Spiral galaxies have most of their stellar mass in a large rotating disk, and only a modest fraction in a central spheroidal bulge. This poses a major challenge for cosmological models of galaxy formation. Galaxies form at the centre of dark matter halos through a combination of hierarchical merging and gas accretion along cold streams, and should rapidly grow their bulge through mergers and instabilities. Cosmological simulations predict galaxies to have most of their mass in the central bulge, and therefore an angular momentum much below the observed level, except in dwarf galaxies. We propose that the continuous return of fresh gas by stellar populations over cosmic times could solve this issue. A population of stars formed at a given instant typically returns half of its initial mass in the form of gas over 10 billion years, and the process is not dominated by rapid supernovae explosions but by the long-term mass-loss from low- and intermediate-mass stars. Using simulations of galaxy formation, we show that this recycling of gas can strongly affect the structural evolution of massive galaxies, potentially solving the bulge fraction issue: we find that the bulge-to-disk ratio of a massive galaxy can be divided by a factor of 3. The continuous recycling of baryons through star formation and stellar mass loss helps the growth of disks and their survival to interactions and mergers. Instead of forming only early-type, spheroid-dominated galaxies (S0 and ellipticals), the standard cosmological model can then successfully account for massive late-type, disk-dominated spiral galaxies (Sb-Sc).
We show that star formation in galaxy bulges is self-regulating through momentum feedback, limiting the stellar bulge mass to M_b ~ sigma^4. Together with a black hole mass M_BH ~ sigma^4 set by AGN momentum feedback, this produces a linear M_BH - M_b relation. At low redshift this gives M_BH/M_b ~ 0.001, close to the observed ratio. We show that AGN feedback can remove any remaining gas from the bulge and terminate star formation once the central black hole reaches the M_BH - sigma value, contrary to earlier claims. We find a mild upward deviation from the sigma^4 law at higher redshift and a…
Supermassive black holes have been detected in all galaxies that contain bulge components when the galaxies observed were close enough so that the searches were feasible. Together with the observation that bigger black holes live in bigger bulges, this has led to the belief that black hole growth and bulge formation regulate each other. That is, black holes and bulges "coevolve". Therefore, reports of a similar correlation between black holes and the dark matter halos in which visible galaxies are embedded have profound implications. Dark matter is likely to be nonbaryonic, so these reports su…
We examine radiation-regulated accretion onto intermediate-mass and massive black holes (BHs) embedded in a bulge component. Using spherically symmetric one-dimensional radiation-hydrodynamics simulations, we track the growth of BHs accreting from a cold, neutral gas reservoir with temperature T=10^4 K. We find that the accretion rate of BHs embedded in bulges is proportional to r_{B,eff}/r_B, where r_{B,eff} is the increased effective Bondi radius that includes the gravitational potential of the bulge, and r_B is the Bondi radius of the BH. The radiative feedback from the BH suppresses the co…
We present a set of hydrodynamical/Nbody controlled simulations of isolated gas rich galaxies that self-consistently include SN feedback and a detailed chemical evolution model, both tested in cosmological simulations. The initial conditions are motivated by the observed star forming galaxies at z ~ 2-3. We find that the presence of a multiphase interstellar media in our models promotes the growth of disc instability favouring the formation of clumps which in general, are not easily disrupted on timescales compared to the migration time. We show that stellar clumps migrate towards the central …
The masses of supermassive black holes are known to correlate with the properties of the bulge components of their host galaxies. In contrast, they appear not to correlate with galaxy disks. Disk-grown pseudobulges are intermediate in properties between bulges and disks. It has been unclear whether they do or do not correlate with black holes in the same way that bulges do, because too few pseudobulges were classified to provide a clear result. At stake are conclusions about which parts of galaxies coevolve with black holes, possibly by being regulated by energy feedback from black holes. Here…
The origins of the bulge and disc components of galaxies are of primary importance to understanding galaxy formation. Here bulge-disc decomposition is performed simultaneously in B- and R-bands for 922 bright galaxies in 8 nearby (z < 0.06) clusters with deep redshift coverage using photometry from the NOAO Fundamental Plane Survey. The total galaxy colours follow a universal colour-magnitude relation (CMR). The discs of L_* galaxies are 0.24 magnitudes bluer in $B-R$ than bulges. Bulges have a significant CMR slope while the CMR slope of discs is flat. Thus the slope of the CMR of the total l…
