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we have developed a parallel code called the voigt profile parameter estimation routine (viper) for automatically fitting the h i lyα forest seen in the spectra of quasi-stellar objects (qsos). we obtained the h i column density distribution function (cddf) and linewidth (b) parameter distribution for z < 0.45 using spectra of 82 qsos obtained using the cosmic origins spectrograph and viper. the consistency of these with existing measurements in the literature validates our code. by comparing this cddf with those obtained from hydrodynamical simulations, we constrain the h i photoionization rate (γ _{h i}) at z < 0.45 in four redshift bins. viper, together with the code for ionization and temperature evolution (cite), which we developed for gadget-2, allows us to explore parameter space and perform χ2 minimization to obtain γ _{h i}. we notice that the b parameters from the simulations are smaller than those derived from observations. we show that the observed b parameter distribution and b versus log {n_{h i}} scatter can be reproduced in simulations by introducing subgrid-scale turbulence. however, it has very little influence on the derived γ _{h i}. the γ _{h i}(z) obtained here, (3.9 ± 0.1) × 10-14 (1 + z)4.98 ± 0.11 s-1, is in good agreement with the values derived by us using flux-based statistics in a previous article. these values are consistent with the hydrogen ionizing ultraviolet (uv) background being dominated mainly by qsos, without needing any contribution from non-standard sources of uv photons. | voigt profile parameter estimation routine (viper): h i photoionization rate at z < 0.5 |
during the peak of their accretion phase, supermassive black holes in galactic cores are known to emit very high levels of ionizing radiation, becoming visible over intergalactic distances as quasars or active galactic nuclei (agn). here, we quantify the extent to which the activity of the supermassive black hole at the center of the milky way, known as sagittarius a* (sgr a*), may have affected the habitability of earth-like planets in our galaxy. we focus on the amount of atmospheric loss and on the possible biological damage suffered by planets exposed to x-ray and extreme ultraviolet (xuv) radiation produced during the peak of the active phase of sgr a*. we find that terrestrial planets could lose a total atmospheric mass comparable to that of present day earth even at large distances ( 1 kiloparsec) from the galactic center. furthermore, we find that the direct biological damage caused by sgr a* to surface life on planets not properly screened by an atmosphere was probably significant during the agn phase, possibly hindering the development of complex life within a few kiloparsecs from the galactic center. | the habitability of the milky way during the active phase of its central supermassive black hole |
we have observed 104 gravitationally lensed quasars at z ∼ 1-4 with herschel/spire, the largest such sample ever studied. by targeting gravitational lenses, we probe intrinsic far-infrared (fir) luminosities and star formation rates (sfrs) more typical of the population than the extremely luminous sources that are otherwise accessible. we detect 72 objects with herschel/spire and find 66 per cent (69 sources) of the sample have spectral energy distributions (seds) characteristic of dust emission. for 53 objects with sufficiently constrained seds, we find a median effective dust temperature of 38^{+12}_{-5} k. by applying the radio-infrared correlation, we find no evidence for an fir excess that is consistent with star-formation-heated dust. we derive a median magnification-corrected fir luminosity of 3.6^{+4.8}_{-2.4} × 10^{11} l_{⊙} and median sfr of 120^{+160}_{-80} m_{⊙} yr^{-1}} for 94 quasars with redshifts. we find ∼10 per cent of our sample have fir properties similar to typical dusty star-forming galaxies at z ∼ 2-3 and a range of sfrs <20-10 000 m⊙ yr-1 for our sample as a whole. these results are in line with current models of quasar evolution and suggests a coexistence of dust-obscured star formation and agn activity is typical of most quasars. we do not find a statistically significant difference in the fir luminosities of quasars in our sample with a radio excess relative to the radio-infrared correlation. synchrotron emission is found to dominate at fir wavelengths for <15 per cent of those sources classified as powerful radio galaxies. | gravitational lensing reveals extreme dust-obscured star formation in quasar host galaxies |
even with several thousand fermi-large area telescope (lat) blazar detections, the γ-ray emission mechanism is poorly understood. we explore correlated optical/γ-ray flux variations for 178 fermi-lat blazars regularly monitored by the katzman automatic imaging telescope, the small and moderate aperture research telescope system, and the steward observatory. out of the 178 sources, 121 show a measurable (>1σ) discrete correlation function peak. using the derived time lags and bayesian block light-curve decompositions, we measure the fraction of common and orphan flares between the two bands. after accounting for sampling and sensitivity limitations we quantify for the first time the true orphan flare rates of optical and γ-ray flares: 54.5% of optical and 20% of γ-ray flares are orphan events. both the intraband temporal relation and the small orphan γ-ray flare fraction point toward leptonic processes as the likely mechanisms for the high-energy emission. motivated to discriminate between synchrotron self-compton (ssc) and external-compton dominance in individual sources, we use the flux-flux variations to determine the slope m of the log f opt-log fγdependence. the slope distribution suggests a bimodal population with high and intermediate synchrotron peak objects showing larger m than low synchrotron peak objects. we find that m is naturally decreased through pollution from the orphan (typically optical) flares and develop a method to statistically recover, given the sources’ measured orphan flare rate, the intrinsic m. while source classes show composite behavior, the majority of bl lac objects favor m = 2, indicating an ssc origin for the γ-rays. no preference for either m is found in flat spectrum radio quasars. | probing blazar emission processes with optical/gamma-ray flare correlations |
in order to better understand how active galactic nuclei (agns) affect the interstellar media of their host galaxies, we perform a meta-analysis of the co emission for a sample of z = 0.01-4 galaxies from the literature with existing co detections and well-constrained agn contributions to the infrared (67 galaxies). using either spitzer/irs mid-infrared spectroscopy or spitzer+herschel colors we determine the fraction of the infrared luminosity in each galaxy that can be attributed to heating by the agns or stars. we calculate new average co spectral line ratios (primarily from carilli & walter) to uniformly scale the higher-j co detections to the ground state and accurately determine our sample’s molecular gas masses. we do not find significant differences in the gas depletion timescales/star formation efficiencies as a function of the mid-infrared agn strength (f(agn)mir or l ir (agn)), which indicates that the presence of an infrared-bright agn is not a sufficient signpost of galaxy quenching. we also find that the dust-to-gas ratio is consistent for all sources, regardless of agn emission, redshift, or l ir, indicating that dust is likely a reliable tracer of gas mass for massive dusty galaxies (albeit with a large degree of scatter). finally, if we classify galaxies as either agn or star formation dominated, we do not find a robust statistically significant difference between their co excitation. | co emission in infrared-selected active galactic nuclei |
we present the discovery of a very hot gas phase of the milky way circumgalactic medium (cgm) at t ≈ 107 k, using deep xmm-newton reflection grating spectrometer observations of the blazar 1es 1553+113. the hot gas, coexisting with a warm-hot phase at t ≈ 106 k is α-enhanced, with [{{o}}/{fe}]={0.9}-0.3+0.7, indicating core-collapse supernovae enrichment. additionally, we find [ne/o] and [{{n}}/{{o}}]={0.7}-0.2+1.6, such that n/ne is consistent with solar. along with the enrichment by asymptotic giant branch stars and core-collapse supernovae, this indicates that some oxygen has depleted onto dust and/or transited to cooler gas phase(s). these results may affect previous baryonic and metallic mass estimations of the warm-hot and hot cgm from the observations of oxygen emission and absorption. our results provide insights on the heating, mixing, and chemical enrichment of the milky way cgm, and provide inputs to theoretical models of galaxy evolution. | discovery of a very hot phase of the milky way circumgalactic medium with non-solar abundance ratios |
galaxy evolution is thought to be driven in large part by the flow of gas between galaxies and the circumgalactic medium (cgm), a halo of metal-enriched gas extending out to ≳100 kpc from each galaxy. studying the spatial structure of the cgm holds promise for understanding these gas flow mechanisms; however, the common method of using background quasar sight lines provides minimal spatial information. recent works have shown the utility of extended background sources such as giant gravitationally lensed arcs. using background lensed arcs from the cswa 38 lens system, we continuously probed, at a resolution element of about 15 kpc2, the spatial and kinematic distribution of mg ii absorption in a star-forming galaxy at z = 0.77 (stellar mass ≈109.7 m⊙, star formation rate ≈10 m⊙ yr-1) at impact parameters d ≃ 5-30 kpc. our results present an anisotropic, optically thick medium whose absorption strength decreases with increasing impact parameter, in agreement with the statistics toward quasars and other gravitational arcs. furthermore, we find generally low line-of-sight velocities in comparison to the relatively high velocity dispersion in the mg ii gas (with typical σ ≈ 50 km s-1). while the galaxy itself exhibits a clear outflow (with mg ii velocities up to ~500 km s-1) in the down-the-barrel spectrum, the outflow component is subdominant and only weakly detected at larger impact parameters probed by the background arcs. our results provide evidence of mainly dispersion-supported, metal-enriched gas recycling through the cgm. | kinematics of the circumgalactic medium of a z = 0.77 galaxy from mg ii tomography |
recently, it was shown that quark matter with only u and d quarks (u d qm ) can be the ground state of matter for baryon numbers a >amin with amin≳300 . in this paper, we explore u d quark stars (u d qss ) that are composed of u d qm , in the context of the two-families scenario in which u d qss and hadronic stars (hss) can coexist. distinct signatures are discussed compared to the conventional study regarding strange quark stars (sqss). we show that the requirements of amin≳300 and the most massive compact star observed being a u d qs together may put stringent constraints on the allowed parameter space of u d qss . then, we study the related gravitational-wave probe of the tidal deformability in binary star mergers, including the u d qs -u d qs and u d qs -hs cases. the obtained values of the tidal deformability at 1.4 solar masses and the average tidal deformability are all in good compatibility with the experimental constraints of gw170817. this study points to a new possible interpretation of the gw170817 binary merger event, where u d qs may be at least one component of the binary system detected. | probing up-down quark matter via gravitational waves |
at redshifts of z ≲ 1.3, early-type galaxies (etgs) and passive galaxies are mainly found in dense environments, such as galaxy clusters. however, it remains unclear whether these well-known morphology-density and passive-density relations have already been established at higher redshifts. to address this question, we performed an in-depth study of galaxies in 16 spectroscopically confirmed clusters at 1.3 < z < 2.8 from the clusters around radio-loud agn (carla) survey. our clusters span a total stellar mass in the range of 11.3 < log(m∗c/m⊙) < 12.6 (approximate halo mass in the range of 13.5 ≲ log(mhc/m⊙) ≲ 14.5). our main finding is that the morphology-density and passive-density relations are already in place at z ∼ 2. the cluster at z = 2.8 shows a similar fraction of etg as in the other clusters in its densest region, however, only one cluster does not provide enough statistics to confirm that the morphology-density relation is already in place at z ∼ 3. the cluster etg and passive fractions depend mainly on local environment and only slightly on galaxy mass; also, they do not depend on the global environment. at lower local densities, where σn < 700 gal/mpc2, the carla clusters exhibit a similar etg fraction as the field, in contradiction to clusters at z = 1, which already exhibit higher etg fractions. this implies that the densest regions influence the morphology of galaxies first, with lower density local environments either taking longer or only influencing galaxy morphology at later cosmological times. interestingly, we find evidence of high merger fractions in our clusters with respect to the candels fields, but the merger fractions do not significantly depend on local environment. this suggests that merger remnants in the lowest density regions can reform disks fueled by cold gas flows, but those in the highest density regions are cut off from the gas supply and will become passive etgs. the percentages of active etgs, with respect to the total etg population, are 21 ± 6% and 59 ± 14% at 1.35 < z < 1.65 and 1.65 < z < 2.05, respectively, and about half of them are mergers or asymmetric in both redshift bins. all the spectroscopically confirmed carla clusters have properties that are consistent with clusters and proto-clusters, confirming that radio-loud active galactic nuclei are lighthouses for dense environments. the differences between our results and other findings that point to enhanced star formation and starbursts in cluster cores at similar redshifts are probably due to differences in the sample selection criteria; for example, selection of different environments hosting galaxies with different accretion and pre-processing histories. the carla photometric catalogue is only available at the cds via anonymous ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/j/a+a/670/a58 | morphology-density relation, quenching, and mergers in carla clusters and protoclusters at 1.4 < z < 2.8 |
combining the exquisite angular resolution of gaia with optical light curves and wise photometry, the gaia gravitational lenses group (gral) uses machine-learning techniques to identify candidate strongly lensed quasars, and has confirmed over two dozen new strongly lensed quasars from the gaia data release 2. this paper reports on the 12 quadruply imaged quasars identified by this effort to date, which is a ~20% increase in the total number of confirmed quadruply imaged quasars. we discuss the candidate selection, spectroscopic follow-up, and lens modeling. we also report our spectroscopic failures as an aid for future investigations. | gaia gral: gaia dr2 gravitational lens systems. vi. spectroscopic confirmation and modeling of quadruply imaged lensed quasars |
to understand the active galactic nuclei (agns) phenomenon and their impact on the evolution of galaxies, a complete agn census is required; however, finding heavily obscured agns is observationally challenging. here we use the deep and extensive multiwavelength data in the cosmos field to select a complete sample of 578 infrared (ir) quasars ($l_{\rm agn,ir}\gt 10^{45}\rm \: erg\: s^{-1}$) at z < 3, with minimal obscuration bias, using detailed uv-to-far-ir spectral energy distribution (sed) fitting. we complement our sed constraints with x-ray and radio observations to further investigate the properties of the sample. overall, 322 of the ir quasars are detected by chandra and have individual x-ray spectral constraints. from a combination of x-ray stacking and $l_{\rm 2-10\rm \,kev}$ - $l_{\rm 6\: \mu m}$ analyses, we show that the majority of the x-ray faint and undetected quasars are heavily obscured (many are likely compton thick), highlighting the effectiveness of the mid-ir band to find obscured agns. we find that 355 (≈61 per cent) ir quasars are obscured ($n_{\rm h}\gt 10^{22}\rm \: cm^{-2}$) and identify differences in the average properties between the obscured and unobscured quasars: (1) obscured quasars have star formation rates ≈3 times higher than unobscured systems for no significant difference in stellar mass and (2) obscured quasars have stronger radio emission than unobscured systems, with a radio-loudness parameter $\approx 0.2 \rm \: dex$ higher. these results are inconsistent with a simple orientation model but in general agreement with either extreme host-galaxy obscuration towards the obscured quasars or a scenario where obscured quasars are an early phase in the evolution of quasars. | a panchromatic view of infrared quasars: excess star formation and radio emission in the most heavily obscured systems |
we present the first full catalog and science results for the nuclear spectroscopic telescope array (nustar) serendipitous survey. the catalog incorporates data taken during the first 40 months of nustar operation, which provide ≈20 ms of effective exposure time over 331 fields, with an areal coverage of 13 deg2, and 497 sources detected in total over the 3-24 kev energy range. there are 276 sources with spectroscopic redshifts and classifications, largely resulting from our extensive campaign of ground-based spectroscopic follow-up. we characterize the overall sample in terms of the x-ray, optical, and infrared source properties. the sample is primarily composed of active galactic nuclei (agns), detected over a large range in redshift from z = 0.002 to 3.4 (median of < z> =0.56), but also includes 16 spectroscopically confirmed galactic sources. there is a large range in x-ray flux, from {log}({f}3-24{kev}/{erg} {{{s}}}-1 {{cm}}-2)≈ -14 to -11, and in rest-frame 10-40 kev luminosity, from {log}({l}10-40{kev}/{erg} {{{s}}}-1)≈ 39 to 46, with a median of 44.1. approximately 79% of the nustar sources have lower-energy (<10 kev) x-ray counterparts from xmm-newton, chandra, and swift xrt. the mid-infrared (mir) analysis, using wise all-sky survey data, shows that mir agn color selections miss a large fraction of the nustar-selected agn population, from ≈15% at the highest luminosities ({l}{{x}}> {10}44 erg s-1) to ≈80% at the lowest luminosities ({l}{{x}}< {10}43 erg s-1). our optical spectroscopic analysis finds that the observed fraction of optically obscured agns (i.e., the type 2 fraction) is {f}{type2}={53}-15+14 % , for a well-defined subset of the 8-24 kev selected sample. this is higher, albeit at a low significance level, than the type 2 fraction measured for redshift- and luminosity-matched agns selected by <10 kev x-ray missions. | the nustar serendipitous survey: the 40-month catalog and the properties of the distant high-energy x-ray source population |
