Search

JWST is discovering star-forming 'candidate' galaxies with photometric redshifts z > 9 and little attenuation. We model presumptive massive black holes (MBHs) in such galaxies and find that their unobscured emission is fainter than the galaxy starlight in JWST filters, and difficult to be detected via colour–colour selection, and X-ray and radio observations. Only MBHs overmassive relative to expected galaxy scaling relations, accreting at high Eddington rates, would be detectable. Their discovery would point to the presence of heavy MBH seeds, but care is needed to exclude the existence of lighter seeds as only overmassive MBHs are detectable in this type of galaxies. Conversely, if no overmassive MBHs are hosted in these galaxies, either there are no heavy seeds or they are rare. The most massive/highest redshift candidate galaxies can attain stellar masses in excess of |$5\times 10^{10}\, {\rm M_\odot }$| by z ∼ 6 if they grow along the star formation rate–mass sequence, and can nurse an MBH growing from |${\sim}10^5 \, {\rm M_\odot }$| up to |${\gt}3\times 10^7\, {\rm M_\odot }$| by z ∼ 6, to become hosts of some z > 6 quasars. Candidate galaxies of |$\log (M_{\rm gal}/\, {\rm M_\odot })\sim 8$| cannot grow their putative seeds fast, unless seeds are |${\gtrsim}10^6\, {\rm M_\odot }$|⁠. The number density of the JWST candidate galaxies far outnumbers that of the highest z quasar hosts and this allows for about only one bright z ∼ 6–7 quasar every 1000 of these galaxies. [ABSTRACT FROM AUTHOR]

The occurrence of dual active galactic nuclei (AGN) on scales of a few tens of kpc can be used to study merger-induced accretion on massive black holes (MBHs) and to derive clues on MBH mergers, using dual AGN as a parent population of precursors. We investigate the properties of dual AGN in the cosmological simulation Horizon-AGN. We create catalogs of dual AGN selected with distance and luminosity criteria, plus sub-catalogs where further mass cuts are applied. We divide the sample into dual AGN hosted in different galaxies, on the way to a merger, and into those hosted in one galaxy, after the galaxy merger has happened. We find that the relation between MBH and galaxy mass is similar to that of general AGN population and we compare the properties of dual AGN also with a control sample, discussing differences and similarities in masses and Eddington ratios. The typical mass ratio of galaxy mergers associated to dual AGN is 0.2, with mass loss in the smaller galaxy decreasing the mass ratio as the merger progresses. Between 30 and 80 per cent of dual AGN with separations between 4 and 30 kpc can be matched to an ensuing MBH merger. The dual AGN fraction increases with redshift and with separation threshold, although above 50 kpc the increase of multiple AGN limits that of duals. Multiple AGN are generally associated with massive haloes, and mass loss of satellites shapes the galaxy–halo relation. [ABSTRACT FROM AUTHOR]

Massive black hole (MBH) coalescences are powerful sources of low-frequency gravitational waves. To study these events in the cosmological context, we need to trace the large-scale structure and cosmic evolution of a statistical population of galaxies, from dim dwarfs to bright galaxies. To cover such a large range of galaxy masses, we analyse two complementary simulations: horizon-AGN with a large volume and low resolution that tracks the high-mass (⁠|$\gt 10^7\, {\rm M_\odot }$|⁠) MBH population, and NewHorizon with a smaller volume but higher resolution that traces the low-mass (|$\lt 10^7\, {\rm M_\odot }$|⁠) MBH population. While Horizon-AGN can be used to estimate the rate of inspirals for pulsar timing arrays, NewHorizon  can investigate MBH mergers in a statistical sample of dwarf galaxies for LISA, which is sensitive to low-mass MBHs. We use the same method to analyse the two simulations, post-processing MBH dynamics to account for time delays mostly determined by dynamical friction and stellar hardening. In both simulations, MBHs typically merge long after galaxies do, so that the galaxy morphology at the time of the MBH merger is no longer determined by the structural disturbances engendered by the galaxy merger from which the MBH coalescence has originated. These time delays cause a loss of high- z MBH coalescences, shifting the peak of the MBH merger rate to z ∼ 1–2. This study shows how tracking MBH mergers in low-mass galaxies is crucial to probing the MBH merger rate for LISA and investigate the properties of the host galaxies. [ABSTRACT FROM AUTHOR]

Recent deep surveys have unravelled a population of faint active galactic nuclei (AGNs) in the high-redshift Universe, leading to various discussions on their nature and their role during the Epoch of Reionization. We use cosmological radiation hydrodynamics simulations of a bright galaxy at z ∼ 6 (⁠|${M_\star } \gtrsim 10^{10}\, {\rm M}_{\odot }$|⁠) hosting an actively growing supermassive black hole to study the properties of these objects. In particular, we study how the black hole and the galaxy coevolve and what is the relative contribution of the AGNs and of the stellar populations to the luminosity budget of the system. We find that the feedback from the AGN has no strong effect on the properties of the galaxy, and does not increase the total ionizing luminosity of the host. The average escape fraction of our galaxy is around |$f_{\rm esc} \sim 5{{\ \rm per\ cent}}$|⁠. While our galaxy would be selected as an AGN in deep X-ray surveys, most of the ultraviolet (UV) luminosity is originating from stellar populations. This confirms that there is a transition in the galaxy population from star-forming galaxies to quasar hosts, with bright Lyman-break galaxies with M UV around −22 falling in the overlap region. Our results also suggest that faint AGNs do not contribute significantly to reionizing the Universe. [ABSTRACT FROM AUTHOR]

High-redshift quasars are believed to reside in highly biased regions of the Universe, where black hole growth is sustained by an enhanced number of mergers and by being at the intersection of filaments bringing fresh gas. This assumption should be supported by an enhancement of the number counts of galaxies in the field of view of quasars. While the current observations of quasar environments do not lead to a consensus on a possible excess of galaxies, the future missions JWST, WFIRST , and Euclid will provide new insights on quasar environments, and will substantially increase the number of study-cases. We are in a crucial period, where we need to both understand the current observations and predict how upcoming missions will improve our understanding of BH environments. Using the large-scale simulation Horizon-AGN, we find that statistically the most massive BHs reside in environments with the largest galaxy number counts. However, we find a large variance in galaxy number counts, and some massive BHs do not show enhanced counts in their neighbourhood. Interestingly, some massive BHs have a very close galaxy companion but no further enhancement at larger scales, in agreement with recent observations. We find that AGN feedback in the surrounding galaxies is able to decrease their luminosity and stellar mass, and therefore to make them unobservable when using restrictive galaxy selection criteria. Radiation from the quasars can spread over large distances, which could affect the formation history of surrounding galaxies, but a careful analysis of these processes requires radiative transfer simulations. [ABSTRACT FROM AUTHOR]

Observations of high-redshift quasars provide information on the massive black holes (MBHs) powering them and the galaxies hosting them. Current observations of z ≳ 6 hosts, at sub-millimetre wavelengths, trace the properties of cold gas, and these are used to compare with the correlations between MBHs and galaxies characterizing the z  = 0 population. The relations at z  = 0, however, rely on stellar-based tracers of the galaxy properties. We perform a very high resolution cosmological zoom-in simulation of a z  = 7 quasar including state-of-the-art non-equilibrium chemistry, MBH formation, growth, and feedback, to assess the evolution of the galaxy host and the central MBH, and compare the results with recent ALMA observations of high-redshift quasars. We measure both the stellar-based quantities used to establish the z  = 0 correlations, as well as the gas-based quantities available in z ≳ 6 observations, adopting the same assumptions and techniques used in observational studies. The high-redshift studies argued that MBHs at high redshift deviate from the local MBH–galaxy correlations. In our analysis of the single galaxy we evolve, we find that the high-redshift population sits on the same correlations as the local one, when using the same tracers used at z  = 0. When using the gas-based tracers, however, MBHs appear to be overmassive. The discrepancy between local and high-redshift MBHs seems to be caused by the different tracers employed, and the necessary assumptions, and not by an intrinsic difference. Better calibration of the tracers, higher resolution data, and availability of facilities that can probe the stellar population will be crucial to assess precisely and accurately high-redshift quasar hosts. [ABSTRACT FROM AUTHOR]

