Quasar Formation Research Articles

Study of the $ 50$ kpc circumgalactic environment around the merger system J2057-0030 at $ z $ sim 4.6 using ALMA

We present ALMA band-7 observations of J2057-0030, a multi-component merger system at $z$ sim 4.68 spanning at least 50 kpc in size, using the C$ ii lambda 157.74 mu m line and underlying far-infrared (FIR) continuum. We find two main components, the quasar (QSO) and a dusty star-forming galaxy (DSFG), both detected in C$ ii and continuum emission as well as multiple neighboring clumps detected only in C$ ii . Three of these clumps form a (tidal) tail that extends from the QSO in a straight direction to the west, covering a projected distance of sim 10 kpc. This perturbed morphology, added to a spatial distance of sim 20 kpc and a velocity offset of $ v $ = 68 km s$^ $ between the QSO and the DSFG, strongly supports a merging scenario. By fitting a spectral energy distribution model to the continuum data, we estimate star formation rates of approx 402 $M_ odot $ yr$^ $ for the QSO host and approx 244 $M_ odot $ yr$^ $ for the DSFG, which locate them on or close to the main sequence of star-forming galaxies. The J2057-0030 QSO was selected for being one of the brightest unobscured quasars at its redshift while presenting a rather modest star formation rate. Based on a commonly accepted paradigm regarding the formation of quasars, this result is expected for a quasar that has already passed an obscured phase of rapid star formation during a major merger. However, we see that the merger event in this system is far from being finished, and it is rather likely somewhere between the first pericenter and subsequent close passages. This is presumably another case of a high-$z$ quasar residing in a high-density environment with a companion obscured galaxy.

Modeling quasar proximity zones in a realistic cosmological environment with a self-consistent light curve

ABSTRACT We study quasar proximity zones in a simulation that includes a self-consistent quasar formation model and realistic intergalactic medium (IGM) environments. The quasar host halo is 1013 M⊙ at z = 6, more massive than typical halos studied in previous work. Between 6 < z < 7.5, the quasar luminosity varies rapidly, with a mean magnitude of MUV, mean = −24.8 and the fluctuation reaching up to two orders of magnitude. Using this light curve to post-process the dense environment around the quasar, we find that the proximity zone size (Rp) ranges between 0.5 and 5 pMpc. We show that the light curve variability causes a similar degree of scatter in Rp as does the density fluctuation, both of which result in a standard deviation of ∼0.3 pMpc. The Rp traces the light curve fluctuations closely but with a time delay of ∼104 yr, breaking the correspondence between the Rp and the contemporaneous MUV. This also indicates that we can only infer quasar activity within the past ∼104 yr instead of the integrated lifetime from Rp in the later part of cosmic reionization. Compared with the variable light curve, a constant light curve underestimates the Rp by 13 per cent at the dim end (MUV ∼ −23.5), and overestimates the Rp by 30 per cent at the bright end (MUV ∼ −26). By calculating the Rp generated by a number of quasars, we show that variable light curves predict a wider Rp distribution than lightbulb models, and readily explain the extremely small Rp values that have been observed.

Dark energy black holes with intermediate masses at high redshifts: An earlier generation of quasars and observations

Dark energy is the largest fraction of the energy density of our universe — yet it remains one of the enduring enigmas of our times. Here we show that dark energy can be used to solve 2 tantalizing mysteries of the observable universe. We build on existing models of dark energy linked to neutrino masses. In these models, dark energy can undergo phase transitions and form black holes. Here we look at the implications of the family structure of neutrinos for the phase transitions in dark energy and associated peaks in black hole formation. It has been previously shown that one of these peaks in black hole formation is associated with the observed peak in quasar formation at redshifts [Formula: see text]. Here, we predict that there will also be an earlier peak in the dark energy black holes at high redshifts [Formula: see text]. These dark energy black holes formed at high redshifts are Intermediate Mass Black Holes (IMBHs). These dark energy black holes at large redshift can help explain both the EDGES observations and the observations of large Supermassive Black Holes (SMBHs) at redshifts of 7 or larger. This work directs us to actively look for these dark energy black holes at these high redshifts as predicted here through targeted searches for these black holes at the redshifts [Formula: see text] near 18. There is a slight dependence of the location of the peak on the lightest neutrino mass. This may enable a measurement of the lightest neutrino mass — something which has eluded us so far. Finding these dark energy black holes of Intermediate Mass should be within the reach of upcoming observations — particularly with the James Webb Space Telescope — but perhaps also through the use of other innovative techniques focusing specifically on the redshifts [Formula: see text] around 18.

