Host Bulge Research Articles

The Black Hole Mass and Photometric Components of NGC 4826

We present infrared photometry and Hubble Space Telescope imaging and spectroscopy of the Sab galaxy NGC 4826. Schwarzschild dynamical modeling is used to measure its central black hole mass M. Photometric decomposition is used to enable a comparison of M to published scaling relations between black hole masses and properties of host bulges. This decomposition implies that NGC 4826 contains classical and pseudobulges of approximately equal mass. The classical bulge has best-fit Sérsic index n = 3.27. The pseudobulge is made up of three parts, an inner lens (n = 0.18 at r ≲ 4″), an outer lens (n = 0.17 at r ≲ 45″), and a n = 0.58 Sérsic component required to match the surface brightness between the lens components. The total V-band luminosity of the galaxy is M VT = −21.07, the ratio of classical bulge to total light is B/T ≃ 0.12, and the ratio of pseudobulge to total light is PB/T ≃ 0.13. The outer disk is exponential (n = 1.07) and makes up D/T = 0.75 of the light of the galaxy. Our best-fit Schwarzschild model has a black hole mass with 1σ uncertainties of M=8.4−0.6+1.7×106M⊙ and a stellar population with a K-band mass-to-light ratio of ϒK=0.46±0.03M⊙L⊙−1 at the assumed distance of 7.27 Mpc. Our modeling is marginally consistent with M = 0 at the 3σ limit. These best-fit parameters were calculated assuming the black hole is located where the velocity dispersion is largest; this is offset from the maximum surface brightness, probably because of dust absorption. The black hole mass—one of the smallest measured by modeling stellar dynamics—satisfies the well known correlations of M with the K-band luminosity, stellar mass, and velocity dispersion of the classical bulge only. In contrast, the black hole is undermassive with respect to the correlation of M with total (classical plus pseudo) bulge luminosity. Thus the composite (classical bulge plus pseudobulge) galaxy NGC 4826 is consistent with previous results on black hole scaling relations and helps to strengthen these results at low black hole masses.

The evolution of supermassive black hole mass–bulge mass relation by a semi-analytical model, ν2GC

ABSTRACT We have investigated the redshift evolution of the relationship between supermassive black hole (SMBH) mass and host bulge mass using a semi-analytical galaxy formation model ν2GC. Our model reproduces the relation in the local universe well. We find that, at high redshift (z ≳ 3), two sequences appear in the SMBH mass–bulge mass plane. The emergence of these two sequences can be attributed to the primary triggers of the growth of the SMBHs and bulges: galaxy mergers and disc instabilities. The growth of SMBHs and bulges as a result of galaxy mergers is responsible for giving rise to the high-mass sequence, in which SMBHs are more massive for a given host bulge mass than in the low-mas sequence. Conversely, disc instabilities are accountable for the emergence of the low-mass sequence. At lower redshifts, galaxy mergers tend to become increasingly deficient in gas, resulting in a preferential increase of bulge mass without a corresponding growth in SMBH mass. This has the effect of causing galaxies in the upper sequence to shift towards the lower one on the SMBH mass–bulge mass plane. The galaxies that undergo dry mergers serve to bridge the gap between the two sequences, eventually leading to convergence into a single relation known in the local universe. Our results suggest that the observations of the SMBH mass–bulge mass relation in high redshifts can provide insight into their growth mechanisms.

Long-term decline of the mid-infrared emission of normal galaxies: dust echo of tidal disruption flare?