The dynamics of black hole (BH) seeds in high-redshift galaxies is key to understand their ability to grow via accretion and to pair in close binaries during galactic mergers. To properly follow the dynamics of BHs we develop a physically motivated model to capture unresolved dynamical friction from stars, dark matter, and gas. We first validate the model and then we use it to investigate the dynamics of seed BHs born at z ∼ 9 in dwarf proto-galaxies. We perform a suite of zoom cosmological simulations with spatial resolution as high as 10 pc and with a stellar and dark matter mass resolution of |$2\times 10^3 \, \, $| and |$2\times 10^5 \, \, \mathrm{ M}_{\odot }$|⁠, respectively. We first explore the dynamics of a seed BH in the galaxy where it is born and show that it is highly erratic if the seed mass is less than |$10^5\, \, \mathrm{ M}_{\odot }$|⁠. The dynamics is dominated by the stellar component, whose distribution is irregular and patchy, thus inducing stochasticity in the orbits: the BH may be anywhere in the proto-galaxy. When this dwarf merges into a larger galaxy, it is paramount to simulate the process with very high spatial and mass resolution in order to correctly account for the stripping of the stellar envelope of the satellite BH. The outcome of the encounter could be either a tight binary or, at least temporary, a wandering BH, leading to multiple BHs in a galaxy, each inherited from a different merger. [ABSTRACT FROM AUTHOR]

The gravitational interaction at parsec to sub-parsec scales between a circumbinary gas disc and a super massive black hole binary (SMBHB) is a promising mechanism to drive the migration of SMBHBs towards coalescence. The typical dynamical evolution can be separated in two main regimes: (I) slow migration (T mig ∼ 103 − 4 × T orb), where viscous torques are not efficient enough to redistribute the extracted angular momentum from the binary, leading to the formation of a low-density cavity around the binary. (II) fast migration (T mig ∼ 101 − 2 × T orb), in which the redistribution of angular momentum is efficient and no low-density cavity is formed in the circumbinary disc. Using N -Body/SPH simulations, we study the effect of AGN feedback in this phase of an SMBHB evolution. We implement an AGN feedback model in the SPH code Gadget-3 that includes momentum feedback from winds, X-ray heating/radial-momentum, and Eddington force. Using this implementation, we run a set of simulations of SMBHB+disc in the two main shrinking regimes. From these simulations, we conclude that the effect of the AGN mechanical feedback is negligible for SMBHBs in the slowly shrinking regime. However, in the fast shrinking regime, the AGN winds excavate a 'feedback cavity' leaving the SMBHB almost naked, thus stalling the orbital decay of the binary. [ABSTRACT FROM AUTHOR]

Understanding the growth of high-redshift massive black holes (MBHs) is a problem of great astrophysical interest. The most luminous quasars at z > 6 are frequently observed but they represent only the tip of the iceberg as the majority of the low-luminosity active galactic nuclei (AGN) population remains undetected. In this study, we perform a radiation hydrodynamics cosmological simulation to study the growth of 'normal' black holes in the high-redshift universe. In our simulation, we model the formation of Pop III and Pop II stars along with their chemical, mechanical, and radiative feedback.We consider both UV and X-ray emission from an accreting BH to simulate its radiative feedback. The selected halo has a mass of 3 x 1010 Mʘ at z = 7.5 and we turn on radiative feedback from a MBH seed of 105Mʘ along with in situ star formation at z = 12 when the halo mass reaches well above the atomic cooling limit. We find that the MBH accretes only about 2200 Mʘ during 320 Myr and the average mass accretion on to the MBH is a few times 10-6 Mʘ yr-1. Our results suggest that the stunted growth of MBH is a consequence of supernovae in tandem with MBH feedback which drive large outflows and evacuate the gas from MBH vicinity. This may explain why a population of low-luminosity AGN has not been detected so-far at z > 6; the large contrast between the star formation rate and the MBH accretion rate may make then hard to detect even in upcoming deep surveys. [ABSTRACT FROM AUTHOR]

Galactic outflows, driven by active galactic nuclei (AGNs), play a crucial role in galaxy formation and in the self-regulated growth of supermassive black holes (BHs). AGN feedback couples to and affects gas, rather than stars, and in many, if not most, gas-rich galaxies cold gas is rotationally supported and settles in a disc. We present a 2D analytical model for AGN-driven outflows in a gaseous disc and demonstrate the main improvements, compared to existing 1D solutions. We find significant differences for the outflow dynamics and wind efficiency. The outflow is energy-driven due to inefficient cooling up to a certain AGN luminosity (~1043 erg s-1 in our fiducial model), above which the outflow remains momentum-driven in the disc up to galactic scales. We reproduce results of 3D simulations that gas is preferentially ejected perpendicular to the disc and find that the fraction of ejected interstellar medium is lower than in 1D models. The recovery time of gas in the disc, defined as the free-fall time from the radius to which the AGN pushes the ISM at most, is remarkably short, of the order 1 Myr. This indicates that AGN-driven winds cannot suppress BH growth for long. Without the inclusion of supernova feedback, we find a scaling of the BH mass with the halo velocity dispersion of MBH ∝ σ4.8. [ABSTRACT FROM AUTHOR]

Super-Eddington accretion has been suggested as a possible formation pathway of 109M⊙ supermassive black holes (SMBHs) 800 Myr after the big bang. However, stellar feedback from BH seed progenitors and winds from BH accretion discs may decrease BH accretion rates. In this work, we study the impact of these physical processes on the formation of z ~ 6 quasar, including new physical prescriptions in the cosmological, data-constrained semi-analytic model GAMETE/QSODUST. We find that the feedback produced by the first stellar progenitors on the surrounding does not play a relevant role in preventing SMBHs formation. In order to grow the z ≳ 6 SMBHs, the accreted gas must efficiently lose angular momentum. Moreover, disc winds, easily originated in super-Eddington accretion regime, can strongly reduce duty cycles. This produces a decrease in the active fraction among the progenitors of z ~ 6 bright quasars, reducing the probability to observe them. [ABSTRACT FROM AUTHOR]

Numerical simulations have become a necessary tool to describe the complex interactions among the different processes involved in galaxy formation and evolution, unfeasible via an analytic approach. The last decade has seen a great effort by the scientific community in improving the sub-grid physics modelling and the numerical techniques used to make numerical simulations more predictive. Although the recently publicly available code GIZMO has proven to be successful in reproducing galaxy properties when coupled with the model of the MUFASA simulations and the more sophisticated prescriptions of the Feedback In Realistic Environment (FIRE) set-up, it has not been tested yet using delayed cooling supernova feedback, which still represent a reasonable approach for large cosmological simulations, for which detailed sub-grid models are prohibitive. In order to limit the computational cost and to be able to resolve the disc structure in the galaxies we perform a suite of zoom-in cosmological simulations with rather low resolution centred around a sub-L* galaxy with a halo mass of 3 × 1011 M☉ at z = 0, to investigate the ability of this simple model, coupled with the new hydrodynamic method of GIZMO, to reproduce observed galaxy scaling relations (stellar to halo mass, stellar and baryonic Tully-Fisher, stellar mass-metallicity and mass-size). We find that the results are in good agreement with the main scaling relations, except for the total stellar mass, larger than that predicted by the abundance matching technique, and the effective sizes for the most massive galaxies in the sample, which are too small. [ABSTRACT FROM AUTHOR]

