Modeling galaxy formation in a cosmological context presents one of the greatest challenges in astrophysics today due to the vast range of scales and numerous physical processes involved. Here we ...review the current status of models that employ two leading techniques to simulate the physics of galaxy formation: semianalytic models and numerical hydrodynamic simulations. We focus on a set of observational targets that describe the evolution of the global and structural properties of galaxies from roughly cosmic high noon (
z
∼ 2-3) to the present. Although minor discrepancies remain, overall, models show remarkable convergence among different methods and make predictions that are in qualitative agreement with observations. Modelers have converged on a core set of physical processes that are critical for shaping galaxy properties. This core set includes cosmological accretion, strong stellar-driven winds that are more efficient at low masses, black hole feedback that preferentially suppresses star formation at high masses, and structural and morphological evolution through merging and environmental processes. However, all cosmological models currently adopt phenomenological implementations of many of these core processes, which must be tuned to observations. Many details of how these diverse processes interact within a hierarchical structure formation setting remain poorly understood. Emerging multiscale simulations are helping to bridge the gap between stellar and cosmological scales, placing models on a firmer, more physically grounded footing. Concurrently, upcoming telescope facilities will provide new challenges and constraints for models, particularly by directly constraining inflows and outflows through observations of gas in and around galaxies.
The dust content of galaxies from z = 0 to z = 9 Popping, Gergö; Somerville, Rachel S; Galametz, Maud
Monthly Notices of the Royal Astronomical Society,
11/2017, Letnik:
471, Številka:
3
Journal Article
Recenzirano
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Abstract
We study the dust content of galaxies from z = 0 to z = 9 in semi-analytic models of galaxy formation that include new recipes to track the production and destruction of dust. We include ...condensation of dust in stellar ejecta, the growth of dust in the interstellar medium (ISM), the destruction of dust by supernovae and in the hot halo, and dusty winds and inflows. The rate of dust growth in the ISM depends on the metallicity and density of molecular clouds. Our fiducial model reproduces the relation between dust mass and stellar mass from z = 0 to z = 7, the number density of galaxies with dust masses less than 108.3 M⊙ and the cosmic density of dust at z = 0. The model accounts for the double power-law trend between dust-to-gas (DTG) ratio and gas-phase metallicity of local galaxies and the relation between DTG ratio and stellar mass. The dominant mode of dust formation is dust growth in the ISM, except for galaxies with M
* < 107 M⊙, where condensation of dust in supernova ejecta dominates. The dust-to-metal ratio of galaxies depends on the gas-phase metallicity, unlike what is typically assumed in cosmological simulations. Model variants, including higher condensation efficiencies, a fixed time-scale for dust growth in the ISM, or no growth at all reproduce some of the observed constraints, but fail to simultaneously reproduce the shape of dust scaling relations and the dust mass of high-redshift galaxies.
We study the evolution of atomic and molecular gas in galaxies in semi-analytic models of galaxy formation that include new modelling of the partitioning of cold gas in galactic discs into atomic, ...molecular, and ionized phases. We adopt two scenarios for the formation of molecules: one pressure based and one metallicity based. We find that both recipes successfully reproduce the gas fractions and gas-to-stellar mass ratios of H i and H2 in local galaxies, as well as the H i and H2 disc sizes up to z ≤ 2. We reach good agreement with the locally observed H i and H2 mass function, although both recipes slightly overpredict the low-mass end of the H i mass function. Both of our models predict that the high-mass end of the H i mass function remains nearly constant at redshifts z < 2.0. The metallicity-based recipe yields a higher cosmic density of cold gas and much lower cosmic H2 fraction over the entire redshift range probed than the pressure-based recipe. These strong differences in H i mass function and cosmic density between the two recipes are driven by low-mass galaxies (log (M
*/M⊙) ≤ 7) residing in low-mass haloes (log (M
vir/M⊙) ≤ 10). Both recipes predict that galaxy gas fractions remain high from z ∼ 6to3 and drop rapidly at lower redshift. The galaxy H2 fractions show a similar trend, but drop even more rapidly. We provide predictions for the CO J = 1-0 luminosity of galaxies, which will be directly comparable with observations with sub-mm and radio instruments.
