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Register a new userOn the Transition of the Galaxy Quenching Mode at 0.5<z<1 in CANDELS
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We investigate the galaxy quenching process at intermediate redshift using a sample of $sim4400$ galaxies with $M_{ast} > 10^{9}M_{odot}$ between redshift 0.5 and 1.0 in all five CANDELS fields. We divide this sample, using the integrated specific star formation rate (sSFR), into four sub-groups: star-forming galaxies (SFGs) above and below the ridge of the star-forming main sequence (SFMS), transition galaxies and quiescent galaxies. We study their $UVI$ ($U-V$ versus $V-I$) color gradients to infer their sSFR gradients out to twice effective radii. We show that on average both star-forming and transition galaxies at all masses are not fully quenched at any radii, whereas quiescent galaxies are fully quenched at all radii. We find that at low masses ($M_{ast} = 10^{9}-10^{10}M_{odot}$) SFGs both above and below the SFMS ridge generally have flat sSFR profiles, whereas the transition galaxies at the same masses generally have sSFRs that are more suppressed in their outskirts. In contrast, at high masses ($M_{ast} > 10^{10.5}M_{odot}$), SFGs above and below the SFMS ridge and transition galaxies generally have varying degrees of more centrally-suppressed sSFRs relative to their outskirts. These findings indicate that at $zsim~0.5-1.0$ the main galaxy quenching mode depends on its already formed stellar mass, exhibiting a transition from the outside-in at $M_{ast} leq 10^{10}M_{odot}$ to the inside-out at $M_{ast} > 10^{10.5}M_{odot}$. In other words, our findings support that internal processes dominate the quenching of massive galaxies, whereas external processes dominate the quenching of low-mass galaxies.
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Several mechanisms for the transformation of blue star-forming to red quiescent galaxies have been proposed, and the green valley (GV) galaxies amid them are widely accepted in a transitional phase. Thus, comparing the morphological and environmental differences of the GV galaxies with early-type disks (ETDs; bulge dominated and having a disk) and late-type disks (LTDs; disk dominated) is suitable for distinguishing the corresponding quenching mechanisms. A large population of massive ($M_* geqslant 10^{10}M_odot$) GV galaxies at $0.5 leqslant z leqslant 1.5$ in 3D-HST/CANDELS is selected using extinction-corrected $(U-V)_{rm rest}$ color. After eliminating any possible active galactic nucleus candidates and considering the mass-matching, we finally construct two comparable samples of GV galaxies with either 319 ETD or 319 LTD galaxies. Compared to the LTD galaxies, it is found that the ETD galaxies possess higher concentration index and lower specific star formation rate, whereas the environments surrounding them are not different. This may suggest that the morphological quenching may dominate the star formation activity of massive GV galaxies rather than the environmental quenching. To quantify the correlation between the galaxy morphology and the star formation activity, we define a dimensionless morphology quenching efficiency $Q_{rm mor}$ and find that $Q_{rm mor}$ is not sensitive to the stellar mass and redshift. When the difference between the average star formation rate of ETD and LTD galaxies is about 0.7 $M_odot rm ;yr^{-1}$, the probability of $Q_{rm mor}gtrsim 0.2$ is higher than 90%, which implies that the degree of morphological quenching in GV galaxies might be described by $Q_{rm mor}gtrsim 0.2$.
Galaxies with stellar masses near M* contain the majority of stellar mass in the universe, and are therefore of special interest in the study of galaxy evolution. The Milky Way (MW) and Andromeda (M31) have present day stellar masses near M*, at 5x10^10 Msol (MW-mass) and 10^11 Msol (M31-mass). We study the typical progenitors of these galaxies using ZFOURGE, a deep medium-band near-IR imaging survey, which is sensitive to the progenitors of these galaxies out to z~3. We use abundance-matching techniques to identify the main progenitors of these galaxies at higher redshifts. We measure the evolution in the stellar mass, rest-frame colors, morphologies, far-IR luminosities, and star-formation rates combining our deep multiwavelength imaging with near-IR HST imaging from CANDELS, and far-IR imaging from GOODS-H and CANDELS-H. The typical MW-mass and M31-mass progenitors passed through the same evolution stages, evolving from blue, star-forming disk galaxies at the earliest stages, to redder dust-obscured IR-luminous galaxies in intermediate stages, and to red, more quiescent galaxies at their latest stages. The progenitors of the MW-mass galaxies reached each evolutionary stage at later times (lower redshifts) and with stellar masses that are a factor of 2-3 lower than the progenitors of the M31-mass galaxies. The process driving this evolution, including the suppression of star-formation in present-day M* galaxies requires an evolving stellar-mass/halo-mass ratio and/or evolving halo-mass threshold for quiescent galaxies. The effective size and star-formation rates imply that the baryonic cold-gas fractions drop as galaxies evolve from high redshift to z~0 and are strongly anticorrelated with an increase in the Sersic index. Therefore, the growth of galaxy bulges in M* galaxies corresponds to a rapid decline in the galaxy gas fractions and/or a decrease in the star-formation efficiency.