we present the results of our alma observations of three active galactic nucleus (agn)-dominated nuclei in optical seyfert 1 galaxies (ngc 7469, i zw 1, and ic 4329 a) and eleven luminous infrared galaxies (lirgs) with various levels of infrared estimated energetic contributions by agns at the hcn and hco+ j = 3 - 2 emission lines. the hcn and hco+ j = 3 - 2 emission lines are clearly detected at the main nuclei of all sources, except for ic 4329 a. the vibrationally excited (v 2 = 1f) hcn j = 3 - 2 and hco+ j = 3 - 2 emission lines are simultaneously covered, and hcn v 2 = 1f j = 3 - 2 emission line signatures are seen in the main nuclei of two lirgs, iras 12112+0305 and iras 22491-1808, neither of which shows clear buried agn signatures in the infrared. if the vibrational excitation is dominated by infrared radiative pumping, through the absorption of infrared 14 μm photons, primarily originating from agn-heated hot dust emission, then these two lirgs may contain infrared-elusive, but (sub)millimeter-detectable, extremely deeply buried agns. these vibrationally excited emission lines are not detected in the three agn-dominated optical seyfert 1 nuclei. however, the observed hcn v 2 = 1f to v = 0 flux ratios in these optical seyferts are still consistent with the intrinsic flux ratios in lirgs with detectable hcn v 2 = 1f emission lines. the observed hcn-to-hco+ j = 3 - 2 flux ratios tend to be higher in galactic nuclei with luminous agn signatures compared with starburst-dominated regions, as previously seen at j = 1 - 0 and j = 4 - 3. | alma hcn and hco+ j =3-2 observations of optical seyfert and luminous infrared galaxies: confirmation of elevated hcn-to-hco+ flux ratios in agns |
as part of the megamaser cosmology project, we present vlbi maps of nuclear water masers toward five galaxies. the masers originate in sub-parsec circumnuclear disks. for three of the galaxies, we fit keplerian rotation curves to estimate their supermassive black hole (smbh) masses, and determine (2.9 ± 0.3) × 106 m⊙ for j0437+2456, (1.7 ± 0.1) × 107 m⊙ for eso 558-g009, and (1.1 ± 0.2) × 107 m⊙ for ngc 5495. in the other two galaxies, mrk 1029 and ngc 1320, the geometry and dynamics are more complicated and preclude robust black hole mass estimates. including our new results, we compiled a list of 15 vlbi-confirmed disk maser galaxies with robust smbh mass measurements. with this sample, we confirm the empirical relation of rout ∝ 0.3msmbh reported in wardle & yusef-zadeh. we also find a tentative correlation between maser disk outer radii and wide-field infrared survey explorer luminosity. we find no correlations of maser disk size with x-ray 2-10 kev luminosity or [o iii] luminosity. | the megamaser cosmology project. ix. black hole masses for three maser galaxies |
we utilize the multi unit spectroscopic explorer (muse) on the very large telescope to search for extended lyα emission around the z ∼ 6.6 qso j0305-3150. after carefully subtracting the point spread function, we reach a nominal 5σ surface-brightness limit of sb5σ= 1.9 × 10-18 erg s-1 cm-2 arcsec-2 over a 1 arcsec2 aperture, collapsing five wavelength slices centered at the expected location of the redshifted lyα emission (i.e., at 9256 å). current data suggest the presence (5σ accounting for systematics) of a lyα nebula that extends for 9 kpc around the qso. this emission is displaced and redshifted by 155 km s-1 with respect to the location of the qso host galaxy traced by the [{{c}} {{ii}}] 158 μm emission line. the total luminosity is l({ly}α ) = (3.0 ± 0.4) × 1042 erg s-1. our analysis suggests that this emission is unlikely to rise from optically thick clouds illuminated by the ionizing radiation of the qso. it is more plausible that the lyα emission is due to the fluorescence of the highly ionized optically thin gas. this scenario implies a high hydrogen volume density of {n}{{h}}∼ 6 cm-3. in addition, we detect a lyα emitter (lae) in the immediate vicinity of the qso, i.e., with a projected separation of ∼12.5 kpc and a line-of-sight velocity difference of 560 km s-1. the luminosity of the lae is l({ly}α ) = (2.1 ± 0.2) × 1042 erg s-1 and its inferred star-formation rate is sfr ∼ 1.3 m ⊙ yr-1. the probability of finding such a close lae is one order of magnitude above the expectations based on the qso-galaxy cross-correlation function. this discovery is in agreement with a scenario where dissipative interactions favor the rapid build-up of supermassive black holes at early cosmic times. | mapping the lyα emission around a z ∼ 6.6 qso with muse: extended emission and a companion at a close separation |
we analysed the parsec-scale linear polarization properties of 436 active galactic nuclei (agns) based on 15 ghz polarimetric very long baseline array observations. we present polarization and total intensity images averaged over at least five epochs since 1996 january 19 through 2019 august 4. stacking improves the image sensitivity down to ~30 μjy beam-1 and effectively fills out the jet cross-section both in total intensity and linear polarization. it delineates the long-term persistent magnetic field configuration and its regularity by restoring spatial distributions of the electric vector position angle (evpa) and fractional polarization, respectively. on average, about 10 yr of stacking period is needed to reveal the stable and most-complete polarization distribution of a source. we find that the degree of polarization significantly increases down and across the jet towards its edges, typically manifesting u or w-shaped transverse profiles, suggesting a presence of a large-scale helical magnetic field associated with the outflow. in some agn jets, mainly bl lacs, we detect quasi-constant fractional polarization profiles across the jet, accompanied by evpas that closely follow the outflow. bl lacs show higher fractional polarization values in their cores and jets than those in quasars up to hectoparsec de-projected scales, while on larger scales, they become comparable. high-synchrotron-peaked bl lac jets are found to be less polarized than intermediate and low-synchrotron-peaked bl lacs. the spatial distribution of the evpas in bl lacs tend to align with the local jet direction, while quasars show an excess of orthogonal polarization orientation. | mojave - xx. persistent linear polarization structure in parsec-scale agn jets |
two groups of astronomers used the large telescopes keck and vlt for decades to observe trajectories of bright stars near the galactic centre. based on results of their observations, the astronomers concluded that trajectories of the stars are roughly elliptical and foci of the orbits are approximately coincide with the galactic centre position. in a last few years, a self-gravitating dark matter core-halo distribution was suggested by ruffini, argüelles, rueda (rar) and this model was actively used in consequent studies. in particular, recently it has been claimed that the rar-model provides a better fit of trajectories of bright stars in comparison to the conventional model with a supermassive black hole. the dark matter distribution with a dense core having a constant density as it was suggested in the rar-model leaves trajectories of stars elliptical like in kepler's two-body problem. however, in this case not the foci of the ellipses coincide with the galactic centre but their centres while the orbital periods do not depend on semi-major axes. these properties are not consistent with the observational data for trajectories of bright stars. | testing the galactic centre potential with s-stars |
the quest for extrasolar planets and their characterisation as well as studies of fundamental physics on cosmological scales rely on capabilities of high-resolution astronomical spectroscopy. a central requirement is a precise wavelength calibration of astronomical spectrographs allowing for extraction of subtle wavelength shifts from the spectra of stars and quasars. here, we present an all-fibre, 400 nm wide near-infrared frequency comb based on electro-optic modulation with 14.5 ghz comb line spacing. tests on the high-resolution, near-infrared spectrometer giano-b show a photon-noise limited calibration precision of <10 cm/s as required for earth-like planet detection. moreover, the presented comb provides detailed insight into particularities of the spectrograph such as detector inhomogeneities and differential spectrograph drifts. the system is validated in on-sky observations of a radial velocity standard star (hd221354) and telluric atmospheric absorption features. the advantages of the system include simplicity, robustness and turn-key operation, features that are valuable at the observation sites. | broadband near-infrared astronomical spectrometer calibration and on-sky validation with an electro-optic laser frequency comb |
the expected level of γγ absorption in the broad line region (blr) radiation field of γ-ray loud flat spectrum radio quasars (fsrqs) is evaluated as a function of the location of the γ-ray emission region. this is done self-consistently with parameters inferred from the shape of the spectral energy distribution (sed) in a single-zone leptonic ec-blr model scenario. we take into account all geometrical effects both in the calculation of the γγ opacity and the normalization of the blr radiation energy density. as specific examples, we study the fsrqs 3c279 and pks 1510-089, keeping the blr radiation energy density at the location of the emission region fixed at the values inferred from the sed. we confirm previous findings that the optical depth due to γγ absorption in the blr radiation field exceeds unity for both 3c279 and pks 1510-089 for locations of the γ-ray emission region inside the inner boundary of the blr. it decreases monotonically, with distance from the central engine and drops below unity for locations within the blr. for locations outside the blr, the blr radiation energy density required for the production of gev γ-rays rapidly increases beyond observational constraints, thus making the ec-blr mechanism implausible. therefore, in order to avoid significant γγ absorption by the blr radiation field, the γ-ray emission region must therefore be located near the outer boundary of the blr. | gamma-gamma absorption in the broad line region radiation fields of gamma-ray blazars |
we present results from deep observations toward the cygnus region using 300 hr of very high energy (vhe) γ-ray data taken with the veritas cerenkov telescope array and over 7 yr of high-energy γ-ray data taken with the fermi satellite at an energy above 1 gev. as the brightest region of diffuse γ-ray emission in the northern sky, the cygnus region provides a promising area to probe the origins of cosmic rays. we report the identification of a potential fermi-lat counterpart to ver j2031+415 (tev j2032+4130) and resolve the extended vhe source ver j2019+368 into two source candidates (ver j2018+367* and ver j2020+368*) and characterize their energy spectra. the fermi-lat morphology of 3fgl j2021.0+4031e (the gamma cygni supernova remnant) was examined, and a region of enhanced emission coincident with ver j2019+407 was identified and jointly fit with the veritas data. by modeling 3fgl j2015.6+3709 as two sources, one located at the location of the pulsar wind nebula ctb 87 and one at the quasar qso j2015+371, a continuous spectrum from 1 gev to 10 tev was extracted for ver j2016+371 (ctb 87). an additional 71 locations coincident with fermi-lat sources and other potential objects of interest were tested for vhe γ-ray emission, with no emission detected and upper limits on the differential flux placed at an average of 2.3% of the crab nebula flux. we interpret these observations in a multiwavelength context and present the most detailed γ-ray view of the region to date. | a very high energy γ-ray survey toward the cygnus region of the galaxy |
we present a neutral hydrogen-selected absorption-line survey of gas with h i column densities 15< {log}{n}{{h}{{i}}}< 19 at z≲ 1 using the cosmic origins spectrograph on the hubble space telescope. our main aim is to determine the metallicity distribution of these absorbers. our sample consists of 224 absorbers selected on the basis of their h i absorption strength. here we discuss the properties of our survey and the immediate empirical results. we find singly and doubly ionized metal species, and h i typically have similar velocity profiles, implying they probe gas in the same or similar environments. the ionic ratios (e.g., {n}{{c}{{ii}}}/{n}{{c}{{iii}}}, {n}{{o}{{i}}}/{n}{{c}{{ii}}}) indicate that the gas in these absorbers is largely ionized, and the ionization conditions are quite comparable across the sampled {n}{{h}{{i}}} range. the doppler parameters of the h i imply t≲ 5× {10}4 k on average, consistent with the gas being photoionized. the mg ii column densities span >2 orders of magnitude at any given {n}{{h}{{i}}}, indicating a wide range of metallicities (from solar to <1/100 solar). in the range of 16.2≲ {log}{n}{{h}{{i}}}≲ 17, there is a gap in the {n}mg{{ii}}} distribution corresponding to gas with ∼10% solar metallicity, consistent with the gap seen in the previously identified bimodal metallicity distribution in this column density regime. less than 3% of the absorbers in our sample show no detectable metal absorption, implying that truly pristine gas at z≲ 1 is uncommon. we find < [fe ii/mg ii]> =-0.4+/- 0.3, and since α-enhancement can affect this ratio, dust depletion is extremely mild. | the cos cgm compendium. i. survey design and initial results |
changing-look active galactic nuclei (cl-agns) as a new subpopulation challenge some fundamental physics of agns because the timescales of the phenomenon can hardly be reconciled with accretion disk models. in this letter, we demonstrate the extreme case: close binaries of supermassive black holes (cb-smbhs) with high eccentricities are able to trigger the cl transition through one orbit. in this scenario, binary black holes build up their own mini-disks by peeling gas off the inner edges of the circumbinary disk during the apastron phase, after which they tidally interact with the disks during the periastron phase to efficiently exchange angular momentum within one orbital period. for mini-disks rotating retrograde to the orbit, the tidal torque rapidly squeezes the tidal parts of the mini-disks into a much smaller radius, which rapidly results in higher accretion and short flares before the disks decline into type-2 agns. prograde-rotation mini-disks gain angular momentum from the binary and rotate outward, which causes a rapid turn-off from type-1 to type-2. turn-on occurs around the apastron phase. cb-smbhs control cycle transitions between type-1 and type-2 with orbital periods but allow diverse properties in cl-agn light curves. | changing-look active galactic nuclei: close binaries of supermassive black holes in action |
coalescing, massive black-hole (mbh) binaries are the most powerful sources of gravitational waves (gws) in the universe, which makes mbh science a prime focus for ongoing and upcoming gw observatories. the laser interferometer space antenna (lisa) -- a gigameter scale space-based gw observatory -- will grant us access to an immense cosmological volume, revealing mbhs merging when the first cosmic structures assembled in the dark ages. lisa will unveil the yet unknown origin of the first quasars, and detect the teeming population of mbhs of $10^4 - 10^7$ solar masses. forming within protogalactic halos. the pulsar timing array, a galactic-scale gw survey, can access the largest mbhs the universe, detecting the cosmic gw foreground from inspiraling mbh binaries of about 10^9 solar masses. lisa can measure mbh spins and masses with precision far exceeding that from electromagnetic (em) probes, and together, both gw observatories will provide the first full census of binary mbhs, and their orbital dynamics, across cosmic time. detecting the loud gravitational signal of these mbh binaries will also trigger alerts for em counterpart searches, from decades (ptas) to hours (lisa) prior to the final merger. by witnessing both the gw and em signals of mbh mergers, precious information will be gathered about the rich and complex environment in the aftermath of a galaxy collision. the unique gw characterization of mbhs will shed light on the deep link between mbhs of $10^4-10^{10}$ solar masses and the grand design of galaxy assembly, as well as on the complex dynamics that drive mbhs to coalescence. | astro2020 science white paper: the gravitational wave view of massive black holes |
we report on an observation of the galactic black hole candidate grs 1739-278 during its 2014 outburst, obtained with nustar. the source was captured at the peak of a rising "low/hard" state, at a flux of ~0.3 crab. a broad, skewed iron line and disk reflection spectrum are revealed. fits to the sensitive nustar spectra with a number of relativistically blurred disk reflection models yield strong geometrical constraints on the disk and hard x-ray "corona." two models that explicitly assume a "lamp post" corona find its base to have a vertical height above the black hole of h = 5+7-2 {gm}/c2 and h = 18 ± 4 gm/c 2 (90% confidence errors); models that do not assume a "lamp post" return emissivity profiles that are broadly consistent with coronae of this size. given that x-ray microlensing studies of quasars and reverberation lags in seyferts find similarly compact coronae, observations may now signal that compact coronae are fundamental across the black hole mass scale. all of the models fit to grs 1739-278 find that the accretion disk extends very close to the black hole—the least stringent constraint is r_in = 5+3-4 gm/c2. only two of the models deliver meaningful spin constraints, but a = 0.8 ± 0.2 is consistent with all of the fits. overall, the data provide especially compelling evidence of an association between compact hard x-ray coronae and the base of relativistic radio jets in black holes. | new constraints on the black hole low/hard state inner accretion flow with nustar |
we present results from a survey designed to probe the star formation properties of 32 damped lyman α systems (dlas) at z ∼ 2.7. by using the `double-dla' technique that eliminates the glare of the bright background quasars, we directly measure the rest-frame far-ultraviolet flux from dlas and their neighbouring galaxies. at the position of the absorbing gas, we place stringent constraints on the unobscured star formation rates (sfrs) of dlas to 2σ limits of dot{ψ }<0.09-0.27m⊙ yr-1, corresponding to sfr surface densities σsfr < 10-2.6-10-1.5m⊙ yr-1 kpc-2. the implications of these limits for the star formation law, metal enrichment, and cooling rates of dlas are examined. by studying the distribution of impact parameters as a function of sfrs for all the galaxies detected around these dlas, we place new direct constraints on the bright end of the uv luminosity function of dla hosts. we find that ≤13 per cent of the hosts have dot{ψ }≥2m⊙ yr-1 at impact parameters b_dla ≤ (dot{ψ }/{m_{⊙} yr^{-1}})^{0.8}+6 kpc, differently from current samples of confirmed dla galaxies. our observations also disfavour a scenario in which the majority of dlas arise from bright lyman-break galaxies at distances 20 ≤ bdla < 100 kpc. these new findings corroborate a picture in which dlas do not originate from highly star-forming systems that are coincident with the absorbers, and instead suggest that dlas are associated with faint, possibly isolated, star-forming galaxies. potential shortcomings of this scenario and future strategies for further investigation are discussed. | directly imaging damped ly α galaxies at z > 2 - iii. the star formation rates of neutral gas reservoirs at z ∼ 2.7 |
using two-dimensional radiation hydrodynamic simulations, we investigate the origin of the ultra-fast outflows (ufos) that are often observed in luminous active galactic nuclei (agns). we found that the radiation force due to the spectral lines generates strong winds (line-driven disk winds) that are launched from the inner region of accretion disks (∼30 schwarzschild radii). a wide range of black hole masses (mbh) and eddington ratios (ɛ) was investigated to study the conditions causing the line-driven winds. for mbh = 106-109 m⊙ and ɛ = 0.1-0.7, funnel-shaped disk winds appear, in which dense matter is accelerated outward with an opening angle of 70°-80° and with 10% of the speed of light. if we observe the wind along its direction, the velocity, the column density, and the ionization state are consistent with those of the observed ufos. as long as obscuration by the torus does not affect the observation of x-ray bands, the ufos could be statistically observed in about 13%-28% of the luminous agns, which is not inconsistent with the observed ratio (∼40%). we also found that the results are insensitive to the x-ray luminosity and the density of the disk surface. thus, we can conclude that ufos could exist in any luminous agns, such as narrow-line seyfert 1s and quasars with ɛ > 0.1, with which fast line-driven winds are associated. | radiation hydrodynamic simulations of line-driven disk winds for ultra-fast outflows |
