Bright Quasars Research Articles

Absorption spectrum of the quasar HS1603+3820

Context.We present multi-wavelength observations of the bright quasar HS1603+3820: the optical data taken with the MMT and Keck telescopes, with the 40–50 km s-1 resolution, and X-ray data taken by the Chandra X-ray Observatory satellite.

Distribution of the Very First Population III Stars and Their Relation to Brightz ≈ 6 Quasars

We discuss the link between dark matter halos hosting the first Population III stars and the rare, massive halos that are generally considered to host bright quasars at high redshift (z ≈ 6). The main question that we intend to answer is whether the supermassive black holes powering these QSOs grew out from the seeds planted by the first intermediate-mass black holes created in the universe. This question involves a dynamical range of 1013 in mass, and we address it by combining N-body simulations of structure formation to identify the most massive halos at z ≈ 6 with a Monte Carlo method based on linear theory to obtain the location and formation times of the first-light halos within the whole simulation box. We show that the descendants of the first ≈106 M☉ virialized halos do not, on average, end in the most massive halos at z ≈ 6, but rather live in a large variety of environments. The oldest Population III progenitors of the most massive halos at z ≈ 6 form instead from density peaks that are on average 1.5 σ more common than the first Population III star formed in the volume occupied by one bright high-z QSO. The intermediate-mass black hole seeds planted by the very first Population III stars at z 40 can easily grow to masses mBH > 109.5 M☉ by z = 6 assuming Eddington accretion with radiative efficiency 0.1. Quenching of the black hole accretion is therefore crucial to avoid an overabundance of supermassive black holes at lower redshift. This can be obtained if the mass accretion is limited to a fraction η ≈ 6 × 10-3 of the total baryon mass of the halo hosting the black hole. The resulting high-end slope of the black hole mass function at z = 6 is α ≈ -3.7, a value within the 1 σ error bar for the bright-end slope of the observed quasar luminosity function at z = 6.

Detection of 1.6 × 10 10 M ⊙ of Molecular Gas in the Host Galaxy of the z = 5.77 SDSS Quasar J0927+2001

We have detected emission by the CO(5-4) and (6-5) rotational transitions at z = 5.7722 ± 0.0006 from the host galaxy of the SDSS quasar J0927+2001 using the Plateau de Bure Interferometer. The peak line flux density for the CO(5-4) line is 0.72 ± 0.09 mJy, with a line FWHM = 610 ± 110 km s^(-1). The implied molecular gas mass is (1.6 ± 0.3) × 10^(10) M_⊙. We also detect the 90 GHz continuum at 0.12 ± 0.03 mJy, consistent with a 47 K dust spectrum extrapolated from higher frequencies. J0927+2001 is the second example of a huge molecular gas reservoir within the host galaxy of a quasar within 1 Gyr of the big bang. Observations of J0927+2001 are consistent with a massive starburst coeval with a bright quasar phase in the galaxy, suggesting the rapid formation of both a supermassive black hole through accretion, and the stellar host spheroid, at a time close to the end of cosmic reionization.

Seoul National University Bright Quasar Survey in Optical (SNUQSO). II. Discovery of 40 Bright Quasars Near the Galactic Plane

We report the discovery of 40 bright quasars and active galactic nuclei (AGNs) at low Galactic latitude (b < ). The low Galactic latitude region has been considered a place to avoid when searching for extragalactic sources, because of the high Galactic extinction, as well as a large number of stars contaminating the sample selection. Bright quasars (R 17) suffer more from such difficulties because they look like bright stars, which are numerous at low b, yet their surface number density is very low. In order to find quasars in this region of the sky less explored for extragalactic sources, we have started a survey of low Galactic latitude bright quasars as a part of the Seoul National University Quasar Survey in Optical (SNUQSO). Quasar candidates have been selected from radio and near-infrared (NIR) data. Out of 88 targets, we identify 29 bright quasars/AGNs around the antigalactic center, and 11 bright quasars/AGNs in the outskirts of the Galactic center, from two observing runs in 2006 at the Bohyunsan Optical Astronomical Observatory (BOAO) in Korea. Our finding demonstrates that quasars/AGNs can be discovered effectively, even at low Galactic latitude, using multiwavelength data.