We report the discovery of a sample of 19 low redshift (z<0.22) spectroscopically non-Seyfert galaxies that show slow declining mid-infrared (MIR) light-curves (LCs), similar to those of tidal disruption event (TDE) candidates with extreme coronal lines. Two sources also showed a relatively fast rising MIR LCs. They consist of 61% sample of the WISE MIR variable non-Seyfert galaxies with SDSS spectra. In a comparison sample of optically selected Seyfert galaxies, the fraction of sources with such a LC is only 15%. After rejecting 5 plausible obscured Seyfert galaxies with red MIR colours, remaining 14 objects are studied in detail in this paper. We fit the declining part of LC with an exponential law, and the decay time is typically one year. The observed peak MIR luminosities ($\nu L_\nu$) after subtracting host galaxies are in the range of a few 10^42 to 10^44 erg~s^-1 with a median of 5x10^43 erg~s^-1 in the W2 band. The black hole masses distribute in a wide range with more than half in between 10^7 to 10^8 ~M_sun, but significantly different from that of optical/UV selected TDEs. Furthermore, MIR luminosities are correlated with black hole masses, the stellar mass or luminosity of their host bulges. Most galaxies in the sample are red and luminous with an absolute magnitude of r between -20 to -23. We estimate the rate of event about 10^-4 gal^-1~yr^-1 among luminous red galaxies. We discuss several possibilities for the variable infrared sources, and conclude that most likely, they are caused by short sporadic fueling to the supermassive black holes via either the instability of accretion flows or tidal disruption of stars.

Hubble Space Telescope Observations of Extended [O iii]λ 5007 Emission in Nearby QSO2s: New Constraints on AGN Host Galaxy Interaction

Abstract We present a Hubble Space Telescope survey of extended [O iii] λ5007 emission for a sample of 12 nearby (z &lt; 0.12), luminous Type 2 quasars (QSO2s), which we use to measure the extent and kinematics of their AGN-ionized gas. We find that the size of the observed [O iii] regions scale with luminosity in comparison to nearby, less luminous Seyfert galaxies and radially outflowing kinematics to exist in all targets. We report an average maximum outflow radius of ∼600 pc, with gas continuing to be kinematically influenced by the central active galactic nucleus (AGN) out to an average radius of ∼1130 pc. These findings question the effectiveness of AGNs being capable of clearing material from their host bulge in the nearby universe and suggest that disruption of gas by AGN activity may prevent star formation without requiring evacuation. Additionally, we find a dichotomy in our targets when comparing [O iii] radial extent and nuclear FWHM, where QSO2s with compact [O iii] morphologies typically possess broader nuclear emission lines.

Limits on the growth rate of supermassive black holes at early cosmic epochs

The effect of AGN wind feedback on the accretion rate and mass evolution of supermassive black holes (SMBH) is considered. It is shown, under reasonable assumptions, that the rate at which gas can be supplied to a SMBH at the center of a young galaxy, is limited to $\sim 20 (\sigma/350~ {\rm km ~s^{-1}})^4~M_\odot/yr$ (where $\sigma$ is the velocity dispersion of the host bulge) by interaction of winds expelled from the innermost regions of the accretion flow with the gas in the bulge. This rate is independent of the black hole mass but is sensitive to the properties of the host bulge. It is further argued that the interaction of the wind and the inflowing gas in the bulge can strongly affect the structure of the accretion flow in the super-Eddington regime, potentially leading to highly super-Eddington accretion into the SMBH. About 300 Myr after the onset of the accretion phase, the AGN wind expels all the gas from the bulge and the accretion rate is strongly suppressed. This scenario is in remarkable agreement with recent observations, as it (i) reveals the origin of the maximal observed accretion rates, (ii) accounts for the inferred growth rate of SMBHs at high redshift (independent of their initial seeds masses), (iii) elucidates the decline in the accretion rate at lower redshifts, and (iv) explains the relation between $\sigma$ and the mass $M_{BH}$ of the central SMBH, measured in the local Universe.

POWERFUL RADIO EMISSION FROM LOW-MASS SUPERMASSIVE BLACK HOLES FAVORS DISK-LIKE BULGES

ABSTRACT The origin of spin of low-mass supermassive black holes (SMBHs) is still a puzzle at present. We report here a study on the host galaxies of a sample of radio-selected nearby (z &lt; 0.05) Seyfert 2 galaxies with a BH mass of 106–7 M ⊙. By modeling the SDSS r-band images of these galaxies through a two-dimensional bulge+disk decomposition, we identify a new dependence of SMBH's radio power on host bulge surface brightness profiles, in which more powerful radio emission comes from an SMBH associated with a more disk-like bulge. This result means low-mass and high-mass SMBHs are spun up by two entirely different modes that correspond to two different evolutionary paths. A low-mass SMBH is spun up by a gas accretion with significant disk-like rotational dynamics of the host galaxy in the secular evolution, while a high-mass one by a BH–BH merger in the merger evolution.