magnetic penrose process (mpp) is not only the most exciting and fascinating process mining the rotational energy of black hole but it is also the favored astrophysically viable mechanism for high energy sources and phenomena. it operates in three regimes of efficiency, namely low, moderate and ultra, depending on the magnetization and charging of spinning black holes in astrophysical setting. in this paper, we revisit mpp with a comprehensive discussion of its physics in different regimes, and compare its operation with other competing mechanisms. we show that mpp could in principle foot the bill for powering engine of such phenomena as ultra-high-energy cosmic rays, relativistic jets, fast radio bursts, quasars, agns, etc. further, it also leads to a number of important observable predictions. all this beautifully bears out the promise of a new vista of energy powerhouse heralded by roger penrose half a century ago through this process, and it has today risen in its magnetically empowered version of mid 1980s from a purely thought experiment of academic interest to a realistic powering mechanism for various high-energy astrophysical phenomena. | fifty years of energy extraction from rotating black hole: revisiting magnetic penrose process |
different massive black hole mass - host galaxy scaling relations suggest that the growth of massive black holes is entangled with the evolution of their host galaxies. the number of measured black hole masses is still limited and additional measurements are necessary to understand the underlying physics of this apparent coevolution. we add six new black hole mass (mbh) measurements of nearby fast rotating early-type galaxies to the known black hole mass sample, namely ngc 584, ngc 2784, ngc 3640, ngc 4570, ngc 4281, and ngc 7049. our target galaxies have effective velocity dispersions (σe) between 170 and 245 km s-1, and thus this work provides additional insight into the black hole properties of intermediate-mass early-type galaxies. we combined high-resolution adaptive-optics sinfoni data with large-scale muse, vimos and sauron data from atlas3d to derive two-dimensional stellar kinematics maps. we then built both jeans anisotropic models and axisymmetric schwarzschild models to measure the central black hole masses. our schwarzschild models provide black hole masses of (1.3 ± 0.5) × 108 m⊙ for ngc 584, (1.0 ± 0.6) × 108 m⊙ for ngc 2784, (7.7 ± 5) × 107 m⊙ for ngc 3640, (5.4 ± 0.8) × 108 m⊙ for ngc 4281, (6.8 ± 2.0) × 107 m⊙ for ngc 4570, and (3.2 ± 0.8) × 108 m⊙ for ngc 7049 at 3σ confidence level, which are consistent with recent mbh-σe scaling relations. ngc 3640 has a velocity dispersion dip and ngc 7049 a constant velocity dispersion in the center, but we can clearly constrain their lower black hole mass limit. we conclude our analysis with a test on ngc 4570 taking into account a variable mass-to-light ratio (m/l) when constructing dynamical models. when considering m/l variations linked mostly to radial changes in the stellar metallicity, we find that the dynamically determined black hole mass from ngc 4570 decreases by 30%. further investigations are needed in the future to account for the impact of radial m/l gradients on dynamical modeling. | six new supermassive black hole mass determinations from adaptive-optics assisted sinfoni observations |
it is not yet clear what triggers the activity of active galactic nuclei (agns), but galaxy merging has been suspected to be one of the main mechanisms fueling the activity. using deep optical images taken at various ground-based telescopes, we investigate the fraction of galaxy mergers in 39 luminous agns (mr ≲ -22.6 mag) at z ≤ 0.3 (a median redshift of 0.155), for which the host galaxies are generally considered as early-type galaxies. through visual inspection of the images, we find that 17 of 39 agn host galaxies (43.6%) show evidence for current or past mergers like tidal tails, shells, and disturbed morphology. in order to see if this fraction is abnormally high, we also examined the merging fraction of normal early-type galaxies in the sloan digital sky survey (sdss) stripe 82 data (a median redshift of 0.04), of which the surface-brightness limit is comparable to our imaging data. to correct for the effects related to the redshift difference of the two samples, we performed an image simulation by putting a bright point source as an artificial agn in the images of sdss early-type galaxies and placing them onto the redshifts of agns. the merging fraction in this realistic sample of simulated agns is only ∼5-15% (1/4 to 1/8 of that of real agns). our result strongly suggests that luminous agn activity is associated with galaxy merging. | correlation between galaxy mergers and luminous active galactic nuclei |
gravitational lens flux-ratio anomalies provide a powerful technique for measuring dark matter substructure in distant galaxies. however, before using these flux-ratio anomalies to test galaxy formation models, it is imperative to ascertain that the given anomalies are indeed due to the presence of dark matter substructure and not due to some other component of the lensing galaxy halo or to propagation effects. here we present the case of class b1555+375, which has a strong radio-wavelength flux-ratio anomaly. our high-resolution near-infrared keck ii adaptive optics imaging and archival hubble space telescope data reveal the lensing galaxy in this system to have a clear edge-on disc component that crosses directly over the pair of images that exhibit the flux-ratio anomaly. we find that simple models that include the disc can reproduce the cm-wavelength flux-ratio anomaly without requiring additional dark matter substructure. although further studies are required, our results suggest the assumption that all flux-ratio anomalies are due to a population of dark matter sub-haloes may be incorrect, and analyses that do not account for the full complexity of the lens macro-model may overestimate the substructure mass fraction in massive lensing galaxies. | sharp - ii. mass structure in strong lenses is not necessarily dark matter substructure: a flux ratio anomaly from an edge-on disc in b1555+375 |
we present and make publicly available the second data release (dr2) of the keck observatory database of ionized absorption toward quasars (kodiaq) survey. kodiaq dr2 consists of a fully reduced sample of 300 quasars at 0.07< {z}{em}< 5.29 observed with hires at high resolution (36,000 ≤ r ≤ 103,000). dr2 contains 831 spectra available in continuum normalized form, representing a sum total exposure time of ∼4.9 megaseconds on source. these co-added spectra arise from a total of 1577 individual exposures of quasars taken from the keck observatory archive (koa) in raw form and uniformly processed. dr2 extends dr1 by adding 130 new quasars to the sample, including additional observations of qsos in dr1. all new data in dr2 were obtained with the single-chip tektronix tk2048 ccd configuration of hires in operation between 1995 and 2004. dr2 is publicly available to the community, housed as a higher level science product at the koa and in the igmspec database (v03). | the second data release of the kodiaq survey |
the existence of luminous quasars (qsos) at the epoch of reionization (eor; i.e., z > 6) powered by well-grown supermassive black holes (smbhs) with masses ≳109 m⊙ challenges models of early smbh formation and growth. to shed light on the nature of these sources, we started a multiwavelength program based on a sample of 18 hyperluminous quasars at the epoch of reionization (hyperion). these are the luminous qsos whose smbhs must have had the most rapid mass growth during the first gigayear of the universe and therefore acquired the largest mass at their respective epochs. in this paper, we present the hyperion sample and report results from the first year of the planned three years of observations of the 2.4 ms xmm-newton multi-year heritage program on which hyperion is based. the goal of this program is to accurately characterise the x-ray nuclear properties of qsos at the eor. through a joint x-ray spectral analysis of ten sources, covering the rest-frame ∼2 − 50 kev energy range, we report a steep average photon index (γ ≈ 2.4 ± 0.1). no absorption is required at levels of 1021 − 1022 cm−2. the measured average γ is inconsistent at ≥4σ level with the canonical value (γ = 1.8 − 2) measured in qsos at z < 6. such a steep spectral slope is also significantly steeper than that reported in lower-z analog qsos with similar luminosity or accretion rate, suggesting genuine redshift evolution. alternatively, we can interpret this result as suggesting the presence of a very low energy cutoff ecut ≈ 20 kev on a standard γ = 1.9 power-law, the likes of which is rarely reported at lower z. we also report mild indications that, on average, hyperion qsos show higher levels of coronal soft x-rays at 2 kev compared to the accretion disk uv at 2500 å than expected for lower-z agn in the high-luminosity regime. we speculate that either a redshift-dependent coupling between the x-ray corona and accretion disk or intrinsically different coronal properties account for the steepness of the x-ray spectral slope, especially in the presence of powerful winds. the reported steep slopes, if confirmed in lower-luminosity regimes, may have an important impact on the design of next-generation x-ray facilities and future surveys designed to investigate the early universe. | hyperluminous quasars at the epoch of reionization (hyperion): a new regime for the x-ray nuclear properties of the first quasars |
we present xmm-newton x-ray observations and analysis of three dark energy survey z > 6.5 quasars (vdes j0020-3653 at z = 6.824, vdes j0244-5008 at z = 6.724, and vdes j0224-4711 at z = 6.526) and six other quasars with 6.438 < z < 6.747 from the xmm-newton public archive. two of the nine quasars are detected at a high (>4σ) significance level: vdes j0224-4711(z = 6.53) at 9σ and pso j159-02 (z = 6.38) at 8σ. they have a photon index of γ =1.82^{+0.29}_{-0.27} and 1.94^{+0.31}_{-0.29}, respectively, which is consistent with the mean value of ∼1.9 found for quasars at all redshifts. the rest-frame 2-10 kev luminosity of vdes j0224-4711 is l_{2-10 kev} = (2.92± 0.43)× 10^{45} erg s^{-1}, which makes this quasar one of the most x-ray luminous quasars at z > 5.5 and the most x-ray luminous quasar at z > 6.5, with a luminosity 6 times and 2.5 times larger than ulas j1120+0641 (z = 7.08) and ulas j1342+0928 (z = 7.54), respectively. the x-ray-to-optical power-law slopes of the nine quasars are consistent with the previously observed anticorrelation of αox with uv luminosity l_{2500 å}. we find no evidence for evolution of αox with redshift when the anticorrelation with uv luminosity is taken into account. similar to previous studies at z ∼ 6, we have found remarkably consistent x-ray spectral properties between low-redshift quasars (z ∼ 1) and high-redshift quasars. our results add further evidence to the picture that the observable properties of high-luminosity quasars over the uv-to-x-ray spectral region have not evolved significantly from z ∼ 7 to the present day and that quasars comparable to local versions existed 800 myr after the big bang. | x-ray properties of z ≳ 6.5 quasars |
we study the x-ray variability properties of distant active galactic nuclei (agns) in the chandradeep field-south region over 17 yr, up to z ∼ 4, and compare them with those predicted by models based on local samples. we use the results of monte carlo simulations to account for the biases introduced by the discontinuous sampling and the low-count regime. we confirm that variability is a ubiquitous property of agns, with no clear dependence on the density of the environment. the variability properties of high-z agns, over different temporal time-scales, are most consistent with a power spectral density (psd) described by a broken (or bending) power law, similar to nearby agns. we confirm the presence of an anticorrelation between luminosity and variability, resulting from the dependence of variability on black hole (bh) mass and accretion rate. we explore different models, finding that our acceptable solutions predict that bh mass influences the value of the psd break frequency, while the eddington ratio λedd affects the psd break frequency and, possibly, the psd amplitude as well. we derive the evolution of the average λedd as a function of redshift, finding results in agreement with measurements based on different estimators. the large statistical uncertainties make our results consistent with a constant eddington ratio, although one of our models suggest a possible increase of λedd with lookback time up to z ∼ 2-3. we conclude that variability is a viable mean to trace the accretion history of supermassive bhs, whose usefulness will increase with future, wide-field/large effective area x-ray missions. | tracing the accretion history of supermassive black holes through x-ray variability: results from the chandradeep field-south |
we use the eagle cosmological, hydrodynamical simulations to predict the column density and equivalent width distributions of intergalactic o vii (e=574 {ev}) and o viii (e=654 {ev}) absorbers at low redshift. these two ions are predicted to account for 40 per cent of the gas-phase oxygen, which implies that they are key tracers of cosmic metals. we find that their column density distributions evolve little at observable column densities from redshift 1 to 0, and that they are sensitive to active galactic nucleus feedback, which strongly reduces the number of strong (column density n ≳ 10^{16} {cm}^{-2}) absorbers. the distributions have a break at n ∼ 10^{16} {cm}^{-2}, corresponding to overdensities of ∼102, likely caused by the transition from sheet/filament to halo gas. absorption systems with n ≳ 10^{16} {cm}^{-2} are dominated by collisionally ionized o vii and o viii, while the ionization state of oxygen at lower column densities is also influenced by photoionization. at these high column densities, o vii and o viii arising in the same structures probe systematically different gas temperatures, meaning their line ratio does not translate into a simple estimate of temperature. while o vii and o viii column densities and covering fractions correlate poorly with the h i column density at {n}_{h {i}} ≳ 10^{15} {cm}^{-2}, o vii and o viii column densities are higher in this regime than at the more common, lower h i column densities. the column densities of o vi and especially ne viii, which have strong absorption lines in the uv, are good predictors of the strengths of o vii and o viii absorption and can hence aid in the detection of the x-ray lines. | the abundance and physical properties of o vii and o viii x-ray absorption systems in the eagle simulations |
we present karl g. jansky very large array observations of the co (2-1) line emission toward three far-infrared luminous quasars at z ∼ 6: sdss j231038.88+185519.7 and sdss j012958.51-003539.7 with ∼0.″6 resolution and sdss j205406.42-000514.8 with ∼2.″1 resolution. all three sources are detected in the co (2-1) line emission—one source is marginally resolved, and the other two appear as point sources. measurements of the co (2-1) line emission allow us to calculate the molecular gas mass even without a co excitation model. the inferred molecular gas masses are (0.8-4.3) × 1010 m ⊙. the widths and redshifts derived from the co (2-1) line are consistent with previous co (6-5) and [c ii] measurements. we also report continuum measurements using herschel for sdss j231038.88+185519.7 and sdss j012958.51-003539.7, and for sdss j231038.88+185519.7 data obtained at ∼140 and ∼300 ghz using the atacama large millimeter/submillimeter array. in the case of sdss j231038.88+185519.7, we present a detailed analysis of the spectral energy distribution and derive the dust temperature (∼40 k), the dust mass (∼109 m ⊙), the far-infrared luminosity (8-1000 μm ∼1013 l ⊙), and the star formation rate (2400-2700 m ⊙ yr-1). finally, an analysis of the photodissociation regions associated with the three high-redshift quasars indicates that the interstellar medium in these sources has similar properties to local starburst galaxies. | star formation and ism properties in the host galaxies of three far-infrared luminous quasars at z ∼ 6 |
intermediate-mass black holes (imbhs) with masses between 100 {and} {10}5{m}⊙are crucial to our understanding of black hole seed formation and are the prime targets for the laser interferometer space antenna, yet black holes in this mass range have eluded detection by traditional optical spectroscopic surveys aimed at finding active galactic nuclei (agns). in this letter, we have modeled for the first time the dependence of the optical narrow emission line strengths on the black hole mass of accreting agn over the range of 100{--}{10}8{m}⊙ . we show that as the black hole mass decreases, the hardening of the spectral energy distribution from the accretion disk changes the ionization structure of the nebula. the enhanced high-energy emission from imbhs results in a more extended partially ionized zone compared with models for higher mass black holes. this effect produces a net decrease in the predicted [o iii]/hβ and [n ii]/hα emission line ratios. based on this model, we demonstrate that the standard optical narrow emission line diagnostics used to identify massive black holes fail when the black hole mass falls below ≈ {10}4{m}⊙for highly accreting imbhs and for radiatively inefficient imbhs with active star formation. our models call into question the ability of common optical spectroscopic diagnostics to confirm agn candidates in dwarf galaxies, and indicate that the low-mass black hole occupation fraction inferred from such diagnostics will be severely biased. | the limitations of optical spectroscopic diagnostics in identifying active galactic nuclei in the low-mass regime |
the amount of cold, molecular gas in high-redshift galaxies is typically inferred from proxies of molecular hydrogen (h2), such as carbon monoxide (co) or neutral atomic carbon ([c i]) and molecular gas mass conversion factors. the use of these proxies, however, relies on modeling and observations that have not been directly measured outside the local universe. here, we use recent samples of high-redshift gamma-ray burst (grb) and quasar molecular gas absorbers to determine this conversion factor ${\alpha }_{[{\rm{c}}{\rm{i}}]}={m}_{\mathrm{mol}}/{l}_{[{\rm{c}}\,{\rm{i}}](1-0)}^{{\prime} }$ from the column density of h2, which gives us the mass per unit column, and the [c i](j = 1) column density, which provides the luminosity per unit column. this technique allows us to make direct measurements of the relative abundances in high-redshift absorption-selected galaxies. our sample spans redshifts of z = 1.9-3.4 and covers two orders of magnitude in gas-phase metallicity. we find that the [c i]-to-mmol conversion factor is metallicity dependent, with α[c i] scaling linearly with the metallicity: $\mathrm{log}{\alpha }_{[{\rm{c}}{\rm{i}}]}=-1.13\times \mathrm{log}(z/{z}_{\odot })+1.33$ , with a scatter of σ α[ci] = 0.2 dex. using a sample of emission-selected galaxies at z ∼ 0-5, with both [c i] and co line detections, we apply the α[c i] conversion to derive independent estimates of the molecular gas mass and the co-to-mmol, αco, conversion factor. we find a remarkable agreement between the molecular gas masses inferred from the absorption-derived α[c i] compared to typical αco-based estimates, which we confirm here to be metallicity-dependent as well, with an inferred slope that is consistent with αci and previous estimates from the literature. these results thus support the use of the absorption-derived α[c i] conversion factor for emission-selected star-forming galaxies and demonstrate that both methods probe the same universal properties of molecular gas in the local and high-redshift universe. | direct measurement of the [c i] luminosity to molecular gas mass conversion factor in high-redshift star-forming galaxies |