Bimodal Active Nuclei in Bimodal Galaxies

By their star content, the galaxies split out into a red and a blue population; their color index peaked around u-r ≈ 2.5 or u-r ≈ 1, respectively, quantifies the ratio of the blue stars newly formed from cold galactic gas, to the redder ones left over by past generations. On the other hand, on accreting substantial gas amounts the central massive black holes energize active galactic nuclei (AGNs); here we investigate whether these show a similar, and possibly related, bimodal partition as for current accretion activity relative to the past. To this aim we use an updated semianalytic model; based on Monte Carlo simulations, this follows with a large statistics the galaxy assemblage, the star generations, and the black hole accretions in the cosmological framework over the redshift span from z = 10 to z = 0. We test our simulations for yielding in close detail the observed split of galaxies into a red, early and a blue, late population. We find that the black hole accretion activities likewise give rise to two source populations: early, bright quasars and later, dimmer AGNs. We predict for their Eddington parameter λE—the ratio of the current to the past black hole accretions—a bimodal distribution; the two branches sit now under λE ≈ 0.01 (mainly contributed by low-luminosity AGNs) and around λE ≈ 0.3-1. These not only mark out the two populations of AGNs, but also will turn out to correlate strongly with the red or blue color of their host galaxies.

A Census of Intrinsic Narrow Absorption Lines in the Spectra of Quasars at z = 2–4

We use Keck HIRES spectra of 37 optically bright quasars at z = 2-4 to study narrow absorption lines that are intrinsic to the quasars (intrinsic NALs, produced in gas that is physically associated with the quasar central engine). We identify 150 NAL systems, which contain 124 C IV, 12 N V, and 50 Si IV doublets, of which 18 are associated systems (within 5000 km s-1 of the quasar redshift). We use partial coverage analysis to separate intrinsic NALs from NALs produced in cosmologically intervening structures. We find 39 candidate intrinsic systems (28 reliable determinations and 11 that are possibly intrinsic). We estimate that 10%-17% of C IV systems at blueshifts of 5000-70,000 km s-1 relative to quasars are intrinsic. At least 32% of quasars contain one or more intrinsic C IV NALs. Considering N V and Si IV doublets showing partial coverage as well, at least 50% of quasars host intrinsic NALs. This result constrains the solid angle subtended by the absorbers to the background source(s). We identify two families of intrinsic NAL systems, those with strong N V absorption and those with negligible absorption in N V but with partial coverage in the C IV doublet. We discuss the idea that these two families represent different regions or conditions in accretion disk winds. Of the 26 intrinsic C IV NAL systems, 13 have detectable low-ionization absorption lines at similar velocities, suggesting that these are two-phase structures in the wind rather than absorbers in the host galaxy. We also compare possible models for quasar outflows, including radiatively accelerated disk-driven winds, magnetocentrifugally accelerated winds, and pressure-driven winds, and we discuss ways of distinguishing between these models observationally.