Quasar feedback outflows are commonly invoked to drive gas out of galaxies in the early gas-rich epoch to terminate growth of galaxies. Here we present simulations that show that AGN feedback may drive not only gas but also stars out of their host galaxies under certain conditions. The mechanics of this process is as following: (1) AGN-driven outflows accelerate and compress gas filling the host galaxy; (2) the accelerated dense shells become gravitationally unstable and form stars on radial trajectories. For the spherically symmetric initial conditions explored here, the black hole needs to e…
We analyze and compare the bulges of a sample of L* spiral galaxies in hydrodynamical simulations in a cosmological context, using two different codes, P-DEVA and GASOLINE. The codes regulate star formation in very different ways, with P-DEVA simulations inputing low star formation efficiency under the assumption that feedback occurs on subgrid scales, while the GASOLINE simulations have feedback which drives large scale outflows. In all cases, the marked knee-shape in mass aggregation tracks, corresponding to the transition from an early phase of rapid mass assembly to a later slower one, sep…
We present a simple theoretical framework for massive galaxies at high redshift, where the main assembly and star formation occurred, and report on the first cosmological simulations that reveal clumpy disks consistent with our analysis. The evolution is governed by the interplay between smooth and clumpy cold streams, disk instability, and bulge formation. Intense, relatively smooth streams maintain an unstable dense gas-rich disk. Instability with high turbulence and giant clumps, each a few percent of the disk mass, is self-regulated by gravitational interactions within the disk. The clumps…
Recent results are reviewed on galaxy dynamics, bar evolution, destruction and re-formation, cold gas accretion, gas radial flows and AGN fueling, minor mergers. Some problems of galaxy evolution are discussed in particular, exchange of angular momentum, radial migration through resonant scattering, and consequences on abundance gradients, the frequency of bulgeless galaxies, and the relative role of secular evolution and hierarchical formation.
Galaxy formation in the current cosmological paradigm is a very complex process in which inflows, outflows, interactions and mergers are common events. These processes can redistribute the angular momentum content of baryons. Recent observational results suggest that disc formed conserving angular momentum while elliptical galaxies, albeit losing angular momentum, determine a correlation between the specific angular momentum of the galaxy and the stellar mass. These observations provide stringent constraints for galaxy formation models in a hierarchical clustering scenario. We aim to analyse t…
Active galactic nucleus (AGN) feedback is expected to impact the amount of cold gas in galaxies by driving strong galactic winds, by preventing external gas inflows, or by changing the thermodynamical state of the gas. We use molecular gas mass estimates based on dust absorption (H$α$/H$β$) to study gas content of large samples of type 2 AGN host galaxies in comparison with inactive galaxies. Using sparse principal component and clustering analysis, we analyze a suite of stellar and structural parameters of $\sim 27,100$ face-on, central galaxies at redshift $z = 0.02-0.15$ and with stellar ma…
We analyze the first cosmological simulations that recover the fragmentation of high-redshift galactic discs driven by cold streams. The fragmentation is recovered owing to an AMR resolution better than 70 pc with cooling below 10^4 K. We study three typical star-forming galaxies in haloes of approx. 5 10^11 Msun at z=2.3, when they were not undergoing a major merger. The steady gas supply by cold streams leads to gravitationally unstable, turbulent discs, which fragment into giant clumps and transient features on a dynamical timescale. The disc clumps are not associated with dark-matter haloe…
We report results from XMM-Newton and Chandra observations of the nearby (z = 0.067) giant radio galaxy 3C 35. We find evidence for an X-ray emitting gas belt, orthogonal to and lying between the lobes of 3C 35, which we interpret as fossil-group gas driven outwards by the expanding radio lobes. We also detect weak emission from a second, more extended group-type environment, as well as inverse-Compton X-ray emission from the radio lobes. The morphological structure of the radio lobes and gas belt point to co-evolution. Furthermore, the radio source is powerful enough to eject galaxy-scale gas…