Massive black holes (BHs) inhabit local galaxies, including the Milky Way and some dwarf galaxies. BH formation, occurring at early cosmic times, must account for the properties of BHs in today's galaxies, notably why some galaxies host a BH, and others do not. We investigate the formation, distribution and growth of BH 'seeds' by using the adaptive mesh refinement code RAMSES. We develop an implementation of BH formation in dense, lowmetallicity environments, as advocated by models invoking the collapse of the first generation of stars, or of dense nuclear star clusters. The seed masses are computed one-by-one on-thefly, based on the star formation rate and the stellar initial mass function. This self-consistent method to seed BHs allows us to study the distribution of BHs in a cosmological context and their evolution over cosmic time. We find that all high-mass galaxies tend to host a BH, whereas low-mass counterparts have a lower probability of hosting a BH. After the end of the epoch of BH formation, this probability is modulated by the growth of the galaxy. The simulated BHs connect to low-redshift observational samples, and span a similar range in accretion properties as Lyman-break analogs. The growth of BHs in low-mass galaxies is stunted by strong supernova (SN) feedback. The properties of BHs in dwarf galaxies thus remain a testbed for BH formation. Simulations with strong SN feedback, which is able to quench BH accretion in shallow potential wells, produce galaxies and BHs in better agreement with observational constraints. [ABSTRACT FROM AUTHOR]

The gravitational wave (GW) antenna LISA will detect the signal from coalescing massive black hole binaries (MBHBs) of 104 − 107 M⊙, providing clues as to their formation and growth throughout cosmic history. Some of these events will be localised with a precision of several to less than a deg2, enabling the possible identification of their host galaxy. This work explores the properties of the host galaxies of LISA MBHBs below z ≲ 3. We generate a simulated lightcone using the semi-analytical model L-Galaxies applied to the merger trees of the high-resolution N-body cosmological simulation Millennium-II. The model shows that LISA MBHBs are expected to be found in optically dim (r > 20), star-forming (sSFR > 10−10 yr−1), gas-rich (fgas > 0.6), and disc-dominated (B/T < 0.7) low-mass galaxies of stellar masses 108 − 109 M⊙. However, these properties are indistinguishable from those of galaxies harbouring single massive black holes of comparable mass, making it difficult to select LISA hosts among the whole population of low-mass galaxies. Motivated by this, we explore the possibility of using merger signatures to select LISA hosts. We find that 40%−80% of the galaxies housing LISA MBHBs display merger features related to the interaction that brought the secondary MBH to the galaxy. Despite this, around 60% of dwarf galaxies placed in the surroundings of the LISA hosts will show these kinds of features as well, challenging the unequivocal detection of LISA hosts through the search for merger signatures. Consequently, the detection of an electromagnetic transient associated with the MBHB merger will be vital in order to pinpoint the star-forming dwarf galaxy where these binary systems evolve and coalesce. [ABSTRACT FROM AUTHOR]

Using recent empirical constraints on the dark matter halo–galaxy–supermassive black hole (SMBH) connection from z  = 0–7, we infer how undermassive, typical, and overmassive SMBHs contribute to the quasar luminosity function (QLF) at z  = 6. We find that beyond L bol = 5 × 1046 erg s−1, the z  = 6 QLF is dominated by SMBHs that are at least 0.3 dex above the z  = 6 median M • –M * relation. The QLF is dominated by typical SMBHs (i.e. within ±0.3 dex around the M •– M * relation) at L bol ≲ 1045 erg s−1. At z ∼ 6, the intrinsic M • –M * relation for all SMBHs is slightly steeper than the z  = 0 scaling, with a similar normalization at |$M_* \sim 10^{11} \, \mathrm{M}_\odot$|⁠. We also predict the M • –M * relation for z  = 6 bright quasars selected by different bolometric luminosity thresholds, finding very good agreement with observations. For quasars with L bol > 3 × 1046 (1048) erg s−1, the scaling relation is shifted upwards by ∼0.35 (1.0) dex for 1011M⊙ galaxies. To accurately measure the intrinsic M • –M * relation, it is essential to include fainter quasars with L bol ≲ 1045 erg s−1. At high redshifts, low-luminosity quasars are thus the best targets for understanding typical formation paths for SMBHs in galaxies. [ABSTRACT FROM AUTHOR]

This is likely because ABHMFs only specify the abundance of active SMBHs at given SMBH masses, but not whether the SMBHs are overmassive/undermassive compared to their host haloes/galaxies. Erratum: Trinity I: self-consistently modeling the dark matter halo-galaxy-supermassive black hole connection from z = 0-10 Errata, addenda, galaxies: evolution, galaxies: haloes, quasars: supermassive black holes Keywords: errata; addenda; galaxies: evolution; galaxies: haloes; quasars: supermassive black holes EN errata addenda galaxies: evolution galaxies: haloes quasars: supermassive black holes 3627 3630 4 05/18/23 20230701 NES 230701 1 PROBLEMS IN THE ORIGINAL PARAMETRIZATION OF trinity In the original version of Trinity, we parametrized the correlation coefficient between supermassive black hole (SMBH) accretion rate and SMBH mass at fixed dark matter halo mass, SB BH sb , as a function of redshift: $$\begin{eqnarray*} \rho \mathrm{BH}{}\ (z) = \rho {\mathrm{BH},0} + \rho {\mathrm{BH},a} \left(\frac{1}{1 + z}-1\right) + \rho {\mathrm{BH},z}\ z. \end{eqnarray*}$$ (1) We believed that at I z i 2, SB BH sb was constrained by active black hole mass functions (ABHMFs), i.e. the mass functions of quasars with Eddington ratios >= 0.01. [Extracted from the article]

The population of supermassive black holes (SMBHs) is split between those that are quiescent, such as those seen in local galaxies including the Milky Way, and those that are active, resulting in quasars and active galactic nuclei (AGN). Outside our neighborhood, all the information we have on SMBHs is derived from quasars and AGN, giving us a partial view. We study the evolution of the SMBH population, total and active, by the continuity equation, backwards in time from z = 0 to z = 4. Type-1 and type-2 AGN are differentiated in our model on the basis of their respective Eddington ratio distributions, chosen on the basis of observational estimates. The duty cycle is obtained by matching the luminosity function of quasars, and the average radiative efficiency is the only free parameter in the model. For higher radiative efficiencies (&0:07), a large fraction of the SMBH population, most of them quiescent, must already be in place by z = 4. For lower radiative efficiencies (~0:05), the duty cycle increases with the redshift and the SMBH population evolves dramatically from z = 4 onwards. The mass function of active SMBHs does not depend on the choice of the radiative efficiency or of the local SMBH mass function, but it is mainly determined by the quasar luminosity function once the Eddington ratio distribution is fixed. Only direct measurement of the total black-hole mass function at redshifts z ≳ 2 could break these degeneracies, offering important constraints on the average radiative efficiency. Focusing on type-1 AGN, for which observational estimates of the mass function and Eddington ratio distribution exist at various redshifts, models with lower radiative efficiencies better reproduce the high-mass end of the mass function at high z, but tend to over-predict it at low z, and vice-versa for models with higher radiative efficiencies. [ABSTRACT FROM AUTHOR]