Millimeter and Radio Observations ofz~ 6 Quasars

We present millimeter and radio observations of 13 SDSS quasars at redshifts z ~ 6. We observed 11 of them with the Max Planck Millimeter Bolometer Array (MAMBO-2) at the IRAM 30 m telescope at 250 GHz and all of them with the Very Large Array (VLA) at 1.4 GHz. Four sources are detected by MAMBO-2 and six are detected by the VLA at the 3 σ level. These sources, together with another six published in previous papers, yield a submillimeter/millimeter- and radio-observed SDSS quasar sample at z ~ 6. We use this sample to investigate the far-infrared (FIR) and radio properties of optically bright quasars in the early universe. We compare this sample to lower redshift samples of quasars observed in the submillimeter and millimeter wavelengths [(sub)mm] and find that the distribution of the FIR-to-B-band optical luminosity ratio (LFIR/LB) is similar from z ~ 2 to 6. We find a weak correlation between the FIR luminosity (LFIR) and B-band optical luminosity (LB) by including the (sub)mm observed samples at all redshifts. Some strong (sub)mm detections in the z ~ 6 sample have radio-to-FIR ratios within the range defined by star-forming galaxies, which suggests possible coeval star-forming activity with the powerful AGN in these sources. We calculate the rest-frame radio-to-optical ratios (R = Lν,1.4 GHz/Lν,4400 A) for all of the VLA-observed sources in the z ~ 6 quasar sample. Only one radio detection in this sample, J083643.85+005453.3, has R ~ 40 and can be considered radio-loud. There are no strong radio sources (R ≥ 100) among these SDSS quasars at z ~ 6. These data are consistent with, although do not set strong constraints on, a decreasing radio-loud quasar fraction with increasing redshift.

Line and continuum variability of two intermediate-redshift, high-luminosity quasars

Context. It has been shown that the luminosity of active galactic nuclei and the size of their broad line region obey a simple relation of the type R-BLR = aL(gamma), from faint Seyfert nuclei to bright quasars, allowing single-epoch determination of the central black hole mass M-BH = bL(gamma) Delta(2) H-beta from their luminosity L and width of H-beta emission line. Adopting this mass determination for cosmological studies requires the extrapolation to high redshift and luminosity of a relation whose calibration relies so far on reverberation mapping measurements performed for L less than or similar to 1046 erg s(-1) and redshift z less than or similar to 0.4. Aims. We initiated a campaign for the spectrophotometric monitoring of a few luminous, intermediate redshift quasars whose apparent magnitude, V < 15.7, allows observations with a 1.8 m telescope, aimed at proving that emission lines vary and respond to continuum variations even for luminosities less than or similar to 1047 erg s(-1), and determining eventually their MBH from reverberation mapping. Methods. We have repeatedly performed simultaneous spectrophotometric observations of quasars and reference stars to determine relative variability of continuum and emission lines. We describe the observations and methods of analysis. Results. For the quasars PG 1634+ 706 and PG 1247+ 268 we obtain light-curves respectively for CIII](lambda lambda 1909 angstrom), MgII(lambda lambda 2798 angstrom) and for CIV(lambda lambda 1549 angstrom), CIII](lambda lambda 1909 angstrom) emission lines with the relevant continua. During 3.2 years of observation, in the former case no continuum variability was detected and the evidence for line variability is marginal, while in the latter case both continuum and line variability are detected with high significance and the line variations appear correlated with continuum variations. Conclusions. The detection of the emission line variability in a quasar with L similar to 10(47) erg s(-1) encourages the continuation of the monitoring campaign which should provide a black hole mass estimate in another 5-6 years, constraining the mass-luminosity relation in a poorly explored range of luminosity.

On-axis spectroscopy of the host galaxies of 20 optically luminous quasars at z 0.3

We present the analysis of a sample of 20 bright low-redshift quasars (M B < - 23 and z < 0.35) observed spectroscopically with the Very Large Telescope (VLT). The Focal Reducer/low dispersion Spectrograph (FORS1) spectra, obtained in Multi-Object Spectroscopy (MOS) mode, allow to observe simultaneously the quasars and several reference stars used to spatially deconvolve the data. Applying the Magain, Courbin & Sohy (MCS) deconvolution method, we are able to separate the individual spectra of the quasar and of the underlying host galaxy. Contrary to some previous claims, we find that luminous quasars are not exclusively hosted by massive ellipticals. Most quasar host galaxies harbour large amounts of gas, irrespective of their morphological type. Moreover, the stellar content of half of the hosts is a young Sc-like population, associated with a rather low-metallicity interstellar medium. A significant fraction of the galaxies contain gas ionized at large distances by the quasar radiation. This large distance ionization is always associated with signs of gravitational interactions (as detected from images or disturbed rotation curves). The spectra of the quasars themselves provide evidence that gravitational interactions bring dust and gas in the immediate surrounding of the super massive black hole, allowing to feed it. The quasar activity might thus be triggered (1) in young gas-rich spiral galaxies by local events and (2) in more evolved galaxies by gravitational interactions or collisions. The latter mechanism gives rises to the most powerful quasars. Finally, we derive mass models for the isolated spiral host galaxies and we show that the most reliable estimators of the systemic redshift in the quasar spectrum are the tips of the Ha and Hβ lines.