A new model for coevolution of galaxies and supermassive black holes (SMBH) is presented that is physically based. The evolutionary track starts with an event that triggers a significant starburst in the central region of a galaxy. In this model, the main SMBH growth takes place in post-starburst phase fueled by recycled gas from inner bulge stars in a self-regulated fashion on a time scale that is substantially longer than 100Myrs and at a diminishing Eddington ratio with time. We argue that the SMBH cannot gorge itself during the starburst phase, despite the abundant supply of cold gas, beca…
We describe simple useful toy models for key processes of galaxy formation in its most active phase, at z > 1, and test the approximate expressions against the typical behaviour in a suite of high-resolution hydro-cosmological simulations of massive galaxies at z = 4-1. We address in particular the evolution of (a) the total mass inflow rate from the cosmic web into galactic haloes based on the EPS approximation, (b) the penetration of baryonic streams into the inner galaxy, (c) the disc size, (d) the implied steady-state gas content and star-formation rate (SFR) in the galaxy subject to mass …
Gravitational-wave background from supermassive black holes without merger trees: Tidally regulated mergers and direct inference from the NANOGrav 15 yr data
GRAPPA Institute, University of Amsterdam（阿姆斯特丹大学 GRAPPA 研究所）；Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI), University of Tokyo（东京大学 宇宙物理数学 Kavli 研究所）
This paper aims at explaining the two phases in the observed specific star formation rate (sSFR), namely the high (>3/Gyr) values at z>2 and the smooth decrease since z=2. In order to do this, we compare to observations the specific star formation rate evolution predicted by well calibrated models of chemical evolution for elliptical and spiral galaxies, using the additional constraints on the mean stellar ages of these galaxies (at a given mass). We can conclude that the two phases of the sSFR evolution across cosmic time are due to different populations of galaxies. At z>2 the contribution c…
Giant elliptical galaxies, believed to be built from the merger of lesser galaxies, are known to house a massive black hole at their center rather than a compact star cluster. If low- and intermediate-mass galaxies do indeed partake in the hierarchical merger scenario, then one needs to explain why their dense nuclear star clusters are not preserved in merger events. A valuable clue may the recent revelation that nuclear star clusters and massive black holes frequently co-exist in intermediate mass bulges and elliptical galaxies. In an effort to understand the physical mechanism responsible fo…
We use time-varying models of the coupled evolution of the HI, H_2 gas phases and stars in galaxy-sized numerical simulations to: a) test for the emergence of the Kennicutt-Schmidt (K-S) and the H_2-pressure relation, b) explore a realistic H_2-regulated star formation recipe which brings forth a neglected and potentially significant SF-regulating factor, and c) go beyond typical galactic environments (for which these galactic empirical relations are deduced) to explore the early evolution of very gas-rich galaxies. In this work we model low mass galaxies ($M_{\rm baryon} \le 10^9 \msun$), whi…
Grain growth by the accretion of metals in interstellar clouds (called `grain growth') could be one of the dominant processes that determine the dust content in galaxies. The importance of grain size distribution for the grain growth is demonstrated in this paper. First, we derive an analytical formula that gives the grain size distribution after the grain growth in individual clouds for any initial grain size distribution. The time-scale of the grain growth is very sensitive to grain size distribution, since the grain growth is mainly regulated by the surface to volume ratio of grains. Next, …
Disk galaxies at high redshift have been predicted to maintain high gas surface densities due to continuous feeding by intense cold streams leading to violent gravitational instability, transient features and giant clumps. Gravitational torques between the perturbations drive angular momentum out and mass in, and the inflow provides the energy for keeping strong turbulence. We use analytic estimates of the inflow for a self-regulated unstable disk at a Toomre stability parameter Q~1, and isolated galaxy simulations capable of resolving the nuclear inflow down to the central parsec. We predict …
Molecular hydrogen (H2) is the primary component of the reservoirs of cold, dense gas that fuel star formation in our galaxy. While the H2 abundance is ultimately regulated by physical processes operating on small scales in the interstellar medium (ISM), observations have revealed a tight correlation between the ratio of molecular to atomic hydrogen in nearby spiral galaxies and the pressure in the mid-plane of their disks. This empirical relation has been used to predict H2 abundances in galaxies with potentially very different ISM conditions, such as metal-deficient galaxies at high redshift…