The rate at which matter flows into a galactic nucleus during early phases of galaxy evolution can sometimes exceed the Eddington limit of the growing central black hole by several orders of magnitude. We discuss the necessary conditions for the black hole to actually accrete this matter at such a high rate, and consider the observational appearance and detectability of a hyperaccreting black hole. In order to be accreted at a hyper-Eddington rate, the infalling gas must have a sufficiently low angular momentum. Although most of the gas is accreted, a significant fraction accumulates in an optically thick envelope with luminosity ~LEdd, probably pierced by jets of much higher power. If ... > 10³ ...Edd, the envelope spectrum resembles a blackbody with a temperature of a few thousand kelvin, but for lower (but still hyper-Eddington) accretion rates the spectrum becomes a very dilute and hard Wien spectrum. We consider the likelihood of various regimes of hyperaccretion, and discuss its possible observational signatures. [ABSTRACT FROM AUTHOR]

Supermassive black holes (BHs) reside in the centre of most local galaxies, but they also power active galactic nuclei and quasars, detected up to z = 7. These quasars put constraints on early BH growth and the mass of BH seeds. The scenario of ‘direct collapse’ is appealing as it leads to the formation of large mass BH seeds, 104–106 M⊙, which eases explaining how quasars at z = 6–7 are powered by BHs with masses >109 M⊙. Direct collapse, however, appears to be rare, as the conditions required by the scenario are that gas is metal-free, the presence of a strong photodissociating Lyman–Werner flux, and large inflows of gas at the centre of the halo, sustained for 10–100 Myr. We performed several cosmological hydrodynamical simulations that cover a large range of box sizes and resolutions, thus allowing us to understand the impact of several physical processes on the distribution of direct collapse BHs. We identify haloes where direct collapse can happen, and derive the number density of BHs. We also investigate the discrepancies between hydrodynamical simulations, direct or post-processed, and semi-analytical studies. Under optimistic assumptions, we find that for direct collapse to account for BHs in normal galaxies, the critical Lyman–Werner flux required for direct collapse must be about two orders of magnitude lower than predicted by 3D simulations that include detailed chemical models. However, when supernova feedback is relatively weak, enough direct collapse BHs to explain z = 6–7 quasars can be obtained for Lyman–Werner fluxes about one order of magnitude lower than found in 3D simulations. [ABSTRACT FROM AUTHOR]

Quasars powered by massive black holes (BHs) with mass estimates above a billion solar masses have been identified at redshift 6 and beyond. The existence of such BHs requires almost continuous growth at the Eddington limit for their whole lifetime, of the order of one billion years. In this paper, we explore the possibility that positively skewed scale-dependent non-Gaussian primordial fluctuations may ease the assembly of massive BHs. In particular, they produce more low-mass haloes at high redshift, thus altering the production of metals and ultraviolet flux, believed to be important factors in BH formation. Additionally, a higher number of progenitors and of nearly equal-mass halo mergers would boost the mass increase provided by BH-BH mergers and merger-driven accretion. We use a set of two cosmological simulations, with either Gaussian or scale-dependent non-Gaussian primordial fluctuations to perform a proof-of-concept experiment to estimate how BH formation and growth are altered. We estimate the BH number density and the fraction of haloes where BHs form, for both simulations and for two popular scenarios of BH formation (remnants of the first generation of stars and direct collapse in the absence of metals and molecular hydrogen). We find that the fractions of haloes where BHs form are almost identical, but that non-Gaussian primordial perturbations increase the total number density of BHs for both BH formation scenarios by a factor of 2. We also evolve BHs using merger trees extracted from the simulations and find that both the mean BH mass and the number of the most massive BHs at z = 6.5 are up to twice the values expected for Gaussian primordial density fluctuations. [ABSTRACT FROM AUTHOR]

The observational evidence that Super-Massive Black Holes (M. ~ 109-10 M⊙) are already in place less than 1 Gyr after the big bang poses stringent time constraints on the growth efficiency of their seeds. Among proposed possibilities, the formation of massive (~103-6 M⊙) seeds and/or the occurrence of super-Eddington (Ṁ>ṀEdd) accretion episodes may contribute to the solution of this problem. In this work, using a set of astrophysically motivated initial conditions, we analytically and numerically investigate the accretion flow on to high-redshift (z ~ 10) black holes to understand the physical requirements favouring rapid and efficient growth. Our model identifies a 'feeding-dominated' accretion regime and a 'feedback-limited' one, the latter being characterized by intermittent (duty cycles D≲0.5) and inefficient growth, with recurring outflow episodes. We find that low-mass seeds (≲103-4 M⊙) evolve in the feedback-limited regime, while more massive seeds (≳105-6 M⊙) grow very rapidly as they are found in the feeding-dominated regime. In addition to the standard accretion model with a fixed matter-energy conversion factor (ε = 0.1), we have also explored slim disc models, appropriate for super-Eddington accretion, where radiation is trapped in the disc and the radiative efficiency is reduced (ε ≲ 0.04), which may ensure a continuous growth with Ṁ≫ṀEdd (up to ~300ṀEdd in our simulations). Under these conditions, outflows play a negligible role and a black hole can accrete 80-100?per?cent of the gas mass of the host halo (~107 M⊙) in ~10 Myr, while in feedback-limited systems we predict that black holes can accrete only up to ~15 per cent of the available mass. [ABSTRACT FROM AUTHOR]

The growth of a supermassive black hole (BH) is determined by how much gas the host galaxy is able to feed it, which in turn is controlled by the cosmic environment, through galaxy mergers and accretion of cosmic flows that time how galaxies obtain their gas, and also by internal processes in the galaxy, such as star formation and feedback from stars and the BH itself. In this paper, we study the growth of a 1012 M⊙ halo at z = 2, which is the progenitor of a group of galaxies at z = 0, and of its central BH by means of a high-resolution zoomed cosmological simulation, the Seth simulation. We study the evolution of the BH driven by the accretion of cold gas in the galaxy, and explore the efficiency of the feedback from supernovae (SNe). For a relatively inefficient energy input from SNe, the BH grows at the Eddington rate from early times, and reaches self-regulation once it is massive enough. We find that at early cosmic times z > 3.5, efficient feedback from SNe forbids the formation of a settled disc as well as the accumulation of dense cold gas in the vicinity of the BH and starves the central compact object. As the galaxy and its halo accumulate mass, they become able to confine the nuclear inflows provided by major mergers and the BH grows at a sustained near-to-Eddington accretion rate. We argue that this mechanism should be ubiquitous amongst low-mass galaxies, corresponding to galaxies with a stellar mass below ≲ 109 M⊙ in our simulations. [ABSTRACT FROM AUTHOR]

We present a new suite of hydrodynamical simulations and use it to study, in detail, black hole and galaxy properties. The high time, spatial and mass resolution, and realistic orbits and mass ratios, down to 1:6 and 1:10, enable us to meaningfully compare star formation rate (SFR) and BH accretion rate (BHAR) time-scales, temporal behaviour, and relative magnitude. We find that (i) BHAR and galaxy-wide SFR are typically temporally uncorrelated, and have different variability time-scales, except during the merger proper, lasting ~0.2-0.3 Gyr. BHAR and nuclear (<100 pc) SFR are better correlated, and their variability are similar. Averaging over time, the merger phase leads typically to an increase by a factor of a few in the BHAR/SFR ratio. (ii) BHAR and nuclear SFR are intrinsically proportional, but the correlation lessens if the long-term SFR is measured. (iii) Galaxies in the remnant phase are the ones most likely to be selected as systems dominated by an active galactic nucleus, because of the long time spent in this phase. (iv) The time-scale over which a given diagnostic probes the SFR has a profound impact on the recovered correlations with BHAR, and on the interpretation of observational data. [ABSTRACT FROM AUTHOR]

