Black holes across a broad range of masses play a key role in the evolution of galaxies. The initial seeds of black holes formed at $z \sim 30$ and grew over cosmic time by gas accretion and mergers. Using observational data for quasars and theoretical models for the hierarchical assembly of dark matter halos, we study the relative importance of gas accretion and mergers for black hole growth, as a function of redshift ($0<z<10$) and black hole mass ($ 10^3 \, \mathrm{M_{\odot}} < M_{\bullet} < 10^{10} \, \mathrm{M_{\odot}}$). We find that (i) growth by accretion is dominant in a large fraction of the parameter space, especially at $M_{\bullet} > 10^8 \, \mathrm{M_{\odot}}$ and $z>6$; and (ii) growth by mergers is dominant at $M_{\bullet} < 10^5 \, \mathrm{M_{\odot}}$ and $z>5.5$, and at $M_{\bullet} > 10^8 \, \mathrm{M_{\odot}}$ and $z<2$. As the growth channel has direct implications for the black hole spin (with gas accretion leading to higher spin values), we test our model against $\sim 20$ robust spin measurements available thus far. As expected, the spin tends to decline toward the merger-dominated regime, thereby supporting our model. The next generation of X-ray and gravitational-wave observatories (e.g. Lynx, AXIS, Athena and LISA) will map out populations of black holes up to very high redshift ($z\sim 20)$, covering the parameter space investigated here in almost its entirety. Their data will be instrumental to providing a clear picture of how black holes grew across cosmic time.
The role of major mergers in triggering super-Eddington accretion
Dipartimento di Fisica, “Sapienza” Università di Roma（罗马大学物理系）；INAF, Osservatorio Astronomico di Roma（罗马天文台）；INFN, Sezione Roma1（罗马第一国家核物理研究所）；Sapienza School for Advanced Studies（萨皮恩扎高等研究学院）；Como Lake Center for Astrophysics, DiSAT, Università degli Studi dell’Insubria（因苏布里亚大学迪萨特科莫湖天体物理学中心）；INFN, Sezione di Milano-Bicocca（米兰比可卡国家核物理研究所）；INAF, Osservatorio di Astrofisica e Scienza dello Spazio di Bologna（博洛尼亚空间天体物理学与科学天文台）
The majority of gravitational wave (GW) events detected so far by LIGO/Virgo originate from binary black hole (BBH) mergers. Among the different binary evolution paths, the merger of BBHs in accretion discs of active galactic nuclei (AGNs) is a possible source of GW detections. We consider an idealised analytical model of the orbital evolution of BBHs embedded in an AGN accretion disc. In this framework, the disc-binary interaction increases the orbital eccentricity and decreases the orbital separation, driving the BBH into a regime where GW emission eventually leads to coalescence. We compute…
Building galaxy merger trees from a state-of-the-art cosmological hydrodynamics simulation, Horizon-AGN, we perform a statistical study of how mergers and smooth accretion drive galaxy morphologic properties above $z > 1$. More specifically, we investigate how stellar densities, effective radii and shape parameters derived from the inertia tensor depend on mergers of different mass ratios. We find strong evidence that smooth accretion tends to flatten small galaxies over cosmic time, leading to the formation of disks. On the other hand, mergers, and not only the major ones, exhibit a propensit…
Two Mpc-size contact discontinuities have recently been identified in the XMM-Newton and Suzaku X-ray observations of the outskirts of the Perseus cluster (Walker et al. 2020). These structures have been tentatively interpreted as "sloshing cold fronts", which are customarily associated with differential motions of the cluster gas, perturbed by a merger. In this study we consider an alternative scenario, namely, that the most prominent discontinuity near the cluster virial radius is the result of the collision between the accretion shock and the "runaway" merger shock. We also discuss the poss…
Several types/classes of shocks naturally arise during formation and evolution of galaxy clusters. One such class is represented by accretion shocks, associated with deceleration of infalling baryons. Such shocks, characterized by a very high Mach number, are present even in 1D models of cluster evolution. Another class is composed of "runaway merger shocks", which appear when a merger shock, driven by a sufficiently massive infalling subcluster, propagates away from the main-cluster center. We argue that, when the merger shock overtakes the accretion shock, a new long-living shock is formed t…
