Using cosmological simulations, we address the properties of high-redshift star-forming galaxies (SFGs) across their main sequence (MS) in the plane of star formation rate (SFR) versus stellar mass. ...We relate them to the evolution of galaxies through phases of gas compaction, depletion, possible replenishment, and eventual quenching. We find that the high-SFR galaxies in the upper envelope of the MS are compact, with high gas fractions and short depletion times (‘blue nuggets’), while the lower SFR galaxies in the lower envelope have lower central gas densities, lower gas fractions, and longer depletion times, consistent with observed gradients across the MS. Stellar-structure gradients are negligible. The SFGs oscillate about the MS ridge on time-scales ∼0.4t
Hubble (∼1 Gyr at z ∼ 3). The propagation upwards is due to gas compaction, triggered, e.g. by mergers, counter-rotating streams, and/or violent disc instabilities. The downturn at the upper envelope is due to central gas depletion by peak star formation and outflows while inflow from the shrunken gas disc is suppressed. An upturn at the lower envelope can occur once the extended disc has been replenished by fresh gas and a new compaction can be triggered, namely as long as the replenishment time is shorter than the depletion time. The mechanisms of gas compaction, depletion, and replenishment confine the SFGs to the narrow (±0.3 dex) MS. Full quenching occurs in massive haloes (M
vir > 1011.5 M⊙) and/or at low redshifts (z < 3), where the replenishment time is long compared to the depletion time, explaining the observed bending down of the MS at the massive end.
Abstract
We present new determinations of the stellar-to-halo mass relation (SHMR) at z = 0–10 that match the evolution of the galaxy stellar mass function, the star formation rate (SFR)–M
* relation ...and the cosmic SFR. We utilize a compilation of 40 observational studies from the literature and correct them for potential biases. Using our robust determinations of halo mass assembly and the SHMR, we infer star formation histories, merger rates and structural properties for average galaxies, combining star-forming and quenched galaxies. Our main findings are as follows: (1) The halo mass M
50 above which 50 per cent of galaxies are quenched coincides with sSFR/sMAR ∼ 1, where sSFR is the specific SFR and sMAR is the specific halo mass accretion rate. (2) M
50 increases with redshift, presumably due to cold streams being more efficient at high redshifts, while virial shocks and active galactic nucleus feedback become more relevant at lower redshifts. (3) The ratio sSFR/sMAR has a peak value, which occurs around
${M_{\rm vir}}\sim 2\times 10^{11}\,{M_{{\odot }}}$
. (4) The stellar mass density within 1 kpc, Σ1, is a good indicator of the galactic global sSFR. (5) Galaxies are statistically quenched after they reach a maximum in Σ1, consistent with theoretical expectations of the gas compaction model; this maximum depends on redshift. (6) In-situ star formation is responsible for most galactic stellar mass growth, especially for lower mass galaxies. (7) Galaxies grow inside-out. The marked change in the slope of the size–mass relation when galaxies became quenched, from
${\rm d}\log {R_{\rm eff}}/{\rm d}\log {M_*}\sim 0.35$
to ∼2.5, could be the result of dry minor mergers.
We use cosmological simulations to study a characteristic evolution pattern of high-redshift galaxies. Early, stream-fed, highly perturbed, gas-rich discs undergo phases of dissipative contraction ...into compact, star-forming systems (‘blue’ nuggets) at z ∼ 4–2. The peak of gas compaction marks the onset of central gas depletion and inside-out quenching into compact ellipticals (red nuggets) by z ∼ 2. These are sometimes surrounded by gas rings or grow extended dry stellar envelopes. The compaction occurs at a roughly constant specific star formation rate (SFR), and the quenching occurs at a constant stellar surface density within the inner kpc (Σ1). Massive galaxies quench earlier, faster, and at a higher Σ1 than lower mass galaxies, which compactify and attempt to quench more than once. This evolution pattern is consistent with the way galaxies populate the SFR-size–mass space, and with gradients and scatter across the main sequence. The compaction is triggered by an intense inflow episode, involving (mostly minor) mergers, counter-rotating streams or recycled gas, and is commonly associated with violent disc instability. The contraction is dissipative, with the inflow rate >SFR, and the maximum Σ1 anticorrelated with the initial spin parameter. The central quenching is triggered by the high SFR and stellar/supernova feedback (maybe also active galactic nucleus feedback) due to the high central gas density, while the central inflow weakens as the disc vanishes. Suppression of fresh gas supply by a hot halo allows the long-term maintenance of quenching once above a threshold halo mass, inducing the quenching downsizing.