recent observations and simulations have challenged the long-held paradigm that mergers are the dominant mechanism driving the growth of both galaxies and supermassive black holes (smbh), in favour of non-merger (secular) processes. in this pilot study of merger-free smbh and galaxy growth, we use keck cosmic web imager spectral observations to examine four low-redshift (0.043 < z < 0.073) disc-dominated 'bulgeless' galaxies hosting luminous active galactic nucleus (agn), assumed to be merger-free. we detect blueshifted broadened [o iii] emission from outflows in all four sources, which the $\mathrm{[o\, \small {iii}]}$/$\rm {h}\beta$ ratios reveal are ionized by the agn. we calculate outflow rates in the range $0.12{-}0.7~\rm {m}_{\odot }~\rm {yr}^{-1}$, with velocities of $675{-}1710~\rm {km}~\rm {s}^{-1}$, large radial extents of $0.6{-}2.4~\rm {kpc}$, and smbh accretion rates of $0.02{-}0.07~\rm {m}_{\odot }~\rm {yr}^{-1}$. we find that the outflow rates, kinematics, and energy injection rates are typical of the wider population of low-redshift agn, and have velocities exceeding the galaxy escape velocity by a factor of ~30, suggesting that these outflows will have a substantial impact through agn feedback. therefore, if both merger-driven and non-merger-driven smbh growth lead to co-evolution, this suggests that co-evolution is regulated by feedback in both scenarios. simulations find that bars and spiral arms can drive inflows to galactic centers at rates an order of magnitude larger than the combined smbh accretion and outflow rates of our four targets. this work therefore provides further evidence that non-merger processes are sufficient to fuel smbh growth and agn outflows in disc galaxies. | kiloparsec-scale agn outflows and feedback in merger-free galaxies |
changing-look active galactic nuclei (clagn) are agn that change type as their broad emission lines appear or disappear, which is usually accompanied by strong flux changes in their blue featureless continuum. we search for turn-on clagn by selecting type-2 agn from the spectroscopic six-degree field galaxy survey (6dfgs), whose colours, observed ~15 yr later by the skymapper southern survey, are suggestive of type-1 agn. starting from 1092 type-2 agn, we select 20 candidates for follow-up and confirm that 14 of them have changed into type-1 and are thus turn-on clagn; further observations reveal 11 more turn-on clagn. while our search was not tailored to efficiently discover turn-off clagn, we discover two such cases as well. the result suggests a turn-on clagn rate of over 3 per cent over ~15 yr and imply a total clagn rate of more than ~6 per cent over this period. finally, we present observations of agn that are atypical for the clagn phenomenology, including j1109146 - a type-1 that did not appear as an agn at all in 6dfgs; j1406507 - the second reported changing-look narrow-line seyfert 1; and j1340153 - a clagn with a change time-scale of 3 months. | skymapper colours of seyfert galaxies and changing-look agn - ii. newly discovered changing-look agn |
proximity zones of high-redshift quasars are unique probes of their central supermassive black holes as well as the intergalactic medium (igm) in the last stages of reionization. we present 22 new measurements of proximity zones of quasars with redshifts between 5.8 and 6.6, using the enlarged xqr-30 sample of high-resolution, high-snr quasar spectra. the quasars in our sample have ultraviolet magnitudes of m1450 ~ -27 and black hole masses of 109-1010 m⊙. our inferred proximity zone sizes are 2-7 physical mpc, with a typical uncertainty of less than 0.5 physical mpc, which, for the first time, also includes uncertainty in the quasar continuum. we find that the correlation between proximity zone sizes and the quasar redshift, luminosity, or black hole mass, indicates a large diversity of quasar lifetimes. two of our proximity zone sizes are exceptionally small. the spectrum of one of these quasars, with z = 6.02, displays, unusually for this redshift, damping wing absorption without any detectable metal lines, which could potentially originate from the igm. the other quasar has a high-ionization absorber ~0.5 pmpc from the edge of the proximity zone. this work increases the number of proximity zone measurements available in the last stages of cosmic reionization to 87. this data will lead to better constraints on quasar lifetimes and obscuration fractions at high redshift, that in turn will help probe the seed mass and formation redshift of supermassive black holes. | new quasar proximity zone size measurements at z 6 using the enlarged xqr-30 sample |
putting constraints on a possible lorentz invariance violation (liv) from astrophysical sources such as gamma-ray bursts (grbs) is essential for finding evidences of new theories of quantum gravity (qg) that predict an energy-dependent speed of light. this search has its own difficulties, so usually, the effect of the cosmological model is understudied, with the default model being a fixed-parameters λcdm.in this work, we use various astrophysical datasets to study the effect of a number of dark energy models on liv constraints. to this end, we combine two public time-delay (td) grb datasets with the supernovae pantheon dataset, several measurements of angular baryonic acoustic oscillations (bao), the cosmic microwave background (cmb) distance prior and an optional grb or quasars dataset. for the liv parameter α, we find the expected from previous works average value of $\alpha \sim 4 \times 10^{-4}$ , corresponding to $e_\textrm{qg}\geqslant 10^{17}$ gev for both td datasets, with the second one being more sensitive to the cosmological model. the cosmology results in a minimum 20% deviation in our constraints on the energy. interestingly, adding the td points makes the de models less-preferable statistically and shifts the value of the parameter $c/(h_0 r_d)$ down, making it smaller than the expected value. we observe that possible liv measurements critically depend on the transparency of the assumptions behind the published data concerning cosmology, and taking this into account may be an important contribution in the case of possible detection. | impact of cosmology on lorentz invariance violation constraints from grb time-delays |
we determine here the peculiar motion of the solar system, first time from the m-z hubble diagram of quasars. observer's peculiar motion causes a systematic shift in the m-z plane between sources lying along the velocity vector and those in the opposite direction, providing a measure of the peculiar velocity. accordingly, from a sample of ~1.2 × 105 mid-infrared quasars with measured spectroscopic redshifts, we arrive at a peculiar velocity ~22 times larger than that from the cosmic microwave background radiation (cmbr) dipole but direction matching within ~2σ. previous findings from number count, sky brightness, or redshift dipoles observed in samples of distant active galactic nuclei or supernovae type ia too had yielded values 2-10 times larger than the cmbr value, though the direction in all cases agreed with the cmbr dipole. since a genuine solar peculiar velocity cannot vary from one data set to another, an order of magnitude, statistically significant, discordant dipoles might imply that we may instead have to look for some other cause for the genesis of these dipoles, including that of the cmbr. at the same time, a common direction for all these dipoles, determined from completely independent surveys by different groups employing different techniques, might indicate that these dipoles are not resulting from some systematics in the observations or in the data analysis, but could instead suggest a preferred direction in the universe due to an inherent anisotropy, which, in turn, would be against the cosmological principle, the most basic tenet of the modern cosmology. | solar system peculiar motion from the hubble diagram of quasars and testing the cosmological principle |
the novel gaia multi peak (gmp) technique has proven to be able to successfully select dual and lensed agn candidates at sub-arcsec separations. both populations are important because dual agns represent one of the central, still largely untested, predictions of lamdacdm cosmology, and compact lensed quasars allow to probe the central regions of the lensing galaxies. in this work, we present high spatial resolution spectroscopy of twelve gmp-selected systems. we use the the adaptive-optics assisted integral-field spectrograph muse at vlt to resolve each system and study the nature of each component. all the targets reveal the presence of two components confirming the gmp selection. we classify five targets as dual agns, two as lensed systems, and five as a chance alignment of a star and and agn. having separations between 0.30" and 0.86", these dual and lensed systems are, to date, among the most compact ever discovered at z >0.3. this is the largest sample of distant dual agns with sub-arcsec separations ever presented in a single paper. | muse ao spectroscopy confirms five dual agns and two strongly lensed qsos at sub-arcsec separation |
one of the most protracted problems in astronomy has been understanding the evolution of galaxy morphology. much discussion has surrounded how lenticular galaxies may form a bridging population between elliptical and spiral galaxies. however, with recourse to a galaxy's central black hole mass, accretion-built spiral galaxies have emerged as the bridging population between low-mass lenticular galaxies and the dusty merger-built lenticular galaxies contiguous with elliptical galaxies and 'brightest cluster galaxies' in the black hole/galaxy mass diagram. spiral galaxies, including the milky way, appear built from gas accretion and minor mergers onto what were initially lenticular galaxies. these connections are expressed as a new morphology sequence, dubbed the 'triangal', which subsumes elements of the hubble sequence and the van den bergh trident and reveals the bridging nature of the often overlooked ellicular galaxies. furthermore, a quadratic black hole/galaxy mass relation is found to describe ordinary elliptical galaxies. the relation is roughly parallel to the quadratic-like relations observed for the central spheroidal component of spiral galaxies, dust-rich lenticular galaxies, and old dust-poor lenticular galaxies. the brightest cluster galaxies are offset according to expectations from an additional major merger. the findings have implications for feedback from active galactic nuclei, mapping morphology into simulations, and predicting gravitational wave signals from colliding supermassive black holes. a new galaxy speciation model is presented. it disfavours the 'monolithic collapse' scenario for spiral, dusty lenticular, and elliptical galaxies. it reveals substantial orbital angular momentum in the universe's first galaxies and unites dwarf and ordinary 'early-type' galaxies. | resequencing the hubble sequence and the quadratic (black hole mass)-(spheroid stellar mass) relation for elliptical galaxies |
large-scale magnetic fields in the nuclear regions of protogalaxies can promote the formation and early growth of supermassive black holes (smbhs) by direct collapse and magnetically boosted accretion. turbulence associated with gravitational infall and star formation can drive the rms field strength toward equipartition with the mean gas kinetic energy; this field has a generic tendency to self-organize into large coherent structures. if the poloidal component of the field (relative to the rotational axis of a star-forming disc) becomes organized on scales ≲r and attains an energy of order a few per cent of the turbulent energy in the disc, then dynamo effects are expected to generate magnetic torques capable of increasing the inflow speed and thickening the disc. the accretion flow can transport matter towards the centre of mass at a rate adequate to create and grow a massive direct-collapse black hole seed and fuel the subsequent agn at a high rate, without becoming gravitationally unstable. fragmentation and star formation are thus suppressed and do not necessarily deplete the mass supply for the accretion flow, in contrast to prevailing models for growing and fuelling smbhs through disc accretion. | magnetic fields catalyse massive black hole formation and growth |
modern hydrodynamical simulations reproduce many properties of the real universe. these simulations model various physical processes, but many of these are included using 'subgrid models' due to resolution limits. although different subgrid models have been successful in modelling the effects of supernovae (sne) and active galactic nuclei (agns) feedback on galactic properties, it remains unclear if, and by how much, these differing implementations affect observable halo gas properties. in this work, we use 'zoom-in' cosmological initial conditions of two volumes selected to resemble the local group (lg) evolved with both the auriga and apostle galaxy formation models. while the subgrid physics models in both simulations reproduce realistic stellar components of l⋆ galaxies, they exhibit different gas properties. namely, auriga predicts that the milky way is almost baryonically closed, whereas apostle suggests that only half of the expected baryons reside within the halo. furthermore, apostle predicts that this baryon deficiency extends to the lg (r ≤ 1 mpc). some of the baryon deficiency in apostle is due to sne feedback at high redshift, which generates halo-wide outflows, with high covering fractions and radial velocities, which both eject baryons and significantly impede cosmic gas accretion. conversely, in auriga, gas accretion into the halo appears to be almost unaffected by feedback. these differences appear to result from the different energy injection methods from feedback (both sne and agns) to gas. our results suggest that both quasar absorption lines and fast radio burst dispersion measures could constrain these two regimes with future observations. | apostle-auriga: effects of different subgrid models on the baryon cycle around milky way-mass galaxies |
we present a comprehensive 5-43 ghz vlba study of the blazar 3c 273 initiated after an onset of a strong γ-ray flare in this source. we have analysed the kinematics of newborn components, light curves and position of the apparent core to pinpoint the location of the γ-ray emission. estimated location of the γ-ray emission zone is close to the jet apex, 2-7 pc upstream from the observed 7 mm core. this is supported by ejection of a new component. the apparent core position was found to be inversely proportional to frequency. the brightness temperature in the 7 mm core reached values up to at least 1013 k during the flare. this supports the dominance of particle energy density over that of magnetic field in the 7 mm core. particle density increased during the radio flare at the apparent jet base, affecting synchrotron opacity. this manifested itself as an apparent core shuttle along the jet during the 7 mm flare. it is also shown that a region where optical depth decreases from τ ∼ 1 to τ ≪ 1 spans over several parsecs along the jet. the jet bulk flow speed estimated at the level of 12c on the basis of time lags between 7 mm light curves of stationary jet features is 1.5 times higher than that derived from very long baseline interferometry apparent kinematics analysis. | a connection between γ-ray and parsec-scale radio flares in the blazar 3c 273 |
the mechanisms that bring galaxies to strongly reduce their star formation activity (star-formation quenching) remain poorly understood. to better study galaxy evolution, we propose a classification based on maps of ionised hydrogen distribution traced by the kiloparsec-resolved, equivalent width of hα maps, and the nuclear activity of the galaxies using information from the baldwin-philips-terlevich diagnostic diagrams. using these tools, we group a sample of 238 galaxies from the calar alto legacy integral field spectroscopy area survey in six quenching stages (qss): (i) objects dominated by recent star formation; (ii) systems that present a quiescent-nuclear-ring structure in their centre; (iii) galaxies that are centrally quiescent; (iv) galaxies with no clear pattern in their ionisation gas distribution (mixed); (v) systems that posses only a few star-forming regions (nearly retired), or (vi) galaxies that are completely quiescent (fully retired). regarding their nuclear activity, we further divide the galaxies into two groups: active systems that host a weak or strong active galactic nucleus (agn) at their centre, and non-active objects. galaxies grouped into quenching-stage classes occupy specific locations on the star-formation-rate versus stellar mass diagram. the `blue cloud' is populated by the star-forming and the quiescent-nuclear-ring galaxies, the `green valley' is populated by centrally quiescent and mixed systems, and the `red sequence' by the nearly- and fully retired objects. generally, galaxies that host a weak or strong agn show properties comparable to those of their non-active counterparts at the same qss, except for the agn-hosting star-forming systems. the degree of star-formation quenching increases along the present emission-line pattern sequence from star-forming to fully retired. the proposed emission-line classes reinforce the `inside-out' quenching scenario, which foresees that the suppression of star formation begins from the central regions of the galaxies. | star formation quenching stages of active and non-active galaxies |
galaxies and galaxy groups located along the line of sight towards gravitationally lensed quasars produce high-order perturbations of the gravitational potential at the lens position. when these perturbation are too large, they can induce a systematic error on h0 of a few per cent if the lens system is used for cosmological inference and the perturbers are not explicitly accounted for in the lens model. in this work, we present a detailed characterization of the environment of the lens system wfi 2033-4723 (z_src = 1.662, z_lens= 0.6575), one of the core targets of the h0licow project for which we present cosmological inferences in a companion paper. we use the gemini and eso-very large telescopes to measure the spectroscopic redshifts of the brightest galaxies towards the lens, and use the eso-muse integral field spectrograph to measure the velocity-dispersion of the lens (σ _{los}= 250^{+15}_{-21} km s-1) and of several nearby galaxies. in addition, we measure photometric redshifts and stellar masses of all galaxies down to i < 23 mag, mainly based on dark energy survey imaging (dr1). our new catalogue, complemented with literature data, more than doubles the number of known galaxy spectroscopic redshifts in the direct vicinity of the lens, expanding to 116 (64) the number of spectroscopic redshifts for galaxies separated by less than 3 arcmin (2 arcmin ) from the lens. using the flexion-shift as a measure of the amplitude of the gravitational perturbation, we identify two galaxy groups and three galaxies that require specific attention in the lens models. the eso muse data enable us to measure the velocity-dispersions of three of these galaxies. these results are essential for the cosmological inference analysis presented in rusu et al. | h0licow - x. spectroscopic/imaging survey and galaxy-group identification around the strong gravitational lens system wfi 2033-4723 |
