Molecular Gas Reservoirs in Cluster Galaxies at z = 1.46

Abstract

We present molecular gas reservoirs of eighteen galaxies associated with the XMMXCS J2215.9-1738 cluster at z = 1.46. From Band 7 and Band 3 data of the Atacama Large Millimeter/submillimeter Array (ALMA), we detect dust continuum emission at 870 µm and CO J = 2-1 emission line from 8 and 17 member galaxies respectively within a cluster-centric radius of R 200 . The molecular gas masses derived from the CO and/or dust continuum luminosities show that the fraction of molecular gas mass and the depletion time scale for the cluster galaxies are larger than expected from the scaling relations of molecular gas on stellar mass and offset from the main sequence of star-forming galaxies in general fields. The galaxies closer to the cluster center in terms of both projected position and accretion phase seem to show a larger deviation from the scaling relations. We speculate that the environment of galaxy cluster helps feed the gas through inflow to the member galaxies and also reduce the efficiency of star formation. The stacked Band 3 spectrum of 12 quiescent galaxies with M stellar ∼ 10 11 M within 0.5R 200 shows no detection of CO emission line, giving the upper limit of molecular gas mass and molecular gas fraction to be 10 10 M and 10%, respectively. Therefore, the massive galaxies in the cluster core quench the star formation activity while consuming most of the gas reservoirs.

On the Gas Content, Star Formation Efficiency, and Environmental Quenching of Massive Galaxies in Protoclusters at z ≈ 2.0–2.5

“…In line with these results, Noble et al (2017) found depletion timescales systematically higher than the scaling relation for nine CO(3 − 2)-detected galaxies in a cluster at z ∼ 1.6, although most are within a one standard deviation of the relation (plus several non-detection whose upper limits are in agreement with the field). Similarly, Hayashi et al (2018) presented CO(3 − 2) observations in several cluster galaxies at z ∼ 1.5 finding again systematically longer depletion timescales, although ∼ 50% of their sample might be in agreement the expected relation for the field (when non-detections are taken into account).…”

“…The effects of the environment are more evident when looking at the fraction of quenched galaxies. The larger number of massive gas-poor galaxies (ALMA non-detections) in the proto-clusters in comparison to the field (Figures 4 and 7) suggests that these protocluster galaxies are undergoing an accelerated evolution (see also Hayashi et al 2018;Shimakawa et al 2018;Wang et al 2018). These massive gas-poor systems have low gas mass fractions of f gas 6 − 10 % (Figure 4) and red colors ( Figures 5 and 6) which are in agreement with those found for post-starburst and quiescent galaxies at lower redshifts (e.g.…”

“…For example, the results of Noble et al (2017), who presents one of the best lines of evidence for the existence of sources with enhanced gas masses, are based on the detection of only seven indivudal sources from a parent sample of 49 cluster members. Similarly, the gas-rich galaxies found by Hayashi et al (2018) come from 18 detections out of a parent sample of 65 sources. Although cluster-to-cluster variations, reflecting different evolutionary stages (e.g.…”

The Typical Massive Quiescent Galaxy at z ∼ 3 is a Post-starburst

“…Our SFR thus converts into M mol =(1.5±0.6)×10 10 M , hence f mol ∼ 9 ± 4%. We compare it to CO or dust-continuum-based gas fractions and upper limits (converted to Salpeter) for quiescent and post-starburst galaxies: Davis et al (2014) and Saintonge et al (2011) for local massive PEGs; Sargent et al (2015), Bezanson et al (2019), Spilker et al (2018), Zavala et al (2019), Rudnick et al (2017), Suess et al (2017), Spilker et al (2018), Hayashi et al (2018), Gobat et al (2018) for intermediate-z quiescent galaxies; Schreiber et al (2018) and Valentino et al (2020) for z∼3-4 galaxies. Despite the uncertainties, our data at z∼3 seems to disfavor the steep (1+z) 4−5 trend inferred from z = 0 to 1.5-2, suggesting a flattening in the M mol /M evolution (or equivalently, of the sSFR).…”

Evidence for Inside-out Galaxy Growth and Quenching of a z ∼ 2 Compact Galaxy From High-resolution Molecular Gas Imaging

“…Spilker et al (2018a) presented CO(2-1) observations of 8 massive and passive galaxies at z ∼ 0.7, in which we found very low gas fractions but also relatively short gas depletion times 1 Gyr. This picture largely continues to z ∼ 1.5 (Sargent et al 2015;Rudnick et al 2017;Hayashi et al 2018;Bezanson et al 2019), where a total sample of four quiescent galaxies all exhibit strikingly low gas fractions (t dep is more difficult to constrain as reliable SFRs become more challenging to measure). In summary, these observations of older quiescent galaxies all point to very efficient molecular gas depletion, in agreement with our current understanding of the future evolution of COSMOS 27289 following its imminent depletion of molecular gas.…”