Different methodologies lead to order-of-magnitude variations in predicted galaxy merger rates. We examine and quantify the dominant uncertainties. Different halo merger rates and subhalo 'destruction' rates agree to within a factor ~2 given proper care in definitions. If however (sub)halo masses are not appropriately defined or are under-resolved, the major merger rate can be dramatically suppressed. The dominant differences in galaxy merger rates owe to baryonic physics. Hydrodynamic simulations without feedback and older models that do not agree with the observed galaxy mass function propag…
The energy and momentum deposited by the radiation from accretion onto the supermassive black holes (BHs) that reside at the centres of virtually all galaxies can halt or even reverse gas inflow, providing a natural mechanism for supermassive BHs to regulate their growth and to couple their properties to those of their host galaxies. However, it remains unclear whether this self-regulation occurs on the scale at which the BH is gravitationally dominant, on that of the stellar bulge, the galaxy, or that of the entire dark matter halo. To answer this question, we use self-consistent simulations …
Stellar mass distribution in M31 is estimated using optical and infrared imaging data. Combining the derived stellar mass model with various kinematical data, properties of the DM halo of the galaxy are constrained. SDSS observations through the ugriz filters and the Spitzer imaging at 3.6 microns are used to sample the SED of the galaxy at each imaging pixel. Intrinsic dust extinction effects are taken into account by using far-infrared observations. Synthetic SEDs created with different stellar population synthesis models are fitted to the observed SEDs, providing estimates for the stellar m…
We investigate the time evolution of dust properties, molecular hydrogen (H_2) contents, and star formation histories in galaxies by using our original chemodynamical simulations. The simulations include the formation of dust in the stellar winds of supernovae (SNe) and asymptotic giant branch (AGB) stars, the growth and destruction processes of dust in the interstellar medium (ISM), the formation of polycyclic aromatic hydrocarbon (PAH) dust in carbon-rich AGB stars, the H_2 formation on dust grains, and the H_2 photo-dissociation due to far ultra-violet (FUV) light in a self-consistent manne…
We introduce an extension of the ELVIS project to account for the effects of the Milky Way galaxy on its subhalo population. Our simulation suite, Phat ELVIS, consists of twelve high-resolution cosmological dark matter-only (DMO) zoom simulations of Milky Way-size $Λ$CDM~ haloes ($M_{\rm v} = 0.7-2 \times 10^{12} \,\mathrm{M}_\odot$) along with twelve re-runs with embedded galaxy potentials grown to match the observed Milky Way disk and bulge today. The central galaxy potential destroys subhalos on orbits with small pericenters in every halo, regardless of the ratio of galaxy mass to halo mass…
Star-forming disk galaxies at high redshift are often subject to violent disk instability, characterized by giant clumps whose fate is yet to be understood. The main question is whether the clumps disrupt within their dynamical timescale (<50Myr), like molecular clouds in today's galaxies, or whether they survive stellar feedback for more than a disk orbital time (~300Myr) in which case they can migrate inward and help building the central bulge. We present 3.5-7pc resolution AMR simulations of high-redshift disks including photo-ionization, radiation pressure, and supernovae feedback (Renaud …
The reservoir of molecular gas (H$_{\rm 2}$) represents the fuel for the star formation (SF) of a galaxy. Connecting the star formation rate (SFR) to the available H$_{\rm 2}$ is key to accurately model SF in cosmological simulations of galaxy formation. We investigate how modifying the underlying modelling of H$_{\rm 2}$ and the description of stellar feedback in low-metallicity environments (LMF, i.e. low-metallicity stellar feedback) in cosmological, zoomed-in simulations of a Milky Way-size halo influences the formation history of the forming, spiral galaxy and its final properties. We exp…
Using X-ray stacking analyses we estimate the average amounts of supermassive black hole (SMBH) growth taking place in star-forming galaxies (SFGs) at z~1 and z~2 as a function of galaxy stellar mass (M*). We find the average SMBH growth rate follows remarkably similar trends with M* and redshift as the average star-formation rates (SFRs) of their host galaxies (i.e., (i.e., dM_BH/dt ~ M*^(0.86+/-0.39) for the z~1 sample and dM_BH/dt ~ M*^(1.05+/-0.36) for the z~2 sample). It follows that the ratio of SMBH growth rate to SFR is (a) flat with respect to M* (b) not evolving with redshift and (c)…