The mass function of high-redshift seed black holes

Abstract In this Letter we derive the mass function of seed black holes that result from the central mass concentrated via disc accretion in collapsed haloes at redshift z ≈ 15. Using standard arguments including stability, we show that these pregalactic discs can assemble a significant mass concentration in the inner regions, providing fuel for the formation and initial growth of supermassive black holes. Assuming that these mass concentrations do result in central seed black holes, we determine the mass distribution of these seeds as a function of key halo properties. The seed mass distribution determined here turns out to be asymmetric and skewed to higher masses. Starting with these initial seeds, building up to 109 solar masses by z = 6 to power the bright quasars is not a problem in the standard Λ cold dark matter cosmogony. These seed black holes in gas-rich environments are likely to grow into the supermassive black holes at later times via mergers and accretion. Gas accretion on to these seeds at high redshift will produce miniquasars that likely play an important role in the reionization of the Universe. Some of these seed black holes, on the other hand, could be wandering in galaxy haloes as a consequence of frequent mergers, powering the off-nuclear ultra-luminous X-ray sources detected in nearby galaxies.

Observational Evidence for the Coevolution of Galaxy Mergers, Quasars, and the Blue/Red Galaxy Transition

We compile a number of observations to estimate the time-averaged rate of formation or buildup of red sequence galaxies, as a function of mass and redshift. Comparing this with the mass functions of mergers and quasar hosts, and independently comparing their clustering properties as a function of redshift, we find that these populations trace the same mass distribution, with similar evolution, at redshifts 0 < z ≲ 1.5. Knowing one of the quasar, merger, or elliptical mass/luminosity functions, it is possible to predict the others. Allowing for greater model dependence, we compare the rate of early-type buildup with the implied merger and quasar triggering rates as a function of mass and redshift and find agreement. Over this redshift range, observed merger fractions can account for the entire bright quasar luminosity function and buildup of the red sequence at all but the highest masses at low redshift (≳1011 M☉ at z ≲ 0.3) where "dry" mergers appear to dominate. This supports a necessary prediction of theories where mergers between gas-rich galaxies produce ellipticals with an associated phase of quasar activity, after which the remnant becomes red. These populations trace a similar characteristic transition mass, possibly reflecting the mass above which the elliptical population is mostly (≳50%) assembled at a given redshift, which increases with redshift over the observed range in a manner consistent with suggestions that cosmic downsizing may apply to red galaxy assembly as well as star formation. These mass distributions as a function of redshift do not uniformly trace the all/red/blue galaxy population, ruling out models in which quasar activity is generically associated with star formation or is long lived in "old" systems.

Gamma-ray absorption method (GRAM) application to the identification of EGRET unidentified sources

Recently we reported the very first detection of γ -ray resonant absorption along the line of sight toward γ -ray bright quasars (QSOs) like 3C 273, 3C 279, PKS 0528+0134, and BL Lacertae. These detections resulted from the analysis of absorption troughs in SEDs derived on the base of mostly EGRET data that were collected during monitoring campaigns of the Virgo and galactic anticenter regions by the Compton Gamma Ray Observatory (CGRO), as well as during ToO observations of QSOs flares. Among three resonant absorption mechanisms that affect the γ -ray spectrum of point-like sources, we now pinpoint the Δ -isobar resonance that has a very stable peak energy of the absorption cross-section for all elements (nuclei) and for individual nucleons. From two absorbers that are usually detected on the sight lines towards γ -ray bright QSOs, we concentrate here on the only one that is at the QSO rest frame. We discuss the advantages and drawbacks of this method distinguishing between a galactic and extragalactic origin of the EGRET unidentified sources (EUIDs). This is compared to the multiwavelength identification approach that was succesfully used in a few cases to identify galactic and extragalactic objects among EUIDs. We applied the GRAM to identifying two of the EGRET unidentified sources as blazars, and predict their respective redshifts.