large-scale outflows are believed to be an important mechanism in the evolution of galaxies. we can determine the impact of these outflows by studying either current galaxy outflows and their effect in the galaxy or by studying the effect of past outflows on the gas surrounding the galaxy. in this work, we examine the co(7-6), [c i] ($^{3} \rm p_{1} \rightarrow {\rm ^3 p}_{0}$), h2o 211-202, and dust continuum emission of 15 extremely red quasars at z ~ 2.3 using alma. by investigating the radial surface brightness profiles of both the individual sources and the stacked emission, we detect extended cold gas and dust emission on scales of ~14 kpc in co(7-6), [c i](2-1), and dust continuum. this is the first time that the presence of a large amount of molecular gas was detected on large, circumgalactic medium scales around quasar host galaxies using [c i] extended emission. we estimate the dust and molecular gas mass of these haloes to be 107.6 and 1010.6 m⊙, indicating significant dust and molecular gas reservoirs around these extreme quasars. by estimating the time-scale at which this gas can reach these distances by molecular gas outflows (7-32 myr), we conclude that these haloes are a relic of past agn or starburst activity, rather than an effect of the current episode of extreme quasar activity. | evidence of extended cold molecular gas and dust haloes around z 2.3 extremely red quasars with alma |
we investigate the abundance and distribution of metals in the high-redshift intergalactic medium and circum-galactic medium through the analysis of a sample of almost 600 si iv absorption lines detected in high- and intermediate-resolution spectra of 147 quasars. the evolution of the number density of si iv lines, the column density distribution function, and the cosmic mass density are studied in the redshift interval 1.7 ≲ z ≲ 6.2 and for log n(si iv) ≥ 12.5. all quantities show a rapid increase between z ~ 6 and z ≲ 5 and then an almost constant behaviour to z ~ 2 in very good agreement with what is already observed for c iv absorption lines. the present results are challenging for numerical simulations: when simulations reproduce our si iv results, they tend to underpredict the properties of c iv, and when the properties of c iv are reproduced, the number of strong si iv lines [log n(si iv) > 14] is overpredicted. | the evolution of the si iv content in the universe from the epoch of reionization to cosmic noon |
we reanalyze the mid-infrared (5-40 μm) spitzer spectra of 86 low-redshift (z < 0.5) palomar-green quasars to investigate the nature of polycyclic aromatic hydrocarbon (pah) emission and its utility as a star formation rate (sfr) indicator for the host galaxies of luminous active galactic nuclei (agns). we decompose the spectra with our recently developed template-fitting technique to measure pah fluxes and upper limits, which we interpret using mock spectra that simulate the effects of agn dilution. while luminous quasars can severely dilute and affect the detectability of emission lines, pahs are intrinsically weak in some sources that are otherwise gas-rich and vigorously forming stars, conclusively demonstrating that powerful agns destroy pah molecules. comparing pah-based sfrs with independent sfrs derived from the mid-infrared fine-structure neon lines and the total infrared luminosity reveals that pahs can trace star formation activity in quasars with bolometric luminosities ≲1046 erg s-1, but increasingly underestimate the sfr for more powerful quasars, typically by ~0.5 dex. relative to star-forming galaxies and low-luminosity agns, quasars have a comparable pah 11.3 μm/7.7 μm ratio but characteristically lower ratios of 6.2 μm/7.7 μm, 8.6 μm/7.7 μm, and 11.3 μm/17.0 μm. we suggest that these trends indicate that powerful agns preferentially destroy small grains and enhance the pah ionization fraction. | the ionization and destruction of polycyclic aromatic hydrocarbons in powerful quasars |
we totally published 9,026,365 targets in this table, including 8,183,160 stars, 152,863 galaxies, 52,453 quasars, and 637,889 unknown objects. in addition, there are 5,808,985 objects with g band s/ns larger than 10, 7,701,235 objects with i band s/ns larger than 10, and 5,734,239 objects with g band s/ns larger than 10 and i band s/ns larger than 10. on the website http://dr5.lamost.org/catalogue, we provide two format lamost general catalogs, which include a fits table and a csv table, and the two catalog files have the same contents. (5 data files). | vizier online data catalog: lamost dr5 catalogs (luo+, 2019) |
we conduct a comprehensive study of the effects of incorporating galaxy morphology information in photometric redshift estimation. using machine learning methods, we assess the changes in the scatter and outlier fraction of photometric redshifts when galaxy size, ellipticity, sérsic index, and surface brightness are included in training on galaxy samples from the sdss and the cfht stripe-82 survey (cs82). we show that by adding galaxy morphological parameters to full ugriz photometry, only mild improvements are obtained, while the gains are substantial in cases where fewer passbands are available. for instance, the combination of grz photometry and morphological parameters almost fully recovers the metrics of 5-band photometric redshifts. we demonstrate that with morphology it is possible to determine useful redshift distribution n(z) of galaxy samples without any colour information. we also find that the inclusion of quasar redshifts and associated object sizes in training improves the quality of photometric redshift catalogues, compensating for the lack of a good star-galaxy separator. we further show that morphological information can mitigate biases and scatter due to bad photometry. as an application, we derive both point estimates and posterior distributions of redshifts for the official cs82 catalogue, training on morphology and sdss stripe-82 ugriz bands when available. our redshifts yield a 68th percentile error of 0.058(1 + z), and a outlier fraction of 5.2 per cent. we further include a deep extension trained on morphology and single i-band cs82 photometry. | morpho-z: improving photometric redshifts with galaxy morphology |
we present a spectroscopically complete sample of 147 infrared-color-selected active galactic nuclei (agns) down to a 22 μm flux limit of 20 mjy over the ∼270 deg2 of the sloan digital sky survey stripe 82 region. most of these sources are in the qso luminosity regime (l bol ≳ 1012 l ⊙) and are found out to z ≃ 3. we classify the agns into three types, finding 57 blue, unobscured type-1 (broad-lined) sources; 69 obscured, type-2 (narrow-lined) sources; and 21 moderately reddened type-1 sources (broad-lined and e(b - v) > 0.25). we study a subset of this sample in x-rays and analyze their obscuration to find that our spectroscopic classifications are in broad agreement with low, moderate, and large amounts of absorption for type-1, red type-1, and type-2 agns, respectively. we also investigate how their x-ray luminosities correlate with other known bolometric luminosity indicators such as [o iii] line luminosity (l [o iii]) and infrared luminosity (l 6μm). while the x-ray correlation with l [o iii] is consistent with previous findings, the most infrared-luminous sources appear to deviate from established relations such that they are either underluminous in x-rays or overluminous in the infrared. finally, we examine the luminosity function evolution of our sample, and by agn type, in combination with the complementary, infrared-selected, agn sample of lacy et al. (2013), spanning over two orders of magnitude in luminosity. we find that the two obscured populations evolve differently, with reddened type-1 agns dominating the obscured agn fraction (∼30%) for l 5μm > 1045 erg s-1, while the fraction of type-2 agns with l 5μm < 1045 erg s-1 rises sharply from 40% to 80% of the overall agn population. based in part on data obtained at the w. m. keck observatory, which is operated as a scientific partnership among the california institute of technology, the university of california, and nasa and was made possible by the generous financial support of the w. m. keck foundation. | luminous wise-selected obscured, unobscured, and red quasars in stripe 82 |
we investigate the effects of extended multiyear light curves (9 yr photometry and 5 yr spectroscopy) on the detection of time lags between the continuum variability and broad-line response of quasars at z ≳ 1.5, and compare with the results using 4 yr photometry+spectroscopy presented in a companion paper. we demonstrate the benefits of the extended light curves in three cases: (1) lags that are too long to be detected by the shorter-duration data but can be detected with the extended data; (2) lags that are recovered by the extended light curves but are missed in the shorter-duration data due to insufficient light-curve quality; and (3) lags for different broad-line species in the same object. these examples demonstrate the importance of long-term monitoring for reverberation mapping to detect lags for luminous quasars at high redshift, and the expected performance of the final data set from the sloan digital sky survey reverberation mapping project that will have 11 yr photometric and 7 yr spectroscopic baselines. | the sloan digital sky survey reverberation mapping project: improving lag detection with an extended multiyear baseline |
the origin of supermassive black holes (smbhs) in galactic nuclei is one of the major unsolved problems in astrophysics. one hypothesis is that they grew from ≳ 105 m⊙ black holes that formed in the `direct collapse' of massive gas clouds that have low concentrations of both metals and molecular hydrogen (h2). such clouds could form in the early (z ≳ 10) universe if pre-galactic gas is irradiated by h2-photodissociating, far-ultraviolet (fuv) light from a nearby star-forming galaxy. in this work, we re-examine the critical fuv flux jcrit that is required to keep h2 photodissociated and lead to direct collapse. we submit that the same galaxies that putatively supply the extraordinary fuv fluxes required for direct collapse should also produce copious amounts of soft x-rays, which work to offset h2 photodissociation by increasing the ionization fraction and promoting h2 formation. accounting for this effect increases the value of jcrit by a factor of at least 3-10, depending on the brightness temperature of fuv radiation. this enhancement of jcrit suppresses the abundance of potential direct collapse sites at z > 10 by several orders of magnitude. recent studies - without accounting for the soft x-rays from the fuv source galaxies - had already arrived at large values of jcrit that implied that direct collapse may occur too rarely to account for the observed abundance of high-redshift quasars. our results suggest that jcrit should be even higher than previously estimated, and pose an additional challenge for the direct collapse scenario via strong fuv radiation to explain the high-redshift quasar population. | the suppression of direct collapse black hole formation by soft x-ray irradiation |
we report a candidate centi-parsec supermassive black hole binary (smbhb) in the radio-quiet quasar sdss j0159+0105 at z = 0.217. with a modified lomb-scargle code (glsdedrw) and auto-correlation analysis, we detect two significant (at p > 99%) periodic signals at ∼741 day and ∼1500 day from the 8.1 yr catalina v-band light curve of this quasar. the period ratio, which is close to 1:2, is typical of a black hole binary system with a mass ratio of 0.05 < q < 0.8 according to recent numerical simulations. sdss j0159+0105 has two sdss spectroscopic observations separated by ∼10 yr. there is a significant change in the broad hβ profile between the two epochs, which can be explained by a single broad-line region (blr) around the binary system illuminated by the aforementioned mini-disks, or a stream of gas flowing from the circumbinary disk to one of the smbhs. from the single blr assumption and the orbital period t orb ∼ 1500 day, we estimate the total virial masses of m smbhb ∼ 1.3 × 108 m ⊙, the average distances of blr of ∼0.04 pc (∼50 lt-day, with ±0.3 dex uncertainty), and an smbhb separation of d = (0.01 pc){m}8,{tot}1/3 (t rest/3.3 yr)2/3 ∼ 0.013 pc (15 lt-day). based on analytical work, the postulated circumbinary disk has an inner radius of 2d = 0.026 pc (30 lt-day). sdss j0159+0105 also displays unusual spectral energy distribution. the unique properties of sdss j0159+0105 are consistent with it being a centi-parsec smbhb. this paper uses data from the sloan digital sky survey (sdss), catalina real-time transient survey (crts), swift, galex, 2mass, and wise archive. | sdss j0159+0105: a radio-quiet quasar with a centi-parsec supermassive black hole binary candidate |
we present a catalog of quasars with their corresponding redshifts derived from the photometric kilo-degree survey (kids) data release 4. we achieved it by training machine learning (ml) models, using optical ugri and near-infrared zyjhks bands, on objects known from sloan digital sky survey (sdss) spectroscopy. we define inference subsets from the 45 million objects of the kids photometric data limited to 9-band detections, based on a feature space built from magnitudes and their combinations. we show that projections of the high-dimensional feature space on two dimensions can be successfully used, instead of the standard color-color plots, to investigate the photometric estimations, compare them with spectroscopic data, and efficiently support the process of building a catalog. the model selection and fine-tuning employs two subsets of objects: those randomly selected and the faintest ones, which allowed us to properly fit the bias versus variance trade-off. we tested three ml models: random forest (rf), xgboost (xgb), and artificial neural network (ann). we find that xgb is the most robust and straightforward model for classification, while ann performs the best for combined classification and redshift. the ann inference results are tested using number counts, gaia parallaxes, and other quasar catalogs that are external to the training set. based on these tests, we derived the minimum classification probability for quasar candidates which provides the best purity versus completeness trade-off: p(qsocand) > 0.9 for r < 22 and p(qsocand) > 0.98 for 22 < r < 23.5. we find 158 000 quasar candidates in the safe inference subset (r < 22) and an additional 185 000 candidates in the reliable extrapolation regime (22 < r < 23.5). test-data purity equals 97% and completeness is 94%; the latter drops by 3% in the extrapolation to data fainter by one magnitude than the training set. the photometric redshifts were derived with ann and modeled with gaussian uncertainties. the test-data redshift error (mean and scatter) equals 0.009 ± 0.12 in the safe subset and −0.0004 ± 0.19 in the extrapolation, averaged over a redshift range of 0.14 < z < 3.63 (first and 99th percentiles). our success of the extrapolation challenges the way that models are optimized and applied at the faint data end. the resulting catalog is ready for cosmology and active galactic nucleus (agn) studies. a copy of the catalog 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/649/a81 we publicly release the catalog at https://kids.strw.leidenuniv.nl/dr4/quasarcatalog.php and the code at github.com/snakoneczny/kids-quasars | photometric selection and redshifts for quasars in the kilo-degree survey data release 4 |
narrow-line seyfert 1 galaxies (nls1s) are an interesting subclass of active galactic nuclei (agn), which tipically does not exhibit any strong radio emission. seven percent of them, though, are radio-loud and often show a flat radio-spectrum (f-nls1s). this, along to the detection of γ-ray emission coming from them, is usually interpreted as a sign of a relativistic beamed jet oriented along the line of sight. an important aspect of these agn that must be understood is the nature of their parent population, in other words how do they appear when observed under different angles. in the recent literature it has been proposed that a specific class of radio-galaxies, compact-steep sources (css) classified as high excitation radio galaxies (herg), can represent the parent population of f-nls1s. to test this hypothesis in a quantitative way,in this paper we analyzed the only two statistically complete samples of css/hergs and f-nls1s available in the literature. we derived the black hole mass and eddington ratio distributions, and we built for the first time the radio luminosity function of f-nls1s. finally, we applied a relativistic beaming model to the luminosity function of css/hergs, and compared the result with the observed function of f-nls1s. we found that compact steep-spectrum sources are valid parent candidates and that f-nls1s, when observed with a different inclination, might actually appear as css/hergs. | compact steep-spectrum sources as the parent population of flat-spectrum radio-loud narrow-line seyfert 1 galaxies |
we use the high-resolution simulation massiveblackii to examine scaling relations between black hole (bh) mass and host galaxy properties (σ, total m* and lv), finding good agreement with recent observational data, especially at the high-mass end. we find gaussian intrinsic scatter (∼half the observed scatter) about all three relations, except among the most massive objects. below z ∼ 2 the slope of the relations remain roughly z-independent, and only steepen by 50 per cent by z ∼ 4. the normalization of the σ, lv relations evolve by 0.3, 0.43 dex, while the m* correlation does not evolve out to at least z ∼ 2. testing for selection biases, we find mbh- or m*-selected samples have steeper slopes than random samples, suggesting a constant-mass selection function can exhibit faster evolution than a random sample. we find a potential bias among high-lbh subsamples due to their more massive hosts, but that bright (active) active galactic nuclei exhibit no intrinsic bias relative to fainter (inactive) bhs in equivalent-mass hosts. finally, we show that bhs below the local relation tend to grow faster than their host (72 per cent of bhs >0.3 dex below the mean relation have an mbh-m* trajectory steeper than the local relation), while those above have shallower trajectories (only 14 per cent are steeper than local). thus bhs tend to grow faster than their hosts until surpassing the local relation, when their growth is suppressed, bringing them back towards the mean relation. | scaling relations between black holes and their host galaxies: comparing theoretical and observational measurements, and the impact of selection effects |
