the nucleus region of quasars or even the accretion disc. | the evolution of chemical abundance in quasar broad line region |
context. multiply imaged gravitationally lensed quasars are among the most interesting and useful observable extragalactic phenomena. because their study constitutes a unique tool in various fields of astronomy, they are highly sought, but difficult to find. even in this era of all-sky surveys, discovering them remains a great challenge, with barely a few hundred systems currently known.aims: we aim to discover new multiply imaged quasar candidates in the recently published gaia data release 2 (dr2), which is the astrometric and photometric all-sky survey with the highest spatial resolution that achieves effective resolutions from 0.4″ to 2.2″.methods: we cross-matched a merged list of quasars and candidates with gaia dr2 and found 1 839 143 counterparts within 0.5″. we then searched matches with more than two gaia dr2 counterparts within 6″. we further narrowed the resulting list using astrometry and photometry compatibility criteria between the gaia dr2 counterparts. a supervised machine-learning method, called extremely randomized trees, was finally adopted to assign a probability of being lensed to each remaining system.results: we report the discovery of two quadruply imaged quasar candidates that are fully detected in gaia dr2. these are the most promising new quasar lens candidates from gaia dr2 and a simple singular isothermal ellipsoid lens model is able to reproduce their image positions to within 1 mas. this letter demonstrates the discovery potential of gaia for gravitational lenses. | gaia gral: gaia dr2 gravitational lens systems. i. new quadruply imaged quasar candidates around known quasars |
while theoretical arguments predict that most of the early growth of supermassive black holes (smbhs) happened during heavily obscured phases of accretion, current methods used for selecting z > 6 quasars (qsos) are strongly biased against obscured qsos, thus considerably limiting our understanding of accreting smbhs during the first gigayear of the universe from an observational point of view. we report the chandra discovery of the first heavily obscured qso candidate in the early universe, hosted by a close (≈5 kpc) galaxy pair at z = 6.515. one of the members is an optically classified type-1 qso, pso167-13. the companion galaxy was first detected as a [c ii] emitter by atacama large millimeter array (alma). an x-ray source is significantly (p = 0.9996) detected by chandra in the 2-5 kev band, with < 1.14 net counts in the 0.5-2 kev band, although the current positional uncertainty does not allow a conclusive association with either pso167-13 or its companion galaxy. from x-ray photometry and hardness-ratio arguments, we estimated an obscuring column density of nh > 2 × 1024 cm-2 and nh > 6 × 1023 cm-2 at 68% and 90% confidence levels, respectively. thus, regardless of which of the two galaxies is associated with the x-ray emission, this source is the first heavily obscured qso candidate at z > 6. | discovery of the first heavily obscured qso candidate at z > 6 in a close galaxy pair |
we present rest-frame near-ultraviolet (nuv) spectroscopy of star-forming galaxies (sfgs) at 0.6 < z < 1.2 from the extended baryon oscillation spectroscopic survey (eboss) in sdss-iv. one of the eboss programs is to obtain 2″ (about 15 kpc) fiber spectra of about 200,000 emission-line galaxies (elgs) at redshift z ≳ 0.6. we use the data from the pilot observations of this program, including 8620 spectra of sfgs at 0.6 < z < 1.2. the median composite spectra of these sfgs at 2200 å < λ < 4000 å feature asymmetric, preferentially blueshifted non-resonant emission, fe ii*, and blueshifted resonant absorption, e.g., fe ii and mg ii, indicating ubiquitous outflows driven by star formation at these redshifts. for the absorption lines, we find a variety of velocity profiles with different degrees of blueshift. comparing our new observations with the literature, we do not observe the non-resonant emission in the small-aperture (<40 pc) spectra of local star-forming regions with the hubble space telescope, and find the observed line ratios in the sfg spectra to be different from those in the spectra of local star-forming regions, as well as those of quasar absorption-line systems in the same redshift range. we introduce an outflow model that can simultaneously explain the multiple observed properties and suggest that the variety of absorption velocity profiles and the line ratio differences are caused by scattered fluorescent emission filling in on top of the absorption in the large-aperture eboss spectra. we develop an observation-driven, model-independent method to correct the emission infill to reveal the true absorption profiles. finally, we show that the strengths of both the non-resonant emission and the emission-corrected resonant absorption increase with [o ii] λλ3727, 3730 rest equivalent width and luminosity, with a slightly larger dependence on the former. our results show that the eboss and future dark-energy surveys (e.g., dark energy spectroscopic instrument survey and prime focus spectrograph survey) will provide rich data sets of rest-frame nuv spectroscopy for astrophysical applications. | near-ultraviolet spectroscopy of star-forming galaxies from eboss: signatures of ubiquitous galactic-scale outflows |
we investigate the relationship between x-ray and optical line emission in 340 nearby (z ≃ 0.04) agn selected above 10 kev using swift bat. we find a weak correlation between the extinction corrected [o iii] and hard x-ray luminosity (l_[o iii]^{int} ∝ l_{14-195}) with a large scatter (rpear = 0.64, σ = 0.62 dex) and a similarly large scatter with the intrinsic 2-10 kev to [o iii] luminosities (rpear = 0.63, σ = 0.63 dex). correlations of the hard x-ray fluxes with the fluxes of high-ionization narrow lines ([o iii], he ii, [ne iii] and [ne v]) are not significantly better than with the low-ionization lines (h α, [s ii]). factors like obscuration or physical slit size are not found to be a significant part of the large scatter. in contrast, the optical emission lines show much better correlations with each other (σ = 0.3 dex) than with the x-ray flux. the inherent large scatter questions the common usage of narrow emission lines as agn bolometric luminosity indicators and suggests that other issues such as geometrical differences in the scattering of the ionized gas or long-term agn variability are important. | bat agn spectroscopic survey-ii. x-ray emission and high-ionization optical emission lines |
the inner regions of active galaxies host the most extreme and energetic phenomena in the universe including, relativistic jets, supermassive black hole binaries, and recoiling supermassive black holes. however, many of these sources cannot be resolved with direct observations. i review how strong gravitational lensing can be used to elucidate the structures of these sources from radio frequencies up to very high energy gamma rays. the deep gravitational potentials surrounding galaxies act as natural gravitational lenses. these gravitational lenses split background sources into multiple images, each with a gravitationally-induced time delay. these time delays and positions of lensed images depend on the source location, and thus, can be used to infer the spatial origins of the emission. for example, using gravitationally-induced time delays improves angular resolution of modern gamma-ray instruments by six orders of magnitude (× 106), and provides evidence that gamma-ray outbursts can be produced at even thousands of light years from a supermassive black hole, and that the compact radio emission does not always trace the position of the supermassive black hole. these findings provide unique physical information about the central structure of active galaxies, force us to revise our models of operating particle acceleration mechanisms, and challenge our assumptions about the origin of compact radio emission. future surveys, including lsst, ska, and euclid, will provide observations for hundreds of thousands of gravitationally lensed sources, which will allow us to apply strong gravitational lensing to study the multi-wavelength structure for large ensembles of sources. this large ensemble of gravitationally lensed active galaxies will allow us to elucidate the physical origins of multi-wavelength emissions, their connections to supermassive black holes, and their cosmic evolution. | gravitational lenses as high-resolution telescopes |
observations of metal absorption systems in the spectra of distant quasars allow one to constrain a possible variation of the fine-structure constant throughout the history of the universe. such a test poses utmost demands on the wavelength accuracy and previous studies were limited by systematics in the spectrograph wavelength calibration. a substantial advance in the field is therefore expected from the new ultra-stable high-resolution spectrograph espresso, which was recently installed at the vlt. in preparation of the fundamental physics related part of the espresso gto program, we present a thorough assessment of the espresso wavelength accuracy and identify possible systematics at each of the different steps involved in the wavelength calibration process. most importantly, we compare the default wavelength solution, which is based on the combination of thorium-argon arc lamp spectra and a fabry-pérot interferometer, to the fully independent calibration obtained from a laser frequency comb. we find wavelength-dependent discrepancies of up to 24 m s-1. this substantially exceeds the photon noise and highlights the presence of different sources of systematics, which we characterize in detail as part of this study. nevertheless, our study demonstrates the outstanding accuracy of espresso with respect to previously used spectrographs and we show that constraints of a relative change of the fine-structure constant at the 10-6 level can be obtained with espresso without being limited by wavelength calibration systematics. | fundamental physics with espresso: towards an accurate wavelength calibration for a precision test of the fine-structure constant |
we present a study of the distribution of radio jet position angles of radio galaxies over an area of 1 square degree in the elais n1 field. elais n1 was observed with the giant metrewave radio telescope at 612 mhz to an rms noise level of 10 μjy and angular resolution of 6 arcsec × 5 arcsec. the image contains 65 resolved radio galaxy jets. the spatial distribution reveals a prominent alignment of jet position angles along a `filament' of about 1°. we examine the possibility that the apparent alignment arises from an underlying random distribution and find that the probability of chance alignment is less than 0.1 per cent. an angular covariance analysis of the data indicates the presence of spatially coherence in position angles on scales >0 .^{circ}5. this angular scales translates to a comoving scale of >20 mpc at a redshift of 1. the implied alignment of the spin axes of massive black holes that give rise to the radio jets suggest the presence of large-scale spatial coherence in angular momentum. our results reinforce prior evidence for large-scale spatial alignments of quasar optical polarization position angles. | alignments of radio galaxies in deep radio imaging of elais n1 |
