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Register a new userEnvironmental Quenching of Low-Mass Field Galaxies
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In the local Universe, there is a strong division in the star-forming properties of low-mass galaxies, with star formation largely ubiquitous amongst the field population while satellite systems are predominantly quenched. This dichotomy implies that environmental processes play the dominant role in suppressing star formation within this low-mass regime (${M}_{star} sim 10^{5.5-8}~{rm M}_{odot}$). As shown by observations of the Local Volume, however, there is a non-negligible population of passive systems in the field, which challenges our understanding of quenching at low masses. By applying the satellite quenching models of Fillingham et al. (2015) to subhalo populations in the Exploring the Local Volume In Simulations (ELVIS) suite, we investigate the role of environmental processes in quenching star formation within the nearby field. Using model parameters that reproduce the satellite quenched fraction in the Local Group, we predict a quenched fraction -- due solely to environmental effects -- of $sim 0.52 pm 0.26$ within $1< R/R_{rm vir} < 2$ of the Milky Way and M31. This is in good agreement with current observations of the Local Volume and suggests that the majority of the passive field systems observed at these distances are quenched via environmental mechanisms. Beyond $2~R_{rm vir}$, however, dwarf galaxy quenching becomes difficult to explain through an interaction with either the Milky Way or M31, such that more isolated, field dwarfs may be self-quenched as a result of star-formation feedback.
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We investigate the environmental quenching of galaxies, especially those with stellar masses (M*)$<10^{9.5} M_odot$, beyond the local universe. Essentially all local low-mass quenched galaxies (QGs) are believed to live close to massive central galaxies, which is a demonstration of environmental quenching. We use CANDELS data to test {it whether or not} such a dwarf QG--massive central galaxy connection exists beyond the local universe. To this purpose, we only need a statistically representative, rather than a complete, sample of low-mass galaxies, which enables our study to $zgtrsim1.5$. For each low-mass galaxy, we measure the projected distance ($d_{proj}$) to its nearest massive neighbor (M*$>10^{10.5} M_odot$) within a redshift range. At a given redshift and M*, the environmental quenching effect is considered to be observed if the $d_{proj}$ distribution of QGs ($d_{proj}^Q$) is significantly skewed toward lower values than that of star-forming galaxies ($d_{proj}^{SF}$). For galaxies with $10^{8} M_odot < M* < 10^{10} M_odot$, such a difference between $d_{proj}^Q$ and $d_{proj}^{SF}$ is detected up to $zsim1$. Also, about 10% of the quenched galaxies in our sample are located between two and four virial radii ($R_{Vir}$) of the massive halos. The median projected distance from low-mass QGs to their massive neighbors, $d_{proj}^Q / R_{Vir}$, decreases with satellite M* at $M* lesssim 10^{9.5} M_odot$, but increases with satellite M* at $M* gtrsim 10^{9.5} M_odot$. This trend suggests a smooth, if any, transition of the quenching timescale around $M* sim 10^{9.5} M_odot$ at $0.5<z<1.0$.
A clear transition feature of galaxy quenching is identified in the multi-parameter space of stellar mass ($M_*$), bulge to total mass ratio ($B/T_{rm m}$), halo mass ($M_{rm h}$) and halo-centric distance ($r/r_{180}$). For given halo mass, the characteristic stellar mass ($M_{*, rm ch}$) for the transition is about one-fifth of that of the corresponding central galaxy, and almost independent of $B/T_{rm m}$. Once $B/T_{rm m}$ is fixed, the quenched fraction of galaxies with $M_{*} < M_{*, rm ch}$ increases with $M_{rm h}$, but decreases with $M_*$ in the inner part of halos ($r/r_{180} < 0.5$). In the outer part ($r/r_{180} > 0.5$), the trend with $M_{rm h}$ remains but the correlation with $M_*$ is absent or becomes positive. For galaxies above $M_{rm *, ch}$ and with $B/T_{rm m}$ fixed, the quenched fraction increases with $M_{rm *}$, but depends only weakly on $M_{rm h}$ in both the inner and outer regions. At fixed $B/T_{rm m}$ and $M_*$, the quenched fraction increases with decreasing $r/r_{180}$ for galaxies with $M_{*} < M_{*, rm ch}$, and depends only weakly on $r/r_{180}$ for galaxies with $M_{*} > M_{*, rm ch}$. Our finding provides a physically-motivated way to classify galaxies in halos into two classes based on their quenching properties: an `upper class with $M_{*} > M_{rm *,ch}$ and a `lower class with $M_{*} < M_{rm *,ch}$. Environmental quenching is important for `lower class galaxies, while internal quenching plays the dominating role for the `upper class.