The collapse of atomically cooled primordial haloes – I. High Lyman–Werner backgrounds

ABSTRACT Pristine, atomically cooled haloes may be the sites of primordial quasar formation because atomic cooling triggers rapid baryon collapse that can create 104–105 M⊙ black hole seeds. However, no numerical simulation has ever followed the collapse of these haloes for the times required to form supermassive stars and direct-collapse black holes (DCBHs). We have now modelled baryon collapse in atomically cooled haloes with a wide range of spin parameters and assembly histories for times that are sufficient for DCBH formation. Fragmentation of accretion discs after ∼500 kyr is nearly ubiquitous in these haloes and in most cases leads to the formation of binary or multiple supermassive stellar systems. They also confirm that rapid baryon collapse proceeds for the times required for these stars to form DCBHs. Our simulations suggest that binary or even multiple DCBH formation was the rule rather than the exception in the primordial Universe.

The X–shooter/ALMA Sample of Quasars in the Epoch of Reionization. II. Black Hole Masses, Eddington Ratios, and the Formation of the First Quasars

We present measurements of black hole masses and Eddington ratios (λ Edd) for a sample of 38 bright (M 1450 < −24.4 mag) quasars at 5.8 ≲ z ≲ 7.5, derived from Very Large Telescope/X–shooter near–IR spectroscopy of their broad C iv and Mg ii emission lines. The black hole masses (on average, M BH ∼ 4.6 × 109 M ⊙) and accretion rates (0.1 ≲ λ Edd ≲ 1.0) are broadly consistent with that of similarly luminous 0.3 ≲ z ≲ 2.3 quasars, but there is evidence for a mild increase in the Eddington ratio above z ≳ 6. Combined with deep Atacama Large Millimeter/submillimeter Array (ALMA) observations of the [C II] 158 μm line from the host galaxies and VLT/MUSE investigations of the extended Lyα halos, this study provides fundamental clues to models of the formation and growth of the first massive galaxies and black holes. Compared to local scaling relations, z ≳ 5.7 black holes appear to be over-massive relative to their hosts, with accretion properties that do not change with host galaxy morphologies. Assuming that the kinematics of the T ∼ 104 K gas, traced by the extended Lyα halos, are dominated by the gravitational potential of the dark matter halo, we observe a similar relation between black hole mass and circular velocity as reported for z ∼ 0 galaxies. These results paint a picture where the first supermassive black holes reside in massive halos at z ≳ 6 and lead the first stages of galaxy formation by rapidly growing in mass with a duty cycle of order unity. The duty cycle needs to drastically drop toward lower redshifts, while the host galaxies continue forming stars at a rate of hundreds of solar masses per year, sustained by the large reservoirs of cool gas surrounding them.

The formation of the first quasars: the black hole seeds, accretion, and feedback models