we investigated, using spectral-timing analysis, the characterization of highly ionized outflows in seyfert galaxies, the so-called warm absorbers. here, we present our results of the extensive 600 ks of xmm-newton archival observations of the bright and highly variable seyfert 1 galaxy ngc 4051 whose spectrum has revealed a complex multicomponent wind. making use of both rgs and epic-pn data, we performed a detailed analysis through a time-dependent photoionization code in combination with spectral and fourier spectral-timing techniques. the source light curves and the warm absorber parameters obtained from the data were used to simulate the response of the gas to variations in the ionizing flux of the central source. the resulting time variable spectra were employed to predict the effects of the warm absorber on the time lags and coherence of the energy dependent light curves. we have found that, in the absence of any other lag mechanisms, a warm absorber with the characteristics of the one observed in ngc 4051, is able to produce soft lags, up to 100 s, on timescales of hours. the time delay is associated with the response of the gas to changes in the ionizing source, either by photoionization or radiative recombination, which is dependent on its density. the range of radial distances that, under our assumptions, yield longer time delays are distances r 0.3-1.0 × 1016 cm, and hence gas densities n 0.4-3.0 × 107 cm-3. since these ranges are comparable to the existing estimates of the location of the warm absorber in ngc 4051, we suggest that it is likely that the observed x-ray time lags may carry a signature of the warm absorber response time to changes in the ionizing continuum. our results show that the warm absorber in ngc 4051 does not introduce lags on the short timescales associated with reverberation, but will likely modify the hard continuum lags seen on longer timescales, which in this source have been measured to be on the order of 50 s. hence, these results highlight the importance of understanding the contribution of the warm absorber to the agn x-ray time lags since it is also vital information for interpreting the lags associated with propagation and reverberation effects in the inner emitting regions. | timing the warm absorber in ngc 4051 |
we present the results of a search for cold gas at high redshift along quasar lines of sight carried out without any a priori assumption on the neutral atomic-hydrogen content of the absorption-line systems. to do this, we systematically looked for neutral-carbon (c i) λλ1560, 1656 transition lines in 41 696 low-resolution quasar spectra (1.5 < zem < 4.46) from the sdss-ii - data release 7 - database. c i absorption lines should indeed probe the shielded gas in the neutral interstellar medium of galaxies more efficiently than traditional tracers such as neutral atomic-hydrogen (h i) damped lyman-α (dla) and/or mg ii systems. we built up a sample of 66 c i absorbers with redshifts in the range 1.5 < z < 3.1 and rest-frame equivalent widths 0.1 <wr(λ1560) < 1.7 å. the completeness limit of our survey is wr,lim(λ1560) ≃ 0.4 å. c i systems stronger than that are more than one hundred times rarer than dlas at zabs = 2.5. the number of c i systems per unit redshift is found to increase significantly below z = 2. we suggest that these c i absorbers are closely related to the process of star formation and the production of dust in galaxies and that their cosmic evolution is driven by the interplay between dust shielding and the evolution of the ultra-violet background at ~10 ev. we derive the neutral atomic-hydrogen content of the c i systems observable from the southern hemisphere from vlt/uves spectroscopy and find that a majority of them are sub-dlas with n(h i) ~ 1020 atoms cm-2. the dust content of these absorbers is yet significant as seen from the redder optical colours of the corresponding background quasars and their reddened spectral energy distributions, with e(b-v) values up to ~0.3. the overall n(h i) distribution of c i systems is, however, relatively flat. as a consequence, among the c i systems classifying as dlas, there is a probable excess of strong dlas with log n(h i) > 21 (atoms cm-2) compared to systematic dla surveys. whilst the dust content of such systems is significant, their dust-to-gas ratio must still be limited. indeed, strong dlas having large amounts of shielded gas and dust producing stronger reddening and extinction of the background quasars, if they exist, should have been missed in the current magnitude-limited quasar sample. we study the empirical relations between wr(c i), n(h i), e(b-v), and the strength of the 2175 å extinction feature. the latter is detected in about 30% of the c i absorbers. we show that, at equal amount of reddening, the 2175 å feature is weak compared to galactic lines of sight. this is probably the consequence of current or past star formation in the vicinity of the c i systems. we also find that the strongest c i systems tend to have the largest amounts of dust and that the metallicity of the gas and its molecular fraction is likely to be high in a large number of cases. the c i-absorber sample presented here hence provides ideal targets for detailed studies of the dust composition and molecular species at high redshift. based on data from the sloan digital sky survey (sdss) and dedicated follow-up observations carried out at the european southern observatory (eso) under programmes 082.a-0544 and 083.a-0454 (p.i. ledoux) using the ultra-violet and visual echelle spectrograph (uves) installed at the nasmyth-b focus of the very large telescope (vlt), unit-2 (kueyen), on cerro paranal, chile. | neutral atomic-carbon quasar absorption-line systems at z> 1.5. sample selection, h i content, reddening, and 2175 å extinction feature |
we investigate how uncertainties in the chemical and cooling rate coefficients relevant for a metal-free gas influence our ability to determine the critical ultraviolet field strength required to suppress h2 cooling in high-redshift atomic cooling haloes. the suppression of h2 cooling is a necessary prerequisite for the gas to undergo direct collapse and form an intermediate mass black hole. these black holes can then act as seeds for the growth of the supermassive black holes (smbhs) observed at redshifts z ∼ 6. the viability of this model for smbh formation depends on the critical ultraviolet field strength, jcrit: if this is too large, then too few seeds will form to explain the observed number density of smbhs. we show in this paper that there are five key chemical reactions whose rate coefficients are uncertain enough to significantly affect jcrit. the most important of these is the collisional ionization of hydrogen by collisions with other hydrogen atoms, as the rate for this process is very poorly constrained at the low energies relevant for direct collapse. the total uncertainty introduced into jcrit by this and the other four reactions could in the worst case approach a factor of five. we also show that the use of outdated or inappropriate values for the rates of some chemical reactions in previous studies of the direct collapse mechanism may have significantly affected the values of jcrit determined by these studies. | simulating the formation of massive seed black holes in the early universe - ii. impact of rate coefficient uncertainties |
time domain optical surveys have discovered roughly a dozen candidate stellar tidal disruption flares in the last five years, and future surveys like the large synoptic survey telescope will likely find hundreds to thousands more. these tidal disruption events (tdes) present an interesting puzzle: a majority of the current tde sample is hosted by rare post-starburst galaxies, and tens of percents of the galaxies are hosted in even rarer e+a galaxies, which make up ∼ 0.1 % of all galaxies in the local universe. e+as are therefore overrepresented among tde hosts by 1-2 orders of magnitude, a discrepancy unlikely to be accounted for by selection effects. we analyze hubble space telescope photometry of one of the nearest e+a galaxies, ngc 3156, to estimate the rate of stellar tidal disruption produced as two-body relaxation diffuses stars onto orbits in the loss cone of the central supermassive black hole. the rate of tdes produced by two-body relaxation in ngc 3156 is large when compared to other galaxies with similar black hole mass: {\dot{n}}{{tde}}∼ 1× {10}-3 {{{yr}}}-1. this suggests that the preference of tdes for e+a hosts may be due to central stellar overdensities produced in recent starbursts. | an enhanced rate of tidal disruptions in the centrally overdense e+a galaxy ngc 3156 |
inverse compton cooling limits the brightness temperature of the radiating plasma to a maximum of 1011.5 k. relativistic boosting can increase its observed value, but apparent brightness temperatures much in excess of 1013 k are inaccessible using ground-based very long baseline interferometry (vlbi) at any wavelength. we present observations of the quasar 3c 273, made with the space vlbi mission radioastron on baselines up to 171,000 km, which directly reveal the presence of angular structure as small as 26 μas (2.7 light months) and brightness temperature in excess of 1013 k. these measurements challenge our understanding of the non-thermal continuum emission in the vicinity of supermassive black holes and require a much higher doppler factor than what is determined from jet apparent kinematics. | radioastron observations of the quasar 3c273: a challenge to the brightness temperature limit |
we have monitored the quasar 3c 273 in the optical v, r, and i bands from 2005 to 2016. intraday variability (idv) is detected on seven nights. the variability amplitudes on most of the nights are less than 10%, and on four nights, more than 20%. when considering the nights with time spans >4 hr, the duty cycle (dc) is 14.17%. over the 12 years, the overall magnitude and color index variabilities are {{δ }}i=0\buildrel{{m}}\over{.} 67, {{δ }}r=0\buildrel{{m}}\over{.} 72, {{δ }}v=0\buildrel{{m}}\over{.} 68, and {{δ }}(v-r)=0\buildrel{{m}}\over{.} 25, respectively. the largest clear idv has an amplitude of 42% over just 5.8 minutes, and the weakest detected idv is 5.4% over 175 minutes. the bwb (bluer when brighter) chromatic trend is dominant for 3c 273 and appears at different flux levels on intraday timescales. the bwb trend exists for short-term timescales and intermediate-term timescales but different timescales have different correlations. there is no bwb trend for our whole time-series data sets. a significant anticorrelation between the bwb trend and length of timescales is found. combining with v-band data from previous works, we find a possible quasi-periodicity of p = 3918 ± 1112 days. the possible explanations for the observed variability, bwb chromatic trend, and periodicity are discussed. | multicolor optical monitoring of the quasar 3c 273 from 2005 to 2016 |
galaxy mergers and gas accretion from the cosmic web drove the growth of galaxies and their central black holes at early epochs. we report spectroscopic imaging of a multiple merger event in the most luminous known galaxy, wise j224607.56-052634.9 (w2246-0526), a dust-obscured quasar at redshift 4.6, 1.3 billion years after the big bang. far-infrared dust continuum observations show three galaxy companions around w2246-0526 with disturbed morphologies, connected by streams of dust likely produced by the dynamical interaction. the detection of tidal dusty bridges shows that w2246-0526 is accreting its neighbors, suggesting that merger activity may be a dominant mechanism through which the most luminous galaxies simultaneously obscure and feed their central supermassive black holes. | the multiple merger assembly of a hyperluminous obscured quasar at redshift 4.6 |
