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Register a new userThe GOGREEN Survey: A deep stellar mass function of cluster galaxies at 1.0<z<1.4 and the complex nature of satellite quenching
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Remco van der Burg Dr.
Publication date
2020
fields
Physics
and research's language is
English
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We study the stellar mass functions (SMFs) of star-forming and quiescent galaxies in 11 galaxy clusters at 1.0<z<1.4, drawn from the Gemini Observations of Galaxies in Rich Early Environments (GOGREEN) survey. Based on more than 500 hours of Gemini/GMOS spectroscopy, and deep multi-band photometry taken with a range of observatories, we probe the SMFs down to a stellar mass limit of 10^9.7 Msun (10^9.5 Msun for star-forming galaxies). At this early epoch, the fraction of quiescent galaxies is already highly elevated in the clusters compared to the field at the same redshift. The quenched fraction excess (QFE) represents the fraction of galaxies that would be star-forming in the field, but are quenched due to their environment. The QFE is strongly mass dependent, and increases from ~30% at Mstar=10^9.7 Msun, to ~80% at Mstar=10^11.0 Msun. Nonetheless, the shapes of the SMFs of the two individual galaxy types, star-forming and quiescent galaxies, are identical between the clusters and the field - to high statistical precision. Yet, along with the different quiescent fractions is the total galaxy SMF environmentally dependent, with a relative deficit of low-mass galaxies in the clusters. These results are in stark contrast with findings in the local Universe, and thus require a substantially different quenching mode to operate at early times. We discuss these results in the light of several popular quenching models.
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We present results on the measured shapes of 832 galaxies in 11 galaxy clusters at 1.0 < z <1.4 from the GOGREEN survey. We measure the axis ratio ($q$), the ratio of the minor to the major axis, of the cluster galaxies from near-infrared Hubble Space Telescope imaging using Sersic profile fitting and compare them with a field sample. We find that the median $q$ of both star-forming and quiescent galaxies in clusters increases with stellar mass, similar to the field. Comparing the axis ratio distributions between clusters and the field in four mass bins, the distributions for star-forming galaxies in clusters are consistent with those in the field. Conversely, the distributions for quiescent galaxies in the two environments are distinct, most remarkably in $10.1leqlog(M/{rm M}_{odot})<10.5$ where clusters show a flatter distribution, with an excess at low $q$. Modelling the distribution with oblate and triaxial components, we find that the cluster and field sample difference is consistent with an excess of flattened oblate quiescent galaxies in clusters. The oblate population contribution drops at high masses, resulting in a narrower $q$ distribution in the massive population than at lower masses. Using a simple accretion model, we show that the observed $q$ distributions and quenched fractions are consistent with a scenario where no morphological transformation occurs for the environmentally quenched population in the two intermediate mass bins. Our results suggest that environmental quenching mechanism(s) likely produce a population that has a different morphological mix than those resulting from the dominant quenching mechanism in the field.
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.
We present the stellar mass functions (SMFs) of passive and star-forming galaxies with a limiting mass of 10$^{10.1}$ M$_{odot}$ in four spectroscopically confirmed Spitzer Adaptation of the Red-sequence Cluster Survey (SpARCS) galaxy clusters at 1.37 $<$ z $<$ 1.63. The clusters have 113 spectroscopically confirmed members combined, with 8-45 confirmed members each. We construct $Ks$-band-selected photometric catalogs for each cluster with an average of 11 photometric bands ranging from $u$ to 8 $mu$m. We compare our cluster galaxies to a field sample derived from a similar $Ks$-band-selected catalog in the UltraVISTA/COSMOS field. The SMFs resemble those of the field, but with signs of environmental quenching. We find that 30 $pm$ 20% of galaxies that would normally be forming stars in the field are quenched in the clusters. The environmental quenching efficiency shows little dependence on projected cluster-centric distance out to $sim$ 4 Mpc, providing tentative evidence of pre-processing and/or galactic conformity in this redshift range. We also compile the available data on environmental quenching efficiencies from the literature, and find that the quenching efficiency in clusters and in groups appears to decline with increasing redshift in a manner consistent with previous results and expectations based on halo mass growth.
We use photometric redshifts and statistical background subtraction to measure stellar mass functions in galaxy group-mass ($4.5-8times10^{13}~mathrm{M}_odot$) haloes at $1<z<1.5$. Groups are selected from COSMOS and SXDF, based on X-ray imaging and sparse spectroscopy. Stellar mass ($M_{mathrm{stellar}}$) functions are computed for quiescent and star-forming galaxies separately, based on their rest-frame $UVJ$ colours. From these we compute the quiescent fraction and quiescent fraction excess (QFE) relative to the field as a function of $M_{mathrm{stellar}}$. QFE increases with $M_{mathrm{stellar}}$, similar to more massive clusters at $1<z<1.5$. This contrasts with the apparent separability of $M_{mathrm{stellar}}$ and environmental factors on galaxy quiescent fractions at $zsim 0$. We then compare our results with higher mass clusters at $1<z<1.5$ and lower redshifts. We find a strong QFE dependence on halo mass at fixed $M_{mathrm{stellar}}$; well fit by a logarithmic slope of $mathrm{d}(mathrm{QFE})/mathrm{d}log (M_{mathrm{halo}}) sim 0.24 pm 0.04$ for all $M_{mathrm{stellar}}$ and redshift bins. This dependence is in remarkably good qualitative agreement with the hydrodynamic simulation BAHAMAS, but contradicts the observed dependence of QFE on $M_{mathrm{stellar}}$. We interpret the results using two toy models: one where a time delay until rapid (instantaneous) quenching begins upon accretion to the main progenitor (no pre-processing) and one where it starts upon first becoming a satellite (pre-processing). Delay times appear to be halo mass dependent, with a significantly stronger dependence required without pre-processing. We conclude that our results support models in which environmental quenching begins in low-mass ($<10^{14}M_odot$) haloes at $z>1$.
We investigate the velocity vs. position phase space of z ~ 1 cluster galaxies using a set of 424 spectroscopic redshifts in 9 clusters drawn from the GCLASS survey. Dividing the galaxy population into three categories: quiescent, star-forming, and poststarburst, we find that these populations have distinct distributions in phase space. Most striking are the poststarburst galaxies, which are commonly found at small clustercentric radii with high clustercentric velocities, and appear to trace a coherent ``ring in phase space. Using several zoom simulations of clusters we show that the coherent distribution of the poststarbursts can be reasonably well-reproduced using a simple quenching scenario. Specifically, the phase space is best reproduced if satellite quenching occurs on a rapid timescale (0.1 < tau_{Q} < 0.5 Gyr) after galaxies make their first passage of R ~ 0.5R_{200}, a process that takes a total time of ~ 1 Gyr after first infall. We compare this quenching timescale to the timescale implied by the stellar populations of the poststarburst galaxies and find that the poststarburst spectra are well-fit by a rapid quenching (tau_{Q} = 0.4^{+0.3}_{-0.4} Gyr) of a typical star-forming galaxy. The similarity between the quenching timescales derived from these independent indicators is a strong consistency check of the quenching model. Given that the model implies satellite quenching is rapid, and occurs well within R_{200}, this would suggest that ram-pressure stripping of either the hot or cold gas component of galaxies are the most plausible candidates for the physical mechanism. The high cold gas consumption rates at z ~ 1 make it difficult to determine if hot or cold gas stripping is dominant; however, measurements of the redshift evolution of the satellite quenching timescale and location may be capable of distinguishing between the two.
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