CHANDRA X-RAY AND HUBBLE SPACE TELESCOPE IMAGING OF OPTICALLY SELECTED KILOPARSEC-SCALE BINARY ACTIVE GALACTIC NUCLEI. II. HOST GALAXY MORPHOLOGY AND AGN ACTIVITY*

ABSTRACT Binary active galactic nuclei (AGNs) provide clues to how gas-rich mergers trigger and fuel AGNs and how supermassive black hole (SMBH) pairs evolve in a gas-rich environment. While significant effort has been invested in their identification, the detailed properties of binary AGNs and their host galaxies are still poorly constrained. In a companion paper, we examined the nature of ionizing sources in the double nuclei of four kiloparsec-scale binary AGNs with redshifts between 0.1 and 0.2. Here, we present their host galaxy morphology based on F336W (U-band) and F105W (Y-band) images taken by the Wide Field Camera 3 on board the Hubble Space Telescope. Our targets have double-peaked narrow emission lines and were confirmed to host binary AGNs with follow-up observations. We find that kiloparsec-scale binary AGNs occur in galaxy mergers with diverse morphological types. There are three major mergers with intermediate morphologies and a minor merger with a dominant disk component. We estimate the masses of the SMBHs from their host bulge stellar masses and obtain Eddington ratios for each AGN. Compared with a representative control sample drawn at the same redshift and stellar mass, the AGN luminosities and Eddington ratios of our binary AGNs are similar to those of single AGNs. The U − Y color maps indicate that clumpy star-forming regions could significantly affect the X-ray detection of binary AGNs, e.g., the hardness ratio. Considering the weak X-ray emission in AGNs triggered in merger systems, we suggest that samples of X-ray-selected AGNs may be biased against gas-rich mergers.

The young nuclear stellar disc in the SB0 galaxy NGC 1023

Small kinematically-decoupled stellar discs with scalelengths of a few tens of parsec are known to reside in the centre of galaxies. Different mechanisms have been proposed to explain how they form, including gas dissipation and merging of globular clusters. Using archival Hubble Space Telescope imaging and ground-based integral-field spectroscopy, we investigated the structure and stellar populations of the nuclear stellar disc hosted in the interacting SB0 galaxy NGC 1023. The stars of the nuclear disc are remarkably younger and more metal rich with respect to the host bulge. These findings support a scenario in which the nuclear disc is the end result of star formation in metal enriched gas piled up in the galaxy centre. The gas can be of either internal or external origin, i.e. from either the main disc of NGC 1023 or the nearby satellite galaxy NGC 1023A. The dissipationless formation of the nuclear disc from already formed stars, through the migration and accretion of star clusters into the galactic centre is rejected.

The impact of dust in host galaxies on quasar luminosity functions

Abstract We have investigated effects of dust attenuation on quasar luminosity functions at z ∼ 2 using a semi-analytic galaxy formation model combined with a large cosmological N-body simulation. We estimate the dust attenuation of quasars self-consistently with that of galaxies by considering the dust in their host bulges. We find that the luminosity of the bright quasars is strongly dimmed by the dust attenuation, ∼2 mag in the B-band. Assuming the empirical bolometric corrections for active galactic nuclei (AGNs) by Marconi et al., we find that this dust attenuation is too strong to explain the B-band and X-ray quasar luminosity functions simultaneously. We consider two possible mechanisms that weaken the dust attenuation. As such a mechanism, we introduce a time delay for AGN activity, that is, gas fuelling to a central black hole starts sometime after the beginning of the starburst induced by a major merger. The other is the anisotropy in the dust distribution. We find that in order to make the dust attenuation of the quasars negligible, either the gas accretion into the black holes has to be delayed at least three times the dynamical time-scale of their host bulges or the dust covering factor is as small as ∼0.1.