We study supermassive black holes (BHs) in merging galaxies, using a suite of hydrodynamical simulations with very high spatial (∼10 pc) and temporal (∼1 Myr) resolution, where we vary the initial mass ratio, the orbital configuration, and the gas fraction. (i) We address the question of when and why, during a merger, increased BH accretion occurs, quantifying gas inflows and BH accretion rates. (ii) We also quantify the relative effectiveness in inducing active galactic nuclei activity of merger-related versus secular-related causes, by studying different stages of the encounter: the stochastic (or early) stage, the (proper) merger stage, and the remnant (or late) stage. (iii) We assess which galaxy mergers preferentially enhance BH accretion, finding that the initial mass ratio is the most important factor. (iv) We study the evolution of the BH masses, finding that the BH mass contrast tends to decrease in minor mergers and to increase in major mergers. This effect hints at the existence of a preferential range of mass ratios for BHs in the final pairing stages. (v) In both merging and dynamically quiescent galaxies, the gas accreted by the BH is not necessarily the gas with low angular momentum, but the gas that loses angular momentum. [ABSTRACT FROM AUTHOR]

We present Trinity , a flexible empirical model that self-consistently infers the statistical connection between dark matter haloes, galaxies, and supermassive black holes (SMBHs). Trinity is constrained by galaxy observables from 0 < z < 10 [galaxies' stellar mass functions, specific and cosmic star formation rates (SFRs), quenched fractions, and UV luminosity functions] and SMBH observables from 0 < z < 6.5 (quasar luminosity functions, quasar probability distribution functions, active black hole mass functions, local SMBH mass–bulge mass relations, and the observed SMBH mass distributions of high-redshift bright quasars). The model includes full treatment of observational systematics [e.g. active galactic nucleus (AGN) obscuration and errors in stellar masses]. From these data, Trinity infers the average SMBH mass, SMBH accretion rate, merger rate, and Eddington ratio distribution as functions of halo mass, galaxy stellar mass, and redshift. Key findings include: (1) the normalization and the slope of the SMBH mass–bulge mass relation increases mildly from z  = 0 to z  = 10; (2) The best-fitting AGN radiative+kinetic efficiency is ∼0.05–0.06, but can be in the range ∼0.035–0.07 with alternative input assumptions; (3) AGNs show downsizing, i.e. the Eddington ratios of more massive SMBHs start to decrease earlier than those of lower mass objects; (4) The average ratio between average SMBH accretion rate and SFR is ∼10−3 for low-mass galaxies, which are primarily star-forming. This ratio increases to ∼10−1 for the most massive haloes below z ∼ 1, where star formation is quenched but SMBHs continue to accrete. [ABSTRACT FROM AUTHOR]

We explore how the co-evolution of massive black holes (MBHs) and galaxies is affected by environmental effects, addressing in particular MBHs hosted in the central cluster galaxies (we will refer to these galaxies in general as "CCGs"). Recently, the sample of MBHs in CCGs with dynamically measured masses has increased, and it has been suggested that these MBH masses (MBH) deviate from the expected correlations with velocity dispersion (σ) and mass of the bulge (Mbulge) of the host galaxy: MBHs in CCGs appear to be "overmassive." This discrepancy is more pronounced when considering the MBH-σ relation than the MBH-Mbulge one. We show that this behavior stems from a combination of two natural factors: (1) CCGs experience more mergers involving spheroidal galaxies and their MBHs and (2) such mergers are preferentially gas poor. We use a combination of analytical and semi-analytical models to investigate the MBH-galaxy co-evolution in different environments and find that the combination of these two factors is in accordance with the trends observed in current data sets. [ABSTRACT FROM AUTHOR]

The existence of massive black holes (MBHs) was postulated in the 1960s, when the first quasars were discovered. In the late 1990s their reality was proven beyond doubt in the Milky way and a handful nearby galaxies. Since then, enormous theoretical and observational efforts have been made to understand the astrophysics of MBHs. We have discovered that some of the most massive black holes known, weighing billions of solar masses, powered luminous quasars within the first billion years of the Universe. The first MBHs must therefore have formed around the time the first stars and galaxies formed. Dynamical evidence also indicates that black holes with masses of millions to billions of solar masses ordinarily dwell in the centers of today's galaxies. MBHs populate galaxy centers today, and shone as quasars in the past; the quiescent black holes that we detect now in nearby bulges are the dormant remnants of this fiery past. In this review we report on basic, but critical, questions regarding the cosmological significance of MBHs. What physical mechanisms led to the formation of the first MBHs? How massive were the initial MBH seeds? When and where did they form? How is the growth of black holes linked to that of their host galaxy? The answers to most of these questions are works in progress, in the spirit of these reports on progress in physics. [ABSTRACT FROM AUTHOR]

ABSTRACT In this paper, we compare the observationally derived black hole mass function (BHMF) of luminous (>1045-1046 erg s−1) broad-line quasars (BLQSOs) at 1 < z < 4.5 drawn from the Sloan Digital Sky Survey (SDSS) presented by Kelly et al., with models of merger-driven black hole (BH) growth in the context of standard hierarchical structure formation models. In these models, we explore two distinct black hole seeding prescriptions at the highest redshifts: 'light seeds'- remnants of Population III stars and 'massive seeds' that form from the direct collapse of pre-galactic discs. The subsequent merger triggered mass build-up of the black hole population is tracked over cosmic time under the assumption of a fixed accretion rate as well as rates drawn from the distribution derived by Merloni & Heinz. Four model snapshots at z= 1.25, 2, 3.25 and 4.25 are compared with the SDSS-derived BHMFs of BLQSOs. We find that the light seed models fall short of reproducing the observationally derived mass function of BLQSOs at MBH > 109 M⊙ throughout the redshift range; the massive seed models with a fixed accretion rate of 0.3 Edd, or with accretion rates drawn from the Merloni & Heinz distribution provide the best fit to the current observational data at z > 2, although they overestimate the high-mass end of the mass function at lower redshifts. At low redshifts, a drastic drop in the accretion rate is observed and this is explained as arising due to the diminished gas supply available due to consumption by star formation or changes in the geometry of the inner feeding regions. Therefore, the overestimate at the high-mass end of the black hole mass function for the massive seed models can be easily modified, as the accretion rate is likely significantly lower at these epochs than what we assume. For the Merloni & Heinz model, examining the Eddington ratio distributions fEdd, we find that they are almost uniformly sampled from fEdd= 10−2 to 1 at z≃ 1, while at high redshift, current observations suggest accretion rates close to Eddington, if not mildly super-Eddington, at least for these extremely luminous quasars. Our key findings are that the duty cycle of super-massive black holes powering BLQSOs increases with increasing redshift for all models and models with Population III remnants as black hole seeds are unable to fit the observationally derived BHMFs for BLQSOs, lending strong support for the massive seeding model. [ABSTRACT FROM AUTHOR]

We investigate the formation of the first massive black holes (MBHs) in high redshift galaxies, with the goal of providing insights to which galaxies do or do not host MBHs. We adopt a novel approach to forming seed black holes in galaxy halos in cosmological SPH+N-body simulations. The formation of MBH seeds is dictated directly by the local gas density, temperature, and metallicity, and motivated by physical models of MBH formation. We explore seed black hole populations as a function of halo mass and redshift, and examine how varying the efficiency of MBH seed formation affects the relationship between black holes and their hosts. Seed black holes tend to form in halos with mass between 107 and 109 M⊙, and the formation rate is suppressed around z = 5 due to the diffusion of metals throughout the intergalactic medium. We find that the time of MBH formation and the occupation fraction of black holes are a function of the host halo mass. By z = 5, halos with mass Mhalo > 3 x 109 M⊙ host MBHs regardless of the efficiency of seed formation, while the occupation fraction for smaller halos increases with black hole formation efficiency. Our simulations explain why MBHs are found in some bulgeless and dwarf galaxies, but we also predict that their occurrence becomes rarer and rarer in low-mass systems. [ABSTRACT FROM AUTHOR]