ABSTRACT
Supermassive black hole feedback is thought to be responsible for the lack of star formation, or quiescence, in a significant fraction of galaxies. We explore how observable correlations ...between the specific star formation rate (sSFR), stellar mass (Mstar), and black hole mass (MBH) are sensitive to the physics of black hole feedback in a galaxy formation model. We use the IllustrisTNG simulation suite, specifically the TNG100 simulation and 10 model variations that alter the parameters of the black hole model. Focusing on central galaxies at z = 0 with Mstar > 1010 M⊙, we find that the sSFR of galaxies in IllustrisTNG decreases once the energy from black hole kinetic winds at low accretion rates becomes larger than the gravitational binding energy of gas within the galaxy stellar radius. This occurs at a particular MBH threshold above which galaxies are found to sharply transition from being mostly star forming to mostly quiescent. As a result of this behaviour, the fraction of quiescent galaxies as a function of Mstar is sensitive to both the normalization of the MBH–Mstar relation and the MBH threshold for quiescence in IllustrisTNG. Finally, we compare these model results to observations of 91 central galaxies with dynamical MBH measurements with the caveat that this sample is not representative of the whole galaxy population. While IllustrisTNG reproduces the observed trend that quiescent galaxies host more massive black holes, the observations exhibit a broader scatter in MBH at a given Mstar and show a smoother decline in sSFR with MBH.
We implement physically motivated recipes for partitioning cold gas into different phases (atomic, molecular, and ionized) in galaxies within semi-analytic models of galaxy formation based on ...cosmological merger trees. We then model the conversion of molecular gas into stars using empirical recipes motivated by recent observations. We explore the impact of these new recipes on the evolution of fundamental galaxy properties such as stellar mass, star formation rate (SFR), and gas and stellar phase metallicity. We present predictions for stellar mass functions, stellar mass versus SFR relations, and cold gas phase and stellar mass–metallicity relations for our fiducial models, from redshift z ∼ 6 to the present day. In addition we present predictions for the global SFR, mass assembly history, and cosmic enrichment history. We find that the predicted stellar properties of galaxies (stellar mass, SFR, metallicity) are remarkably insensitive to the details of the recipes used for partitioning gas into H i and H2. We see significant sensitivity to the recipes for H2 formation only in very low mass haloes (
$M_{\rm h} \lesssim 10^{10.5}\, {{\rm M}_{{\odot }}}$
), which host galaxies with stellar masses
$m_* \lesssim 10^8\, {{\rm M}_{{\odot }}}$
. The properties of low-mass galaxies are also quite insensitive to the details of the recipe used for converting H2 into stars, while the formation epoch of massive galaxies does depend on this significantly. We argue that this behaviour can be interpreted within the framework of a simple equilibrium model for galaxy evolution, in which the conversion of cold gas into stars is balanced on average by inflows and outflows.
We use cosmological hydrodynamical simulations to investigate the role of feedback from accreting black holes in the evolution of the size, compactness, stellar core density, and specific star ...formation of massive galaxies with stellar masses of . We perform two sets of cosmological zoom-in simulations of 30 halos to z = 0: (1) without black holes and active galactic nucleus (AGN) feedback and (2) with AGN feedback arising from winds and X-ray radiation. We find that AGN feedback can alter the stellar density distribution, reduce the core density within the central 1 kpc by 0.3 dex from z = 1, and enhance the size growth of massive galaxies. We also find that galaxies simulated with AGN feedback evolve along tracks similar to those characterized by observations of specific star formation rate versus compactness. We confirm that AGN feedback plays an important role in transforming galaxies from blue compact galaxies into red extended galaxies in two ways: (1) it effectively quenches the star formation, transforming blue compact galaxies into compact quiescent galaxies, and (2) it also removes and prevents new accretion of cold gas, shutting down in situ star formation and causing subsequent mergers to be gas-poor or mixed. Gas-poor minor mergers then build up an extended stellar envelope. AGN feedback also puffs up the central region through fast AGN-driven winds as well as the slow expulsion of gas while the black hole is quiescent. Without AGN feedback, large amounts of gas accumulate in the central region, triggering star formation and leading to overly massive blue galaxies with dense stellar cores.