Large‐Scale Simulations of Reionization

We use cosmological simulations to explore the large-scale effects of reionization. Since reionization is a process that involves a large dynamic range—from galaxies to rare bright quasars—we need to be able to cover a significant volume of the universe in our simulation without losing the important small-scale effects from galaxies. Here we have taken an approach that uses clumping factors derived from small-scale simulations to approximate the radiative transfer on subcell scales. Using this technique, we can cover a simulation size up to 1280 h-1 Mpc with 10 h-1 Mpc cells. This allows us to construct synthetic spectra of quasars similar to observed spectra of Sloan Digital Sky Survey (SDSS) quasars at high redshifts and compare them to the observational data. These spectra can then be analyzed for H II region sizes, the presence of the Gunn-Peterson trough, and the Lyα forest.

Hubble Space TelescopeUltraviolet Spectroscopy of 14 Low-Redshift Quasars

We present low-resolution ultraviolet spectra of 14 low-redshift (zem ≲ 0.8) quasars observed with the Hubble Space Telescope STIS as part of a Snapshot project to understand the relationship between quasar outflows and luminosity. By design, all observations cover the C IV emission line. Ten of the quasars are from the Hamburg-ESO catalog, three are from the Palomar-Green catalog, and one is from the Parkes catalog. The sample contains a few interesting quasars, including two broad absorption line (BAL) quasars (HE 0143-3535 and HE 0436-2614), one quasar with a mini-BAL (HE 1105-0746), and one quasar with associated narrow absorption (HE 0409-5004). These BAL quasars are among the brightest known (although not the most luminous) since they lie at zem < 0.8. We compare the properties of these BAL quasars to the zem < 0.5 Palomar-Green and zem > 1.4 Large Bright Quasar Survey samples. By design, our objects sample luminosities in between these two surveys, and our four absorbed objects are consistent with the v ∼ L0.62 relation derived by Laor & Brandt (2002). Another quasar, HE 0441-2826, contains extremely weak emission lines, and our spectrum is consistent with a simple power-law continuum. The quasar is radio-loud but has a steep spectral index and a lobe-dominated morphology, which argues against it being a blazar. The unusual spectrum of this quasar resembles the spectra of the quasars PG 1407+265, SDSS J1136+0242, and PKS 1004+13, for which several possible explanations have been entertained.

Constraining quasar host halo masses with the strength of nearby Lyα forest absorption

Using cosmological hydrodynamic simulations we measure the mean transmitted flux in the Lyman alpha forest for quasar sightlines that pass near a foreground quasar. We find that the trend of absorption with pixel-quasar separation distance can be fitted using a simple power law form including the usual correlation function parameters r_{0} and \gamma so that (<F(r)> = \sum exp(-tau_eff*(1+(r/r_{0})^(-\gamma)))). From the simulations we find the relation between r_{0} and quasar mass and formulate this as a way to estimate quasar host dark matter halo masses, quantifying uncertainties due to cosmological and IGM parameters, and redshift errors. With this method, we examine data for ~3000 quasars from the Sloan Digital Sky Survey (SDSS) Data Release 3, assuming that the effect of ionizing radiation from quasars (the so-called transverse proximity effect) is unimportant (no evidence for it is seen in the data.) We find that the best fit host halo mass for SDSS quasars with mean redshift z=3 and absolute G band magnitude -27.5 is log10(M/M_sun) = 12.48^{+0.53}_{-0.89}. We also use the Lyman-Break Galaxy (LBG) and Lyman alpha forest data of Adelberger et al in a similar fashion to constrain the halo mass of LBGs to be log10(M/M_sun) = 11.13^{+0.39}_{-0.55}, a factor of ~20 lower than the bright quasars. In addition, we study the redshift distortions of the Lyman alpha forest around quasars, using the simulations. We use the quadrupole to monopole ratio of the quasar-Lyman alpha forest correlation function as a measure of the squashing effect. We find that this does not have a measurable dependence on halo mass, but may be useful for constraining cosmic geometry.