In this paper, we examine whether the properties of central black holes in galactic nuclei correlate with their host dark matter halos. We analyze the entire sample of galaxies where black hole mass, velocity dispersion σ, and asymptotic circular velocity Vc. have all been measured. We fit MBH-σ and MBH-Vc to a power law, and find that in both relationships the scatter and slope are similar. This model-independent analysis suggests that although the black hole masses are not uniquely determined by dark matter halo mass, when considered for the current sample as a whole, the MBH-Vc correlation may be as strong (or as weak) as MBH-σ. Although the data are sparse, there appears to be more scatter in the correlation for both cr and V,, at the low-mass end. This is not unexpected given our current understanding of galaxy and black hole assembly. In fact, there are several compelling reasons that account for this: (1) supermassive black hole (SMBH) formation is likely less efficient in low-mass galaxies with large angular momentum content, (2) SMBH growth is less efficient in low-mass disk galaxies that have not experienced major mergers, and (3) dynamical effects, such as gravitational recoil, increase scatter preferentially at the low-mass end. Therefore, the recent observational claim of the absence of central SMBHs in bulgeless, low-mass galaxies, or deviations from the correlations defined by high-mass black holes in large galaxies today is, in fact, predicated by current models of black hole growth. We show how this arises as a direct consequence of the coupling between dark matter halos and central black holes at the earliest epochs. [ABSTRACT FROM AUTHOR]

We explore the cosmic evolution of massive black hole (MBH) seeds forming within 'quasi-stars' (QSs), accreting black holes embedded within massive hydrostatic gaseous envelopes. These structures could form if the infall of gas into the centre of a halo exceeds about . The collapsing gas traps its own radiation and forms a radiation pressure-supported supermassive star. When the core of the supermassive star collapses, the resulting system becomes a quasi-star. We use a merger-tree approach to estimate the rate at which supermassive stars might form as a function of redshift, and the statistical properties of the resulting QS and seed black hole populations. We relate the triggering of runaway infall to major mergers of gas-rich galaxies and to a threshold for global gravitational instability, which we link to the angular momentum of the host. This is the main parameter of our models. Once infall is triggered, its rate is determined by the halo potential; the properties of the resulting supermassive star, QS and seed black hole depend on this rate. After the epoch of QSs, we model the growth of MBHs within their hosts in a merger-driven accretion scenario. We compare MBH seeds grown inside quasi-stars to a seed model that derives from the remnants of the first metal-free stars, and also study the case in which both channels of MBH formation operate simultaneously. We find that a limited range of supermassive star/QS/MBH formation efficiencies exists that allows one to reproduce observational constraints. Our models match the density of quasars, the cumulative mass density accreted on to MBHs (according to Sołtan's argument) and the current mass density of MBHs. The mass function of QSs peaks at , and we calculate the number counts for the James Webb Space Telescope ( JWST) m band. We find that JWST could detect up to several QSs per field at . [ABSTRACT FROM AUTHOR]

We assess the influence of massive black hole (MBH) ejections from galaxy centres due to gravitational radiation recoil, along the cosmic merger history of the MBH population. We discuss the ‘danger’ of recoil for MBHs as a function of different MBH spin-orbit configurations and of the host halo cosmic bias, and on how that reflects on the occupation fraction of MBHs. We assess ejection probabilities for mergers occurring in a gas-poor environment, in which the MBH binary coalescence is driven by stellar dynamical processes and the spin-orbit configuration is expected to be isotropically distributed. We contrast this case with the ‘aligned’ case. The latter is the more realistic situation for gas-rich, i.e. ‘wet’, mergers, which are expected for high-redshift galaxies. We find that if all haloes at host an MBH, the probability of the Milky Way (or similar size galaxy) to host an MBH today is less than 50 per cent, unless MBHs form continuously in galaxies. The occupation fraction of MBHs, intimately related to halo bias and MBH formation efficiency, plays a crucial role in increasing the retention fraction. Small haloes, with shallow potential wells and low escape velocities, have a high ejection probability, but the MBH merger rate is very low along their galaxy formation merger hierarchy: MBH formation processes are likely inefficient in such shallow potential wells. Recoils can decrease the overall frequency of MBHs in small galaxies to ∼60 per cent, while they have little effect on the frequency of MBHs in large galaxies (at most a 20 per cent effect). [ABSTRACT FROM AUTHOR]

In this paper, we explore the establishment and evolution of the empirical correlation between black hole mass ( MBH) and velocity dispersion (σ) with redshift. We trace the growth and accretion history of massive black holes (MBHs) starting from high-redshift seeds that are planted via physically motivated prescriptions. Two seeding models are explored in this work: ‘light seeds’, derived from Population III remnants, and ‘heavy seeds’, derived from direct gas collapse. Even though the seeds themselves do not satisfy the relation initially, we find that the relation can be established and maintained at all times if self-regulating accretion episodes are associated with major mergers. The massive end of the relation is established early, and lower mass MBHs migrate on to it as hierarchical merging proceeds. How MBHs migrate towards the relation depends critically on the seeding prescription. Light seeds initially lie well below the relation, and MBHs can grow via steady accretion episodes unhindered by self-regulation. In contrast, for the heavy seeding model, MBHs are initially over-massive compared to the empirical correlation, and the host haloes assemble prior to kick-starting the growth of the MBH. We find that the existence of the correlation is purely a reflection of the merging hierarchy of massive dark matter haloes. The slope and scatter of the relation however appear to be a consequence of the seeding mechanism and the self-regulation prescription. We expect flux limited active galactic nucleus surveys to select MBHs that have already migrated on to the relation. Similarly, the Laser Interferometer Space Antenna (LISA) is also likely to be biased towards detecting merging MBHs that preferentially inhabit the . These results are a consequence of major mergers being more common at high redshift for the most massive, biased, galaxies that host MBHs which have already migrated on to the relation. We also predict the existence of a large population of low-mass ‘hidden’ MBHs at high redshift which can easily escape detection. Additionally, we find that if MBH seeds are massive, , the low-mass end of the flattens towards an asymptotic value, creating a characteristic ‘plume’. [ABSTRACT FROM AUTHOR]

We investigate the distribution of massive black holes (MBHs) in the Virgo cluster. Observations suggest that active galactic nuclei activity is widespread in massive galaxies ( M*≳ 1010 M⊙), while at lower galaxy masses star clusters are more abundant, which might imply a limited presence of central black holes in these galaxy-mass regimes. We explore if this possible threshold in MBH hosting is linked to nature, nurture or a mixture of both. The nature scenario arises naturally in hierarchical cosmologies, as MBH formation mechanisms typically are efficient in biased systems, which would later evolve into massive galaxies. Nurture, in the guise of MBH ejections following MBH mergers, provides an additional mechanism that is more effective for low mass, satellite galaxies. The combination of inefficient formation, and lower retention of MBHs, leads to the natural explanation of the distribution of compact massive objects in Virgo galaxies. If MBHs arrive to the correlation with the host mass and velocity dispersion during merger-triggered accretion episodes, sustained tidal stripping of the host galaxies creates a population of MBHs which lie above the expected scaling between the holes and their host mass, suggesting a possible environmental dependence. [ABSTRACT FROM AUTHOR]

We investigate the evolution of high-redshift seed black hole masses at late times and their observational signatures. The massive black hole seeds studied here form at extremely high redshifts from the direct collapse of pre-galactic gas discs. Populating dark matter haloes with seeds formed in this way, we follow the mass assembly of these black holes to the present time using a Monte Carlo merger tree. Using this machinery, we predict the black hole mass function at high redshifts and at the present time, the integrated mass density of black holes and the luminosity function of accreting black holes as a function of redshift. These predictions are made for a set of three seed models with varying black hole formation efficiency. Given the accuracy of present observational constraints, all three models can be adequately fitted. Discrimination between the models appears predominantly at the low-mass end of the present-day black hole mass function which is not observationally well constrained. However, all our models predict that low surface brightness, bulgeless galaxies with large discs are least likely to be sites for the formation of massive seed black holes at high redshifts. The efficiency of seed formation at high redshifts has a direct influence on the black hole occupation fraction in galaxies at . This effect is more pronounced for low-mass galaxies. This is the key discriminant between the models studied here and the Population III remnant seed model. We find that there exist a population of low-mass galaxies that do not host nuclear black holes. Our prediction of the shape of the MBH–σ relation at the low-mass end is in agreement with the recent observational determination from the census of low-mass galaxies in the Virgo cluster. [ABSTRACT FROM AUTHOR]