Gas Accretion versus BH Merger driven Growth Modes of Supermassive Black Holes and Implications for the Little Red Dots
Istituto Nazionale di Astrofisica (INAF) - Osservatorio Astronomico di Trieste (OATs)（意大利国家天体物理研究所（INAF）- 的里雅斯特天文台（OATs））；Centro de Ciências Naturais e Humanas - Universidade Federal do ABC（自然与人类科学中心 - 圣保罗联邦ABC大学）；Núcleo de Astrofísica - Universidade Cidade de São Paulo（天体物理学核心 - 圣保罗城市大学）
We present post-Newtonian $N$-body simulations on mergers of accreting stellar-mass black holes (BHs), where such general relativistic effects as the pericenter shift and gravitational wave (GW) emission are taken into consideration. The attention is concentrated on the effects of the dynamical friction and the Hoyle-Lyttleton mass accretion by ambient gas. We consider a system composed of ten BHs with initial mass of $30~M_\odot$. As a result, we show that mergers of accreting stellar-mass BHs are classified into four types: a gas drag-driven, an interplay-driven, a three body-driven, or an a…
We present an analysis of the instantaneous supermassive black hole (SMBH) accretion rates in a collection of 1563 post-merger galaxies drawn from the IllustrisTNG simulation. Our sample consists of galaxies that have experienced a merger in the last simulation snapshot (within ~160 Myrs of coalescence) in the redshift range 0<z<1, with merger stellar mass ratios >1:10 and post-merger stellar masses > $10^{10} M_{\odot}$. We find that, on average, the accretion rates of the post-mergers are ~1.7 times higher than in a control sample and that post-mergers are 3-4 times more likely to experience…
We use a semi-analytic galaxy formation model to study the co-evolution of supermassive black holes (SMBHs) with their host galaxies. Although the coalescence of SMBHs is not important, the quasar-mode accretion induced by mergers plays a dominant role in the growth of SMBHs. Mergers play a more important role in the growth of SMBH host galaxies than in the SMBH growth. It is the combined contribution from quasar mode accretion and mergers to the SMBH growth and the combined contribution from starburst and mergers to their host galaxy growth that determine the observed scaling relation between…
In this paper we quantify the gas accretion rate from minor mergers onto star-forming galaxies in the Local Universe using HI observations of 148 nearby spiral galaxies (WHISP sample). We developed a dedicated code that iteratively analyses HI data-cubes, finds dwarf gas-rich satellites around larger galaxies and estimates an upper limit to the gas accretion rate. We found that 22% of the galaxies have at least one detected dwarf companion. We made the very stringent assumption that all satellites are going to merge in the shortest possible time transferring all their gas to the main galaxies.…
Being able to distinguish between galaxies that have recently undergone major merger events, or are experiencing intense star formation, is crucial for making progress in our understanding of the formation and evolution of galaxies. As such, we have developed a machine learning framework based on a convolutional neural network (CNN) to separate star forming galaxies from post-mergers using a dataset of 160,000 simulated images from IllustrisTNG100 that resemble observed deep imaging of galaxies with Hubble. We improve upon previous methods of machine learning with imaging by developing a new a…
Recent observations of AGN activity in massive galaxies (log Mstar / Msun > 10.4) show that: 1) at z < 1, AGN-hosting galaxies do not show enhanced merger signatures compared to normal galaxies, 2) also at z < 1, most AGNs are hosted by quiescent galaxies; and 3) at z > 1, percentage of AGNs in star forming galaxies increases and becomes comparable to AGN percentage in quiescent galaxies at z ~ 2. How can major mergers explain AGN activity in massive quiescent galaxies which have no merger features and no star formation to indicate recent galaxy merger? By matching merger events in a cosmologi…