in modern astrophysics, machine learning has increasingly gained popularity with its incredibly powerful ability to make predictions or calculated suggestions for large amounts of data. we describe an application of the supervised machine-learning algorithm, random forests (rf), to the star/galaxy/qso classification and the stellar effective temperature regression based on the combination of large sky area multi-object fiber spectroscopic telescope and sloan digital sky survey spectroscopic data. this combination enables us to obtain reliable predictions with one of the largest training samples ever used. the training samples are built with a nine-color data set of about three million objects for the classification and a seven-color data set of over one million stars for the regression. the performance of the classification and regression is examined with validation and blind tests on the objects in the radial velocity extension, 6dfgs, uv-bright quasar survey and apache point observatory galactic evolution experiment surveys. we demonstrate that rf is an effective algorithm, with classification accuracies higher than 99% for stars and galaxies, and higher than 94% for qsos. these accuracies are higher than machine-learning results in former studies. the total standard deviations of the regression are smaller than 200 k, which is similar to those of some spectrum-based methods. the machine-learning algorithm with the broad-band photometry provides us with a more efficient approach for dealing with massive amounts of astrophysical data than do traditional color cuts and spectral energy distribution fits. | machine learning applied to star-galaxy-qso classification and stellar effective temperature regression |
we study the redshift evolution of the quasar (qso) uv luminosity function (lf) for 0.5 < z < 6.5, by collecting the most up to date observational data and, in particular, the recently discovered population of faint active galactic nuclei (agns). we fit the qso lf using either a double power-law function or a schechter function, finding that both forms provide good fits to the data. we derive empirical relations for the lf parameters as a function of redshift and, based on these results, predict the qso uv lf at z = 8. from the inferred lf evolution, we compute the redshift evolution of the qso/agn comoving ionizing emissivity and hydrogen photoionization rate. if faint agns are included, the contribution of qsos to reionization increases substantially. however, their level of contribution critically depends on the detailed shape of the qso lf, which can be constrained by efficient searches of high-z qsos. to this aim, we predict the expected (i) number of z > 6 qsos detectable by ongoing and future near-infrared surveys (as euclid and wide-field infrared survey telescope), and (ii) number counts for a single radio-recombination line observation with square kilometre array-mid (fov = 0.49 deg2) as a function of the hnα flux density, at 0 < z < 8. these surveys (even at z < 6) will be fundamental to better constrain the role of qsos as reionization sources. | quasar uv luminosity function evolution up to z = 8 |
we present the results of photometric and spectroscopic monitoring campaigns of the changing look agn ngc 3516 carried out in 2018 to 2020 covering the wavelength range from the x-ray to the optical. the facilities included the telescopes of the cmo sai msu, the 2.3-m wiro telescope, and the xrt and uvot of swift. we found that ngc 3516 brightened to a high state and could be classified as sy1.5 during the late spring of 2020. we have measured time delays in the responses of the balmer and he ii λ4686 lines to continuum variations. in the case of the best-characterized broad h β line, the delay to continuum variability is about 17 d in the blue wing and is clearly shorter, 9 d, in the red, which is suggestive of inflow. as the broad lines strengthened, the blue side came to dominate the balmer lines, resulting in very asymmetric profiles with blueshifted peaks during this high state. during the outburst the x-ray flux reached its maximum on 2020 april 1 and it was the highest value ever observed for ngc 3516 by the swift observatory. the x-ray hard photon index became softer, ~1.8 in the maximum on 2020 april 21 compared to the mean ~0.7 during earlier epochs before 2020. we have found that the uv and optical variations correlated well (with a small time delay of 1-2 d) with the x-ray until the beginning of 2020 april, but later, until the end of 2020 june, these variations were not correlated. we suggest that this fact may be a consequence of partial obscuration by compton-thick clouds crossing the line of sight. | multiwavelength monitoring and reverberation mapping of a changing look event in the seyfert galaxy ngc 3516 |
we present the results from the search for lyman alpha emitters (laes) in the proximity of 11 c iv absorption systems at z > 4.7 in the spectrum of the qso j1030+0524, using data from multi-unit spectroscopic explorer. we have found multiple lae candidates close to four c iv systems at $z_{{\rm{c {\small iv}}}}=4.94$ -5.74 with $\log _{10}(n_{{\rm{c {\small iv}}}}[$ cm-2]) > 13.5. at z = 5-6, c iv systems with w $_0({\rm{c {\small iv}}})\gt 0.2$ å seem more likely to have galaxies with ly α emission within ρ < 200 proper kpc (4/5 cases) than the c iv systems with w $_0({\rm{c {\small iv}}})\lt 0.2$ å (0/6 cases). the impact parameter of lae-c iv systems with equivalent widths w0(c iv) > 0.5 å is in the range $11\, \lesssim \, \rho \, \lesssim \, 200$ proper kpc (pkpc). furthermore, all candidates are in the luminosity range 0.18-1.15 l $^{\star }_{\rm{{ly\alpha}}}(z=5.7)$ , indicating that the environment of c iv systems within 200 pkpc is populated by the faint end of the ly α luminosity function. we report a 0.28 l $^{\star }_{\rm{{ly\alpha}}}$ galaxy at a separation of ρ = 11 pkpc from a strong c iv absorption ( $\log _{10}(n_{{\rm{c {\small iv}}}}[$ cm-2]) = 14.52) at $z_{{\rm{c {\small iv}}}}=5.72419$ . the prevalence of sub-l $^{\star }_{\rm{{ly\alpha}}}$ galaxies in the proximity of z > 4.9 c iv systems suggest that the absorbing material is rather young, likely ejected in the recent past of the identified galaxies. the connection between faint laes and high-ionization absorption systems reported in this work is potentially a consequence of the role of low-mass galaxies in the early evolution of the circum-galactic and intergalactic media. | faint laes near z > 4.7 c iv absorbers revealed by muse |
the bright emission from high-redshift quasars completely conceals their host galaxies in the rest-frame ultraviolet/optical, with detection of the hosts in these wavelengths eluding even the hubble space telescope (hst) using detailed point spread function (psf) modelling techniques. in this study, we produce mock images of a sample of z = 7 quasars extracted from the bluetides simulation, and apply markov chain monte carlo-based psf modelling to determine the detectability of their host galaxies with the james webb space telescope (jwst). while no statistically significant detections are made with hst, we predict that at the same wavelengths and exposure times jwst nircam imaging will detect $\sim 50{{\ \rm per\ cent}}$ of quasar host galaxies. we investigate various observational strategies, and find that nircam wide-band imaging in the long-wavelength filters results in the highest fraction of successful quasar host detections, detecting $\gtrsim 80{{\ \rm per\ cent}}$ of the hosts of bright quasars in exposure times of 5 ks. exposure times of ≳ 5 ks are required to detect the majority of host galaxies in the nircam wide-band filters, however, even 10 ks exposures with miri result in $\lesssim 30{{\ \rm per\ cent}}$ successful host detections. we find no significant trends between galaxy properties and their detectability. the psf modelling can accurately recover the host magnitudes, radii, and spatial distribution of the larger scale emission, when accounting for the central core being contaminated by residual quasar flux. care should be made when interpreting the host properties measured using psf modelling. | observing the host galaxies of high-redshift quasars with jwst: predictions from the bluetides simulation |
since its launch in 1999, the chandra x-ray observatory has discovered several dozen x-ray jets associated with powerful quasars. in many cases, the x-ray spectrum is hard and appears to come from a second spectral component. the most popular explanation for the kpc-scale x-ray emission in these cases has been inverse-compton (ic) scattering of cosmic microwave background (cmb) photons by relativistic electrons in the jet (the ic/cmb model). requiring the ic/cmb emission to reproduce the observed x-ray flux density inevitably predicts a high level of gamma-ray emission, which should be detectable with the fermi large area telescope (lat). in previous work, we found that gamma-ray upper limits from the large-scale jets of 3c 273 and pks 0637-752 violate the predictions of the ic/cmb model. here, we present fermi/lat flux density upper limits for the x-ray jets of four additional sources: pks 1136-135, pks 1229-021, pks 1354+195, and pks 2209+080. we show that these limits violate the ic/cmb predictions at a very high significance level. we also present new hubble space telescope observations of the quasar pks 2209+080 showing a newly detected optical jet, and atacama large millimeter/submillimeter array band 3 and 6 observations of all four sources, which provide key constraints on the spectral shape that enable us to rule out the ic/cmb model. | fermi non-detections of four x-ray jet sources and implications for the ic/cmb mechanism |
the bimodal absorption system imaging campaign (basic) aims to characterize the galaxy environments of a sample of 36 h i-selected partial lyman limit systems (pllss) and lyman limit systems (llss) in 23 qso fields at z ≲ 1. these pllss/llss provide a unique sample of absorbers with unbiased and well-constrained metallicities, allowing us to explore the origins of metal-rich and low-metallicity circumgalactic medium (cgm) at z < 1. here we present keck/kcwi and very large telescope/muse observations of 11 of these qso fields (19 pllss) that we combine with hubble space telescope/advanced camera for surveys imaging to identify and characterize the absorber-associated galaxies at 0.16 ≲ z ≲ 0.84. we find 23 unique absorber-associated galaxies, with an average of one associated galaxy per absorber. for seven absorbers, all with <10% solar metallicities, we find no associated galaxies with $\mathrm{log}{m}_{\star }\gtrsim 9.0$ within ρ/r vir and ∣δv∣/v esc ≤ 1.5 with respect to the absorber. we do not find any strong correlations between the metallicities or h i column densities of the gas and most of the galaxy properties, except for the stellar mass of the galaxies: the low-metallicity ([x/h] ≤ -1.4) systems have a probability of ${0.39}_{-0.15}^{+0.16}$ for having a host galaxy with $\mathrm{log}{m}_{\star }\geqslant 9.0$ within ρ/r vir ≤ 1.5, while the higher metallicity absorbers have a probability of ${0.78}_{-0.13}^{+0.10}$ . this implies metal-enriched pllss/llss at z < 1 are typically associated with the cgm of galaxies with $\mathrm{log}{m}_{\star }\gt 9.0$ , whereas low-metallicity pllss/llss are found in more diverse locations, with one population arising in the cgm of galaxies and another more broadly distributed in overdense regions of the universe. using absorbers not associated with galaxies, we estimate the unweighted geometric mean metallicity of the intergalactic medium to be [x/h] ≲ -2.1 at z < 1, which is lower than previously estimated. | the bimodal absorption system imaging campaign (basic). i. a dual population of low-metallicity absorbers at z < 1 |
