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Register a new userGalaxy Sizes Since $z=2$ from the Perspective of Stellar Mass Distribution within Galaxies
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How stellar mass assembles within galaxies is still an open question. We present measurements of the stellar mass distribution on kpc-scale for $sim5500$ galaxies with stellar masses above $log(M_{ast}/M_{odot})geqslant9.8$ up to the redshift $2.0$. We create stellar mass maps from Hubble Space Telescope observations by means of the pixel-by-pixel SED fitting method. These maps are used to derive radii encompassing $20%$, $50%$, and $80%$ ($r_{20}$, $r_{50}$ and $r_{80}$) of the total stellar mass from the best-fit Sersic models. The reliability and limitations of the structural parameter measurements are checked extensively using a large sample ($sim3000$) of simulated galaxies. The size-mass relations and redshift evolution of $r_{20}$, $r_{50}$ and $r_{80}$ are explored for star-forming and quiescent galaxies. At fixed mass, the star-forming galaxies do not show significant changes in their $r_{20}$, $r_{50}$ and $r_{80}$ sizes, indicating self-similar growth. Only above the pivot stellar mass of $log(M_{ast}/M_{odot})simeq10.5$, $r_{80}$ evolves as $r_{80}propto(1+z)^{-0.85pm0.20}$, indicating that mass builds up in the outskirts of these systems (inside-out growth). The Sersic values also increase for the massive star-forming galaxies towards late cosmic time. Massive quiescent galaxies show stronger size evolution at all radii, in particular the $r_{20}$ sizes. For these massive galaxies, Sersic values remain almost constant since at least $zsim1.3$, indicating that the strong size evolution is related to the changes in the outer parts of these galaxies. We make all the structural parameters publicly available.
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We study the history from $zsim2$ to $zsim0$ of the stellar mass assembly of quiescent and star-forming galaxies in a spatially resolved fashion. For this purpose we use multi-wavelength imaging data from the Hubble Space Telescope (HST) over the GOODS fields and the Sloan Digital Sky Survey (SDSS) for the local population. We present the radial stellar mass surface density profiles of galaxies with $M_{ast}>10^{10} M_{odot}$, corrected for mass-to-light ratio ($M_{ast}/L$) variations, and derive the half-mass radius ($R_{m}$), central stellar mass surface density within 1 kpc ($Sigma_{1}$) and surface density at $R_{m}$ ($Sigma_{m}$) for star-forming and quiescent galaxies and study their evolution with redshift. At fixed stellar mass, the half-mass sizes of quiescent galaxies increase from $zsim2$ to $zsim0$ by a factor of $sim3-5$, whereas the half-mass sizes of star-forming galaxies increase only slightly, by a factor of $sim2$. The central densities $Sigma_{1}$ of quiescent galaxies decline slightly (by a factor of $lesssim1.7$) from $zsim2$ to $zsim0$, while for star-forming galaxies $Sigma_{1}$ increases with time, at fixed mass. We show that the central density $Sigma_{1}$ has a tighter correlation with specific star-formation rate (sSFR) than $Sigma_{m}$ and for all masses and redshifts galaxies with higher central density are more prone to be quenched. Reaching a high central density ($Sigma_{1} gtrsim 10^{10} M_{odot} mathrm{kpc}^2$) seems to be a prerequisite for the cessation of star formation, though a causal link between high $Sigma_{1}$ and quenching is difficult to prove and their correlation can have a different origin.
Using observations from the FourStar Galaxy Evolution Survey (ZFOURGE), we obtain the deepest measurements to date of the galaxy stellar mass function at 0.5 < z < 2.5. ZFOURGE provides well-constrained photometric redshifts made possible through deep medium-bandwidth imaging at 1-2um . We combine this with HST imaging from the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS), allowing for the efficient selection of both blue and red galaxies down to stellar masses ~10^9.5 Msol at z ~ 2.5. The total surveyed area is 316 arcmin^2 distributed over three independent fields. We supplement these data with the wider and shallower NEWFIRM Medium-Band Survey (NMBS) to provide stronger constraints at high masses. Several studies at z<=1 have revealed a steepening of the slope at the low-mass end of the stellar mass function (SMF), leading to an upturn at masses <10^10 Msol that is not well-described by a standard single-Schechter function. We find evidence that this feature extends to at least z ~ 2, and that it can be found in both the star-forming and quiescent populations individually. The characteristic mass (M*) and slope at the lowest masses (alpha) of a double-Schechter function fit to the SMF stay roughly constant at Log(M/Msol) ~ 10.65 and ~-1.5 respectively. The SMF of star-forming galaxies has evolved primarily in normalization, while the change in shape is relatively minor. This is not the case for quiescent galaxies: the depth of our imaging allows us to show for the first time significantly more evolution at Log(M/Msol) < 10.5 than at higher masses. We find that the total mass density (down to 10^9 Msol) in star-forming galaxies has increased by a factor of ~2.2 since z ~ 2.5, whereas in quiescent galaxies it has increased by a factor of ~12 .