The formation, merging and accretion history of massive black holes (MBHs) along the hierarchical build-up of cosmic structures leaves a unique imprint on the background of gravitational waves (GWs) at mHz frequencies. We study here, by means of dedicated simulations of black hole build-up, the possibility of constraining different models of black hole cosmic evolution using future GW space-borne missions, such as LISA. We consider two main scenarios for black hole formation, namely, one where seeds are light ( , remnant of Population III stars) and one where seeds are heavy ( , direct collapse). In all the models we have investigated, MBH binary coalescences do not produce a stochastic GW background, but rather, a set of individual resolved events. Detection of several hundreds merging events in a 3-yr LISA mission will be the sign of a heavy seed scenario with efficient formation of black hole seeds in a large fraction of high-redshift haloes. At the other extreme, a low event rate, about a few tens in 3 yr, is peculiar of scenarios where either the seeds are light, and many coalescences do not fall into the LISA band, or seeds are massive, but rare. In this case a decisive diagnostic is provided by the shape of the mass distribution of detected events. Light binaries are predicted in a fairly large number in Population III remnant models, but are totally absent in direct collapse models. Finally, a further, helpful diagnostic of black hole formation models lies in the distribution of the mass ratios in binary coalescences. While heavy seed models predict that most of the detected events involve equal-mass binaries, in the case of light seeds, mass ratios are equally distributed in the range 0.1–1. [ABSTRACT FROM AUTHOR]

We investigate how hierarchical models for the co-evolution of the massive black hole (MBH) and active galactic nucleus (AGN) population can reproduce the observed faint X-ray counts. We find that the main variable influencing the theoretical predictions is the Eddington ratio of accreting sources. We compare three different models proposed for the evolution of an AGN Eddington ratio, fEdd: constant decreasing with redshift and fEdd depending on the AGN luminosity, as suggested by simulations of galactic mergers including MBHs and AGN feedback. We follow the full assembly of MBHs and host haloes from early times to the present in a Λ cold dark matter (ΛCDM) cosmology. An AGN activity is triggered by halo major mergers and MBH accrete mass until they satisfy the observed correlation with velocity dispersion. We find that all the three models can reproduce fairly well the total faint X-ray counts. The redshift distribution is, however, poorly matched in the first two models. The Eddington ratios suggested by merger simulations predict no turn-off of the faint end of the AGN optical luminosity function at redshifts z≳ 1, down to very low luminosity. [ABSTRACT FROM AUTHOR]

We describe a mechanism by which supermassive black holes (SMBHs) can form directly in the nuclei of protogalaxies, without the need for ‘seed’ black holes left over from early star formation. Self-gravitating gas in dark matter haloes can lose angular momentum rapidly via runaway, global dynamical instabilities, the so-called ‘bars within bars’ mechanism. This leads to the rapid build-up of a dense, self-gravitating core supported by gas pressure – surrounded by a radiation pressure-dominated envelope – which gradually contracts and is compressed further by subsequent infall. We show that these conditions lead to such high temperatures in the central region that the gas cools catastrophically by thermal neutrino emission, leading to the formation and rapid growth of a central black hole. We estimate the initial mass and growth rate of the black hole for typical conditions in metal-free haloes with , which are the most likely to be susceptible to runaway infall. The initial black hole should have a mass of , but in principle could grow at a super-Eddington rate until it reaches . Rapid growth may be limited by feedback from the accretion process and/or disruption of the mass supply by star formation or halo mergers. Even if super-Eddington growth stops at , this process would give black holes ample time to attain quasar-size masses by a redshift of 6, and could also provide the seeds for all SMBHs seen in the present Universe. [ABSTRACT FROM AUTHOR]

We investigate the consequences of a model of the assembly and growth of massive black holes (MBHs) from primordial seeds, remnants of the first generation of stars in a hierarchical structure formation scenario. Our model traces the build-up of MBHs from an early epoch, and follows the merger history of dark matter haloes and their associated holes via Monte Carlo realizations of the merger hierarchy, from early times to the present time, in aΛ cold dark matter cosmology. The sequence of minor and major mergers experienced by galactic haloes in their hierarchical growth affects the merger history of MBHs embedded in their nuclei. So, if the formation route for the assembly of supermassive black holes dates back to the early universe, a large number of black hole (BH) interactions is inevitable. The coalescence time-scales of binary black holes can be long enough for a third BH to fall in and interact with the central binary. These BH triple interactions lead typically to the final expulsion of one of the three bodies and to the recoil of the binary. Also, asymmetric emission of gravitational waves in the last stages of the BH merging can give a recoil velocity to the centre of mass of the coalescing binary. This scenario leads to the prediction of a population of intermediate-mass black holes (IMBHs) wandering in galaxy haloes at the present epoch. We compute the luminosity distribution produced by these IMBHs accreting from their circumstellar medium. We find that in a Milky Way-sized galaxy they are unable to account for sources with luminosities, unless they carry a baryonic remnant from which they are able to accrete for a long time. We also find that, for typical spiral galaxies, the bright end of the point-source distribution correlates with the mass of the galaxy and the most luminous sources are expected to be found in the disc. [ABSTRACT FROM AUTHOR]

Recent systematic searches for massive black holes (BHs) in local dwarf galaxies led to the discovery of a population of faint active galactic nuclei (AGNs). We investigate the agreement of the BH and AGN populations in the Illustris, TNG, Horizon-AGN, EAGLE, and SIMBA simulations with current observational constraints in low-mass galaxies. We find that some of these simulations produce BHs that are too massive, and that the BH occupation fraction (OF) at z  = 0 is not inherited from the simulation seeding modelling. The ability of BHs and their host galaxies to power an AGN depends on BH and galaxy subgrid modelling. The fraction of AGN in low-mass galaxies is not used to calibrate the simulations, and thus can be used to differentiate galaxy formation models. AGN fractions at z  = 0 span two orders of magnitude at fixed galaxy stellar mass in simulations, similarly to observational constraints, but uncertainties and degeneracies affect both observations and simulations. The agreement is difficult to interpret due to differences in the masses of simulated and observed BHs, BH OF affected by numerical choices, and an unknown fraction of obscured AGN. Our work advocates for more thorough comparisons with observations to improve the modelling of cosmological simulations, and our understanding of BH and galaxy physics in the low-mass regime. The mass of BHs, their ability to efficiently accrete gas, and the AGN fraction in low-mass galaxies have important implications for the build-up of the entire BH and galaxy populations with time. [ABSTRACT FROM AUTHOR]