The Coevolution of Galaxies and Supermassive Black Holes: Insights from Surveys of the Contemporary Universe

We summarize what large surveys of the contemporary Universe have taught us about the physics and phenomenology of the processes that link the formation and evolution of galaxies with their central supermassive black holes. We present a picture in which the population of active galactic nuclei (AGNs) can be divided into two distinct populations. The radiative-mode AGNs are associated with black holes (BHs) that produce radiant energy powered by accretion at rates in excess of ∼1% of the Eddington limit. They are primarily associated with less massive BHs growing in high-density pseudobulges at a rate sufficient to produce the total mass budget in these BHs in ∼10 Gyr. The circumnuclear environment contains high-density cold gas and associated star formation. Major mergers are not the primary mechanism for transporting this gas inward; secular processes appear dominant. Stellar feedback is generic in these objects, and strong AGN feedback is seen only in the most powerful AGNs. In jet-mode AGNs the bulk of energetic output takes the form of collimated outflows (jets). These AGNs are associated with the more massive BHs in more massive (classical) bulges and elliptical galaxies. Neither the accretion onto these BHs nor star formation in their host bulge is significant today. These AGNs are probably fueled by the accretion of slowly cooling hot gas that is limited by the feedback/heating provided by AGN radio sources. Surveys of the high-redshift Universe paint a similar picture. Noting that the volume-averaged ratio of star formation to BH growth has remained broadly constant over the past 10 Gyrs, we argue that the processes that linked the cosmic evolution of galaxies and BHs are still at play today.

THE INFLUENCE OF DARK MATTER HALOS ON DYNAMICAL ESTIMATES OF BLACK HOLE MASS: 10 NEW MEASUREMENTS FOR HIGH-σ EARLY-TYPE GALAXIES

Adaptive-Optics assisted SINFONI observations of the central regions of ten early-type galaxies are presented. Based primarily on the SINFONI kinematics, ten black hole masses occupying the high-mass regime of the M_BH-sigma relation are derived using three-integral Schwarzschild models. The effect of dark matter inclusion on the black hole mass is explored. The omission of a dark matter halo in the model results in a higher stellar mass-to-light ratio, especially when extensive kinematic data are used in the model. However, when the diameter of the sphere of influence -- computed using the black hole mass derived without a dark halo -- is at least 10 times the PSF FWHM during the observations, it is safe to exclude a dark matter component in the dynamical modeling, i.e. the change in black hole mass is negligible. When the spatial resolution is marginal, restricting the mass-to-light ratio to the right value returns the correct M_BH although dark halo is not present in the model. Compared to the M_BH-sigma and M_BH-L relations of McConnell et al. (2011), the ten black holes are all more massive than expected from the luminosities and seven black hole masses are higher than expected from the stellar velocity dispersions of the host bulges. Using new fitted relations which include the ten galaxies, we find that the space density of the most massive black holes (M_BH >~ 10^9 Msun) estimated from the M_BH-L relation is higher than the estimate based on the M_BH-sigma relation and the latter is higher than model predictions based on quasar counts, each by about an order of magnitude.

CHARACTERIZATION OF A SAMPLE OF INTERMEDIATE-TYPE ACTIVE GALACTIC NUCLEI. II. HOST BULGE PROPERTIES AND BLACK HOLE MASS ESTIMATES

We present a study of the host bulge properties and their relations with the black hole mass on a sample of 10 intermediate-type active galactic nuclei (AGN). Our sample consists mainly of early type spirals, four of them hosting a bar. For 70$^{+10}_{-17}%$ of the galaxies we have been able to determine the type of the bulge, and find that these objects probably harbor a pseudobulge or a combination of classical bulge/ pseudobulge, suggesting that pseudobulges might be frequent in intermediate-type AGN. In our sample, 50\pm14% of the objects show double-peaked emission lines. Therefore, narrow double-peaked emission lines seem to be frequent in galaxies harboring a pseudobulge or a combination of classical bulge/ pseudobulge. Depending on the bulge type, we estimated the black hole mass using the corresponding $M_{BH} - {\sigma*}$ relation and found them with a range of: 5.69$\pm$0.21 $<$ $\log M_{BH}^{\sigma*}$ $<$ 8.09$\pm$0.24. Comparing these $M_{BH}^{\sigma*}$ values with masses derived from the FWHM of H$\beta$ and the continuum luminosity at 5100 \AA from their SDSS-DR7 spectra ($M_{BH}$) we find that eight out of ten (80$^{+7}_{-17}$%) galaxies have black hole masses that are compatible within a factor of 3. This result would support that $M_{BH}$ and $M_{BH}^{\sigma*}$ are the same for intermediate-type AGN as has been found for type 1 AGN. However, when the type of the bulge is taken into account only 3 out of the 7 (43$^{+18}_{-15}%$) objects of the sample have their $M_{BH}^{\sigma*}$ and $M_{BH}$ compatible within 3-$\sigma$ errors. We also find that estimations based on the $M_{BH}-\sigma*$ relation for pseudobulges are not compatible in 50$\pm20%$ of the objects.