ABSTRACT
The diffuse extragalactic background light (EBL) is formed by ultraviolet (UV), optical, and infrared (IR) photons mainly produced by star formation processes over the history of the ...Universe and contains essential information about galaxy evolution and cosmology. Here, we present a new determination of the evolving EBL spectral energy distribution using a novel approach purely based on galaxy data aiming to reduce current uncertainties on the higher redshifts and IR intensities. Our calculations use multiwavelength observations from the UV to the far-IR of a sample of approximately 150 000 galaxies detected up to z ∼ 6 in the five fields of the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey from the Hubble Space Telescope. This is one of the most comprehensive and deepest multiwavelength galaxy data sets ever obtained. These unprecedented resources allow us to derive the overall EBL evolution up to z ∼ 6 and its uncertainties. Our results agree with cosmic observables estimated from galaxy surveys and γ-ray attenuation such as monochromatic luminosity densities, including those in the far-IR, and star formation rate densities, also at the highest redshifts. Optical depths from our EBL approximation, which will be robust at high redshifts and for γ-rays up to tens of TeV, will be reported in a companion paper.
We study the evolution of the scaling relations that compare the effective density ( ) and core density ( kpc) to the stellar masses of star-forming galaxies (SFGs) and quiescent galaxies. These ...relations have been fully in place since and have exhibited almost constant slope and scatter since that time. For SFGs, the zero points in and decline by only . This fact plus the narrowness of the relations suggests that galaxies could evolve roughly along the scaling relations. Quiescent galaxies follow different scaling relations that are offset to higher densities at the same mass and redshift. Furthermore, the zero point of their core density has declined by only since , while the zero point of the effective density declines by . When galaxies quench, they move from the star-forming relations to the quiescent relations. This involves an increase in the core and effective densities, which suggests that SFGs could experience a phase of significant core growth relative to the average evolution along the structural relations. The distribution of massive galaxies relative to the SFR-M and the quiescent relations exhibits an L-shape that is independent of redshift. The knee of this relation consists of a subset of "compact" SFGs that are the most likely precursors of quiescent galaxies forming at later times. The compactness selection threshold in exhibits a small variation from z = 3 to 0.5, M kpc−2, allowing the most efficient identification of compact SFGs and quiescent galaxies at every redshift.
Using cosmological simulations, we address the interplay between structure and star formation in high-redshift galaxies via the evolution of surface density profiles. Our sample consists of 26 ...galaxies evolving in the redshift range z = 7 − 1, spanning the stellar mass range (0.2–6.4) × 1010 M⊙ at z = 2. We recover the main trends by stacking the profiles in accordance to their evolution phases. Following a wet compaction event that typically occurs when the stellar mass is ∼109.5 M⊙ at z ∼ 2–4, the gas develops a cusp inside the effective radius, associated with a peak in star formation rate (SFR). The SFR peak and the associated feedback, in the absence of further gas inflow to the centre, marks the onset of gas depletion from the central 1 kpc, leading to quenching of the central SFR. An extended, star-forming ring that forms by fresh gas during the central quenching process shows as a rising specific SFR (sSFR) profile, which is interpreted as inside-out quenching. Before quenching, the stellar density profile grows self-similarly, maintaining its log–log shape because the sSFR is similar at all radii. During the quenching process, the stellar density saturates to a constant value, especially in the inner 1 kpc. The stellar mass and SFR profiles deduced from observations show very similar shapes, consistent with the scenario of wet compaction leading to inside-out quenching and the subsequent saturation of a dense stellar core. We predict a cuspy gas profile during the blue nugget phase, and a gas-depleted core, sometimes surrounded by a ring, in the post-blue nugget phase.
Studying giant star-forming clumps in distant galaxies is important to understand galaxy formation and evolution. At present, however, observers and theorists have not reached a consensus on whether ...the observed "clumps" in distant galaxies are the same phenomenon that is seen in simulations. In this paper, as a step to establish a benchmark of direct comparisons between observations and theories, we publish a sample of clumps constructed to represent the commonly observed "clumps" in the literature. This sample contains 3193 clumps detected from 1270 galaxies at 0.5 ≤ z < 3.0 . The clumps are detected from rest-frame UV images, as described in our previous paper. Their physical properties (e.g., rest-frame color, stellar mass ( M * ), star formation rate (SFR), age, and dust extinction) are measured by fitting the spectral energy distribution (SED) to synthetic stellar population models. We carefully test the procedures of measuring clump properties, especially the method of subtracting background fluxes from the diffuse component of galaxies. With our fiducial background subtraction, we find a radial clump U − V color variation, where clumps close to galactic centers are redder than those in outskirts. The slope of the color gradient (clump color as a function of their galactocentric distance scaled by the semimajor axis of galaxies) changes with redshift and M * of the host galaxies: at a fixed M * , the slope becomes steeper toward low redshift, and at a fixed redshift, it becomes slightly steeper with M * . Based on our SED fitting, this observed color gradient can be explained by a combination of a negative age gradient, a negative E(B − V) gradient, and a positive specific SFR gradient of the clumps. We also find that the color gradients of clumps are steeper than those of intra-clump regions. Correspondingly, the radial gradients of the derived physical properties of clumps are different from those of the diffuse component or intra-clump regions.