We use the Cosmic Assembly Deep Near-infrared Extragalactic Legacy Survey (CANDELS) data to study the relationship between quenching and the stellar mass surface density within the central radius of 1 kpc ($Sigma_1$) of low-mass galaxies (stellar mass $M_* lesssim 10^{9.5} M_odot$) at $0.5 leq z < 1.5$. Our sample is mass complete down to $sim 10^9 M_odot$ at $0.5 leq z < 1.0$. We compare the mean $Sigma_1$ of star-forming galaxies (SFGs) and quenched galaxies (QGs) at the same redshift and $M_*$. We find that low-mass QGs have higher $Sigma_1$ than low-mass SFGs, similar to galaxies above $10^{10} M_odot$. The difference of $Sigma_1$ between QGs and SFGs increases slightly with $M_*$ at $M_* lesssim 10^{10} M_odot$ and decreases with $M_*$ at $M_* gtrsim 10^{10} M_odot$. The turnover mass is consistent with the mass where quenching mechanisms transition from internal to environmental quenching. At $0.5 leq z < 1.0$, we find that the $Sigma_1$ of galaxies increases by about 0.25 dex in the green valley (i.e., the transitioning region from star forming to fully quenched), regardless of their $M_*$. Using the observed specific star formation rate (sSFR) gradient in the literature as a constraint, we estimate that the quenching timescale (i.e., time spent in the transition) of low-mass galaxies is a few ($sim4$) Gyrs at $0.5 leq z < 1.0$. The mechanisms responsible for quenching need to gradually quench star formation in an outside-in way, i.e., preferentially ceasing star formation in outskirts of galaxies while maintaining their central star formation to increase $Sigma_1$. An interesting and intriguing result is the similarity of the growth of $Sigma_1$ in the green valley between low-mass and massive galaxies, which suggests that the role of internal processes in quenching low-mass galaxies is a question worthy of further investigation.
We measure the rate of environmentally-driven star formation quenching in galaxies at $zsim 1$, using eleven massive ($Mapprox 2times10^{14},mathrm{M}_odot$) galaxy clusters spanning a redshift range $1.0<z<1.4$ from the GOGREEN sample. We identify three different types of transition galaxies: green valley (GV) galaxies identified from their rest-frame $(NUV-V)$ and $(V-J)$ colours; blue quiescent (BQ) galaxies, found at the blue end of the quiescent sequence in $(U-V)$ and $(V-J)$ colour; and spectroscopic post-starburst (PSB) galaxies. We measure the abundance of these galaxies as a function of stellar mass and environment. For high stellar mass galaxies ($log{M/mathrm{M}_odot}>10.5$) we do not find any significant excess of transition galaxies in clusters, relative to a comparison field sample at the same redshift. It is likely that such galaxies were quenched prior to their accretion in the cluster, in group, filament or protocluster environments. For lower stellar mass galaxies ($9.5<log{M/mathrm{M}_odot}<10.5$) there is a small but significant excess of transition galaxies in clusters, accounting for an additional $sim 5-10$ per cent of the population compared with the field. We show that our data are consistent with a scenario in which 20--30 per cent of low-mass, star-forming galaxies in clusters are environmentally quenched every Gyr, and that this rate slowly declines from $z=1$ to $z=0$. While environmental quenching of these galaxies may include a long delay time during which star formation declines slowly, in most cases this must end with a rapid ($tau<1$ Gyr) decline in star formation rate.
Recent studies of galaxies in the local Universe, including those in the Local Group, find that the efficiency of environmental (or satellite) quenching increases dramatically at satellite stellar masses below ~ $10^8 {rm M}_{odot}$. This suggests a physical scale where quenching transitions from a slow starvation mode to a rapid stripping mode at low masses. We investigate the plausibility of this scenario using observed HI surface density profiles for a sample of 66 nearby galaxies as inputs to analytic calculations of ram-pressure and viscous stripping. Across a broad range of host properties, we find that stripping becomes increasingly effective at $M_{*} < 10^{8-9} {rm M}_{odot}$, reproducing the critical mass scale observed. However, for canonical values of the circumgalactic medium density ($n_{rm halo} < 10^{-3.5}$ ${rm cm}^{-3}$), we find that stripping is not fully effective; infalling satellites are, on average, stripped of < 40 - 70% of their cold gas reservoir, which is insufficient to match observations. By including a host halo gas distribution that is clumpy and therefore contains regions of higher density, we are able to reproduce the observed HI gas fractions (and thus the high quenched fraction and short quenching timescale) of Local Group satellites, suggesting that a host halo with clumpy gas may be crucial for quenching low-mass systems in Local Group-like (and more massive) host halos.
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