We studied the final phases of galactic mergers, focusing on interactions between supermassive black holes (SMBHs) and the interstellar medium in a central sub-kpc region, using an N-body/hydrodynamics code. This numerical experiment aims to understand the fate of the gas supplied by mergers of two or more galaxies with SMBHs, whose masses are $10^7 M_\odot$. We observed that the mass accretion rate to one SMBH exceeds the Eddington accretion rate when the distance between two black holes (BHs) rapidly decreases. However, this rapid accretion phase does not last for more than $10^7$ yrs, and i…
Neutron star mergers are believed to occur in accretion disks around supermassive black holes. Here we show that a putative jet launched from the merger of a binary neutron star (BNS) or a neutron star--black hole (NSBH) merger occurring at the migration trap in an active galactic nucleus (AGN) disk would be choked. The jet energy is deposited within the disk materials to power a hot cocoon. The cocoon is energetic enough to break out from the AGN disk and produce a bright X-ray shock breakout transient peaking at $\sim0.15\,{\rm d}$ after the merger. The peak luminosity is estimated as $\sim …
We introduce a new model for the accretion and feedback of supermassive black hole (SMBH) binaries to the KETJU code, which enables us to resolve the evolution of SMBH binaries down to separations of tens of Schwarzschild radii in gas-rich galaxy mergers. Our subgrid binary accretion model extends the widely used Bondi--Hoyle--Lyttleton accretion into the binary phase and incorporates preferential mass accretion onto the secondary SMBH, which is motivated by results from small-scale hydrodynamical circumbinary disc simulations. We perform idealised gas-rich disc galaxy merger simulations using…
Accretion disks around supermassive black holes (SMBH) are promising sites for stellar mass black hole (BH) mergers due to mass segregation and merger acceleration by disk gas torques. Here we show that a GW-kick at BH merger causes ram-pressure stripping of gas within the BH Hill sphere. If $R_{H}\geq H$, the disk height, an off-center UV flare at $a_{\rm BH} \sim 10^{3}r_{g}$ emerges within $t_{\rm UV} \sim \rm{O}(2 {\rm days})(a_{\rm BH}/10^{3}r_{g})(M_{\rm SMBH}/10^{8}M_{\odot})(v_{\rm kick}/10^{2}\rm{km/s})$ post-merger and lasts O$(R_{H}/v_{\rm kick}) \sim \rm{O}(5 t_{\rm UV}$). The flar…
In this paper we continue the first ever study of magnetized mini-disks coupled to circumbinary accretion in a supermassive binary black hole (SMBBH) approaching merger reported in Bowen et al. 2018. We extend this simulation from 3 to 12 binary orbital periods. We find that relativistic SMBBH accretion acts as a resonant cavity, where quasi-periodic oscillations tied to the the frequency at which the black hole's orbital phase matches a non-linear $m=1$ density feature, or ``lump'', in the circumbinary accretion disk permeate the system. The rate of mass accretion onto each of the mini-disks …
We study the statistical properties of mergers between central and satellite galaxies in galaxy clusters in the redshift range $0<z<1$, using a sample of dark-matter only cosmological N-body simulations from Le SBARBINE dataset. Using a spherical overdensity algorithm to identify dark-matter haloes, we construct halo merger trees for different values of the over-density $Δ_c$. While the virial overdensity definition allows us to probe the accretion of satellites at the cluster virial radius $r_{vir}$, higher overdensities probe satellite mergers in the central region of the cluster, down to $\…
Many galaxies are expected to harbor binary supermassive black holes (SMBHs) in their centers. Their interaction with the surrounding gas results in accretion and exchange of angular momentum via tidal torques, facilitating binary inspiral. Here we explore the non-trivial coupling between these two processes and analyze how the global properties of externally supplied circumbinary disks depend on the binary accretion rate. By formulating our results in terms of the angular momentum flux driven by internal stresses, we come up with a very simple classification of the possible global disk struct…
Using a new, high-resolution cosmological hydrodynamic simulation of a Milky Way-type (MW-type) galaxy, we explore how a merger-rich assembly history affects the mass budget of the central supermassive black hole (SMBH). We examine a MW-mass halo at the present epoch whose evolution is characterized by several major mergers to isolate the importance of merger history on black hole accretion. This study is an extension of Bellovary et. al. 2013, which analyzed the accretion of high mass, high redshift galaxies and their central black holes, and found that the gas content of the central black ho…