Black holes in pseudobulges: demography and models

There is mounting evidence that a significant fraction of Black Holes (BHs) today live in late-type galaxies, including bulge-less galaxies and those hosting pseudobulges, and are significantly undermassive with respect to the scaling relations followed by their counterpart BHs in classical bulges of similar stellar (or even bulge) mass. Here we discuss the predictions of two state-of-the-art hierarchical galaxy formation models in which BHs grow via mergers and, in one, also via disk instability. Our aim is to understand if the wealth of new data on local BH demography is consistent with standard models. We follow the merger trees of representative subsamples of BHs and compute the fractional contributions of different processes to the final BH mass. We show that the model in which BHs always closely follow the growth of their host bulges, also during late disk instabilities (i.e., bars), produces too narrow a distribution of BHs at fixed stellar mass to account for the numerous low-mass BHs now detected in later-type galaxies. Models with a looser connection between BH growth and bar instability instead predict the existence of a larger number of undermassive BHs, in better agreement with the observations. The scatter in the updated local BH-bulge mass relation (with no restriction on galaxy type) appears to be quite large when including later-type systems, but it can still be managed to be reproduced within current hierarchical models. However, the fuelling of BHs during the late bar-instability mode needs to be better quantified/improved to properly fit the data. We conclude discussing how the possibly large number of BHs in later type galaxies demands for an in-depth revision of the local BH mass function and its modelling.

The role of secular evolution in the black hole growth of narrow-line Seyfert 1 galaxies

Narrow-Line Seyfert 1 (NLS1) galaxies show extreme properties with respect to the other Seyfert galaxies. Indeed, they are thought to be accreting at Eddington rates and to possess low mass black holes. Therefore, they may represent a key class of objects for understanding the co-evolution of black holes and their host galaxies. We propose that NLS1s represent a class of AGN in which the black hole growth is, and has always been, dominated by secular evolution. Firstly, by looking at the NLS1 host galaxy properties in the literature, we show that the evolution of NLS1s is presently driven by secular processes, much more so than for Broad-Line Seyfert 1s (BLS1s). Secondly, we study the bulges of NLS1 and BLS1 galaxies. Our results demonstrate that NLS1 host bulges are pseudo-bulges and are statistically different from BLS1 bulges. This difference points to the particular importance of secular processes in the past evolution of their hosts. We build on this result to understand the implications on their evolution and the duration of their duty cycle. We show that NLS1s are not necessarily in a special phase of black hole growth and that several Gyr are required for their black hole masses to become similar to BLS1s. Finally, in the light of our results, we discuss the location of NLS1 galaxies on the MBH-\sigma plane and speculate about the connection between the NLS1 galaxy properties and their black hole spin.

On the evolution of the intrinsic scatter in black hole versus galaxy mass relations