quasars (qsos) hosting supermassive black holes are believed to reside in massive halos harboring galaxy overdensities. however, many observations revealed average or low galaxy densities around z ≳ 6 qsos. this could be partly because they measured galaxy densities in only tens of arcmin2 around qsos and might have overlooked potential larger-scale galaxy overdensities. some previous studies also observed only lyman break galaxies (lbgs; massive older galaxies) and missed low-mass young galaxies, like lyα emitters (laes), around qsos. here we present observations of lae and lbg candidates in ∼700 arcmin2 around a z = 6.61 luminous qso using the subaru telescope suprime-cam with narrowband/broadband. we compare their sky distributions, number densities, and angular correlation functions with those of laes/lbgs detected in the same manner and comparable data quality in our control blank field. in the qso field, laes and lbgs are clustering in 4-20 comoving mpc angular scales, but laes show mostly underdensity over the field while lbgs are forming 30 × 60 comoving mpc2 large-scale structure containing 3σ-7σ high-density clumps. the highest-density clump includes a bright (23.78 mag in the narrowband) extended (≳16 kpc) lyα blob candidate, indicative of a dense environment. the qso could be part of the structure but is not located exactly at any of the high-density peaks. near the qso, laes show underdensity while lbgs average to 4σ excess densities compared to the control field. if these environments reflect halo mass, the qso may not be in the most massive halo but still in a moderately massive one. based on data collected at subaru telescope, which is operated by the national astronomical observatory of japan. | large-scale environment of a z = 6.61 luminous quasar probed by lyα emitters and lyman break galaxies |
we present a method of selecting quasars up to redshift ≈6 with random forests, a supervised machine-learning method, applied to pan-starrs1 and wise data. we find that, thanks to the increasing set of known quasars, we can assemble a training set that enables supervised machine-learning algorithms to become a competitive alternative to other methods up to this redshift. we present a candidate set for the redshift range 4.8-6.3, which includes the region around z = 5.5 where selecting quasars is difficult due to their photometric similarity to red and brown dwarfs. we demonstrate that, under our survey restrictions, we can reach a high completeness (66% ± 7% below redshift 5.6/ ${83}_{-9}^{+6} \% $ above redshift 5.6) while maintaining a high selection efficiency (${78}_{-8}^{+10} \% $/ ${94}_{-8}^{+5} \% $). our selection efficiency is estimated via a novel method based on the different distributions of quasars and contaminants on the sky. the final catalog of 515 candidates includes 225 known quasars. we predict the candidate catalog to contain additional ${148}_{-33}^{+41}$ new quasars below redshift 5.6 and ${45}_{-8}^{+5}$ above, and we make the catalog publicly available. spectroscopic follow-up observations of 37 candidates led us to discover 20 new high redshift quasars (18 at 4.6 ≤ z ≤ 5.5, 2 z ~ 5.7). these observations are consistent with our predictions on efficiency. we argue that random forests can lead to higher completeness because our candidate set contains a number of objects that would be rejected by common color cuts, including one of the newly discovered redshift 5.7 quasars. | random forests as a viable method to select and discover high-redshift quasars |
small angle scattering by dust grains causes a significant contribution to the total interstellar extinction for any x-ray instrument with sub-arcminute resolution (chandra, swift, xmm-newton). however, the dust-scattering component is not included in the current absorption models: phabs, tbabs, and tbnew. we simulate a large number of chandra spectra to explore the bias in the spectral fit and nh measurements obtained without including extinction from dust scattering. we find that without incorporating dust scattering, the measured nh will be too large by a baseline level of 25 per cent. this effect is modulated by the imaging resolution of the telescope, because some amount of unresolved scattered light will be captured within the aperture used to extract point source information. in high-resolution spectroscopy, dust scattering significantly enhances the total extinction optical depth and the shape of the photoelectric absorption edges. we focus in particular on the fe-l edge at 0.7 kev, showing that the total extinction template fits well to the high-resolution spectrum of three x-ray binaries from the chandra archive: gx 9+9, xte j1817-330, and cyg x-1. in cases where dust is intrinsic to the source, a covering factor based on the angular extent of the dusty material must be applied to the extinction curve, regardless of angular imaging resolution. this approach will be particularly relevant for dust in quasar absorption line systems and might constrain clump sizes in active galactic nuclei. | the dust-scattering component of x-ray extinction: effects on continuum fitting and high-resolution absorption edge structure |
supernovae are considered as prime sources of dust in space. observations of local supernovae over the past couple of decades have detected the presence of dust in supernova ejecta. the reddening of the high redshift quasars also indicate the presence of large masses of dust in early galaxies. considering the top heavy imf in the early galaxies, supernovae are assumed to be the major contributor to these large amounts of dust. however, the composition and morphology of dust grains formed in a supernova ejecta is yet to be understood with clarity. moreover, the dust masses inferred from observations in mid-infrared and submillimeter wavelength regimes differ by two orders of magnitude or more. therefore, the mechanism responsible for the synthesis of molecules and dust in such environments plays a crucial role in studying the evolution of cosmic dust in galaxies. this review summarises our current knowledge of dust formation in supernova ejecta and tries to quantify the role of supernovae as dust producers in a galaxy. | dust in supernovae and supernova remnants i: formation scenarios |
the european space agency is studying two large-class missions bound to operate in the decade of the 30s, and aiming at investigating the most energetic and violent phenomena in the universe. athena is poised to study the physical conditions of baryons locked in large-scale structures from the epoch of their formation, as well as to yield an accurate census of accreting supermassive black holes down to the epoch of reionization; lisa will extend the hunt for gravitational wave (gw) events to the hitherto unexplored mhz regime. we discuss in this paper the science that their concurrent operation could yield, and present possible athena observational strategies. we focus on supermassive (m$\lesssim 10^7\, \rm {m_\odot }$) black hole mergers (smbhms), potentially accessible to athena up to z ~ 2. the simultaneous measurement of their electromagnetic (em) and gw signals may enable unique experiments in the domains of astrophysics, fundamental physics, and cosmography, such as the magnetohydrodynamics of fluid flows in a rapidly variable space-time, the formation of coronae and jets in active galactic nuclei, and the measurement of the speed of gw, among others. key to achieve these breakthrough results will be the lisa capability of locating a smbhm event with an error box comparable to, or better than the field-of-view of the athena wide field imager ($\simeq 0.4\,$ deg2) and athena capability to slew fast to detect the source during the inspiral phase and the post-merger phase. together, the two observatories will open in principle the exciting possibility of truly concurrent em and gw studies of the smbhms | chasing supermassive black hole merging events with athena and lisa |
we present luminosity functions derived from a spectroscopic survey of active galactic nuclei (agns) selected from spitzer space telescope imaging surveys. selection in the mid-infrared is significantly less affected by dust obscuration. we can thus compare the luminosity functions of obscured and unobscured agns in a more reliable fashion than by using optical or x-ray data alone. we find that the agn luminosity function can be well described by a broken power-law model in which the break luminosity decreases with redshift. at high redshifts (z\gt 1.6), we find significantly more agns at a given bolometric luminosity than found by either optical quasar surveys or hard x-ray surveys. the fraction of obscured agns decreases rapidly with increasing agn luminosity, but, at least at high redshifts, appears to remain at ≈ 50% even at bolometric luminosities ∼ {{10}14} {{l}⊙ }. the data support a picture in which the obscured and unobscured populations evolve differently, with some evidence that high luminosity obscured quasars peak in space density at a higher redshift than their unobscured counterparts. the amount of accretion energy in the universe estimated from this work suggests that agns contribute about 12% to the total radiation intensity of the universe, and a high radiative accretion efficiency ≈ 0.18-0.07+0.12 is required to match current estimates of the local mass density in black holes. | the spitzer mid-infrared agn survey. ii. the demographics and cosmic evolution of the agn population |
rapid gamma-ray flares pose an astrophysical puzzle, requiring mechanisms both to accelerate energetic particles and to produce fast observed variability. these dual requirements may be satisfied by collisionless relativistic magnetic reconnection. on the one hand, relativistic reconnection can energize gamma-ray emitting electrons. on the other hand, as previous kinetic simulations have shown, the reconnection acceleration mechanism preferentially focuses high energy particles - and their emitted photons - into beams, which may create rapid blips in flux as they cross a telescope's line of sight. using a series of 2d pair-plasma particle-in-cell simulations, we explicitly demonstrate the critical role played by radiative (specifically inverse compton) cooling in mediating the observable signatures of this 'kinetic beaming' effect. only in our efficiently cooled simulations do we measure kinetic beaming beyond one light crossing time of the reconnection layer. we find a correlation between the cooling strength and the photon energy range across which persistent kinetic beaming occurs: stronger cooling coincides with a wider range of beamed photon energies. we also apply our results to rapid gamma-ray flares in flat-spectrum radio quasars, suggesting that a paradigm of radiatively efficient kinetic beaming constrains relevant emission models. in particular, beaming-produced variability may be more easily realized in two-zone (e.g. spine-sheath) set-ups, with compton seed photons originating in the jet itself, rather than in one-zone external compton scenarios. | kinetic beaming in radiative relativistic magnetic reconnection: a mechanism for rapid gamma-ray flares in jets |