Quasar X-Ray Jets: Gamma-Ray Diagnostics of the Synchrotron and Inverse Compton Hypotheses: The Case of 3C 273

The process responsible for the Chandra-detected X-ray emission from the large scale jets of powerful quasars is a matter of ongoing debate. The two main contenders are external Compton (EC) scattering off the cosmic microwave background (CMB) photons (EC/CMB) and synchrotron emission from a population of electrons separate from those producing the radio - IR emission. So far, no clear diagnostics have been presented to distinguish which of the two, if any, is the actual X-ray emission mechanism. Here we present such diagnostics based on a fundamental difference between these two models: the production of synchrotron X-rays requires multi - TeV electrons, while the EC/CMB model requires a cutoff in the electron energy distribution (EED) below TeV energies. This has significant implications for the gamma-ray emission predicted by these two models, that can be tested through GeV and TeV observations of the nearby bright quasar 3C 273. We show how existing and future GeV and TeV observations can confirm or refute one or both of the above hypotheses.

The effect of stellar feedback and quasar winds on the active galactic nucleus population

In order to constrain the physical processes that regulate and downsize the active galactic nucleus (AGN) population, the predictions of the model for the rise of galaxies and active nuclei (MORGANA) are compared to luminosity functions (LFs) of AGNs in the optical, soft and hard X-ray bands, to the local black hole (BH)‐bulge mass relation and to the observed X-ray number counts and background. We also give predictions on the accretion rate of AGNs in units of the Eddington rate and on the BH‐bulge relation expected at high redshift. We find that it is possible to reproduce the downsizing of AGNs within the hierarchical Lambda cold dark matter cosmogony and that the most likely cause of this downsizing is the stellar kinetic feedback that arises in star-forming bulges as a consequence of the high level of turbulence and leads to a massive removal of cold gas in small elliptical galaxies. At the same time, to obtain good fits to the number of bright quasars we require that quasar-triggered galactic winds self-limit the accretion on to BHs; however, the very high degree of complexity of the physics of these winds, coupled with our poor understanding of it, hampers more robust conclusions. In all cases, the predicted BH‐bulge relation steepens considerably with respect to the observed one at bulge masses <10 11 M � ; this problem is related to a known excess in the predicted number of small bulges, common to most similar models, so that the reproduction of the correct number of faint AGNs is done at the cost of underestimating their BH masses. This highlights an insufficient downsizing of elliptical galaxies, and hints at another feedback mechanism able to act on the compact discs that form and soon merge at high redshift. The results of this paper reinforce the need for direct investigations of the feedback mechanisms in active galaxies that will be possible with the next generation of astronomical telescopes from submm to

The evolution of Lyman α absorbers in the redshift range $0.5&lt;\textit{z}&lt;1.9$

We investigate the evolution and the statistical properties of the Ly α absorbers of the intergalactic medium (IGM) in the largely unexplored redshift range z = 0.5−1.9. We use high-resolution (R ≥ 30 000) UV (STIS) and optical (VLT/UVES and Keck/HIRES) spectra of nine bright quasars with zem 10 13.64 cm −2 ) thin out faster (γ = 1.50 ± 0.45). The break in their evolution predicted for z = 1.5−1.7 cannot be seen down to z = 0.7. On the other hand, a comparison with values from the literature for the local number density gives a hint that this break occurs at lower redshift. 2. The distribution of the column densities of the absorbers is complete down to NHI = 10 12.90 cm −2 . It can be approximated by a single power law with the exponent β = 1.60 ± 0.03 over almost three orders of magnitude. β is redshift independent. 3. The Ly α lines with lower column densities as well as the higher column density lines show marginal clustering with a 2σ significance over short distances (∆ v< 200 km s −1 and ∆ v< 100 km s −1 , respectively). We do not see any difference in the clustering with either column density or redshift. 4. The distribution of the Doppler parameters has a mean value of b = (34± 22) km s −1 . This value is typical for the analyzed region.