ABSTRACT Supermassive black holes (SMBHs) of $\sim 10^9\, \rm M_{\odot }$ are generally believed to be the central engines of the luminous quasars observed at z ≳ 6, but their astrophysical origin remains elusive. To investigate the formation of these distant quasars, we perform a suite of zoom-in simulations on a favourable halo, with a mass of $\sim 10^{13}\, \rm M_{\odot }$ at z = 6 and a history of multiple major mergers, ideal for BH growth. We test BH seeds of $10 {\!-\!} 10^6\, \rm M_{\odot }$, and various accretion and feedback models, including thin-disc and slim-disc accretion. We find that abundant gas supply and efficient angular momentum transport by gravitational torques are critical to BH accretion, and that the final BH mass depends strongly on the seed mass and radiative efficiency which in turn depends on feedback model. In our simulations, heavy seeds of $\gtrsim 10^4\, \rm M_{\odot }$ can grow rapidly to SMBHs of $10^8 {\!-\!} 10^9\, \rm M_{\odot }$ by z ∼6 in both thin and slim disc accretion models, provided that the duty cycle of near-Eddington accretion with an Eddington ratio λEdd ≳ 0.6 is maintained at $\gtrsim 40{{\ \rm per\ cent}}$. In particular, for a $10^5\, \rm M_{\odot }$ seed, both our fiducial model and the supercritical accretion model with no spin produce bright quasars with SMBHs of $\sim 10^9\, \rm M_{\odot }$ at z ∼ 7.5. On the other hand, the light seeds of $\lesssim 10^3\, \rm M_{\odot }$ failed to grow to $10^8\, \rm M_{\odot }$ by z ∼ 6 in our simulations. We caution that the results are inconclusive due to limitations of our numerical methods and physical models, and we stress the need for further investigations on the growth of BH seeds with more advanced methods.

Kinematics and star formation of high-redshift hot dust-obscured quasars as seen by ALMA

Hot, dust-obscured galaxies (Hot DOGs) are a population of hyper-luminous obscured quasars identified by WISE. We present ALMA observations of the [C II] 158 μm fine-structure line and underlying dust continuum emission in a sample of seven of the most extremely luminous (EL; Lbol ≥ 1014 L⊙) Hot DOGs, at redshifts of z ≃ 3.0−4.6. The [C II] line is robustly detected in four objects, tentatively in one, and likely to have been red-shifted out of the spectral window in the remaining two, based on additional data. On average, [C II] is red-shifted by ≃780 km s−1 from rest-frame ultraviolet emission lines. EL Hot DOGs consistently exhibit very high [C II] surface densities, with Σ[CII] ≃ 1−2 × 109 L⊙ kpc−2, which is as high as the most extreme cases seen in other high-redshift quasars. As a population, EL Hot DOG hosts seem to be roughly centered on the main sequence of star-forming galaxies, but the uncertainties are substantial and individual sources can fall above and below. The average, intrinsic [C II] and dust continuum sizes (FWHMs) are ≃2.1 kpc and ≃1.6 kpc, respectively, with a very narrow range of line-to-continuum size ratios, 1.61 ± 0.10, suggesting they could be linearly proportional. The [C II] velocity fields of EL Hot DOGs are diverse: from barely rotating structures, to resolved hosts with ordered, circular motions, to complex, disturbed systems that are likely the result of ongoing mergers. In contrast, all sources display large line-velocity dispersions, FWHM[CII] ≳ 500 km s−1, which are, on average, larger than optically and IR-selected quasars at similar or higher redshifts. We argue that one possible hypothesis that explains the lack of a common velocity structure, the systematically large dispersion of the ionized gas, and the presence of nearby companion galaxies, may be that the EL Hot DOG phase could be recurrent, rather than a single event. The dynamical friction from the frequent in-fall of neighbor galaxies and gas clumps, along with the subsequent quasar feedback, would contribute to the high turbulence of the gas within the host in a process that could potentially trigger not only one continuous EL, obscured event –but instead a number of recurrent, shorter-lived episodes as long as external accretion continues.