the tidal disruption of a star by a supermassive black hole can result in transient radio emission. the electrons producing these synchrotron radio flares could either be accelerated inside a relativistic jet or externally by shocks resulting from an outflow interacting with the circumnuclear medium. until now, evidence for the internal emission mechanism has been lacking; nearly all tidal disruption flare studies have adopted the external shock model to explain the observed properties of radio flares. here we report a result that presents a challenge to external emission models: we discovered a cross-correlation between the soft x-ray (0.3-1 kev) and 16 ghz radio flux of the tidal disruption flare asassn-14li. variability features in the x-ray light curve appear again in the radio light curve, but after a time lag of {12}-5+6 days. this demonstrates that the soft x-ray-emitting accretion disk regulates the radio emission. this coupling appears to be inconsistent with all previous external emission models for this source but is naturally explained if the radio emission originates from a freely expanding jet. we show that emission internal to an adiabatically expanding jet can also reproduce the observed evolution of the radio spectral energy distribution. furthermore, both the correlation between x-ray and radio luminosity as well as our radio spectral modeling imply an approximately linear coupling between the accretion rate and jet power. | discovery of a time lag between the soft x-ray and radio emission of the tidal disruption flare asassn-14li: evidence for linear disk-jet coupling |
we report an identification of sdss j141324+530527.0 (sbs 1411+533) at z = 0.456344 as a new “changing-look” quasar with a “turn-on” spectral type transition from type-1.9/2 to type-1 within a rest-frame timescale of 1-10 yr by a comparison of our new spectroscopic observation and the sloan digital sky survey (sdss) archive database. the sdss dr7 spectrum taken in 2003 is dominated by a starlight emission from host galaxy redward of the balmer limit, and has a non-detectable broad hβ line. the new spectrum taken by us on 2017 june 1 and the sdss dr14 spectrum taken on 2017 may 29 indicate that the object has a typical quasar spectrum with a blue continuum and strong balmer broad emission lines. in addition, an intermediate spectral type can be identified in the sdss dr13 spectrum taken in 2015. the invariability of the line wing of mg ii λ2800 emission and timescale argument (the invariability of [o iii]λ5007 line blue asymmetry) suggests that a variation of obscuration (an accelerating outflow) is not a favorable scenario. the timescale argument allows us to believe the type transition is possibly caused by either a viscous radial inflow or a disk instability around a ∼ (5{--}9)× {10}7 {m}⊙black hole. | identification of sdss j141324.27+530527.0 as a new “changing-look” quasar with a “turn-on” transition |
observing the light emitted by the first accreting black holes (bhs) would dramatically improve our understanding of the formation of quasars at z > 6, possibly unveiling the nature of their supermassive black hole (smbh) seeds. in previous works, we explored the relative role of the two main competing bh seed formation channels, population iii remnants (low-mass seeds) and direct collapse bhs (high-mass seeds), investigating the properties of their host galaxies in a cosmological context. building on this analysis, we predict here the spectral energy distribution and observational features of low- and high-mass bh seeds selected among the progenitors of a z ∼ 6 smbh. we derive the processed emission from both accreting bhs and stars by using the photoionization code cloudy, accounting for the evolution of metallicity and dust-to-gas mass ratio in the interstellar medium of the host galaxies, as predicted by the cosmological data-constrained model gamete/qsodust. we show how future missions like james webb space telescope (jwst) and advanced telescope for high energy astrophysics (athena) will be able to detect the light coming from smbh progenitors already at z ∼ 16. we build upon previous complementary studies and propose a method based on the combined analysis of near-infrared colours, ir excess (irx), and uv continuum slopes (i.e. colour-colour and irx-β diagrams) to distinguish growing seed bh host galaxies from starburst-dominated systems in jwst surveys. sources selected through this criterion would be the best target for follow-up x-ray observations. | chasing the observational signatures of seed black holes at z > 7: candidate observability |
the {m}\bullet {--}σ relation establishes a connection between central black holes (bhs) and their host spheroids. supported by observations at {m}\bullet ≳ {10}5 {m}⊙ , there is limited data on its validity at lower masses. employing a semi-analytical model to simulate the combined evolution of bhs and their host galaxies, we predict the observational consequences of assuming a bimodality in the accretion efficiency of bhs, with low-mass bhs ({m}\bullet ≲ {10}5 {m}⊙ ) accreting inefficiently. we predict a departure from the {m}\bullet {--}σ relation at a transitional bh mass ∼ {10}5 {m}⊙ , with lower-mass bhs unable to reach the mass dictated by the relation and becoming disconnected from the evolution of the host galaxy. this prediction is an alternative to previous works suggesting a flattening of the relation at ∼ {10}5{--}{10}6 {m}⊙ . furthermore, we predict a deficit of bhs shining at bolometric luminosities ∼ {10}42 {erg} {{{s}}}-1. joined with a detection bias, this could partly explain the scarce number of intermediate-mass bhs detected. conversely, we predict an increase in source density at lower bolometric luminosities, < {10}42 {erg} {{{s}}}-1. because our predictions assume a bimodal population of high-redshift bh seeds, future observations of fainter bhs will be fundamental for constraining the nature of these seeds. | glimmering in the dark: modeling the low-mass end of the m •-σ relation and of the quasar luminosity function |
we present the detection of the average h2 absorption signal in the overall population of neutral gas absorption systems at z∼ 3 using composite absorption spectra built from the sloan digital sky survey-iii damped lyman α catalogue. we present a new technique to directly measure the h2 column density distribution function f_h_2(n) from the average h2 absorption signal. assuming a power-law column density distribution, we obtain a slope β = -1.29 ± 0.06(stat) ± 0.10 (sys) and an incidence rate of strong h2 absorptions [with n(h2) ≳ 1018 cm-2] to be 4.0 ± 0.5(stat) ± 1.0 (sys) per cent in h i absorption systems with n(h i) ≥1020 cm-2. assuming the same inflexion point where f_h_2(n) steepens as at z = 0, we estimate that the cosmological density of h2 in the column density range log n(h_2) (cm^{-2})= 18{-}22 is {∼ } 15 per cent of the total. we find one order of magnitude higher h2 incident rate in a sub-sample of extremely strong damped lyman α absorption systems (dlas) [log n(h i) (cm^{-2}) ≥ 21.7], which, together with the derived shape of f_h_2(n), suggests that the typical h i-h2 transition column density in dlas is log n(h)(cm-2) ≳ 22.3 in agreement with theoretical expectations for the average (low) metallicity of dlas at high-z. | constraining the h2 column density distribution at z ∼ 3 from composite dla spectra |
we report on a hubble space telescope search for rest-frame ultraviolet emission from the host galaxies of five far-infrared-luminous z ≃ 6 quasars and the z = 5.85 hot-dust-free quasar sdss j0005-0006. we perform 2d surface brightness modeling for each quasar using a markov chain monte carlo estimator, to simultaneously fit and subtract the quasar point source in order to constrain the underlying host galaxy emission. we measure upper limits for the quasar host galaxies of mj > 22.7 mag and mh > 22.4 mag, corresponding to stellar masses of m* < 2 × 1011m⊙. these stellar mass limits are consistent with the local mbh - m* relation. our flux limits are consistent with those predicted for the uv stellar populations of z ≃ 6 host galaxies, but likely in the presence of significant dust ($\langle {a}_{\mathrm{uv}}\rangle \simeq 2.6$ mag). we also detect a total of up to nine potential z ≃ 6 quasar companion galaxies surrounding five of the six quasars, separated from the quasars by 1"4-3"2, or 8.4-19.4 kpc, which may be interacting with the quasar hosts. these nearby companion galaxies have uv absolute magnitudes of -22.1 to -19.9 mag and uv spectral slopes β of -2.0 to -0.2, consistent with luminous star-forming galaxies at z ≃ 6. these results suggest that the quasars are in dense environments typical of luminous z ≃ 6 galaxies. however, we cannot rule out the possibility that some of these companions are foreground interlopers. infrared observations with the james webb space telescope will be needed to detect the z ≃ 6 quasar host galaxies and better constrain their stellar mass and dust content. | limits to rest-frame ultraviolet emission from far-infrared-luminous z ≃ 6 quasar hosts |
the imaging channel on the mid-infrared instrument (miri) is equipped with four coronagraphs that provide high contrast imaging capabilities for studying faint point sources and extended emission that would otherwise be overwhelmed by a bright point-source in its vicinity. such bright sources might include stars that are orbited by exoplanets and circumstellar material, mass-loss envelopes around post-main-sequence stars, the near-nuclear environments in active galaxies, and the host galaxies of distant quasars. this paper describes the coronagraphic observing modes of miri, as well as performance estimates based on measurements of the miri flight model during cryo-vacuum testing. a brief outline of coronagraphic operations is also provided. finally, simulated miri coronagraphic observations of a few astronomical targets are presented for illustration. | the mid-infrared instrument for the james webb space telescope, v: predicted performance of the miri coronagraphs |
substantial evidence points to dusty, geometrically thick tori obscuring the central engines of active galactic nuclei (agns), but so far no mechanism satisfactorily explains why cool dust in the torus remains in a puffy geometry. near-eddington infrared (ir) and ultraviolet (uv) luminosities coupled with high dust opacities at these frequencies suggest that radiation pressure on dust can play a significant role in shaping the torus. to explore the possible effects of radiation pressure, we perform three-dimensional radiative hydrodynamics simulations of an initially smooth torus. our code solves the hydrodynamics equations, the time-dependent multi-angle group ir radiative transfer (rt) equation, and the time-independent uv rt equation. we find a highly dynamic situation. ir radiation is anisotropic, leaving primarily through the central hole. the torus inner surface exhibits a break in axisymmetry under the influence of radiation and differential rotation; clumping follows. in addition, uv radiation pressure on dust launches a strong wind along the inner surface; when scaled to realistic agn parameters, this outflow travels at ∼ 5000 {(m/{10}7{m}⊙ )}1/4 {[{l}{uv}/(0.1{l}{{e}})]}1/4 {km} {{{s}}}-1 and carries ∼ 0.1 {(m/{10}7{m}⊙ )}3/4 {[{l}{uv}/(0.1{l}{{e}})]}3/4 m ⊙ yr-1, where m, {l}{uv}, and {l}{{e}} are the mass, uv luminosity, and eddington luminosity of the central object respectively. | radiation-driven outflows from and radiative support in dusty tori of active galactic nuclei |