The Environmental Switch in Black Hole Feeding: Bar-Driven vs. Merger-Driven Growth in IllustrisTNG50
Indian Institute of Science, Education and Research (IISER) Tirupati（印度科学教育与研究学院提鲁帕蒂分校）；Department of Space, Platenary and Astronomical Science and Engineering, Indian Institute of Technology (IIT), Kanpur（坎普尔印度理工学院空间、行星与天文学科学与工程系）
The recently discovered gravitational wave sources GW190521 and GW190814 have shown evidence of BH mergers with masses and spins that could be outside of the range expected from isolated stellar evolution. These merging objects could have undergone previous mergers. Such hierarchical mergers are predicted to be frequent in active galactic nuclei (AGN) disks, where binaries form and evolve efficiently by dynamical interactions and gaseous dissipation. Here we compare the properties of these observed events to the theoretical models of mergers in AGN disks, which are obtained by performing one-d…
We present the first fully relativistic prediction of the electromagnetic emission from the surrounding gas of a supermassive binary black hole system approaching merger. Using a ray-tracing code to post-process data from a general relativistic 3-d MHD simulation, we generate images and spectra, and analyze the viewing angle dependence of the light emitted. When the accretion rate is relatively high, the circumbinary disk, accretion streams, and mini-disks combine to emit light in the UV/EUV bands. We posit a thermal Compton hard X-ray spectrum for coronal emission; at high accretion rates, it…
We report results from simulations in general relativity of magnetized disks accreting onto merging black hole binaries, starting from relaxed disk initial data. The simulations feature an effective, rapid radiative cooling scheme as a limiting case of future treatments with radiative transfer. Here we evolve the systems after binary-disk decoupling through inspiral and merger, and analyze the dependence on the binary mass ratio with $q\equiv m_{\rm bh}/M_{\rm BH}=1,1/2,$ and $1/4$. We find that the luminosity associated with local cooling is larger than the luminosity associated with matter k…
Binary black hole (BBH) mergers are the primary sources of gravitational wave (GW) events detected by LIGO/Virgo. Binary black holes embedded in the accretion discs of active galactic nuclei (AGN) are possible candidates for such GW events. We develop an idealised analytic model for the orbital evolution of BBHs in AGN accretion discs by combining the evolution equations of disc-binary interaction and GW inspiral. We investigate the coupled `disc+GW'-driven evolution of BBHs transitioning from the disc-driven regime at large orbital separations into the GW-driven regime at small separations. I…
We apply our recently proposed "quadratic genetic modification" approach to generating and testing the effects of alternative mass accretion histories for a single $Λ$CDM halo. The goal of the technique is to construct different formation histories, varying the overall contribution of mergers to the fixed final mass. This enables targeted studies of galaxy and dark matter halo formation's sensitivity to the smoothness of mass accretion. Here, we focus on two dark matter haloes, each with four different mass accretion histories. We find that the concentration of both haloes systematically decre…
We make black hole (BH) merger trees from Millennium and Millennium-II simulations to find under what conditions 10^9Msun SMBH can form by redshift z=7. In order to exploit both: large box size in the Millennium simulation; and large mass resolution in the Millennium-II simulation, we develop a method to combine these two simulations together, and use the Millennium-II merger trees to predict the BH seeds to be used in the Millennium merger trees. We run multiple semi-analytical simulations where SMBHs grow through mergers and episodes of gas accretion triggered by major mergers. As a constrai…