The Infrared Emission and Vigorous Star Formation of Low-redshift Quasars

Abstract The star formation activity of the host galaxies of active galactic nuclei provides valuable insights into the complex interconnections between black hole growth and galaxy evolution. A major obstacle arises from the difficulty of estimating accurate star formation rates (SFRs) in the presence of a strong active galactic nucleus. Analyzing the 1–500 μm spectral energy distributions and high-resolution mid-infrared spectra of low-redshift (z &lt; 0.5) Palomar–Green quasars with bolometric luminosity of ∼1044.5–1047.5 erg s−1, we find, from comparison with an independent SFR indicator based on [Ne II] 12.81 μm and [Ne III] 15.56 μm, that the torus-subtracted, total infrared (8–1000 μm) emission yields robust SFRs in the range of ∼1–250 M ⊙ yr−1. Combined with available stellar mass estimates, the vast majority (∼75%–90%) of the quasars lie on or above the main sequence of local star-forming galaxies, including a significant fraction (∼50%–70%) that would qualify as starburst systems. This is further supported by the high star formation efficiencies derived from the gas content inferred from the dust masses. Inspection of high-resolution Hubble Space Telescope images reveals a wide diversity of morphological types, including a number of starbursting hosts that have not experienced significant recent dynamical perturbations. The origin of the high star formation efficiency is unknown.

Unveiling early black hole growth with multifrequency gravitational wave observations

ABSTRACT Third-generation ground-based gravitational wave interferometers, like the Einstein Telescope (ET), Cosmic Explorer, and the Laser Interferometer Space Antenna (LISA), will detect coalescing binary black holes over a wide mass spectrum and across all cosmic epochs. We track the cosmological growth of the earliest light and heavy seeds that swiftly transit into the supermassive domain using a semi-analytical model for the formation of quasars at z = 6.4, 2, and 0.2, in which we follow black hole coalescences driven by triple interactions. We find that light-seed binaries of several $10^2 \, {\rm M_\odot }$ are accessible to ET with a signal-to-noise ratio (S/N) of 10–20 at 6 &amp;lt; z &amp;lt; 15. They then enter the LISA domain with larger S/N as they grow to a few $10^4 \, {\rm M_\odot }$. Detecting their gravitational signal would provide first time evidence that light seeds form, grow, and dynamically pair during galaxy mergers. The electromagnetic emission of accreting black holes of similar mass and redshift is too faint to be detected even for the deepest future facilities. ET will be our only chance to discover light seeds forming at cosmic dawn. At 2 &amp;lt; z &amp;lt; 8, we predict a population of ‘starved binaries’, long-lived marginally growing light-seed pairs, to be loud sources in the ET bandwidth (S/N &amp;gt; 20). Mergers involving heavy seeds (${\sim} 10^5\!-\!10^6 \, {\rm M_\odot }$) would be within reach up to z = 20 in the LISA frequency domain. The lower z model predicts $11.25 \, (18.7)$ ET (LISA) events per year, overall.

Cosmic variance of z &amp;gt; 7 galaxies: prediction from bluetides

ABSTRACT In the coming decade, a new generation of telescopes, including JWST and WFIRST, will probe the period of the formation of first galaxies and quasars, and open up the last frontier for structure formation. Recent simulations and observations have suggested that these galaxies are strongly clustered (with large-scale bias ≳6), and therefore have significant cosmic variance. In this work, we use bluetides, the largest volume cosmological simulation of galaxy formation, to directly estimate the cosmic variance for current and upcoming surveys. Given its resolution and volume, bluetides can probe the bias and cosmic variance of z &amp;gt; 7 galaxies between magnitude MUV ∼ −16 and MUV ∼ −22 over survey areas ∼0.1 arcmin2 to ∼10 deg2. Within this regime, the cosmic variance decreases with survey area/ volume as a power law with exponents between ∼−0.25 and ∼−0.45. For the planned 10 deg2 field of WFIRST, the cosmic variance is between $3{{\ \rm per\ cent}}$ and $10{{\ \rm per\ cent}}$. Upcoming JWST medium/ deep surveys with areas up to A ∼ 100 arcmin2 will have cosmic variance ranging from ${\sim}20\,\mathrm{ to}\,50{{\ \rm per\ cent}}$. Lensed surveys have the highest cosmic variance ${\gtrsim}40{{\ \rm per\ cent}}$; the cosmic variance of MUV ≲ −16 galaxies is ${\lesssim}100{{\ \rm per\ cent}}$ up to z ∼ 11. At higher redshifts such as z ∼ 12 (14), effective volumes of ≳ (8 Mpc h−1)3 (≳(12 Mpc h−1)3) are required to limit the cosmic variance to within $100{{\ \rm per\ cent}}$. Finally, we find that cosmic variance is larger than Poisson variance and forms the dominant component of the overall uncertainty in all current and upcoming surveys. We present our calculations in the form of simple fitting functions and an online cosmic variance calculator (CV_AT_COSMIC_DAWN) that we publicly release.