we present a search for h i in the circumgalactic medium (cgm) of 21 massive (< {log}{m}\star > ∼ 11.4), luminous red galaxies (lrgs) at z ∼ 0.5. using uv spectroscopy of qso sightlines projected within 500 kpc (∼{r}vir}) of these galaxies, we detect h i absorption in 11/21 sightlines, including two partial lyman limit systems and two lyman limit systems. the covering factor of {log}n({{h}} {{i}})≥slant 16.0 gas within the virial radius of these lrgs is {f}c(ρ ≤slant {r}vir})={0.27}-0.10+0.11, while for optically thick gas ({log}n({{h}} {{i}})≥slant 17.2) it is {f}c(ρ ≤slant {r}vir})={0.15}-0.07+0.10. combining this sample of massive galaxies with previous galaxy-selected cgm studies, we find no strong dependence of the h i covering factor on galaxy mass, although star-forming galaxies show marginally higher covering factors. there is no evidence for a critical mass above which dense, cold (t ∼ 104 k) gas is suppressed in the cgm of galaxies (spanning stellar masses 9.5≲ {log}{m}\star ≲ 11.8). the metallicity distribution in lrgs is indistinguishable from those found about lower-mass star-forming galaxies, and we find low-metallicity gas with [{{x}}/{{h}}]≈ -1.8 (1.5% solar) and below about massive galaxies. about half the cases show supersolar [fe ii/{mg} {{ii}}] abundances as seen previously in cool gas near massive galaxies. while the high-metallicity cold gas seen in lrgs could plausibly result from condensation from a corona, the low-metallicity gas is inconsistent with this interpretation. | the red dead redemption survey of circumgalactic gas about massive galaxies. i. mass and metallicity of the cool phase |
context. most investigations of the x-ray variability of active galactic nuclei (agn) have been concentrated on the detailed analyses of individual, nearby sources. a relatively small number of studies have treated the ensemble behaviour of the more general agn population in wider regions of the luminosity-redshift plane.aims: we want to determine the ensemble variability properties of a rich agn sample, called multi-epoch xmm serendipitous agn sample (mexsas), extracted from the fifth release of the xmm-newton serendipitous source catalogue (xmmssc-dr5), with redshift between ~0.1 and ~5, and x-ray luminosities in the 0.5-4.5 kev band between ~1042 erg/s and ~1047 erg/s.methods: we urge caution on the use of the normalised excess variance (nxs), noting that it may lead to underestimate variability if used improperly. we use the structure function (sf), updating our previous analysis for a smaller sample. we propose a correction to the nxs variability estimator, taking account of the light curve duration in the rest frame on the basis of the knowledge of the variability behaviour gained by sf studies.results: we find an ensemble increase of the x-ray variability with the rest-frame time lag τ, given by sf ∝ τ0.12. we confirm an inverse dependence on the x-ray luminosity, approximately as sf ∝ lx-0.19. we analyse the sf in different x-ray bands, finding a dependence of the variability on the frequency as sf ∝ ν-0.15, corresponding to a so-called softer when brighter trend. in turn, this dependence allows us to parametrically correct the variability estimated in observer-frame bands to that in the rest frame, resulting in a moderate (≲15%) shift upwards (v-correction).conclusions: ensemble x-ray variability of agns is best described by the structure function. an improper use of the normalised excess variance may lead to an underestimate of the intrinsic variability, so that appropriate corrections to the data or the models must be applied to prevent these effects. full table 1 is 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/593/a55 | ensemble x-ray variability of active galactic nuclei. ii. excess variance and updated structure function |
the boss quasar sample is used to study cosmic homogeneity with a 3d survey in the redshift range 2.2 < z < 2.8. we measure the count-in-sphere, n(< r), i.e. the average number of objects around a given object, and its logarithmic derivative, the fractal correlation dimension, d2(r). for a homogeneous distribution n(< r) propto r3 and d2(r) = 3. due to the uncertainty on tracer density evolution, 3d surveys can only probe homogeneity up to a redshift dependence, i.e. they probe so-called ``spatial isotropy". our data demonstrate spatial isotropy of the quasar distribution in the redshift range 2.2 < z < 2.8 in a model-independent way, independent of any flrw fiducial cosmology, resulting in 3 - langled2rangle < 1.7 × 10-3 (2 σ) over the range 250 < r < 1200 h-1 mpc for the quasar distribution. if we assume that quasars do not have a bias much less than unity, this implies spatial isotropy of the matter distribution on large scales. then, combining with the copernican principle, we finally get homogeneity of the matter distribution on large scales. alternatively, using a flat λcdm fiducial cosmology with cmb-derived parameters, and measuring the quasar bias relative to this λcdm model, our data provide a consistency check of the model, in terms of how homogeneous the universe is on different scales. d2(r) is found to be compatible with our λcdm model on the whole 10 < r < 1200 h-1 mpc range. for the matter distribution we obtain 3 - langled2rangle < 5 × 10-5 (2 σ) over the range 250 < r < 1200 h-1 mpc, consistent with homogeneity on large scales. | a 14 h-3 gpc3 study of cosmic homogeneity using boss dr12 quasar sample |
we report on the identification of a new γ-ray-emitting narrow-line seyfert 1 (nls1) galaxy, sdss j122222.55+041315.7, which increases the number of known objects of this remarkable but rare type of active galactic nuclei to seven. its optical spectrum, obtained in the sloan digital sky survey-baryon oscillation spectroscopic survey, reveals a broad h β emission line with a width (fwhm) of 1734 ± 104 km s-1. this, along with strong optical fe ii multiplets [r4570 = 0.9] and a weak [o iii] λ5007 emission line, makes the object a typical nls1. on the other hand, the source exhibits a high radio brightness temperature, rapid infrared variability, and a flat x-ray spectrum extending up to ∼200 kev. it is associated with a luminous γ-ray source detected significantly with fermi/lat. correlated variability with other wavebands has not yet been tested. the spectral energy distribution can be well modelled by a one-zone leptonic jet model. this new member is by far the most distant γ-ray-emitting nls1, at a redshift of z = 0.966. | identification of a new γ-ray-emitting narrow-line seyfert 1 galaxy, at redshift ∼1 |
since the beginning of the new millennium, more than 100 z 6 quasars have been discovered through several surveys and followed-up with multi-wavelength observations. these data provided a large amounts of information on the growth of supermassive black holes at the early epochs, the properties of quasar host galaxies and the joint formation and evolution of these massive systems. we review the properties of the highest z quasars known so far, especially focussing on some of the most recent results obtained in (sub-)millimetre bands. we discuss key observational challenges and open issues in theoretical models and highlight possible new strategies to improve our understanding of the galaxy black hole formation and evolution in the early universe. | physical properties of the first quasars |
as setti and woltjer noted back in 1973, one can use quasars to construct the hubble diagram; however, the actual application of the idea was not that straightforward. it took years to implement the proposition successfully. most ways to employ quasars for cosmology now require an advanced understanding of their structure, step by step. we briefly review this progress, with unavoidable personal biases, and concentrate on bright unobscured sources. we will mention the problem of the gas flow character close to the innermost stable circular orbit near the black hole, as discussed five decades ago. this problem later led to the development of the slim disk scenario and is recently revived in the context of magnetically arrested disks (mad) and standard and normal evolution (sane) models. we also discuss the hot or warm corona issue, which is still under debate and complicates the analysis of x-ray reflection. we present the scenario of the formation of the low ionization part of the broad line region as a failed wind powered by radiation pressure acting on dust (failed radiatively driven dusty outflow - frado). next, we examine the cosmological constraints currently achievable with quasars, primarily concentrating on light echo methods (continuum time delays and spectral-line time delays to the continuum) that are (or should be) incorporating the progress mentioned above. finally, we briefly discuss prospects in this lively subject area. | accretion disks, quasars and cosmology: meandering towards understanding |
using new ultraviolet (uv) spectra of five background quasars from the cosmic origins spectrograph on the hubble space telescope, we analyze the low-latitude ( $| b| =20^\circ \mbox{--}30^\circ $ ) regions of the fermi bubbles, the giant gamma-ray-emitting lobes at the galactic center. we combine these data with previous uv and atomic hydrogen (h i) data sets to build a comprehensive picture of the kinematics and metal column densities of the cool outflowing clouds entrained in the fermi bubbles. we find that the number of uv absorption components per sight line decreases as a function of increasing latitude, suggesting that the outflowing clouds become less common with increasing latitude. the fermi bubble h i clouds are accelerated up to b ∼ 7°, whereas when we model the uv fermi bubbles clouds' deprojected flow velocities, we find that they are flat or even accelerating with distance from the galactic center. this trend, which holds in both the northern and southern hemispheres, indicates that the nuclear outflow accelerates clouds throughout the fermi bubbles or has an acceleration phase followed by a coasting phase. finally, we note the existence of several blueshifted high-velocity clouds at latitudes exceeding ∼30°, whose velocities cannot be explained by gas clouds confined to the inside of the gamma-ray-defined fermi bubbles. these anomalous-velocity clouds are likely in front of the fermi bubbles and could be remnants from past nuclear outflows. overall, these observations form a valuable set of empirical data on the properties of cool gas in nuclear winds from star-forming galaxies. * based on observations made with the nasa/esa hubble space telescope, obtained at the space telescope science institute, which is operated by the association of universities for research in astronomy, inc., under nasa contract nas5-26555. these observations are associated with program 15339. | mapping outflowing gas in the fermi bubbles: a uv absorption survey of the galactic nuclear wind |
we report on three redshift z > 2 quasars with dramatic changes in their c iv emission lines, the first sample of changing-look quasars (clqs) at high redshift. this is also the first time the changing-look behaviour has been seen in a high-ionization emission line. sdss j1205+3422, j1638+2827, and j2228 + 2201 show interesting behaviour in their observed optical light curves, and subsequent spectroscopy shows significant changes in the c iv broad emission line, with both line collapse and emergence being displayed on rest-frame time-scales of ~240-1640 d. these are rapid changes, especially when considering virial black hole mass estimates of mbh > 109m⊙ for all three quasars. continuum and emission line measurements from the three quasars show changes in the continuum-equivalent width plane with the clqs seen to be on the edge of the full population distribution, and showing indications of an intrinsic baldwin effect. we put these observations in context with recent state-change models, and note that even in their observed low-state, the c iv clqs are generally above ~5 per cent in eddington luminosity. | the first high-redshift changing-look quasars |