We compile observations of the surface mass density profiles of dense stellar systems, including globular clusters in the Milky Way and nearby galaxies, massive star clusters in nearby starbursts, nuclear star clusters in dwarf spheroidals and late-type disks, ultra-compact dwarfs, and galaxy spheroids spanning the range from low-mass cusp bulges and ellipticals to massive core ellipticals. We show that in all cases the maximum stellar surface density attained in the central regions of these systems is similar, Sigma_max ~ 10^11 M_sun/kpc^2 (~20 g/cm^2), despite the fact that the systems span …
We analyze the role of bars in the build-up of central mass concentrations in massive, disk galaxies. Our parent sample consists of 3757 face-on disk galaxies with redshifts between 0.01 and 0.05, selected from the seventh Data Release of the Sloan Digital Sky Survey. 1555 galaxies with bars are identified using position angle and ellipticity profiles of the $i$-band light. We compare the ratio of the specific star formation rate measured in the 1-3 kpc central region of the galaxy to that measured for the whole galaxy. Galaxies with strong bars have centrally enhanced star formation; the degr…
With the aim of investigating whether stellar sources can account for the >10^8 Msun dust masses inferred from mm/sub-mm observations of samples of 5<z<6.4 quasars,we develop a chemical evolution model which follows the evolution of metals and dust on the stellar characteristic lifetimes, taking into account dust destruction mechanisms.Using a grid of stellar dust yields as a function of the initial mass and metallicity over the range 1-40 Msun and 0-1 Zsun,we show that the role of AGB stars in cosmic dust evolution at high redshift might have been over-looked.We apply the chemical evolution m…
We analyze the physical conditions in the interstellar gas of 11 actively star-forming galaxies at z~2, based on integral-field spectroscopy from the ESO-VLT and HST/NICMOS imaging. We concentrate on the high H-alpha surface brightnesses, large line widths, line ratios and the clumpy nature of these galaxies. We show that photoionization calculations and emission line diagnostics imply gas pressures and densities that are similar to the most intense nearby star-forming regions at z=0 but over much larger scales (10-20 kpc). A relationship between surface brightness and velocity dispersion can …
We use simulations with realistic models for stellar feedback to study galaxy mergers. These high resolution (1 pc) simulations follow formation and destruction of individual GMCs and star clusters. The final starburst is dominated by in situ star formation, fueled by gas which flows inwards due to global torques. The resulting high gas density results in rapid star formation. The gas is self gravitating, and forms massive (~10^10 M_sun) GMCs and subsequent super-starclusters (masses up to 10^8 M_sun). However, in contrast to some recent simulations, the bulk of new stars which eventually form…
We track the co-evolution of supermassive black holes (SMBHs) and their host galaxies. The calculation is embedded in the GALFORM semi-analytical model which simulates the formation and evolution of galaxies in a cold dark matter (CDM) universe. During the evolution of the host galaxy, hot and cold gas are added to the SMBH by flows triggered by halo gas cooling, disc instabilities and galaxy mergers. This builds up the mass and spin of the BH, and the resulting accretion power regulates the gas cooling and subsequent star formation. The accretion flow is assumed to form a geometrically thin c…
We address the cosmological evolution of violent gravitational instability in high-redshift, massive, star-forming galactic discs. To this aim, we integrate in time the equations of mass and energy conservation under self-regulated instability of a two-component disc of gas and stars. The disc is assumed to be continuously fed by cold gas at the average cosmological rate. The gas forms stars and is partly driven away by stellar feedback. The gas and stars flow inward through the disc to a central bulge due to torques that drive angular momentum outwards. The gravitational energy released by th…
With the first metal enrichment by Population (Pop) III supernovae (SNe), the formation of the first metal-enriched, Pop II stars becomes possible. In turn, Pop III star formation and early metal enrichment are slowed by the high energy radiation emitted by Pop II stars. Thus, through the SNe and radiation they produce, Populations II and III coevolve in the early Universe, one regulated by the other. We present large (4 Mpc)^3, high resolution cosmological simulations in which we self-consistently model early metal enrichment and the stellar radiation responsible for the destruction of the co…