The galaxy stellar-to-halo mass relation (SHMR) is nearly time-independent for z < 4. We therefore construct a time-independent SHMR model for central galaxies, wherein the in situ star formation ...rate (SFR) is determined by the halo mass accretion rate (MAR), which we call stellar halo accretion rate coevolution (SHARC). We show that the ~0.3 dex dispersion of the halo MAR matches the observed dispersion of the SFR on the star formation main sequence (MS). In the context of 'bathtub'-type models of galaxy formation, SHARC leads to mass-dependent constraints on the relation between SFR and MAR. Despite its simplicity and the simplified treatment of mass growth from mergers, the SHARC model is likely to be a good approximation for central galaxies with M* = 10...-10... M... that are on the MS, representing most of the star formation in the Universe. SHARC predictions agree with observed SFRs for galaxies on the MS at low redshifts, agree fairly well at z ~ 4, but exceed observations at z ... 4. Assuming that the interstellar gas mass is constant for each galaxy (the 'equilibrium condition' in bathtub models), the SHARC model allows calculation of net mass loading factors for inflowing and outflowing gas. With assumptions about preventive feedback based on simulations, SHARC allows calculation of galaxy metallicity evolution. If galaxy SFRs indeed track halo MARs, especially at low redshifts, that may help explain the success of models linking galaxy properties to haloes (including age-matching) and the similarities between two-halo galaxy conformity and halo mass accretion conformity. (ProQuest: ... denotes formulae/symbols omitted.)
z ∼ 2: An Epoch of Disk Assembly Simons, Raymond C.; Kassin, Susan A.; Weiner, Benjamin J. ...
The Astrophysical journal,
07/2017, Letnik:
843, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We explore the evolution of the internal gas kinematics of star-forming galaxies from the peak of cosmic star formation at z ∼ 2 to today. Measurements of galaxy rotation velocity Vrot, which ...quantify ordered motions, and gas velocity dispersion g , which quantify disordered motions, are adopted from the DEEP2 and SIGMA surveys. This sample covers a continuous baseline in redshift over 0.1 < z < 2.5 , spanning 10 Gyr. At low redshift, nearly all sufficiently massive star-forming galaxies are rotationally supported ( V rot > g ). By z = 2, 50% and 70% of galaxies are rotationally supported at low ( 10 9 - 10 10 M ) and high ( 10 10 - 10 11 M ) stellar mass, respectively. For V rot > 3 g , the percentage drops below 35% for all masses. From z = 2 to now, galaxies exhibit remarkably smooth kinematic evolution on average. All galaxies tend toward rotational support with time, and higher-mass systems reach it earlier. This is largely due to a mass-independent decline in g by a factor of 3 since z = 2. Over the same time period, Vrot increases by a factor of 1.5 in low-mass systems but does not evolve at high mass. These trends in Vrot and g are at a fixed stellar mass and therefore should not be interpreted as evolutionary tracks for galaxy populations. When populations are linked in time via abundance matching, g declines as before and Vrot strongly increases with time for all galaxy populations, enhancing the evolution in V rot g . These results indicate that z = 2 is a period of disk assembly, during which strong rotational support is only just beginning to emerge.
Attenuation of high-energy gamma-rays by pair production with ultraviolet, optical and infrared (IR) extragalactic background light (EBL) photons provides a link between the history of galaxy ...formation and high-energy astrophysics. We present results from our latest semi-analytic models (SAMs), which employ the main ingredients thought to be important to galaxy formation and evolution, as well as an improved model for reprocessing of starlight by dust to mid- and far-IR wavelengths. These SAMs are based upon a Λ cold dark matter hierarchical structural formation scenario, and are successful in reproducing a large variety of observational constraints such as number counts, luminosity and mass functions and colour bimodality. Our fiducial model is based upon a Wilkinson Microwave Anisotropy Probe 5-year cosmology, and treats dust emission using empirical templates. This model predicts a background flux considerably lower than optical and near-IR measurements that rely on subtraction of zodiacal and galactic foregrounds, and near the lower bounds set by number counts of resolvable sources at a large number of wavelengths. We also show the results of varying cosmological parameters and dust attenuation model used in our SAM. For each EBL prediction, we show how the optical depth due to electron-positron pair production is affected by redshift and gamma-ray energy, and the effect of gamma-ray absorption on the spectra of a variety of extragalactic sources. We conclude with a discussion of the implications of our work, comparisons to other models and key measurements of the EBL and a discussion of how the burgeoning science of gamma-ray astronomy will continue to help constrain cosmology. The low EBL flux predicted by our fiducial model suggests an optimistic future for further studies of distant gamma-ray sources.
PDF