ABSTRACT
Optical emission-line ratios are traditionally used to estimate gas metallicities from observed galaxy spectra. While such estimators have been calibrated primarily at low redshift, they are ...commonly used to interpret observations of high-redshift galaxies, where their applicability may be questioned. We use comprehensive emission-line catalogues of galaxies from the IllustrisTNG simulation including ionization by stars, active galactic nuclei, and shocks to reassess the calibrations of both optical and ultraviolet metallicity estimators at redshifts $0\lesssim z \lesssim 8$. For present-day galaxies, the predicted optical-line calibrations are consistent with previously published ones, while we find different ultraviolet-line ratios, such as He ii λ1640/C iii λ1908, can provide powerful metallicity diagnostics. At fixed metallicity, most emission-line ratios are predicted to strongly increase or decrease with redshift (with the notable exception of N2O2 = N iiλ6584/O ii λ3727), primarily because of a change in ionization parameter. The predicted dependence of R3 = O iiiλ5007/H β and R23 = (O ii λ3727 + O iiiλ5007)/H β, and to a slightly lesser extent R2 = O ii λ3727/H β and O32 = O iiiλ5007/O ii λ3727, on O abundance for galaxies at z = 4–8 agrees remarkably well with Te-based measurements in 14 galaxies observed with JWST. This success motivates us to provide new calibrations of optical and ultraviolet metallicity estimators specifically designed for galaxies at z > 4, to guide interpretations of future, high-redshift spectroscopic surveys. We further demonstrate that applying classical z = 0 calibrations to high-redshift galaxies can bias oxygen abundance estimates downward by up to 1 dex, leading to the inference of stronger evolution of the mass–metallicity relation than is actually occurring.
ABSTRACT
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
We study the destruction of interstellar dust via sputtering in supernova (SN) shocks using three-dimensional hydrodynamical simulations. With a novel numerical framework, we follow both ...sputtering and dust dynamics governed by direct collisions, plasma drag, and betatron acceleration. Grain–grain collisions are not included and the grain-size distribution is assumed to be fixed. The amount of dust destroyed per SN is quantified for a broad range of ambient densities and fitting formulae are provided. Integrated over the grain-size distribution, non-thermal (inertial) sputtering dominates over thermal sputtering for typical ambient densities. We present the first simulations that explicitly follow dust sputtering within a turbulent multiphase interstellar medium. We find that the dust destruction time-scales τ are 0.35 Gyr for silicate dust and 0.44 Gyr for carbon dust in solar neighbourhood conditions. The SN environment has an important impact on τ. SNe that occur in pre-existing bubbles destroy less dust as the destruction is limited by the amount of dust in the shocked gas. This makes τ about 2.5 times longer than the estimate based on results from a single SN explosion. We investigate the evolution of the dust-to-gas mass ratio (DGR), and find that a spatial inhomogeneity of ∼14 per cent develops for scales below 10 pc. It locally correlates positively with gas density but negatively with gas temperature even in the exterior of the bubbles due to incomplete gas mixing. This leads to an ∼30 per cent lower DGR in the volume filling warm gas compared to that in the dense clouds.
ABSTRACT
The James Webb Space Telescope (JWST) is expected to observe galaxies at z > 10 that are presently inaccessible. Here, we use a self-consistent empirical model, the universemachine, to ...generate mock galaxy catalogues and light-cones over the redshift range z = 0−15. These data include realistic galaxy properties (stellar masses, star formation rates, and UV luminosities), galaxy–halo relationships, and galaxy–galaxy clustering. Mock observables are also provided for different model parameters spanning observational uncertainties at z < 10. We predict that Cycle 1 JWST surveys will very likely detect galaxies with M* > 107 M⊙ and/or M1500 < −17 out to at least z ∼ 13.5. Number density uncertainties at z > 12 expand dramatically, so efforts to detect z > 12 galaxies will provide the most valuable constraints on galaxy formation models. The faint-end slopes of the stellar mass/luminosity functions at a given mass/luminosity threshold steepen as redshift increases. This is because observable galaxies are hosted by haloes in the exponentially falling regime of the halo mass function at high redshifts. Hence, these faint-end slopes are robustly predicted to become shallower below current observable limits (M* < 107 M⊙ or M1500 > −17). For reionization models, extrapolating luminosity functions with a constant faint-end slope from M1500 = −17 down to M1500 = −12 gives the most reasonable upper limit for the total UV luminosity and cosmic star formation rate up to z ∼ 12. We compare to three other empirical models and one semi-analytic model, showing that the range of predicted observables from our approach encompasses predictions from other techniques. Public catalogues and light-cones for common fields are available online.
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