We present results on the evolution of the intrinsic scatter of black hole masses considering different implementations of a model in which black holes only grow via mergers. We demonstrate how merger driven growth affects the correlations between black hole mass and host bulge mass. The simple case of an initially log-normal distributed scatter in black hole and bulge masses combined with random merging within the galaxy population results in a decreasing scatter with merging generation/number as predicted by the Central-limit theorem. In general we find that the decrease in scatter {\sigma} is well approximated by {\sigma}merg(m) = {\sigma}ini \times (m + 1)^(-a/2) with a = 0.42 for a range of mean number of mergers m < 50. For a large mean number of mergers (m > 100) we find a convergence to a = 0.61. This is valid for a wide range of different initial distributions, refill-scenarios or merger mass-ratios. Growth scenarios based on halo merger trees of a (100 Mpc)^3 dark matter LambdaCDM-simulation show a similar behaviour with a scatter decrease of a = 0.30 with typical number of mergers m < 50 consistent with random merging (best matching model: a = 0.34). Assuming a present day scatter of 0.3 dex in black hole mass and a mean number of mergers not exceeding m = 50 our results imply a scatter of 0.6 dex at z = 3 and thus a possible scenario in which overmassive (and undermassive) black holes at high redshift are a consequence of a larger intrinsic scatter in black hole mass. A simple toy model connecting the growth of black holes to the growth of LambdaCDM dark matter halos via mergers, neglecting any contribution from accretion, yields a consistent M\cdot -MBulge relation at z = 0 - if we assume the correct initial relation.

Discriminating between the physical processes that drive spheroid size evolution

Massive galaxies at high-z have smaller effective radii than those today, but similar central densities. Their size growth therefore relates primarily to the evolving abundance of low-density material. Various models have been proposed to explain this evolution, which have different implications for galaxy, star, and BH formation. We compile observations of spheroid properties as a function of redshift and use them to test proposed models. Evolution in progenitor gas-richness with redshift gives rise to initial formation of smaller spheroids at high-z. These systems can then evolve in apparent or physical size via several channels: (1) equal-density 'dry' mergers, (2) later major or minor 'dry' mergers with less-dense galaxies, (3) adiabatic expansion, (4) evolution in stellar populations & mass-to-light-ratio gradients, (5) age-dependent bias in stellar mass estimators, (6) observational fitting/selection effects. If any one of these is tuned to explain observed size evolution, they make distinct predictions for evolution in other galaxy properties. Only model (2) is consistent with observations as a dominant effect. It is the only model which allows for an increase in M_BH/M_bulge with redshift. Still, the amount of merging needed is larger than that observed or predicted. We therefore compare cosmologically motivated simulations, in which all these effects occur, & show they are consistent with all the observational constraints. Effect (2), which builds up an extended low-density envelope, does dominate the evolution, but effects 1,3,4, & 6 each contribute ~20% to the size evolution (a net factor ~2). This naturally also predicts evolution in M_BH-sigma similar to that observed.

Applying the jet feedback mechanism to core-collapse supernova explosions

I examine a mechanism by which two fast narrow jets launched by a newly formed neutron star (NS), or a black hole (BH), at the center of a core collapse supernovae (CCSN), form two slow massive wide (SMW) jets. Such SMW jets are assumed as initial conditions in some numerical simulations that demonstrate that SMW jets can expel the rest of the collapsing star. The original fast narrow jets must deposit their energy inside the star via shock waves, and form two hot bubbles that accelerate a much larger mass to form SMW jets. To prevent the jets from penetrating through the still infalling gas and escape instead of forming the hot bubbles, the jets should encounter fresh infalling gas. This condition is met if the jets' axis changes its direction. The exact condition is derived. In addition, to maintain a small neutrino cooling the fast narrow jets must be shocked at a distance r>1000 km from the core, such that most of the post-shock energy is in radiation, and temperature is not too high. The scenario proposed here was shown to be able to suppress star formation in newly formed galaxies, and in forming SMW jets in cooling flow clusters of galaxies and in planetary nebulae. Namely, I suggest that NSs (or BHs) at the center of CCSNs shut off their own growth and expel the rest of the mass available for accretion by the same mechanism that super-massive BHs shut off their own growth, as well as that of their host bulge, in young galaxies.