We measure the role of major and minor mergers in forming the stellar masses of galaxies over $0<z<3$ using a combination of $\sim 3.25$ deg$^{2}$ of the deepest ground based near-infrared imaging taken to date as part of the REFINE survey. We measure the pair fraction and merger fractions for galaxy mergers of different mass ratios, and quantify the merger rate with newly measured time-scales derived from the Illustris simulation as a function of redshift and merger mass ratio. We find that over $0 < z < 3$ major mergers with mass ratios greater than 1:4 occur $0.85^{+0.19}_{-0.20}$ times on …
We study stellar and black hole mass assembly in a sample of 42 infrared-luminous galaxy mergers at z<0.3 by combining results from radiative transfer modelling with archival measures of molecular gas and black hole mass. The ratios of stellar mass, molecular gas mass, and black hole mass to each other are consistent with those of massive gas-rich galaxies at z<0.3. The advanced mergers may show increased black hole mass to stellar mass ratios, consistent with the transition from AGN to ellipticals and implying substantial black hole mass growth over the course of the merger. Star formation ra…
Representing simultaneous black hole accretion during a merger, binary active galactic nuclei (AGNs) could provide valuable observational constraints to models of galaxy mergers and AGN triggering. High-resolution radio interferometer imaging offers a promising method to identify a large and uniform sample of binary AGNs, because it probes a generic feature of nuclear activity and is free from dust obscuration. Our previous search yielded 52 strong candidates of kpc-scale binaries over the 92 deg$^2$ of the Sloan Digital Sky Survey (SDSS) Stripe 82 area with 2"-resolution Very Large Array (VLA…
OH megamasers (OHMs) are rare, luminous masers found in gas-rich major galaxy mergers. In untargeted neutral hydrogen ($\mathrm{HI}$) emission-line surveys, spectroscopic redshifts are necessary to differentiate the $λ_\text{rest}=18$ cm masing lines produced by OHMs from $\mathrm{HI}$ 21 cm lines. Next generation $\mathrm{HI}$ surveys will detect an unprecedented number of galaxies, most of which will not have spectroscopic redshifts. We present predictions for the numbers of OHMs that will be detected and the potential "contamination" they will impose on $\mathrm{HI}$ surveys. We examine Loo…
We have developed a new tool to analyse galaxies in the EAGLE simulations as close as possible to observations.We investigated the evolution of their kinematic properties by means of the angular momentum proxy parameter,$ λ_{Re} $for galaxies with $M_{*} \ge 5 \times 10^{9} M_{\odot}$ in the RefL0100N1504 simulation up to redshift two (z = 2). Galaxies in the simulation show a wide variety of kinematic features, similiar to those found in integral-field spectroscopic studies. At z=0 the distribution of galaxies in the $λ_{Re}-ε$ plane is also in good agreement with results from observations. S…
We present results from the first fully general relativistic, magnetohydrodynamic (GRMHD) simulations of an equal-mass black hole binary (BHBH) in a magnetized, circumbinary accretion disk. We simulate both the pre and post-decoupling phases of a BHBH-disk system and both "cooling" and "no-cooling" gas flows. Prior to decoupling, the competition between the binary tidal torques and the effective viscous torques due to MHD turbulence depletes the disk interior to the binary orbit. However, it also induces a two-stream accretion flow and mildly relativistic polar outflows from the BHs. Following…
Recent observations and simulations have revealed the dominance of secular processes over mergers in driving the growth of both supermassive black holes (SMBH) and galaxy evolution. Here we obtain narrowband imaging of AGN powered outflows in a sample of $12$ galaxies with disk-dominated morphologies, whose history is assumed to be merger-free. We detect outflows in $10/12$ sources in narrow band imaging of the [OIII] $5007 \unicode{x212B}$ emission using filters on the Shane-3m telescope. We calculate a mean outflow rate for these AGN of $0.95\pm0.14~\rm{M}_{\odot}~\rm{yr}^{-1}$. This exceeds…
The accretion history of the Milky Way V. The kinematics of most globular clusters trace the merger epochs
Observatoire de Paris, Université PSL, CNRS（巴黎天文台，巴黎文理研究大学，法国国家科学研究中心）；Center for Astronomy, Space Science and Astrophysics, Independent University, Bangladesh（孟加拉独立大学天体物理、空间科学与天文学中心）