Why Radio Quiet Quasars are Preferred over Radio Loud Quasars Regardless of Environment and Redshift

Evidence has accumulated suggesting the clustering of radio loud quasars is greater than for radio quiet quasars. We interpret these results in a context in which the fraction of radio loud quasar formation is less than or equal to that for radio quiet quasars for all environments and redshift. Because we assume that post-merger cold gas onto large black holes produces either a radio loud or a radio quiet quasar, we show that for largest black hole masses that live in largest dark matter halos, fRLQ approaches 0.5 from below but does not exceed it, such that in rich clusters the formation of a radio loud quasar tends to be equally likely to occur as a radio quiet quasar. In dark matter halos with smaller mass, by contrast, radio quiet quasars are more likely to form and the likelihood increases inversely with dark matter halo mass. As a result, averaging over a population of radio loud and radio quiet quasars will necessarily generate lower average black hole masses for the radio quiet subgroup. Hence, despite the fact that the formation of radio quiet quasars is preferred over radio loud quasars in any environment, at any mass scale, at any luminosity, or redshift, averaging over a range of radio loud quasars will give the appearance they are preferred in cluster environments over radio quiet quasars. We show how this also accounts for the order of magnitude difference in the total number of jetted active galaxies compared to non-jetted counterparts.

On the Detection of Supermassive Primordial Stars

Abstract The collapse of supermassive primordial stars in hot, atomically cooled halos may have given birth to the first quasars at z ∼ 15–20. Recent numerical simulations of these rapidly accreting stars reveal that they are cool, red hypergiants shrouded by dense envelopes of pristine atomically cooled gas at 6000–8000 K, with luminosities L ≳ 1010 L ⊙. Could such luminous but cool objects be detected as the first stage of quasar formation in future near-infrared (NIR) surveys? We have now calculated the spectra of supermassive primordial stars in their birth envelopes with the Cloudy code. We find that some of these stars will be visible to the James Webb Space Telescope at z ≲ 20 and that with modest gravitational lensing, Euclid and the Wide-Field Infrared Space Telescope could detect them out to z ∼ 10–12. Rather than obscuring the star, its accretion envelope enhances its visibility in the NIR today by reprocessing its short-wavelength flux into photons that are just redward of the Lyman limit in the rest frame of the star.

Radiation Hydrodynamical Simulations of the First Quasars

Abstract Supermassive black holes (SMBHs) are the central engines of luminous quasars and are found in most massive galaxies today. But the recent discoveries of ULAS J1120+0641, a 2 × 109 black hole (BH) at z = 7.1, and ULAS J1342+0928, a 8.0 × 108 BH at z = 7.5, now push the era of quasar formation up to just 690 Myr after the Big Bang. Here we report new cosmological simulations of SMBHs with X-rays fully coupled to primordial chemistry and hydrodynamics which show that J1120 and J1342 can form from direct collapse black holes if their growth is fed by cold, dense accretion streams, like those thought to fuel rapid star formation in some galaxies at later epochs. Our models reproduce all of the observed properties of J1120: its mass, luminosity, and H ii region as well as star formation rates and metallicities in its host galaxy. They also reproduce the dynamical mass of the innermost 1.5 kpc of its emission region recently measured by ALMA and J-band magnitudes that are in good agreement with those found by the VISTA Hemisphere Survey.