context. time-delay lensing is a powerful tool for measuring the hubble constant h0. however, in order to obtain an accurate estimate of h0 from a sample of time-delay lenses, very good knowledge of the mass structure of the lens galaxies is needed. strong lensing data on their own are not sufficient to break the degeneracy between h0 and the lens model parameters on a single object basis.aims: the goal of this study is to determine whether it is possible to break the h0-lens structure degeneracy with the statistical combination of a large sample of time-delay lenses, relying purely on strong lensing data with no stellar kinematics information.methods: i simulated a set of 100 lenses with doubly imaged quasars and related time-delay measurements. i fitted these data with a bayesian hierarchical method and a flexible model for the lens population, emulating the lens modelling step.results: the sample of 100 lenses on its own provides a measurement of h0 with 3% precision, but with a −4% bias. however, the addition of prior information on the lens structural parameters from a large sample of lenses with no time delays, such as that considered in paper i, allows for a 1% level inference. moreover, the 100 lenses allow for a 0.03 dex calibration of galaxy stellar masses, regardless of the level of prior knowledge of the hubble constant.conclusions: breaking the h0-lens model degeneracy with lensing data alone is possible, but 1% measurements of h0 require either many more than 100 time-delay lenses or knowledge of the structural parameter distribution of the lens population from a separate sample of lenses. | statistical strong lensing. ii. cosmology and galaxy structure with time-delay lenses |
we present atacama large millimeter/submillimeter array (alma) observations of six radio-loud quasar host galaxies at z = 1.4-2.3. we combine the kiloparsec-scale resolution alma observations with high spatial resolution adaptive optics integral field spectrograph data of the ionized gas. we detect molecular gas emission in five quasar host galaxies and resolve the molecular interstellar medium using the co (3-2) or co (4-3) rotational transitions. clumpy molecular outflows are detected in four quasar host galaxies and a merger system 21 kpc away from one quasar. between the ionized and cold molecular gas phases, the majority of the outflowing mass is in a molecular phase, while for three out of four detected multiphase gas outflows, the majority of the kinetic luminosity and momentum flux is in the ionized phase. combining the energetics of the multiphase outflows, we find that their driving mechanism is consistent with energy-conserving shocks produced by the impact of the quasar jets with the gas in the galaxy. by assessing the molecular gas mass to the dynamics of the outflows, we estimate a molecular gas depletion timescale of a few megayears. the gas outflow rates exceed the star formation rates, suggesting that quasar feedback is a major mechanism of gas depletion at the present time. the coupling efficiency between the kinetic luminosity of the outflows and the bolometric luminosity of the quasar of 0.1%-1% is consistent with theoretical predictions. studying multiphase gas outflows at high redshift is important for quantifying the impact of negative feedback in shaping the evolution of massive galaxies. | multiphase outflows in high-redshift quasar host galaxies |
measuring the density of the intergalactic medium using quasar sight lines in the epoch of reionization is challenging due to the saturation of lyα absorption. near a luminous quasar, however, the enhanced radiation creates a proximity zone observable in the quasar spectra where the lyα absorption is not saturated. in this study, we use 10 high-resolution (r ≳ 10,000) z ~ 6 quasar spectra from the extended xqr-30 sample to measure the density field in the quasar proximity zones. we find a variety of environments within 3 pmpc distance from the quasars. we compare the observed density cumulative distribution function (cdf) with models from the cosmic reionization on computers simulation and find a good agreement between 1.5 and 3 pmpc from the quasar. this region is far away from the quasar hosts and hence approaching the mean density of the universe, which allows us to use the cdf to set constraints on the cosmological parameter σ 8 = 0.6 ± 0.3. the uncertainty is mainly due to the limited number of high-quality quasar sight lines currently available. utilizing the more than 200 known quasars at z ≳ 6, this method will allow us to tighten the constraint on σ 8 to the percent level in the future. in the region closer to the quasar within 1.5 pmpc, we find that the density is higher than predicted in the simulation by 1.23 ± 0.17, suggesting that the typical host dark matter halo mass of a bright quasar (m 1450 < -26.5) at z ~ 6 is ${\mathrm{log}}_{10}({m}_{h}/{m}_{\odot })={12.5}_{-0.7}^{+0.4}$ . | measuring the density fields around bright quasars at z 6 with xqr-30 spectra |
the discovery of changing-look active galactic nuclei (clagns) with a significant change in optical broad emission lines (optical clagns) and/or strong variation of line-of-sight column densities (x-ray clagns) challenges the orientation-based agn unification model. we explore mid-infrared (mid-ir) properties for a sample of 57 optical clagns and 11 x-ray clagns based on the wide-field infrared survey explorer archive data. we find that eddington-scaled mid-ir luminosities of both optical and x-ray clagns stay just between those of low-luminosity agns and luminous qsos. the average eddington-scaled mid-ir luminosities for optical and x-ray clagns are ~0.4% and ~0.5%, respectively, which roughly correspond to the bolometric luminosity of transition between a radiatively inefficient accretion flow and a shakura-sunyaev disk. we estimate the time lags of the variation in the mid-ir behind that in the optical band for 13 clagns with strong mid-ir variability, where the tight correlation between the time lag and the bolometric luminosity (τ-l) for clagns roughly follows that found in the luminous qsos. | wise view of changing-look active galactic nuclei: evidence for a transitional stage of agns |
aims: in this work we present a new catalogue of cosmic filaments obtained from the latest sloan digital sky survey (sdss) public data.methods: in order to detect filaments, we implement a version of the subspace-constrained mean-shift algorithm that is boosted by machine learning techniques. this allows us to detect cosmic filaments as one-dimensional maxima in the galaxy density distribution. our filament catalogue uses the cosmological sample of sdss, including data release 16, and therefore inherits its sky footprint (aside from small border effects) and redshift coverage. in particular, this means that, taking advantage of the quasar sample, our filament reconstruction covers redshifts up to z = 2.2, making it one of the deepest filament reconstructions to our knowledge. we follow a tomographic approach and slice the galaxy data in 269 shells at different redshift. the reconstruction algorithm is applied to 2d spherical maps.results: the catalogue provides the position and uncertainty of each detection for each redshift slice. the quality of our detections, which we assess with several metrics, show improvement with respect to previous public catalogues obtained with similar methods. we also detect a highly significant correlation between our filament catalogue and galaxy cluster catalogues built from microwave observations of the planck satellite and the atacama cosmology telescope. a copy of the catalogue is 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/659/a166 | a novel cosmic filament catalogue from sdss data |
we report the discovery of giant (50-100 kpc) [o ii] emitting nebulae with muse in the field of txs 0206-048, a luminous quasar at z = 1.13. "down-the-barrel" uv spectra of the quasar show absorption at velocities coincident with those of the extended nebulae, enabling new insights into inflows and outflows around the quasar host. one nebula exhibits a filamentary morphology extending over 120 kpc from the halo toward the quasar and intersecting with another nebula surrounding the quasar host with a radius of 50 kpc. this is the longest cool filament observed to date and arises at higher redshift and in a less massive system than those in cool-core clusters. the filamentary nebula has line-of-sight velocities >300 km s-1 from nearby galaxies but matches that of the nebula surrounding the quasar host where they intersect, consistent with accretion of cool intergalactic or circumgalactic medium or cooling hot halo gas. the kinematics of the nebulae surrounding the quasar host are unusual and complex, with redshifted and blueshifted spiral-like structures. the emission velocities at 5-10 kpc from the quasar match those of inflowing absorbing gas observed in uv spectra of the quasar. together, the extended nebulae and associated redshifted absorption represent a compelling case of cool, filamentary gas accretion from halo scales into the extended interstellar medium and toward the nucleus of a massive quasar host. the inflow rate implied by the combined emission and absorption constraints is well below levels required to sustain the quasar's radiative luminosity, suggesting anisotropic or variable accretion. | directly tracing cool filamentary accretion over >100 kpc into the interstellar medium of a quasar host at z = 1 |
we analyze a sample of 25 [ne v] (λ3426) emission-line galaxies at 1.4 < z < 2.3 using hubble space telescope/wide field camera 3 g102 and g141 grism observations from the candels lyα emission at reionization (clear) survey. [ne v] emission probes extremely energetic photoionization (creation potential of 97.11 ev) and is often attributed to energetic radiation from active galactic nuclei (agns), shocks from supernovae, or an otherwise very hard ionizing spectrum from the stellar continuum. in this work, we use [ne v] in conjunction with other rest-frame uv/optical emission lines ([o ii] λ λ3726, 3729, [ne iii] λ3869, hβ, [o iii] λ λ4959, 5007, hα+[n ii] λ λ6548, 6583, [s ii] λ λ6716, 6731), deep (2-7 ms) x-ray observations (from chandra), and mid-infrared imaging (from spitzer) to study the origin of this emission and to place constraints on the nature of the ionizing engine. the majority of the [ne v]-detected galaxies have properties consistent with ionization from agns. however, for our [ne v]-selected sample, the x-ray luminosities are consistent with local (z ≲ 0.1) x-ray-selected seyferts, but the [ne v] luminosities are more consistent with those from z ~ 1 x-ray-selected qsos. the excess [ne v] emission requires either reduced hard x-rays or a ~0.1 kev excess. we discuss possible origins of the apparent [ne v] excess, which could be related to the "soft (x-ray) excess" observed in some qsos and seyferts and/or be a consequence of a complex/anisotropic geometry for the narrow-line region, combined with absorption from a warm, relativistic wind ejected from the accretion disk. we also consider implications for future studies of extreme high-ionization systems in the epoch of reionization (z ≳ 6) with the james webb space telescope. | clear: high-ionization [ne v] λ3426 emission-line galaxies at 1.4 < z < 2.3 |