We study galactic star-formation activity as a function of environment and stellar mass over 0.5<z<2.0 using the FourStar Galaxy Evolution (ZFOURGE) survey. We estimate the galaxy environment using a Bayesian-motivated measure of the distance to the third nearest neighbor for galaxies to the stellar mass completeness of our survey, $log(M/M_odot)>9 (9.5)$ at z=1.3 (2.0). This method, when applied to a mock catalog with the photometric-redshift precision ($sigma_z / (1+z) lesssim 0.02$), recovers galaxies in low- and high-density environments accurately. We quantify the environmental quenching efficiency, and show that at z> 0.5 it depends on galaxy stellar mass, demonstrating that the effects of quenching related to (stellar) mass and environment are not separable. In high-density environments, the mass and environmental quenching efficiencies are comparable for massive galaxies ($log (M/M_odot)gtrsim$ 10.5) at all redshifts. For lower mass galaxies ($log (M/M)_odot) lesssim$ 10), the environmental quenching efficiency is very low at $zgtrsim$ 1.5, but increases rapidly with decreasing redshift. Environmental quenching can account for nearly all quiescent lower mass galaxies ($log(M/M_odot) sim$ 9-10), which appear primarily at $zlesssim$ 1.0. The morphologies of lower mass quiescent galaxies are inconsistent with those expected of recently quenched star-forming galaxies. Some environmental process must transform the morphologies on similar timescales as the environmental quenching itself. The evolution of the environmental quenching favors models that combine gas starvation (as galaxies become satellites) with gas exhaustion through star-formation and outflows (overconsumption), and additional processes such as galaxy interactions, tidal stripping and disk fading to account for the morphological differences between the quiescent and star-forming galaxy populations.
We have measured the radial profiles of isophotal ellipticity ($varepsilon$) and disky/boxy parameter A$_4$ out to radii of about three times the semi-major axes for $sim4,600$ star-forming galaxies (SFGs) at intermediate redshifts $0.5<z<1.8$ in the CANDELS/GOODS-S and UDS fields. Based on the average size versus stellar-mass relation in each redshift bin, we divide our galaxies into Small SFGs (SSFGs), i.e., smaller than average for its mass, and Large SFGs (LSFGs), i.e., larger than average. We find that, at low masses ($M_{ast} < 10^{10}M_{odot}$), the SSFGs generally have nearly flat $varepsilon$ and A$_4$ profiles for both edge-on and face-on views, especially at redshifts $z>1$. Moreover, the median A$_4$ values at all radii are almost zero. In contrast, the highly-inclined, low-mass LSFGs in the same mass-redshift bins generally have monotonically increasing $varepsilon$ with radius and are dominated by disky values at intermediate radii. These findings at intermediate redshifts imply that low-mass SSFGs are not disk-like, while low-mass LSFGs appear to harbour disk-like components flattened by significant rotation. At high masses ($M_{ast} > 10^{10}M_{odot}$), highly-inclined SSFGs and LSFGs both exhibit a general, distinct trend for both $varepsilon$ and A$_4$ profiles: increasing values with radius at lower radii, reaching maxima at intermediate radii, and then decreasing values at larger radii. Such a trend is more prevalent for more massive ($M_{ast} > 10^{10.5}M_{odot}$) galaxies or those at lower redshifts ($z<1.4$). The distinct trend in $varepsilon$ and A$_4$ can be simply explained if galaxies possess all three components: central bulges, disks in the intermediate regions, and halo-like stellar components in the outskirts.
We derive the total cold gas, atomic hydrogen, and molecular gas masses of approximately 24 000 galaxies covering four decades in stellar mass at redshifts 0.5 < z < 3.0, taken from the CANDELS survey. Our inferences are based on the inversion of a molecular hydrogen based star formation law, coupled with a prescription to separate atomic and molecular gas. We find that: 1) there is an increasing trend between the inferred cold gas (HI and H2), HI, and H2 mass and the stellar mass of galaxies down to stellar masses of 10^8 Msun already in place at z = 3; 2) the molecular fractions of cold gas increase with increasing stellar mass and look-back time; 3) there is hardly any evolution in the mean HI content of galaxies at fixed stellar mass; 4) the cold gas fraction and relative amount of molecular hydrogen in galaxies decrease at a relatively constant rate with time, independent of stellar mass; 5) there is a large population of low-stellar mass galaxies dominated by atomic gas. These galaxies are very gas rich, but only a minor fraction of their gas is molecular; 6) the ratio between star-formation rate (SFR) and inferred total cold gas mass (HI + H2) of galaxies (i.e., star-formation efficiency; SFE) increases with star-formation at fixed stellar masses. Due to its simplicity, the presented approach is valuable to assess the impact of selection biases on small samples of directly-observed gas masses and to extend scaling relations down to stellar mass ranges and redshifts that are currently difficult to probe with direct measurements of gas content.
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