accretion is thought to primarily contribute to the mass accumulation history of supermassive black holes (smbhs) throughout cosmic time. while this may be true at high redshifts, at lower redshifts and for the most massive black holes (bhs) mergers themselves might add significantly to the mass budget. we explore this in two disparate environments—a massive cluster and a void region. we evolve smbhs from 4 > z > 0 using merger trees derived from hydrodynamical cosmological simulations of these two regions, scaled to the observed value of the stellar mass fraction to account for overcooling. mass gains from gas accretion proportional to bulge growth and bh-bh mergers are tracked, as are bhs that remain "orbiting" due to insufficient dynamical friction in a merger remnant, as well as those that are ejected due to gravitational recoil. we find that gas accretion remains the dominant source of mass accumulation in almost all smbhs; mergers contribute 2.5% ± 0.1% for all smbhs in the cluster and 1.0% ± 0.1% in the void since z = 4. however, mergers are significant for massive smbhs. the fraction of mass accumulated from mergers for central bhs generally increases for larger values of the host bulge mass: in the void, the fraction is 2% at m *, bul = 1010 m ⊙, increasing to 4% at m *, bul >~ 1011 m ⊙, and in the cluster it is 4% at m *, bul = 1010 m ⊙ and 23% at 1012 m ⊙. we also find that the total mass in orbiting smbhs is negligible in the void, but significant in the cluster, in which a potentially detectable 40% of smbhs and ≈8% of the total smbh mass (where the total includes central, orbiting, and ejected smbhs) is found orbiting at z = 0. the existence of orbiting and ejected smbhs requires modification of the soltan argument. we estimate this correction to the integrated accreted mass density of smbhs to be in the range 6%-21%, with a mean value of 11% ± 3%. quantifying the growth due to mergers at these late times, we calculate the total energy output and strain from gravitational waves emitted by merging smbhs, and obtain a signal potentially detectable by pulsar timing arrays. | understanding black hole mass assembly via accretion and mergers at late times in cosmological simulations |
we discuss 76 large amplitude transients (δm > 1.5) occurring in the nuclei of galaxies, nearly all with no previously known active galactic nucleus (agn). they have been discovered as part of the pan-starrs1 (ps1) 3π survey, by comparison with sloan digital sky survey (sdss) photometry a decade earlier, and then monitored with the liverpool telescope, and studied spectroscopically with the william herschel telescope (wht). based on colours, light-curve shape, and spectra, these transients fall into four groups. a few are misclassified stars or objects of unknown type. some are red/fast transients and are known or likely nuclear supernovae. a few are either radio sources or erratic variables and so likely blazars. however the majority (∼66 per cent) are blue and evolve slowly, on a time-scale of years. spectroscopy shows them to be agn at z ∼ 0.3 - 1.4, which must have brightened since the sdss photometry by around an order of magnitude. it is likely that these objects were in fact agn a decade ago, but too weak to be recognized by sdss; they could then be classed as `hypervariable' agn. by searching the sdss stripe 82 quasar database, we find 15 similar objects. we discuss several possible explanations for these slow-blue hypervariables - (i) unusually luminous tidal disruption events; (ii) extinction events; (iii) changes in accretion state; and (iv) large amplitude microlensing by stars in foreground galaxies. a mixture of explanations (iii) and (iv) seems most likely. both hold promise of considerable new insight into the agn phenomenon. | slow-blue nuclear hypervariables in panstarrs-1 |
we introduce an intrinsic lyα emission-line profile reconstruction method for high-z quasars (qsos). this approach utilises a covariance matrix of emission-line properties obtained from a large, moderate-z (2 ≤ z ≤ 2.5), high signal to noise (s/n > 15) sample of boss qsos. for each qso, we complete a monte carlo markov chain fitting of the continuum and emission-line properties and perform a visual quality assessment to construct a large data base of robustly fit spectra. with this data set, we construct a covariance matrix to describe the correlations between the high-ionization emission lines lyα, c iv, si iv +o iv] and c iii], and find it to be well approximated by an n-dimensional gaussian distribution. this covariance matrix characterizes the correlations between the linewidth, peak height and velocity offset from systemic while also allowing for the existence of broad- and narrow-line components for lyα and c iv. we illustrate how this covariance matrix allows us to statistically characterize the intrinsic lyα line solely from the observed spectrum redward of 1275 å. this procedure can be used to reconstruct the intrinsic lyα line emission profile in cases where lyα may otherwise be obscured. applying this reconstruction method to our sample of qsos, we recovered the lyα line flux to within 15 per cent of the measured flux at 1205 å (1220 å) ∼85 (90) per cent of the time. | lyα emission-line reconstruction for high-z qsos |
supermassive binary black holes at subparsec orbital separations have yet to be discovered, with the possible exception of blazar oj 287. in parallel to the global hunt for nanohertz gravitational waves from supermassive binaries using pulsar timing arrays, there has been a growing sample of candidates reported from electromagnetic surveys, particularly searches for periodic variations in the optical light curves of quasars. however, the periodicity search is prone to false positives from quasar red noise and quasiperiodic oscillations from the accretion disk of a single supermassive black hole, especially when the data span fewer than a few signal cycles. we present a bayesian method for the detection of quasar (quasi)periodicity in the presence of red noise. we apply this method to the binary candidate pg 1302-102 and show that (a) there is very strong support (bayes factor >106) for quasiperiodicity and (b) the data slightly favor a quasiperiodic oscillation over a sinusoidal signal, which we interpret as modest evidence against the binary black hole hypothesis. we also find that the prevalent damped random walk red-noise model is disfavored with more than 99.9% credibility. finally, we outline future work that may enable the unambiguous identification of supermassive binary black holes. | toward the unambiguous identification of supermassive binary black holes through bayesian inference |
primordial supermassive stars (smss) formed in atomic-cooling halos at z ~ 15-20 are leading candidates for the seeds of the first quasars. past numerical studies of the evolution of smss have typically assumed constant accretion rates rather than the highly variable flows in which they form. we model the evolution of smss in the cosmological flows that create them using the kepler stellar evolution and implicit hydrodynamics code. we find that they reach masses of 1 - 2 × 105 m⊙ before undergoing direct collapse to black holes (dcbhs) during or at the end of their main-sequence hydrogen burning, at 1-1.5 myr, regardless of halo mass, spin, or merger history. we also find that realistic, highly variable accretion histories allow for a much greater diversity of supermassive stellar structures, including in some cases largely thermally relaxed objects, which may provide a significant source of radiative feedback. our models indicate that the accretion histories predicted for purely atomic-cooling halos may impose a narrow spectrum of masses on the seeds of the first massive quasars; however, further studies incorporating realistic feedback will be essential in order to confirm whether or not this holds true in all cases. our results also indicate that multiple smss at disparate stages of evolution can form in these halos, raising the possibility of sms binaries and supermassive x-ray binaries, as well as dcbh mergers that could be detected by lisa. | on the evolution of supermassive primordial stars in cosmological flows |
massive black hole binaries (mbhbs) form as a consequence of galaxy mergers. however, it is still unclear whether they typically merge within a hubble time, and how accretion may affect their evolution. these questions will be addressed by pulsar timing arrays (ptas), which aim to detect the gravitational wave (gw) background (gwb) emitted by mbhbs during the last myr of inspiral. here, we investigate the influence of differential accretion on mbhb merger rates, chirp masses, and the resulting gwb spectrum. we evolve an mbhb sample from the illustris hydrodynamic cosmological simulation using semi-analytical models and for the first time self-consistently evolve their masses with binary accretion models. in all models, mbhbs coalesce with median total masses up to 1.5 × 108 m⊙, up to 3-4 times larger than in models neglecting accretion. in our model with the largest plausible impact, the median mass ratio of coalescing mbhbs increases by a factor 3.6, the coalescence rate by $52.3{{\ \rm per\ cent}}$ , and the gwb amplitude by a factor 4.0, yielding a dimensionless gwb strain $a_{yr^{-1}} = 1 \times 10^{-15}$ . our model that favours accretion on to the primary mbh reduces the median mass ratio of coalescing mbhbs by a factor of 2.9, and yields a gwb amplitude $a_{yr^{-1}} = 3.1 \times 10^{-16}$ . this is nearly indistinguishable from our model neglecting accretion, despite higher mbhb masses at coalescence. we further predict binary separation and mass ratio distributions of stalled mbhbs in the low-redshift universe, and find that these depend sensitively on binary accretion models. this presents the potential for combined electromagnetic and gw observational constraints on merger rates and accretion models of mbhb populations. | the effect of differential accretion on the gravitational wave background and the present-day mbh binary population |
in this paper we use a newly compiled sample of ultra-compact structure in radio quasars and strong gravitational lensing systems with quasars acting as background sources to constrain six spatially flat and non-flat cosmological models (λcdm, pede, and dgp). these two sets of quasar data (time-delay measurements of six strong lensing systems and 120 intermediate-luminosity quasars calibrated as standard rulers) could break the degeneracy between the cosmological parameters (h0, ωm, and ωk), and therefore provide more stringent cosmological constraints for the six cosmological models we study. a joint analysis of the quasar sample provides model-independent measurements of the hubble constant h0, which are strongly consistent with that derived from the local distance ladder by the sh0es collaboration in the λcdm and pede model. however, in the framework of the dgp cosmology (especially for a flat universe), the measured hubble constant is in good agreement with that derived from the recent planck 2018 results. in addition, our results show that zero spatial curvature is supported by the current lensed and unlensed quasar observations and that there is no significant deviation from a flat universe. for most of the cosmological models we study (flat λcdm, non-flat λcdm, flat pede, and non-flat pede), the derived matter density parameter is completely consistent with ωm ∼ 0.30 in all the data sets, as expected based on the latest cosmological observations. finally, according to the statistical deviance information criterion (dic), the joint constraints provide substantial observational support to the flat pede model; however, they do not rule out dark energy being a cosmological constant and non-flat spatial hypersurfaces. | revising the hubble constant, spatial curvature and dark energy dynamics with the latest observations of quasars |
we present atacama large millimeter/submillimeter array (alma) sub-kiloparsec- to kiloparsec-scale resolution observations of the [c ii], co (9-8), and oh+ (11-01) lines along with their dust continuum emission toward the far-infrared (fir) luminous quasar sdss j231038.88+185519.7 at z = 6.0031, to study the interstellar medium distribution, the gas kinematics, and the quasar-host system dynamics. we decompose the intensity maps of the [c ii] and co (9-8) lines and the dust continuum with two-dimensional elliptical sérsic models. the [c ii] brightness follows a flat distribution with a sérsic index of 0.59. the co (9-8) line and the dust continuum can be fit with an unresolved nuclear component and an extended sérsic component with a sérsic index of ∼1, which may correspond to the emission from an active galactic nucleus dusty molecular torus and a quasar host galaxy, respectively. the different [c ii] spatial distribution may be due to the effect of the high dust opacity, which increases the fir background radiation on the [c ii] line, especially in the galaxy center, significantly suppressing the [c ii] emission profile. the dust temperature drops with distance from the center. the effective radius of the dust continuum is smaller than that of the line emission and the dust mass surface density, but is consistent with that of the star formation rate surface density. this may indicate that the dust emission is a less robust tracer of the dust and gas distribution but is a decent tracer of the obscured star formation activity. the oh+ (11-01) line shows a p-cygni profile with an absorption at ∼-400 km s−1, which may indicate an outflow with a neutral gas mass of (6.2 ± 1.2)×108 m⊙ along the line of sight. we employed a three-dimensional tilted ring model to fit the [c ii] and co (9-8) data cubes. the two lines are both rotation dominated and trace identical disk geometries and gas motions. this suggest that the [c ii] and co (9-8) gas are coplanar and corotating in this quasar host galaxy. the consistent circular velocities measured with [c ii] and co (9-8) lines indicate that these two lines trace a similar gravitational potential. we decompose the circular rotation curve measured from the kinematic model fit to the [c ii] line into four matter components (black hole, stars, gas, and dark matter). the quasar-starburst system is dominated by baryonic matter inside the central few kiloparsecs. we constrain the black hole mass to be 2.97+0.51-0.77 × 109 m⊙; this is the first time that the dynamical mass of a black hole has been measured at z ∼ 6. this mass is consistent with that determined using the scaling relations from quasar emission lines. a massive stellar component (on the order of 109 m⊙) may have already existed when the universe was only ∼0.93 gyr old. the relations between the black hole mass and the baryonic mass of this quasar indicate that the central supermassive black hole may have formed before its host galaxy. | the interstellar medium distribution, gas kinematics, and system dynamics of the far-infrared luminous quasar sdss j2310+1855 at z = 6.0 |
blazars are a peculiar class of active galactic nuclei that enlighten the sky at all wavelengths. the electromagnetic emission of these sources is jet-dominated, resulting in a spectral energy distribution (sed) that has a typical double-humped shape. x-ray photons provide a wealth of information on the physics of each source as in the x-ray band, we can observe the tail of sed first peak, the rise of the second one or the transition between the two. nustar, thanks to its capability of focusing x-rays up to 79 kev provides broad-band data particularly suitable to compute seds in a still poorly explored part of the spectrum. in the context of the open universe initiative, we developed a dedicated pipeline, nustar_spectra, a shell-script that automatically downloads data from the archive, generates scientific products and carries out a complete spectral analysis. the script homogeneously extracts high level scientific products for both nustar's telescopes and the spectral characterization is performed testing two phenomenological models. the corresponding x-ray properties are derived from the data best fit, and the seds are also computed. the systematic processing of all blazar observations of the nustar public archive allowed us to release the first hard x-ray spectroscopic catalogue of blazars (nublazar). the catalogue, updated to 2021 september 30, includes 253 observations of 126 distinct blazars, 30 of which have been multiply observed. | the first hard x-ray spectral catalogue of blazars observed by nustar |
we study the demographics of z ~ 6 broad-line quasars in the black hole (bh) mass-luminosity plane using a sample of more than 100 quasars at 5.7 < z < 6.5. these quasars have well-quantified selection functions and nearly one-third of them also have virial bh masses estimated from near-ir spectroscopy. we use forward modelling of parametrized intrinsic distributions of bh masses and eddington ratios, and account for the sample flux limits and measurement uncertainties of the bh masses and luminosities. we find significant differences between the intrinsic and observed distributions of the quantities due to measurement uncertainties and sample flux limits. there is also marginal evidence that the virial bh masses are susceptible to a positive luminosity-dependent bias (bh mass is overestimated when luminosity is above the average), and that the mean eddington ratio increases with bh mass. our models provide reliable constraints on the z ~ 6 bh mass function at $m_{\rm bh}\gt 10^{8.5}\, m_\odot$, with a median 1σ uncertainty of ~0.5 dex in abundance. the intrinsic eddington ratio distribution of $m_{\rm bh}\gt 10^{8.5}\, m_\odot$ quasars can be approximated by a mass-dependent schechter model, with a broad peak around log (lbol/ledd) ~ -0.9. we also find that, at 4.5 ≲ z ≲ 6, the number densities of more massive bhs tend to decline more rapidly with increasing redshift, contrary to the trend at 2.5 ≲ z ≲ 4.5 reported previously. | demographics of z 6 quasars in the black hole mass-luminosity plane |
high resolution spectra of quasar absorption systems provide the best constraints on temporal or spatial changes of fundamental constants in the early universe. an important systematic that has never before been quantified concerns model non-uniqueness. the absorption structure is generally complicated, comprising many blended lines. this characteristic means any given system can be fitted equally well by many slightly different models, each having a different value of α, the fine structure constant. we use ai monte carlo modelling to quantify non-uniqueness. extensive supercomputer calculations are reported, revealing new systematic effects that guide future analyses: (i) whilst higher signal to noise and improved spectral resolution produces a smaller statistical uncertainty for α, model non-uniqueness adds a significant additional uncertainty. (ii) non-uniqueness depends on the line broadening mechanism used. we show that modelling the spectral data using turbulent line broadening results in far greater non-uniqueness, hence this should no longer be done. instead, for varying α studies, it is important to use the more physically appropriate compound broadening. (iii) we have studied two absorption systems in detail. generalising thus requires caution. nevertheless, if non-uniqueness is present in all or most quasar absorption systems, it seems unavoidable that attempts to determine the existence (or non-existence) of spacetime variations of fundamental constants is best approached using a statistical sample. | non-uniqueness in quasar absorption models and implications for measurements of the fine structure constant |
we present a model for spectrophotometric calibration errors in observations of quasars from the third generation of the sloan digital sky survey baryon oscillation spectroscopic survey (boss) and describe the correction procedure we have developed and applied to this sample. calibration errors are primarily due to atmospheric differential refraction and guiding offsets during each exposure. the corrections potentially reduce the systematics for any studies of boss quasars, including the measurement of baryon acoustic oscillations using the lyα forest. our model suggests that, on average, the observed quasar flux in boss is overestimated by ∼19% at 3600 å and underestimated by ∼24% at 10,000 å. our corrections for the entire boss quasar sample are publicly available. | improved spectrophotometric calibration of the sdss-iii boss quasar sample |