we develop a thermodynamical model of fermionic dark matter halos at finite temperature. statistical equilibrium states may be justified by a process of violent collisionless relaxation in the sense of lynden-bell or from a collisional relaxation of nongravitational origin if the fermions are self-interacting. the most probable state (maximum entropy state) generically has a "core-halo" structure with a quantum core (fermion ball) surrounded by an isothermal atmosphere. the quantum core is equivalent to a polytrope of index n =3 /2 . the pauli exclusion principle creates a quantum pressure that prevents gravitational collapse and solves the core-cusp problem of the cold dark matter model. the isothermal atmosphere (which is similar to the navarro-frenk-white profile of cold dark matter) accounts for the flat rotation curves of the galaxies at large distances. we numerically solve the equation of hydrostatic equilibrium with the fermi-dirac equation of state and determine the density profiles and rotation curves of fermionic dark matter halos. we impose that the surface density of the dark matter halos has the universal value σ0=ρ0rh=141 m⊙/pc2 obtained from the observations. for a fermion mass m =165 ev /c2, the "minimum halo" has a mass (mh)min=108 m⊙ and a radius (rh)min=597 pc similar to dwarf spheroidals like fornax. this ultracompact halo corresponds to a completely degenerate fermion ball at t =0 . this is the ground state of the self-gravitating fermi gas. for ultracompact dark matter halos with a mass (mh)min<mh<(mh)ccp=6.73 ×108 m⊙ (canonical critical point), the quantum core is surrounded by a tenuous classical isothermal atmosphere. dark matter halos with a mass mh>(mh)ccp are dominated by the classical isothermal atmosphere. they may be purely gaseous (similar to the burkert profile) or harbor a fermion ball. the gaseous solution is stable in all statistical ensembles. the core-halo solution is canonically unstable (having a negative specific heat) but, for small dark matter halos with a mass (mh)ccp<mh<(mh)mcp=1.08 ×1010 m⊙ (microcanonical critical point), it is microcanonically stable. by maximizing the entropy at fixed mass and energy we find that the mass of the quantum core scales with the halo mass as mc/(mh)min=1.47 [mh/(mh)min]3/8. this relation is equivalent to the "velocity dispersion tracing" relation according to which the velocity dispersion in the core vc2∼g mc/rc is of the same order as the velocity dispersion in the halo vh2∼g mh/rh. we provide therefore a justification of this relation from thermodynamical arguments. the fermion ball represents a large quantum bulge which is either present now or may have, in the past, triggered the collapse of the surrounding gas, leading to a supermassive black hole and a quasar. when mh>(mh)mcp, the quantum core-halo solution is microcanonically unstable. large dark matter halos may undergo a gravothermal catastrophe leading ultimately to the formation of a small out-of-equilibrium condensed core or, in the case of very large dark matter halos with mh>mov, to a supermassive black hole when the core mass overcomes the oppenheimer-volkoff (ov) limit. the isothermal halo is left undisturbed and is in agreement with the burkert profile. our model has no free parameter (the mass m =165 ev /c2 of the fermionic particle is determined by the minimum halo) so it is completely predictive. it predicts that the milky way should harbor a fermionic dark matter bulge of mass mc=9.45 ×109 m⊙ and radius rc=240 pc in possible agreement with the observations. we also consider another model involving a larger fermion mass m =54.6 kev / c2 . in this model, a fermion ball of mass mc=4.2 ×106 m⊙ and radius rc=6 ×10-4 pc could mimic the effect of a supermassive black hole at the center of the milky way (sagittarius a*). in bigger galaxies, the fermion ball should be replaced by a supermassive black hole of mass mbh=2.10 ×108 m⊙ which could account for active galactic nuclei. for an even larger fermion mass m =386 kev / c2 , a supermassive black hole of mass mbh=4.2 ×106 m⊙ should be formed in the milky way instead of a fermion ball. however, models with a fermion mass m =54.6 kev / c2 predict that ultracompact dark matter halos of mass ∼108 m⊙ should contain a fermionic core of mass mc∼104 m⊙ and radius rc∼5 mpc similar to intermediate mass black holes, a prediction which may be challenged by observations. | predictive model of fermionic dark matter halos with a quantum core and an isothermal atmosphere |
the quasar target selection for the upcoming survey of the dark energy spectroscopic instrument (desi) will be fixed for the next 5 yr. the aim of this work is to validate the quasar selection by studying the impact of imaging systematics as well as stellar and galactic contaminants, and to develop a procedure to mitigate them. density fluctuations of quasar targets are found to be related to photometric properties such as seeing and depth of the data release 9 of the desi legacy imaging surveys. to model this complex relation, we explore machine learning algorithms (random forest and multilayer perceptron) as an alternative to the standard linear regression. splitting the footprint of the legacy imaging surveys into three regions according to photometric properties, we perform an independent analysis in each region, validating our method using extended baryon oscillation spectroscopic survey (eboss) ez-mocks. the mitigation procedure is tested by comparing the angular correlation of the corrected target selection on each photometric region to the angular correlation function obtained using quasars from the sloan digital sky survey (sdss) data release 16. with our procedure, we recover a similar level of correlation between desi quasar targets and sdss quasars in two-thirds of the total footprint and we show that the excess of correlation in the remaining area is due to a stellar contamination that should be removed with desi spectroscopic data. we derive the limber parameters in our three imaging regions and compare them to previous measurements from sdss and the 2df qso redshift survey. | angular clustering properties of the desi qso target selection using dr9 legacy imaging surveys |
we examine massive black hole (mbh) mergers and their associated gravitational wave signals from the large-volume cosmological simulation astrid . astrid includes galaxy formation and black hole models recently updated with an mbh seed population between 3 × 104h-1m⊙ and 3 × 105h-1m⊙ and a sub-grid dynamical friction (df) model to follow the mbh dynamics down to 1.5 ckpc h-1. we calculate the initial eccentricities of mbh orbits directly from the simulation at kpc-scales, and find orbital eccentricities above 0.7 for most mbh pairs before the numerical merger. after approximating unresolved evolution on scales below ${\sim 200\, \text{pc}}$, we find that the in-simulation df on large scales accounts for more than half of the total orbital decay time ($\sim 500\, \text{myr}$) due to df. the binary hardening time is an order of magnitude longer than the df time, especially for the seed-mass binaries (mbh < 2mseed). as a result, only $\lesssim 20{{\rm per \,cent}}$ of seed mbh pairs merge at z > 3 after considering both unresolved df evolution and binary hardening. these z > 3 seed-mass mergers are hosted in a biased population of galaxies with the highest stellar masses of $\gt 10^9\, {\rm m}_\odot$. with the higher initial eccentricity prediction from astrid , we estimate an expected merger rate of 0.3-0.7 per year from the z > 3 mbh population. this is a factor of ~7 higher than the prediction using the circular orbit assumption. the laser interferometer space antenna events are expected at a similar rate, and comprise $\gtrsim 60\,{\rm{per\,cent}}$ seed-seed mergers, $\sim 30\,{\rm{per\,cent}}$ involving only one seed-mass mbh, and $\sim 10\,{\rm{per\,cent}}$ mergers of non-seed mbhs. | massive black hole mergers with orbital information: predictions from the astrid simulation |
the observed lensed fraction of high-redshift quasars (~0.2%) is significantly lower than previous theoretical predictions (≳4%). we revisit the lensed fraction of high-redshift quasars predicted by theoretical models, where we adopt recent measurements of galaxy velocity dispersion functions (vdfs) and explore a wide range of quasar luminosity function (qlf) parameters. we use both analytical methods and mock catalogs, which give consistent results. for ordinary qlf parameters and the depth of current high-redshift quasar surveys (mz≲ 22), our model suggests a multiply imaged fraction of f multi ~ 0.4%-0.8%. the predicted lensed fraction is ~1%-6% for the brightest zs~ 6 quasars (mz≲ 19), depending on the qlf. the systematic uncertainties of the predicted lensed fraction in previous models can be as large as 2-4 times and are dominated by the vdf. applying vdfs from recent measurements decreases the predicted lensed fraction and relieves the tension between observations and theoretical models. given the depth of current imaging surveys, there are ~15 lensed quasars at zs> 5.5 detectable over the sky. upcoming sky surveys like the legacy survey of space and time survey and the euclid survey will find several tens of lensed quasars at this redshift range. | revisiting the lensed fraction of high-redshift quasars |
the baryon acoustic oscillation feature in the clustering of galaxies or quasars provides a `standard ruler' for distance measurements in cosmology. in this work, we report a 2-3σ signal of the baryon acoustic oscillation dip feature in the galaxy density-ellipticity cross-correlation functions using the spectroscopic sample of the baryon oscillation spectroscopic survey cmass, combined with the deep dark energy spectroscopic instrument legacy imaging surveys for precise galaxy shape measurements. we measure the galaxy-ellipticity correlation functions and model them using the linear alignment model. we constrain the distance dv/rd to redshift 0.57 to a precision of 3-5%, depending on the details of modelling. the galaxy-ellipticity measurement reduces the uncertainty of distance measurement by ~10% on top of that derived from the galaxy-galaxy correlation. more importantly, for future large and deep galaxy surveys, the independent galaxy-ellipticity measurements can help sort out the systematics in the baryon acoustic oscillation studies. | evidence for baryon acoustic oscillations from galaxy-ellipticity correlations. |
we present the first empirical constraints on the turbulent velocity field of the diffuse circumgalactic medium around four luminous quasi-stellar objects (qsos) at z ≈ 0.5-1.1. spatially extended nebulae of ≈50-100 physical kpc in diameter centred on the qsos are revealed in [o ii] $\lambda \lambda \, 3727,3729$ and/or [o iii] $\lambda \, 5008$ emission lines in integral field spectroscopic observations obtained using multi-unit spectroscopic explorer on the very large telescope. we measure the second- and third-order velocity structure functions (vsfs) over a range of scales, from ≲5 kpc to ≈20-50 kpc, to quantify the turbulent energy transfer between different scales in these nebulae. while no constraints on the energy injection and dissipation scales can be obtained from the current data, we show that robust constraints on the power-law slope of the vsfs can be determined after accounting for the effects of atmospheric seeing, spatial smoothing, and large-scale bulk flows. out of the four qso nebulae studied, one exhibits vsfs in spectacular agreement with the kolmogorov law, expected for isotropic, homogeneous, and incompressible turbulent flows. the other three fields exhibit a shallower decline in the vsfs from large to small scales. however, with a limited dynamic range in the spatial scales in seeing-limited data, no constraints can be obtained for the vsf slopes of these three nebulae. for the qso nebula consistent with the kolmogorov law, we determine a turbulence energy cascade rate of ≈0.2 cm2 s-3. we discuss the implication of the observed vsfs in the context of qso feeding and feedback in the circumgalactic medium. | empirical constraints on the turbulence in qso host nebulae from velocity structure function measurements |
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