Chasing the observational signatures of seed black holes at z &gt; 7: candidate observability

Observing the light emitted by the first accreting black holes (BHs) would dramatically improve our understanding of the formation of quasars at z > 6, possibly unveiling the nature of their supermassive black hole (SMBH) seeds. In previous works we explored the relative role of the two main competing BH seed formation channels, Population III remnants (low-mass seeds) and direct collapse BHs (high-mass seeds), investigating the properties of their host galaxies in a cosmological context. Building on this analysis, we predict here the spectral energy distribution and observational features of low- and high-mass BH seeds selected among the progenitors of a z~6 SMBH. We derive the processed emission from both accreting BHs and stars by using the photo-ionization code Cloudy, accounting for the evolution of metallicity and dust-to-gas mass ratio in the interstellar medium of the host galaxies, as predicted by the cosmological data- constrained model GAMETE/QSOdust. We show how future missions like JWST and ATHENA will be able to detect the light coming from SMBH progenitors already at z~16. We build upon previous complementary studies and propose a method based on the combined analysis of near infrared (NIR) colors, IR excess (IRX) and UV continuum slopes (i.e. color-color and IRX-Beta diagrams) to distinguish growing seed BH host galaxies from starburst-dominated systems in JWST surveys. Sources selected through this criterion would be the best target for follow-up X-ray observations.

The Formation and Essence of Quasars and Their Connections with Galaxies

The discovery of quasars is one of the four great discoveries of astronomy in 1960s. Although the discovery of quasars is very interesting, but it has also brought some difficult problems for human being: are quasars stars or galaxies? Why the luminosity of the most powerful quasars is thousands of times greater than the luminosity of a large galaxy such as the Milky Way whose size is larger than the quasars by millions of times? Why the observed quasars are distant objects? If the redshift of a quasar is cosmic redshift? These problems have long plagued the people in suspense. Fortunately, the author of this paper, through studying the formation and orbit-variation of satellites, planets and stars, has put forward a new theory of galactic structure, therefore revealing the hierarchical structure of galaxies and the existence and characteristics of black holes as the main nodes of galactic structure, especially revealing the formation and essence of quasars and solving all the problems mentioned above. The author found that quasar is essentially a supermassive black hole covered by an extreme thick and dense atmosphere. When such a black hole revolves around its progenitor and whirls on its axis fast, lots of cloud clumps would bump each other to cause immense electricity and thunder, forming strong radio source and high luminosity. The mass of the ancestral quasar billions of light years away from the earth is about 1000 times the total mass of the entire Milky Way galaxy, so its energy output would be 1000 times more than the energy released by the entire Milky Way galaxy. Since a quasar revolves around its progenitor and whirls on its axis fast, therefore the redshift of a quasar is indeed cosmic redshift.

Black holes on FIRE: stellar feedback limits early feeding of galactic nuclei

Abstract We introduce massive black holes (BHs) in the Feedback In Realistic Environments (FIRE) project and perform high-resolution cosmological hydrodynamic simulations of quasar-mass haloes [Mhalo(z = 2) ≈ 1012.5 M⊙] down to z = 1. These simulations model stellar feedback by supernovae, stellar winds and radiation, and BH growth using a gravitational torque-based prescription tied to the resolved properties of galactic nuclei. We do not include BH feedback. We show that early BH growth occurs through short (≲1 Myr) accretion episodes that can reach or even exceed the Eddington rate. In this regime, BH growth is limited by bursty stellar feedback continuously evacuating gas from galactic nuclei, and BHs remain undermassive in low-mass galaxies relative to the local MBH–Mbulgerelation. BH growth is more efficient at later times, when the nuclear stellar potential retains a significant gas reservoir, star formation becomes less bursty and galaxies settle into a more ordered state. BHs rapidly converge on to the observed scaling relations when the host reaches Mbulge ∼ 1010 M⊙. We show that resolving the effects of stellar feedback on the gas supply in the inner ∼100 pc of galaxies is necessary to accurately capture the growth of central BHs. Our simulations imply that bursty stellar feedback has important implications for BH–galaxy relations, AGN demographics and time variability, the formation of early quasars and massive BH mergers.