although the speed of light has been measured with very high precision, most of these measurements were carried out on earth or in our close cosmic surroundings. in this letter, we propose an original idea to combine the observations of ultra-compact structure in radio quasars and strong gravitational lensing with quasars acting as background sources to estimate the speed of light. the method will provide precise measurements of the speed of light using extragalactic objects at different redshifts. we evaluate if current or future missions such as the large synoptic survey telescope (lsst) and dark energy survey (des) can be sensitive enough to detect any variation of c. our results show that strongly lensed quasars observed by lsst would produce robust constraints on δc/c at the level of 10-4, if the compact radio structure measurements are available. | precise measurements of the speed of light with high-redshift quasars: ultra-compact radio structure and strong gravitational lensing |
we present muse observations of the field of the quasar q0152$-$020 whose spectrum shows a lyman limit system (lls) at redshift $z_{\rm abs} = 0.38$, with a metallicity z $\gtrsim 0.06$ z$_\odot$. the low ionization metal lines associated with the lls present two narrow distinct absorption components with a velocity separation of 26 km ${\rm s}^{-1}$. we detect six galaxies within 600 km ${\rm s}^{-1}$ from the absorption redshift; their projected distances from the quasar sightline range from 60 to 200 kpc. the optical spectra of five of these galaxies exhibit prominent nebular emission lines, from which we deduce extinction-corrected star formation rates in the range sfr = 0.06-1.3 m$_\odot$~yr$^{-1}$, and metallicities between 0.2 z$_\odot$ and z$_\odot$. the sixth galaxy is only detected in the stellar continuum. by combining our data with archival keck/hires spectroscopy of the quasar and hst/wfpc2 imaging of the field, we can relate absorption line and galaxy kinematics; we conclude that the lls is most likely associated with the galaxy closest to the quasar sight-line (galaxy "a"). our morphokinematic analysis of galaxy "a" combined with the absorption line kinematics supports the interpretation that one of the absorption components originates from an extension of the stellar disk of galaxy "a", while the other component may arise in accreting gas in a warped disk with specific angular momentum $\sim 3$ times larger than the specific angular momentum of the galaxy halo. such warped disks are common features in hydrodynamical simulations of cold-flow accretion onto galaxies; the data presented here provide observational evidence in favour of this scenario. | observational signatures of a warped disk associated with cold-flow accretion |
we present a detailed analysis of a recent, 2013 suzaku campaign on the nearby (z = 0.184) luminous (lbol ∼ 1047 erg s-1) quasar pds 456. this consisted of three observations, covering a total duration of ∼1 ms and a net exposure of 455 ks. during these observations, the x-ray flux was unusually low, suppressed by a factor of >10 in the soft x-ray band when compared to previous observations. we investigated the broad-band continuum by constructing a spectral energy distribution (sed), making use of the optical/uv photometry and hard x-ray spectra from the later simultaneous xmm-newton and nustar campaign in 2014. the high-energy part of this low-flux sed cannot be accounted for by physically self-consistent accretion disc and corona models without attenuation by absorbing gas, which partially covers a substantial fraction of the line of sight towards the x-ray continuum. at least two layers of absorbing gas are required, of column density log (nh,low/cm-2) = 22.3 ± 0.1 and log (nh,high/cm-2) = 23.2 ± 0.1, with average line-of-sight covering factors of ∼80 per cent (with typical ∼5 per cent variations) and 60 per cent (±10-15 per cent), respectively. during these observations pds 456 displays significant short-term x-ray spectral variability, on time-scales of ∼100 ks, which can be accounted for by variable covering of the absorbing gas along the line of sight. the partial covering absorber prefers an outflow velocity of v_pc = 0.25^{+0.01}_{-0.05} c at the >99.9 per cent confidence level over the case where vpc = 0. this is consistent with the velocity of the highly ionized outflow responsible for the blueshifted iron k absorption profile. we therefore suggest that the partial covering clouds could be the denser, or clumpy part of an inhomogeneous accretion disc wind. finally estimates are placed upon the size-scale of the x-ray emission region from the source variability. the radial extent of the x-ray emitter is found to be of the order ∼15-20rg, although the hard x-ray (>2 kev) emission may originate from a more compact or patchy corona of hot electrons, which is typically ∼6-8rg in size. | short-term x-ray spectral variability of the quasar pds 456 observed in a low-flux state |
red quasi-stellar objects (qsos) are a subset of the luminous end of the cosmic population of active galactic nuclei (agns), most of which are reddened by intervening dust along the line of sight towards their central engines. in recent work from our team, we developed a systematic technique to select red qsos from the sloan digital sky survey, and demonstrated that they have distinctive radio properties using the faint images of the radio sky at twenty centimetres radio survey. here we expand our study using low-frequency radio data from the lofar two-metre sky survey (lotss). with the improvement in depth that lotss offers, we confirm key results: compared to a control sample of normal 'blue' qsos matched in redshift and accretion power, red qsos have a higher radio detection rate and a higher incidence of compact radio morphologies. for the first time, we also demonstrate that these differences arise primarily in sources of intermediate radio loudness: radio-intermediate red qsos are × 3 more common than typical qsos, but the excess diminishes among the most radio-loud systems and the most radio-quiet systems in our study. we develop monte carlo simulations to explore whether differences in star formation could explain these results, and conclude that, while star formation is an important source of low-frequency emission among radio-quiet qsos, a population of agn-driven compact radio sources is the most likely cause for the distinct low-frequency radio properties of red qsos. our study substantiates the conclusion that fundamental differences must exist between the red and normal blue qso populations. | fundamental differences in the radio properties of red and blue quasars: insight from the lofar two-metre sky survey (lotss) |
we present a detailed study of ionized outflows in a large sample of ∼650 hard x-ray-detected active galactic neuclei (agns). using optical spectroscopy from the bat agn spectroscopic survey (bass), we are able to reveal the faint wings of the [o iii] emission lines associated with outflows covering, for the first time, an unexplored range of low agn bolometric luminosity at low redshift (z ∼0.05). we test if and how the incidence and velocity of ionized outflow is related to agn physical parameters: black hole mass (m_{bh}), gas column density (nh), eddington ratio (λ _{edd}), [o iii], x-ray, and bolometric luminosities. we find a higher occurrence of ionized outflows in type 1.9 (55 per cent) and type 1 agns (46 per cent) with respect to type 2 agns (24 per cent). while outflows in type 2 agns are evenly balanced between blue and red velocity offsets with respect to the [o iii] narrow component, they are almost exclusively blueshifted in type 1 and type 1.9 agns. we observe a significant dependence between the outflow occurrence and accretion rate, which becomes relevant at high eddington ratios [log(λ _{edd}) ≳ -1.7]. we interpret such behaviour in the framework of covering factor-eddington ratio dependence. we do not find strong trends of the outflow maximum velocity with agn physical parameters, as an increase with bolometric luminosity can be only identified when including samples of agns at high luminosity and high redshift taken from literature. | bat agn spectroscopic survey - xix. type 1 versus type 2 agn dichotomy from the point of view of ionized outflows |
blazars, one of the most extreme classes of active galaxies, constitute so far the largest known population of γ-ray sources, and their number is continuously growing in the fermi catalogs. however, in the latest release of the fermi catalog there is still a large fraction of sources that are classified as blazar candidates of uncertain type (bcus) for which optical spectroscopic observations are necessary to confirm their nature and their associations. in addition, about one-third of the γ-ray point sources listed in the third fermi-lat source catalog (3fgl) are still unassociated and lacking an assigned lower-energy counterpart. since 2012 we have been carrying out an optical spectroscopic campaign to observe blazar candidates to confirm their nature. in this paper, the sixth of the series, we present optical spectroscopic observations for 30 γ-ray blazar candidates from different observing programs we carried out with the telescopio nazionale galileo, william herschel telescope, observatorio astronómico nacional, southern astrophysical research telescope, and magellan telescopes. we found that 21 out of 30 sources investigated are bl lac objects, while the remaining targets are classified as flat-spectrum radio quasars showing the typical broad emission lines of normal quasi-stellar objects. we conclude that our selection of γ-ray blazar candidates based on their multifrequency properties continues to be a successful way to discover potential low-energy counterparts of the fermi unidentified gamma-ray sources and to confirm the nature of bcus. | optical spectroscopic observations of gamma-ray blazar candidates. vi. further observations from tng, wht, oan, soar, and magellan telescopes |
in this paper, we report on the observational performance of the swift ultra-violet/optical telescope (uvot) in response to the gravitational wave (gw) alerts announced by the advanced laser interferometer gravitational wave observatory and the advanced virgo detector during the o3 period. we provide the observational strategy for follow-up of gw alerts and provide an overview of the processing and analysis of candidate optical/uv sources. for the o3 period, we also provide a statistical overview and report on serendipitous sources discovered by swift/uvot. swift followed 18 gw candidate alerts, with uvot observing a total of 424 deg2. we found 27 sources that changed in magnitude at the 3σ level compared with archival u- or g-band catalogued values. swift/uvot also followed up a further 13 sources reported by other facilities during the o3 period. using catalogue information, we divided these 40 sources into five initial classifications: 11 candidate active galactic nuclei (agns)/quasars, three cataclysmic variables (cvs), nine supernovae, 11 unidentified sources that had archival photometry, and six uncatalogued sources for which no archival photometry was available. we have no strong evidence to identify any of these transients as counterparts to the gw events. the 17 unclassified sources are likely a mix of agn and a class of fast-evolving transient, and one source may be a cv. | swift/uvot follow-up of gravitational wave alerts in the o3 era |
we present the discovery of eight quasars at z∼ 6 identified in the sloan digital sky survey (sdss) overlap regions. individual sdss imaging runs have some overlap with each other, leading to repeat observations over an area spanning >4000 deg2 (more than one-fourth of the total footprint). these overlap regions provide a unique data set that allows us to select high-redshift quasars more than 0.5 mag fainter in the z band than those found with the sdss single-epoch data. our quasar candidates were first selected as i-band dropout objects in the sdss imaging database. we then carried out a series of follow-up observations in the optical and near-ir to improve photometry, remove contaminants, and identify quasars. the eight quasars reported here were discovered in a pilot study utilizing the overlap regions at high galactic latitude (|b|\gt 30{}^\circ ). these quasars span a redshift range of 5.86\lt z\lt 6.06 and a flux range of 19.3\lt {{z}ab}\lt 20.6 mag. five of them are fainter than {{z}ab}=20 mag, the typical magnitude limit of z∼ 6 quasars used for the sdss single-epoch images. in addition, we recover eight previously known quasars at z∼ 6 that are located in the overlap regions. these results validate our procedure for selecting quasar candidates from the overlap regions and confirming them with follow-up observations, and they provide guidance to a future systematic survey over all sdss imaging regions with repeat observations. | discovery of eight z ∼ 6 quasars in the sloan digital sky survey overlap regions |
we review results from our monitoring observations of several lensed quasars performed in the optical, uv, and x-ray bands. modeling of the multi-wavelength light curves provides constraints on the extent of the optical, uv, and x-ray emission regions. one of the important results of our analysis is that the optical sizes as inferred from the microlensing analysis are significantly larger than those predicted by the theoretical-thin-disk estimate. in a few cases we also constrain the slope of the size-wavelength relation. our size constraints of the soft and hard x-ray emission regions of quasars indicate that in some objects of our sample the hard x-ray emission region is more compact than the soft and in others the soft emission region is smaller. this difference may be the result of the relative strengths of the disk-reflected (harder and extended) versus corona-direct (softer and compact) components in the quasars of our sample. finally, we present the analysis of several strong microlensing events where we detect an evolution of the relativistic fe line profile as the magnification caustic traverses the accretion disk. these caustic crossings are used to provide constraints on the innermost stable circular orbit (isco) radius and the accretion disk inclination angle of the black hole in quasar rx j1131-1231. | gravitational lensing size scales for quasars |
we report the discovery of rapid variations of a high-velocity c iv broad absorption line trough in the quasar sdss j141007.74+541203.3. this object was intensively observed in 2014 as a part of the sloan digital sky survey reverberation mapping project, during which 32 epochs of spectroscopy were obtained with the baryon oscillation spectroscopic survey spectrograph. we observe significant (>4σ) variability in the equivalent width (ew) of the broad (∼4000 km s-1 wide) c iv trough on rest-frame timescales as short as 1.20 days (∼29 hr), the shortest broad absorption line variability timescale yet reported. the ew varied by ∼10% on these short timescales, and by about a factor of two over the duration of the campaign. we evaluate several potential causes of the variability, concluding that the most likely cause is a rapid response to changes in the incident ionizing continuum. if the outflow is at a radius where the recombination rate is higher than the ionization rate, the timescale of variability places a lower limit on the density of the absorbing gas of ne ≳ 3.9 × 105 cm-3. the broad absorption line variability characteristics of this quasar are consistent with those observed in previous studies of quasars, indicating that such short-term variability may in fact be common and thus can be used to learn about outflow characteristics and contributions to quasar/host-galaxy feedback scenarios. | the sloan digital sky survey reverberation mapping project: rapid civ broad absorption line variability |
the formation of supermassive stars is believed to be an essential intermediate step for the formation of the massive black hole seeds that become the supermassive black holes powering the quasars observed in the early universe. numerical simulations have shown that supermassive stars can form in atomic-cooling haloes when protostars reach accretion rates higher than ~10-2 m⊙ yr-1 and fragmentation is suppressed on pc scales. it is, however, still uncertain if a supermassive star still emerges when fragmentation occurs at smaller scales and a cluster of stars is formed instead. in this work, we explore the problem of massive object formation due to the interplay of collisions and accretion in star clusters at low metallicity. we model a small embedded cluster of accreting protostars following subparsec scale fragmentation during the collapse of a primordial gas cloud, and follow its evolution by performing n-body plus hydrodynamical simulations. our results show that supermassive stars with 103 and 104 m⊙ are always formed due to the interplay of collisions and accretion, and in some cases these objects are part of a binary system. the resulting supermassive star is surrounded by tens of smaller stars with typical masses in the range 1-100 m⊙. | formation of supermassive stars in the first star clusters |
we propose a new method for fitting the full-shape of the lyman-α (ly α) forest 3d correlation function in order to measure the alcock-paczynski (ap) effect. our method preserves the robustness of baryon acoustic oscillations (bao) analyses, while also providing extra cosmological information from a broader range of scales. we compute idealized forecasts for the dark energy spectroscopic instrument (desi) using the ly α autocorrelation and its cross-correlation with quasars, and show how this type of analysis improves cosmological constraints. the desi ly α bao analysis is expected to measure h(zeff)rd and dm(zeff)/rd with a precision of $\sim 0.9{{\ \rm per\ cent}}$, where h is the hubble parameter, rd is the comoving bao scale, dm is the comoving angular diameter distance, and the effective redshift of the measurement is zeff ≃ 2.3. by fitting the ap parameter from the full shape of the two correlations, we show that we can obtain a precision of $\sim 0.5-0.6{{\ \rm per\ cent}}$ on each of h(zeff)rd and dm(zeff)/rd. furthermore, we show that a joint full-shape analysis of the ly α auto and cross-correlation with quasars can measure the linear growth rate times the amplitude of matter fluctuations in spheres of 8 h-1mpc, fσ8(zeff). such an analysis could provide the first ever measurement of fσ8(zeff) at redshift zeff > 2. by combining this with the quasar autocorrelation in a joint analysis of the three high-redshift two-point correlation functions, we show that desi could be able to measure fσ8(zeff ≃ 2.3) with a precision of $5-12{{\ \rm per\ cent}}$, depending on the smallest scale fitted. | cosmology beyond bao from the 3d distribution of the lyman-α forest |
we present alma band 9 continuum observation of the ultraluminous quasi-stellar object (qso) sdss j0100+2802 providing a ~10σ detection at ~670 ghz. sdss j0100+2802 is the brightest qso with the most massive supermassive black hole (smbh) known at z > 6, and we study its dust spectral energy distribution in order to determine the dust properties and the star formation rate (sfr) of its host galaxy. we obtain the most accurate estimate so far of the temperature, mass, and emissivity index of the dust, which are t dust = 48.4 ± 2.3 k, m dust = (2.29 ± 0.83) × 107 m ⊙, and β = 2.63 ± 0.23, respectively. this allows us to measure the sfr with the smallest statistical error for this qso, sfr = 265 ± 32 m ⊙yr-1. our results enable us to evaluate the relative growth of the smbh and host galaxy of j0100+2802. we find that the smbh is dominating the process of black-hole galaxy growth in this qso at z = 6.327, when the universe was 865 myr old. such unprecedented constraints on the host-galaxy sfr and dust temperature can only be obtained through high-frequency observations and highlight the importance of alma band 9 to obtain a robust overview of the buildup of the first quasars' host galaxies at z > 6. | accurate dust temperature and star formation rate in the most luminous z > 6 quasar in the hyperluminous quasars at the epoch of reionization (hyperion) sample |