Extended Lyman-α emission around bright quasars

Quasars trace the most massive structures at high redshifts and their presence may influence the evolution of the massive host galaxies. We study the extended Lyman alpha emission line regions (EELRs) around seven bright, mostly radio-quiet quasars (QSOs) at 2.7<z<4.5, and compare luminosities with EELRs around radio-loud QSOs reported in the literature. Using integral field spectroscopy, we analyse the morphology and kinematics of the quiescent Lya EELRs around the QSOs. We find evidence for the presence of EELRs around four radio-quiet and one radio-loud QSO. All EELRs appear asymmetric and the optically brightest QSOs also have the brightest Lya nebulae. For the two brightest nebulae we find velocities between ~600 km s^-1 at the QSO position to ~200 km s^-1 at a distance of 3-4 arcsec from the QSO and surface flux densities up to 2-3*10^{-16} erg cm^-2 s^-1 arcsec^-2. The five EELRs have total Lya luminosities which correspond to ~0.5% of the luminosities from the QSOs broad Lya emission lines. This fraction is an order of magnitude smaller than found for EELRs around radio-loud, steep spectrum QSOs reported in the literature. While the nebulae luminosities are correlated with the QSO Lya luminosities, we find that nebulae luminosities are not correlated with the central QSO ionising fluxes. The presence of gas in the EELRs can be interpreted based on two competing scenarios: either from quasar feedback mechanisms, or from infalling matter. Apart from these two effects, the Lya flux around radio-loud objects can be enhanced due to interactions with the radio jets. The relatively fainter nebulae around radio-quiet QSOs compared to lobe-dominated radio-loud QSOs can be ascribed to this effect, or to significant differences in the environments between the two classes.

Fueling Low‐Level AGN Activity through Stochastic Accretion of Cold Gas

Using a simple description of feedback from black hole growth, we develop an analytic model for the fueling of Seyferts (low-luminosity active galactic nuclei [AGNs]) and their relation to their host galaxies, Eddington ratio distributions, and cosmological evolution. We derive a solution for the time evolution of accretion rates in a feedback-driven blast wave, applicable to large-scale outflows from bright quasars in galaxy mergers, low-luminosity AGNs, and black holes or neutron stars in supernova remnants. Under the assumption that cold gas stochastically accretes onto a central supermassive black hole at a rate set by the dynamics of that gas, our solution determines the evolution of Seyfert light curves. Using this model, we predict the Seyfert luminosity function, duty cycles and AGN lifetimes, and the distribution of host morphologies, Eddington ratios, and obscuration as a function of AGN luminosity and black hole mass, and we find agreement with observations at z = 0. We consider the breakdown of the contribution from this mechanism and from stellar wind and virialized hot gas accretion and merger-driven activity. We also make specific predictions for the weak evolution of the Seyfert luminosity function; i.e., luminosity function of quiescent as opposed to merger-driven activity, as a function of redshift, and for changes in both the slope and scatter of the MBH-σ relation at low MBH. Our modeling provides a quantitative and physical distinction between local, low-luminosity quiescent AGN activity and violent, merger-driven bright quasars. In our picture, the quiescent mode of fueling dominates over a wide range of luminosities (-15 MB -22) at z = 0, where most black hole growth occurs in objects with MBH 107 M☉, in S0 and Sa/b galaxies. However, quasar activity from gas-rich mergers evolves more rapidly with redshift, and by z = 1, quiescent fueling is important only at luminosities an order of magnitude or more below the break in the luminosity function. Consequently, although non-merger-driven fueling is important for black hole growth and the MBH-σ relation at low MBH, it does not significantly contribute to the black hole mass density of the universe or to cosmological backgrounds.