Satellites constitute an important fraction of the overall galaxy population and are believed to form in dark matter subhalos. Here we use the cosmological hydrodynamic simulation TNG100 to investigate how the formation histories of subhalos affect the properties and evolution of their host galaxies. We use a scaled formation time ($a_{\rm nf}$) to characterize the mass assembly histories of the subhalos before they are accreted by massive host halos. We find that satellite galaxies in young subhalos (low $a_{\rm nf}$) are less massive and more gas rich, and have stronger star formation and a …
We study the orbital evolution and accretion history of massive black hole (MBH) pairs in rotationally supported circumnuclear discs up to the point where MBHs form binary systems. Our simulations have high resolution in mass and space which, for the first time, makes it feasible to follow the orbital decay of a MBH either counter- or co-rotating with respect to the circumnuclear disc. We show that a moving MBH on an initially counter-rotating orbit experiences an "orbital angular momentum flip" due to the gas-dynamical friction, i.e., it starts to corotate with the disc before a MBH binary fo…
The Disk of Satellites (DoS) observed in the Andromeda galaxy is a thin and extended group of satellites, nearly perpendicular to the disk plane, that share a common direction of rotation about the centre of Andromeda. Although a DoS is also observed in the Milky Way galaxy, the prevalance of such structures in more distant galaxies remains controversial. Explanations for the formation of such DoSs vary widely from filamentary infall, or flattening due to the potential field from large scale structure, to galaxy interactions in a Mondian paradigm. Here we present an alternative scenario -- dur…
We estimate the accretion rates produced when a circumprimary gas disc is pushed into the primary supermassive black hole (SMBH) by the tidal force of the decaying secondary during a SMBH merger. Using the 3D Smoothed Particle Hydrodynamics (SPH) code {\sc phantom}, we extend previous investigations of co-planar discs to the case where the disc and binary orbital planes are misaligned. We consider a geometrically thin disc with inclination angles varying from 1 to 180 degrees and a binary with mass ratio $q$=$10^{-3}$. We find that discs with small inclination angles (< 10 degrees) produce an …
Explaining the internal distribution and motions of stars and gas in galaxies is a key aspect in understanding their evolution. In previous work we identified five well resolved galaxies with atypical kinematics from a cosmological simulation; two had kinematically distinct cores (KDCs), and three had counter-rotating gas and stars (CRGD). In this paper, we show that i) the KDC galaxies have flattening of stellar [O/Fe] at large galacto-centric radii due to the minor mergers that gave rise to the KDCs, and ii) the CRGD galaxies have an abrupt transition in the gas metallicity maps, from high m…
3D simulations of high mass young stellar object (HMYSO) growth show that their circumstellar discs fragment onto multiple self-gravitating objects. Accretion of these by HMYSO may explain episodic accretion bursts discovered recently. We post-process results of a previous 3D simulation of a HMYSO disc with a 1D code that resolves the disc and object dynamics down to the stellar surface. We find that burst-like deposition of material into the inner disc seen in 3D simulations by itself does not always signify powerful accretion bursts. Only high density post-collapse clumps crossing the inner …
The observation of the shadow of the supermassive black hole M87$^{*}$ by the Event Horizon Telescope (EHT) is sensitive to the spacetime geometry near the circular photon orbit and beyond, and it thus has the potential to test general relativity in the strong field regime. Obstacles to this program, however, include degeneracies between putative deviations from general relativity and both the description of the accretion flow and the uncertainties on "calibration parameters", such as e.g. the mass and spin of the black hole. In this work, we introduce a formalism, based on a principal compone…