dusty quasars might be in a young stage of galaxy evolution with prominent quasar feedback. a recently discovered population of luminous, extremely red quasars at z ~ 2-4 has extreme spectral properties related to exceptionally powerful quasar-driven outflows. we present keck/kcwi observations of the reddest known erq, at z = 2.3184, with extremely fast [o iii] λ5007 outflow at ~6000 km s-1. the lyα halo spans ~100 kpc. the halo is kinematically quiet, with velocity dispersion ~300 km s-1 and no broadening above the dark matter circular velocity down to the spatial resolution ~6 kpc from the quasar. we detect spatially resolved he ii λ1640 and c iv λ1549 emissions with kinematics similar to the lyα halo and a narrow component in the [o iii] λ5007. quasar reddening acts as a coronagraph, allowing views of the innermost halo. a narrow lyα spike in the quasar spectrum is inner halo emission, confirming the broad c iv λ1549 in the unresolved quasar is blueshifted by 2240 km s-1 relative to the halo frame. we propose the inner halo is dominated by moderate-speed outflow driven in the past and the outer halo dominated by inflow. the high central concentration of the halo and the symmetric morphology of the inner region are consistent with the erq being in earlier evolutionary stage than blue quasars. the he ii λ1640/lyα ratio of the inner halo and the asymmetry level of the overall halo are dissimilar to type ii quasars, suggesting unique physical conditions for this erq that are beyond orientation differences from other quasar populations. we find no evidence of mechanical quasar feedback in the lyα-emitting halo. | probing the inner circumgalactic medium and quasar illumination around the reddest 'extremely red quasar' |
intervening c iv absorbers are key tracers of metal-enriched gas in galaxy haloes over cosmic time. previous studies suggest that the c iv cosmic mass density ($\omega _{\rm c \, \small {iv}}$) decreases slowly over 1.5 $\lesssim \, z\lesssim$ 5 before declining rapidly at z ≳ 5, but the cause of this downturn is poorly understood. we characterize the $\omega _{\rm c \, \small {iv}}$ evolution over 4.3 ≲ z ≲ 6.3 using 260 absorbers found in 42 xshooter spectra of z ~ 6 quasars, of which 30 come from the eso large program xqr-30. the large sample enables us to robustly constrain the rate and timing of the downturn. we find that $\omega _{\rm c \, \small {iv}}$ decreases by a factor of 4.8 ± 2.0 over the ~300 myr interval between z ~ 4.7 and ~5.8. the slope of the column density (log n) distribution function does not change, suggesting that c iv absorption is suppressed approximately uniformly across 13.2 ≤ log n/cm-2 < 15.0. assuming that the carbon content of galaxy haloes evolves as the integral of the cosmic star formation rate density (with some delay due to stellar lifetimes and outflow travel times), we show that chemical evolution alone could plausibly explain the fast decline in $\omega _{\rm c \, \small {iv}}$ over 4.3 ≲ z ≲ 6.3. however, the c iv/c ii ratio decreases at the highest redshifts, so the accelerated decline in $\omega _{\rm c \, \small {iv}}$ at z ≳ 5 may be more naturally explained by rapid changes in the gas ionization state driven by evolution of the uv background towards the end of hydrogen reionization. | examining the decline in the c iv content of the universe over 4.3 ≲ z ≲ 6.3 using the e-xqr-30 sample |
as the universe evolves, it develops a web of filamentary structure of matter. this cosmic web is filled with gas, with the most diffuse gas lying in the intergalactic regions. at low redshift, the gas is predominantly warm-hot, and one of its best tracers is x-ray absorption in sightlines to background quasars. in this chapter, we present the theoretical background for the formation of the warm-hot intergalactic medium (whim) and present the physical properties of the whim from cosmological hydro-dynamical simulations. we discuss the feasibility of detecting the whim with x-ray absorption lines, with high-resolution and high signal-to-noise spectra. we present detailed discussion of observing techniques, including the whim ionization balance, observable lines, the curve of growth, and the diagnostics using the x-ray lines. we present the current efforts of detecting the whim with gratings on-board chandra and xmm-newton observatories. we discuss the criticality of whim detections reported in literature, where robust detections are likely from the circumgalactic medium of intervening galaxies, or intra-group medium, rather than truly diffuse gas in the intergalactic medium. secure detections of the most diffuse gas in the low redshift large scale structure may have to await next generation of x-ray telescopes. we end our chapter with the discussion of future missions carrying dispersive and non-dispersive spectrometers. we present figure-of-merit parameters for line detectibility as well as for the number of whim systems that can be detected with future missions. these will define our ability to account for the missing low-redshift baryons and to understand the evolution of the universe over half of its life. | absorption studies of the most diffuse gas in the large scale structure |
the largest fluctuation in the cmb sky is the cmb dipole, which is believed to be caused by the motion of our observation frame with respect to the cmb rest frame. this motion accounts for the known motion of the solar system barycentre with a best-fit amplitude of 369 km/s, in the direction (ℓ= 264°, b=48°) in galactic coordinates. along with the cmb dipole signal, this motion also causes an inevitable signature of statistical anisotropy in the higher multipoles due to the modulation and aberration of the cmb temperature and polarization fields. this leads to a correlation between adjacent cmb multipoles causing a non-zero value of the off-diagonal terms in the covariance matrix which can be captured in terms of the dipolar spectra of the bipolar spherical harmonics (biposh). in our work, we jointly infer the cmb power spectrum and the biposh spectrum in a bayesian framework using the planck-2018 smica temperature map. we detect amplitude and direction of the local motion consistent with the canonical value v=369 km/s inferred from cmb dipole with a statistical significance of 4.54σ, 4.97σ and 5.23σ respectively from the masked temperature map with the available sky fraction 40.1%, 59.1%, and 72.2%, confirming the common origin of both the signals. the bayes factor in favor of the canonical value is between 7 to 8 depending on the choice of mask. but it strongly disagrees (by a value of the bayes factor about 10-10-10-11) with a higher value of local motion which one can infer from the amplitude of the dipole signal obtained from the catwise2020 quasar catalog using the wise and neowise data set. | bayesian estimation of our local motion from the planck-2018 cmb temperature map |
we report the constraints of h0 obtained from wilkinson microwave anisotropy probe (wmap) 9-year data combined with the latest baryonic acoustic oscillations (bao) measurements. we use the bao measurements from 6df galaxy survey (6dfgs), the sdss dr7 main galaxies sample (mgs), the boss dr12 galaxies, and the eboss dr14 quasars. adding the recent bao measurements to the cosmic microwave background (cmb) data from wmap, we constrain cosmological parameters ωm = 0.298 ± 0.005, {h}_{0}={68.36}_{-0.52}(+0.53}{km) * {{s}}(-1) * {{mpc}}(-1) h0=68.36-0.52+0.53kmṡs-1ṡmpc-1 , {sigma }_{8}={0.8170}_{-0.0175}(+0.0159) σ8=0.8170-0.0175+0.0159 in a spatially flat λ cold dark matter (λcdm) model, and ωm = 0.302 ± 0.008, h0 = 67.63 ± 1.30 km ṡ s-1 ṡ mpc-1, {sigma }_{8}={0.7988}_{-0.0338}(+0.0345) σ8=0.7988-0.0338+0.0345 in a spatially flat wcdm model, respectively. our measured h0 results prefer a value lower than 70 km ṡ s-1 ṡ mpc-1, consistent with the recent data on cmb constraints from planck (2018), but in 3.1 and 3.5σ tension with local measurements of sh0es (2018) in λcdm and wcdm framework, respectively. our results indicate that there is a systematic tension on the hubble constant between sh0es and the combination of cmb and bao datasets. | constraints on h 0 from wmap and bao measurements |
we present the novel algorithmically regularized integration method mstar for high-accuracy (|δe/e| ≳ 10-14) integrations of n-body systems using minimum spanning tree coordinates. the twofold parallelization of the o(n_part^2) force loops and the substep divisions of the extrapolation method allow for a parallel scaling up to ncpu = 0.2 × npart. the efficient parallel scaling of mstar makes the accurate integration of much larger particle numbers possible compared to the traditional algorithmic regularization chain (ar-chain) methods, e.g. npart = 5000 particles on 400 cpus for 1 gyr in a few weeks of wall-clock time. we present applications of mstar on few particle systems, studying the kozai mechanism and n-body systems like star clusters with up to npart = 104 particles. combined with a tree or fast multipole-based integrator, the high performance of mstar removes a major computational bottleneck in simulations with regularized subsystems. it will enable the next-generation galactic-scale simulations with up to 109 stellar particles (e.g. m_\star = 100 m_⊙ for an m_\star = 10^{11} m_⊙ galaxy), including accurate collisional dynamics in the vicinity of nuclear supermassive black holes. | mstar - a fast parallelized algorithmically regularized integrator with minimum spanning tree coordinates |
after the discovery of powerful relativistic jets from narrow-line seyfert 1 galaxies, and the understanding of their similarity with those of blazars, a problem of terminology was born. the word blazar is today associated to bl lac objects and flat-spectrum radio quasars, which are somehow different from narrow-line seyfert 1 galaxies. using the same word for all the three classes of agn could drive either toward some misunderstanding, or to the oversight of some important characteristics. i review the main characteristics of these sources, and finally i propose a new scheme of classification. | what we talk about when we talk about blazars? |
we present alma observations of cold dust and molecular gas in four high-luminosity, heavily reddened (av ∼ 2.5-6 mag) type 1 quasars at z ∼ 2.5 with virial mbh ∼ 1010 m⊙, to test whether dusty, massive quasars represent the evolutionary link between submillimetre-bright galaxies and unobscured quasars. all four quasars are detected in both the dust continuum and in the 12co(3-2) line. the mean dust mass is 6 × 108 m⊙ assuming a typical high-redshift quasar spectral energy distribution (t = 41 k, β = 1.95 or t = 47 k, β = 1.6). the implied star formation rates are very high - ≳1000 m⊙ yr-1 in all cases. gas masses estimated from the co line luminosities cover ∼1-5× 1010(αco/0.8)m⊙ and the gas depletion time-scales are very short - ∼5-20 myr. a range of gas-to-dust ratios is observed in the sample. we resolve the molecular gas in one quasar - ulasj2315+0143 (z = 2.561) - which shows a strong velocity gradient over ∼20 kpc. the velocity field is consistent with a rotationally supported gas disc but other scenarios, e.g. mergers, cannot be ruled out at the current resolution of these data. in another quasar - ulasj1234+0907 (z = 2.503) - we detected molecular line emission from two millimetre-bright galaxies within 200 kpc of the quasar, suggesting that this quasar resides in a significant overdensity. the high detection rate of both cold dust and molecular gas in these sources, suggests that reddened quasars could correspond to an early phase in massive galaxy formation associated with large gas reservoirs and significant star formation. | the discovery of gas-rich, dusty starbursts in luminous reddened quasars at z ∼ 2.5 with alma |
while molecular quasar absorption systems provide unique probes of the physical and chemical properties of the gas as well as original constraints on fundamental physics and cosmology, their detection remains challenging. here we present the results from a complete survey for molecular gas in thirty-nine absorption systems selected solely upon the detection of neutral carbon lines in sloan digital sky survey (sdss) spectra, without any prior knowledge of the atomic or molecular gas content. h2 is found in all twelve systems (including seven new detections) where the corresponding lines are covered by the instrument setups and measured to have logn(h2) ≳ 18, indicating a self-shielded regime. we also report seven co detections (7/39) down to logn(co) ~ 13.5, including a new one, and put stringent constraints on n(co) for the remaining 32 systems. n(co) and n(c i) are found to be strongly correlated with n(co)/n(c i) ~ 1/10. this suggests that the c i-selected absorber population is probing gas deeper than the h i-h2 transition in which a substantial fraction of the total hydrogen in the cloud is in the form of h2. we conclude that targeting c i-bearing absorbers is a very efficient way to find high-metallicity molecular absorbers. however, probing the molecular content in lower-metallicity regimes as well as high-column-density neutral gas remains to be undertaken to unravel the processes of gas conversion in normal high-z galaxies. based on observations and archival data from the european southern observatory (eso) prog. ids 060.a-9024, 072.a-0346, 278.a-5062, 080.a-0482, 080.a-0795, 081.a-0242, 081.a-0334, 082.a-0544, 082.a-0569, 083.a-0454, 084.a-0699, 086.a-0074 and 086.a-0643 using the ultraviolet and visual echelle spectrograph (uves) and x-shooter at the very large telescope (vlt), on cerro paranal, chile. | spotting high-z molecular absorbers using neutral carbon. results from a complete spectroscopic survey with the vlt |
using an ultra-deep blind survey with the muse integral field spectrograph on the european southern observatory very large telescope, we obtain spectroscopic redshifts to a depth never before explored: galaxies with observed magnitudes m ab ≳ 30-32. specifically, we detect objects via lyα emission at 2.9 < z < 6.7 without individual continuum counterparts in areas covered by the deepest optical/near-infrared imaging taken by the hubble space telescope, the hubble ultra deep field. in total, we find 102 such objects in 9 square arcminutes at these redshifts. detailed stacking analyses confirm the lyα emission as well as the 1216 å breaks and faint ultraviolet continua (m uv ∼ -15). this makes them the faintest spectroscopically confirmed objects at these redshifts, similar to the sources believed to reionize the universe. a simple model for the expected fraction of detected/undetected lyα emitters as a function of luminosity is consistent with these objects being the high-equivalent width tail of the normal lyα-emitter population at these redshifts. based on observations made with eso telescopes at the la silla paranal observatory under program ids 094.a-2089(b), 095.a-0010(a), 096.a-0045(a), and 096.a-0045(b); and based on data obtained with the nasa/esa hubble space telescope, which is operated by the association of universities for research in astronomy, inc., under nasa contract nas 5-26555. | muse spectroscopic identifications of ultra-faint emission line galaxies with m uv ∼ -15 |
we develop a semi-analytic model to explore different prescriptions of supermassive black hole (smbh) fuelling. this model utilizes a merger-triggered burst mode in concert with two possible implementations of a long-lived steady mode for assembling the mass of the black hole in a galactic nucleus. we improve modelling of the galaxy-halo connection in order to more realistically determine the evolution of a halo's velocity dispersion. we use four model variants to explore a suite of observables: the m•-σ relation, mass functions of both the overall and broad-line quasar population, and luminosity functions as a function of redshift. we find that `downsizing' is a natural consequence of our improved velocity dispersion mappings, and that high-mass smbhs assemble earlier than low-mass smbhs. the burst mode of fuelling is sufficient to explain the assembly of smbhs to z = 2, but an additional steady mode is required to both assemble low-mass smbhs and reproduce the low-redshift luminosity function. we discuss in detail the trade-offs in matching various observables and the interconnected modelling components that govern them. as a result, we demonstrate the utility as well as the limitations of these semi-analytic techniques. | exploring smbh assembly with semi-analytic modelling |
recent theoretical models suggest that the early phase of galaxy formation could involve an epoch when galaxies are gas rich but inefficient at forming stars: a “dark galaxy” phase. here, we report the results of our multi-unit spectroscopic explorer (muse) survey for dark galaxies fluorescently illuminated by quasars at z > 3. compared to previous studies which are based on deep narrowband (nb) imaging, our integral field survey provides a nearly uniform sensitivity coverage over a large volume in redshift space around the quasars as well as full spectral information at each location. thanks to these unique features, we are able to build control samples at large redshift distances from the quasars using the same data taken under the same conditions. by comparing the rest-frame equivalent width (ew0) distributions of the lyα sources detected in proximity to the quasars and in control samples, we detect a clear correlation between the locations of high-ew0 objects and the quasars. this correlation is not seen in other properties, such as lyα luminosities or volume overdensities, suggesting the possible fluorescent nature of at least some of these objects. among these, we find six sources without continuum counterparts and ew0 limits larger than 240 å that are the best candidates for dark galaxies in our survey at z > 3.5. the volume densities and properties, including inferred gas masses and star formation efficiencies, of these dark galaxy candidates are similar to those of previously detected candidates at z ≈ 2.4 in nb surveys. moreover, if the most distant of these are fluorescently illuminated by the quasar, our results also provide a lower limit of t = 60 myr on the quasar lifetime. based on observations obtained at the very large telescope (vlt) of the european southern observatory, paranal, chile (eso programme ids 094.a-0396, 095.a-0708, 096.a-0345, 097.a-0251, 098.a-0678, 094.a-0131, 095.a-0200, 096.a-0222, 097.a-0089, 098.a-0216). | dark galaxy candidates at redshift ∼3.5 detected with muse |
we propose to solve the dark energy problem by postulating the massless sector of closed strings. this sector constitutes the gravitational multiplet of string theory and, when applied to four-dimensional cosmology, predicts that the expansion of an open universe defined in string frame is readily accelerating. we confront the prediction with the late-time cosmological data of type ia supernovae and quasar absorption spectrum, which probe the evolutions of the hubble parameter and possibly the fine-structure constant. we report that the observations are in admirable agreement with the prediction without any dark sector. we estimate the hubble constant, $h_{0}\simeq 71.2\pm 0.2\,\mathrm{km/s/mpc}$. | late-time cosmology without dark sector but with closed string massless sector |
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