The scaling relations between the gas content and star formation rate of galaxies provide useful insights into the processes governing their formation and evolution. We investigated the emergence and the physical drivers of the global Kennicutt–Schmidt (KS) relation at 0.25 ≤ z ≤ 4 in the cosmological hydrodynamic simulation NEWHORIZON, capturing the evolution of a few hundred galaxies with a resolution down to 34 pc. The details of this relation vary strongly with the stellar mass of galaxies and the redshift. A power-law relation ΣSFR ∝ Σgasa with a ≈ 1.4, like that found empirically, emerges at z ≈ 2 − 3 for the more massive half of the galaxy population. However, no such convergence is found in the lower-mass galaxies, for which the relation gets shallower with decreasing redshift. At galactic scales, the star formation activity correlates with the level of turbulence of the interstellar medium, quantified by the Mach number, rather than with the gas fraction (neutral or molecular), confirming the conclusions found in previous works. With decreasing redshift, the number of outliers with short depletion times diminishes, reducing the scatter of the KS relation, while the overall population of galaxies shifts toward low densities. Our results, from parsec-scale star formation models calibrated with local Universe physics, demonstrate that the cosmological evolution of the environmental (e.g., mergers) and internal conditions (e.g., gas fractions) conspire to shape the KS relation. This is an illustration of how the interplay of global and local processes leaves a detectable imprint on galactic-scale observables and scaling relations. [ABSTRACT FROM AUTHOR]

The presence of massive black holes (BHs) with masses of the order of |$10^9\, {\rm M_\odot }$|⁠ , powering bright quasars when the Universe was less than 1 Gyr old, poses strong constraints on their formation mechanism. Several scenarios have been proposed to date to explain massive BH formation, from the low-mass seed BH remnants of the first generation of stars to the massive seed BHs resulting from the rapid collapse of massive gas clouds. However, the plausibility of some of these scenarios to occur within the progenitors of high-z quasars has not yet been thoroughly explored. In this work, we investigate, by combining dark-matter only N-body simulations with a semi-analytic framework, whether the conditions for the formation of massive seed BHs from synchronized atomic-cooling halo pairs and/or dynamically heated (DH) mini-haloes are fulfilled in the overdense regions where the progenitors of a typical high-redshift quasar host form and evolve. Our analysis shows that the peculiar conditions in such regions, i.e. strong halo clustering and high star formation rates, are crucial to produce a non-negligible number of massive seed BH host candidates: we find ≈1400 DH metal-free mini-haloes, including one of these which evolves to a synchronized pair and ends up in the massive quasar-host halo by z  = 6. This demonstrates that the progenitors of high-redshift quasar host haloes can harbour early massive seed BHs. Our results further suggest that multiple massive seed BHs may form in or near the quasar host's progenitors, potentially merging at lower redshifts and yielding gravitational wave events. [ABSTRACT FROM AUTHOR]

We use the Delphi semi-analytic model to study the mass assembly and properties of high-redshift (z > 4) black holes over a wide mass range, |$10^3 \lt M_{\rm bh}/{\rm \rm M_\odot }\lt 10^{10}$|⁠. Our black hole growth implementation includes a critical halo mass (⁠|$M_{\mathrm{ h}}^{\mathrm{ crit}}$|⁠) below which the black hole is starved and above which it is allowed to grow either at the Eddington limit or proportionally to the gas content of the galaxy. As a consequence, after an initial growth phase dominated by black hole mergers down to z  ∼ 7 (9), supermassive black holes in z  = 4 halo masses of |$M_\mathrm{ h}|_{z=4} \sim 10^{11.75} \, (10^{13.4}) \, {\rm \rm M_\odot }$| mainly grow by gas accretion from the interstellar medium. In particular, we find that (i) while most of the accretion occurs in the major branch for |$M_\mathrm{ h}|_{z=4} \sim 10^{11\!-\!12} \, {\rm \rm M_\odot }$| haloes, accretion in secondary branches plays a significant role in assembling the black hole mass in higher mass haloes (⁠|$M_\mathrm{ h}|_{z=4} \gtrsim 10^{12} \, {\rm \rm M_\odot }$|⁠); (ii) while the Eddington ratio increases with decreasing redshift for low-mass (⁠|$M_{\mathrm{ bh}} \lt 10^5 \, {\rm \rm M_\odot }$|⁠) black holes, it shows the opposite trend for larger masses. In addition, since the accretion rate depends on the gas mass present in the host halo, the duty cycle of the Eddington-limited accretion phase – which can last up to ≈650 Myr – is crucially linked to the joint assembly history of the black hole and its host halo. [ABSTRACT FROM AUTHOR]

JWST is unveiling for the first time accreting black holes (BHs) with masses of 106 − 107  M ⊙ at z > 4, with the most distant residing in GNz11 at z  = 10.6. Are we really surprised to find them in the nuclei of z ≃ 5 − 11 galaxies? Here we predict the properties of 4 < z < 11 BHs and their host galaxies considering an Eddington-limited (EL) and a super-Eddington (SE) BH accretion scenario, using the Cosmic Archaeology Tool (CAT) semi-analytical model. We calculate the transmitted spectral energy distribution of CAT synthetic candidates, representative of the BH/galaxy properties of GNz11. We also examine the possibility that the z  = 8.7 galaxy CEERS-1019 could host an active BH. We find that the luminosity of high- z JWST detected BHs are better reproduced by the SE model, where BHs descend from efficiently growing light and heavy seeds. Conversely, the host galaxy stellar masses are better matched in the EL model, in which all the systems detectable with JWST surveys JADES and CEERS descend from heavy BH seeds. We support the interpretation that the central point source of GNz11 could be powered by a SE (λEdd ≃ 2 − 3) accreting BH with mass 1.5 × 106  M ⊙, while the emission from CEERS-1019 is dominated by the host galaxy; if it harbours an active BH, we find it to have a mass of M BH ≃ 107  M ⊙, and to be accreting at sub-Eddington rates (λEdd ≃ 0.5). [ABSTRACT FROM AUTHOR]

We present an analysis of a sample of robust high-redshift galaxies selected from the 'blank' fields of the Prime Extragalactic Areas for Reionization Science (PEARLS) survey and Early Release Observations (ERO) data from JWST with the aim of selecting candidate high-redshift active galactic nuclei (AGN). Sources were identified from this parent sample using a threefold selection procedure, which includes spectral energy distribution (SED) fitting to identify sources that are best fitted by AGN SED templates, a further selection based on the relative performance of AGN and non-AGN models, and finally morphological fitting to identify compact sources of emission, resulting in a purity-oriented procedure. Using this procedure, we identify a sample of nine AGN candidates at 6.5 < z < 12, from which we constrain their physical properties as well as measure a lower bound on the AGN fraction in this redshift range of 5 ± 1 per cent. As this is an extreme lower limit due to our focus on purity and our SEDs being calibrated for unobscured Type 1 AGN, this demonstrates that AGN are perhaps quite common at this early epoch. The rest-frame UV colours of our candidate objects suggest that these systems are potentially candidate obese black hole galaxies (OBGs). We also investigate Chandra and VLA maps of these areas from which we calculate detection limits. Of note is a z  = 11.9 candidate source exhibiting an abrupt morphological shift in the reddest band as compared to bluer bands, indicating a potential merger or an unusually strong outflow. [ABSTRACT FROM AUTHOR]

The rate of tidal disruption events (TDEs) depends sensitively on the stellar properties of the central galactic regions. Simulations show that galaxy mergers cause gas inflows, triggering nuclear starbursts, increasing the central stellar density. Motivated by these numerical results, and by the observed overrepresentation of post-starburst galaxies among TDE hosts, we study the evolution of the TDE rate in high-resolution hydrodynamical simulations of a galaxy merger, in which we capture the evolution of the stellar density around the massive black holes (BHs). We apply analytical estimates of the loss-cone theory, using the stellar density profiles from simulations, to estimate the time evolution of the TDE rate. At the second pericentre, a nuclear starburst enhances the stellar density around the BH in the least massive galaxy, leading to an enhancement of the TDE rate around the secondary BH, although the magnitude and the duration of the increase depend on the stochasticity of star formation on very small scales. The central stellar density around the primary BH remains instead fairly constant, and so is its TDE rate. After the formation of the binary, the stellar density decreases, and so does the TDE rate. [ABSTRACT FROM AUTHOR]