Imprints of the super-Eddington accretion on the quasar clustering

Abstract Super-Eddington mass accretion has been suggested as an efficient mechanism to grow supermassive black holes. We investigate the imprint left by the radiative efficiency of the super-Eddington accretion process on the clustering of quasars using a new semi-analytic model of galaxy and quasar formation based on large-volume cosmological N-body simulations. Our model includes a simple model for the radiative efficiency of a quasar, which imitates the effect of photon trapping for a high mass accretion rate. We find that the model of radiative efficiency affects the relation between the quasar luminosity and the quasar host halo mass. The quasar host halo mass has only weak dependence on quasar luminosity when there is no upper limit for quasar luminosity. On the other hand, it has significant dependence on quasar luminosity when the quasar luminosity is limited by its Eddington luminosity. In the latter case, the quasar bias also depends on the quasar luminosity, and the quasar bias of bright quasars is in agreement with observations. Our results suggest that the quasar clustering studies can provide a constraint on the accretion disc model.

Turbulent gas accretion between supermassive black-holes and star-forming rings in the circumnuclear disk

While supermassive black holes are known to co-evolve with their host galaxy, the precise nature and origin of this co-evolution is not clear. We here explore the possible connection between star formation and black hole growth in the circumnuclear disk (CND) to probe this connection in the vicinity close to the black hole. We adopt here the circumnuclear disk model developed by Kawakatu & Wada (2008) and Wutschik et al. (2013), and explore both the dependence on the star formation recipe as well as the role of the gravitational field, which can be dominated by the central black hole, the CND itself or the host galaxy. A specific emphasis is put on the turbulence regulated star formation model by Krumholz et al. (2005) to explore the impact of a realistic star formation recipe. It is shown that this model helps to introduce realistic fluctuations in the black hole and star formation rate, without overestimating them. Consistent with previous works, we show that the final black hole masses are rather insensitive to the masses of the initial seeds, even for seed masses of up to 10^6 M_sol. In addition, we apply our model to the formation of high-redshift quasars, as well as to the nearby system NGC 6951, where a tentative comparison is made in spite of the presence of a bar in the galaxy. We show that our model can reproduce the high black hole masses of the high-redshift quasars within a sufficiently short time, provided a high mass supply rate from the host galaxy. In addition, it reproduces several of the properties observed in NGC 6951. With respect to the latter system, our analysis suggests that supernova feedback may be important to create the observed fluctuations in the star formation history as a result of negative feedback effects.

On the Formation of the First Quasars

AbstractObservations of the most luminous quasars at redshift z &gt; 6 reveal the existence of numerous supermasssive black holes (&gt;199 M⊙) already in place about 12 billion years ago. In addition, the interstellar medium of the galaxies hosting these black holes are observed to be chemically mature systems, with metallicities (Z &gt; Z⊙) and dust masses (&gt;108 M⊙) similar to that of more evolved, local galaxies. The connection between the rapid growth of the first supermassive black holes and the fast chemical evolution of the host galaxy is one of the most puzzling issues for theoretical models. Here, we review state-of-the-art theoretical models that focus on this problem with particular emphasis on the conditions that lead to the formation of quasar seeds and their subsequent evolution at z ⩾ 6.

Quasar clustering in a galaxy and quasar formation model based on ultra high-resolution N-body simulations

Abstract We investigate clustering properties of quasars using a new version of our semi-analytic model of galaxy and quasar formation with state-of-the-art cosmological N-body simulations. In this study, we assume that a major merger of galaxies triggers cold gas accretion on to a supermassive black hole and quasar activity. Our model can reproduce the downsizing trend of the evolution of quasars. We find that the median mass of quasar host dark matter haloes increases with cosmic time by an order of magnitude from z = 4 (a few 1011 M⊙) to z = 1 (a few 1012 M⊙), and depends only weakly on the quasar luminosity. Deriving the quasar bias through the quasar–galaxy cross-correlation function in the model, we find that the quasar bias does not depend on the quasar luminosity, similar to observed trends. This result reflects the fact that quasars with a fixed luminosity have various Eddington ratios and thus have various host halo masses that primarily determine the quasar bias. We also show that the quasar bias increases with redshift, which is in qualitative agreement with observations. Our bias value is lower than the observed values at high redshifts, implying that we need some mechanisms that make quasars inactive in low-mass haloes and/or that make them more active in high-mass haloes.