THE SINS SURVEY: BROAD EMISSION LINES IN HIGH-REDSHIFT STAR-FORMING GALAXIES

High signal-to-noise, representative spectra of star-forming galaxies at z ~ 2, obtained via stacking, reveal a high-velocity component underneath the narrow Hα and [NII] emission lines. When modeled as a single Gaussian, this broad component has FWHM 1500 km s–1; when modeled as broad wings on the Hα and [N II] features, it has FWHM ≳ 500 km s^(–1). This feature is preferentially found in the more massive and more rapidly star-forming systems, which also tend to be older and larger galaxies. We interpret this emission as evidence of either powerful starburst-driven galactic winds or active supermassive black holes (SMBHs). If galactic winds are responsible for the broad emission, the observed luminosity and velocity of this gas imply mass outflow rates comparable to the star formation rate. On the other hand, if the broad-line regions of active black holes account for the broad feature, the corresponding black holes masses are estimated to be an order of magnitude lower than those predicted by local scaling relations, suggesting a delayed assembly of SMBHs with respect to their host bulges.

CO-EVOLUTION OF SUPERMASSIVE BLACK HOLE AND HOST GALAXY FROMz∼ 1 TOz= 0

Stellar masses of bulges in hosts of active galactic nuclei (AGNs) and black hole masses in the AGNs are derived at z = 0.5-1.15 to study evolution of the black hole-to-bulge mass relation. In order to derive bulge stellar masses, we use a sample of type-2 AGNs to avoid the bright nuclear light. 34 type-2 AGNs are selected from the spectroscopically identified X-ray sources in the Chandra Deep Field South. We use optical images from the Hubble Space Telescope, and near- and mid-infrared photometry from the Very Large Telescope and the Spitzer Space Telescope. The bulge components are derived by fitting the two-dimensional surface brightness model consisting of a bulge and a disk component to the optical images. We derive stellar masses (M bulge) and star formation rates (SFRs) of the bulge components by spectral energy distribution fitting. The derived M bulge ranges over 109-1011 M ☉, and the estimated SFR is 0.01-100 M ☉ yr-1. Masses of supermassive black holes (SMBHs; M •) and black hole accretion rates (BHARs) are estimated with the absorption-corrected X-ray luminosities in the 2-10 keV band under an assumption of the constant Eddington ratio of 0.1 and the constant energy conversion factor of 0.1. Resulting black hole masses and BHARs range over 105.5-108 M ☉ and 0.001-1 M ☉ yr-1, respectively. For luminous AGNs, the estimated M •/M bulge ratio is ~4 × 10–4 in the median, which is lower than that for local galaxies and for type-2 AGNs at z ~ 0.2. However, these differences are within uncertainty and are not significant. This can imply that SMBHs and their host galaxies are evolving almost holding the constant M •/M bulge ratio from z ~ 1.0 to 0 in a cosmological timescale. Meanwhile, the estimated BHAR/SFR ratio is about 60 times larger than the M •/M bulge ratio in the median value. This indicates that growths of SMBHs and their host bulges do not proceed simultaneously in a shorter timescale such as an AGN phase.

A CHARACTERISTIC DIVISION BETWEEN THE FUELING OF QUASARS AND SEYFERTS: FIVE SIMPLE TESTS

Given the existence of the M_BH-sigma relation, models of self-regulated black hole (BH) growth require both a fuel supply and growth of the host bulge to deepen the potential, or else the system will either starve or self-regulate without sustained activity. This suggests that bright quasars must be triggered in major mergers: a large fraction of the galaxy must be converted to new bulge mass in a dynamical time or less. Low-luminosity AGN, in contrast, require little bulge growth and small gas supplies, and could be triggered in more common non-merger events. This predicts a transition to merger-induced fueling around the traditional quasar-Seyfert luminosity divide (growth of BH masses above/below 10^7 M_sun). We compile observations to test several predictions of such a division, including: (1) A transition to bulge-dominated hosts. (2) A transition between 'pseudobulges' and 'classical' bulges hosting the remnant BHs: pseudobulges are formed in secular processes and minor mergers, whereas classical bulges are relics of major mergers. (3) An increase in the amplitude of small-scale clustering where mergers are more efficient. (4) Different redshift evolution, with gas-rich merger rates rising to redshifts z>2 while secular processes are relatively constant in time. (5) An increasing prominence of post-starburst features in more luminous systems. Our compilation of observations provides tentative evidence for the predicted division around the Seyfert-quasar threshold. We discuss how future observations can improve these constraints and break degeneracies between different fueling models.