We investigate the role of galaxy mergers on supermassive black hole (SMBH) accretion and star formation quenching in three state-of-the-art cosmological simulations with contrasting physics models: EAGLE, Illustris and IllustrisTNG. We find that recently coalesced 'post-mergers' in all three simulations have elevated SMBH accretion rates by factors of ~2-5. However, rapid (within 500 Myr of coalescence) quenching of star formation is rare, with incidence rates of 0.4% in Illustris, 4.5% in EAGLE and 10% in IllustrisTNG. The rarity of quenching in post-mergers results from substantial gas rese…
In major galaxy mergers, the orbits of stars are violently perturbed, and gas is torqued to the centre, diluting the gas metallicity and igniting a starburst. In this paper, we study the gas dynamics in and around merging galaxies using a series of cosmological magneto-hydrodynamical (MHD) zoom-in simulations. We find that the gas bridge connecting the merging galaxies pre-coalescence is dominated by turbulent pressure, with turbulent Mach numbers peaking at values of 1.6-3.3. This implies that bridges are dominated by supersonic turbulence, and are thus ideal candidates for studying the impac…
Research over the past decade has shown diminishing empirical evidence for major galaxy mergers being a dominating or even important mechanism for the growth of supermassive black holes in galaxies and the triggering of optically or X-ray selected active galactic nuclei (AGN). We here for the first time test whether such a connection exists at least in the most plausible part of parameter space for this mechanism: the highest specific accretion rate broad-line AGNs at the peak epoch of black hole activity around z = 2. To that end we examine 21 galaxies hosting a high accreting black hole (L/L…
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 AGN activity of merger-related versus secular-related causes, by studying different stages of the encounter: the stochastic (or early) stage…
The formation mechanism of supermassive black holes (SMBHs) in general, and of $\sim 10^9\,{\rm M}_{\odot}$ SMBHs observed as luminous quasars at redshifts $z> 6$ in particular, remains an open fundamental question. The presence of such massive BHs at such early times, when the Universe was less than a billion years old, implies that they grew via either super-Eddington accretion, or nearly uninterrupted gas accretion near the Eddington limit; the latter, at first glance, is at odds with empirical trends at lower redshifts, where quasar episodes associated with rapid BH growth are rare and bri…
The ages and metallicities of globular clusters (GCs) are known to be powerful tracers of the properties of their progenitor galaxies, enabling their use in determining the merger histories of galaxies. However, while useful in separating GCs into individual accretion events, the orbits of GC groups themselves have received less attention as probes of their progenitor galaxy properties. In this work, we use simulations of galaxies and their GC systems from the E-MOSAICS project to explore how the present-day orbital properties of GCs are related to the properties of their progenitor galaxies. …
Stellar halos in early-type galaxies (ETGs) are shaped by their accretion and merger histories. We use a sample of 1114 ETGs in the TNG100 simulation with stellar masses $10^{10.3}\leq M_{*}/M_\odot\leq 10^{12}$, selected at z=0 within the range of g-r colour and lambda-ellipticity diagram populated by observed ETGs. We study how the rotational support and intrinsic shapes of the stellar halos depend on the fraction of accreted stars, overall and separately by major, minor, and mini mergers. Accretion histories in TNG100 ETGs as well as the radial distributions of ex-situ stars $f_{ex}(R)$ str…
The origin of supermassive black holes (with $\gtrsim\!10^9\,M_{\odot}$) in the early universe (redshift $z \sim 7$) remains poorly understood. Gravitational collapse of a massive primordial gas cloud is a promising initial process, but theoretical studies have difficulty growing the black hole fast enough. We focus on the magnetic effects on star formation that occurs in an atomic-cooling gas cloud. Using a set of three-dimensional magnetohydrodynamic (MHD) simulations, we investigate the star formation process in the magnetized atomic-cooling gas cloud with different initial magnetic field s…