Spectroscopic + photometric redshifts, stellar mass estimates, and rest-frame colors from the 3D-HST survey are combined with structural parameter measurements from CANDELS imaging to determine the galaxy size-mass distribution over the redshift range 0<z<3. Separating early- and late-type galaxies on the basis of star-formation activity, we confirm that early-type galaxies are on average smaller than late-type galaxies at all redshifts, and find a significantly different rate of average size evolution at fixed galaxy mass, with fast evolution for the early-type population, R_eff ~ (1+z)^-1.48, and moderate evolution for the late-type population, R_eff ~ (1+z)^-0.75. The large sample size and dynamic range in both galaxy mass and redshift, in combination with the high fidelity of our measurements due to the extensive use of spectroscopic data, not only fortify previous results, but also enable us to probe beyond simple average galaxy size measurements. At all redshifts the slope of the size-mass relation is shallow, R_eff ~ M_star^0.22, for late-type galaxies with stellar mass >3x10^9 M_sol, and steep, R_eff M_star^0.75, for early-type galaxies with stellar mass >2x10^10 M_sol. The intrinsic scatter is <~0.2 dex for all galaxy types and redshifts. For late-type galaxies, the logarithmic size distribution is not symmetric, but skewed toward small sizes: at all redshifts and masses a tail of small late-type galaxies exists that overlaps in size with the early-type galaxy population. The number density of massive (~10^11 M_sol), compact (R_eff < 2 kpc) early-type galaxies increases from z=3 to z=1.5-2 and then strongly decreases at later cosmic times.
We examine the role of environment on the in situ star formation (SF) hosted by the progenitors of the most massive galaxies in the present-day universe, the brightest cluster galaxies (BCGs), from $z sim 3$ to present in the COSMOS field. Progenitors are selected from the COSMOS field using a stellar mass cut motivated by the evolving cumulative comoving number density of progenitors within the Illustris simulation, as well as the Millennium-II simulation and a constant comoving number density method for comparison. We characterize each progenitor using far-ultraviolet--far-infrared observations taken from the COSMOS field and fitting stellar, dust, and active galactic nucleus components to their spectral energy distributions. Additionally, we compare the SF rates of our progenitor sample to the local density maps of the COSMOS field to identify the effects of environment. We find that BCG progenitors evolve in three stages, starting with an in situ SF dominated phase ($z > 2.25$). This is followed by a phase until $z sim 1.25$ where mass growth is driven by in situ SF and stellar mass deposited by mergers (both gas rich and poor) on the same order of magnitude independent of local environment. Finally, at low redshift dry mergers are the dominant stellar mass generation process. We also identify this final transition period as the time when progenitors quench, exhibiting quiescent NUVemph{rJ} colors.
The growth of galaxies is a key problem in understanding the structure and evolution of the universe. Galaxies grow their stellar mass by a combination of star formation and mergers, with a relative importance that is redshift dependent. Theoretical models predict quantitatively different contributions from the two channels; measuring these from the data is a crucial constraint. Exploiting the UltraVISTA catalog and a unique sample of progenitors of local ultra massive galaxies selected with an abundance matching approach, we quantify the role of the two mechanisms from z=2 to 0. We also compare our results to two independent incarnations of semi-analytic models. At all redshifts, progenitors are found in a variety of environments, ranging from being isolated to having 5-10 companions with mass ratio at least 1:10 within a projected radius of 500 kpc. In models, progenitors have a systematically larger number of companions, entailing a larger mass growth for mergers than in observations, at all redshifts. Generally, in both observations and models, the inferred and the expected mass growth roughly agree, within the uncertainties. Overall, our analysis confirms the model predictions, showing how the growth history of massive galaxies is dominated by in situ star formation at z~2, both star-formation and mergers at 1<z<2, and by mergers alone at z<1. Nonetheless, detailed comparisons still point out to tensions between the expected mass growth and our results, which might be due to either an incorrect progenitors-descendants selection, uncertainties on star formation rate and mass estimates, or the adopted assumptions on merger rates.
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