The Environmental Dependence of Gas Properties in Dense Cores of a Protocluster at z ∼ 2.5 Revealed with ALMA

Abstract

In a protocluster USS1558-003 at z = 2.53, galaxies in the dense cores show systematically elevated star-forming activity compared to those in less dense regions. To understand its origin, we look into the gas properties of the galaxies in the dense cores by conducting deep 1.1 mm observations with the Atacama Large Millimeter/submillimeter Array. We detect interstellar dust continuum emission from 12 member galaxies and estimate their molecular gas masses. Comparing these gas masses with our previous measurements from the CO(3–2) line, we infer that the latter might be overestimated. We find that the gas to stellar mass ratios of the galaxies in the dense cores tend to be higher (at M * ∼ 1010 M ⊙ where we see the enhanced star-forming activity), suggesting that such large gas masses can sustain their high star-forming activity. However, if we compare the gas properties of these protocluster galaxies with the gas scaling relations constructed for field galaxies at a similar cosmic epoch, we find no significant environmental difference at the same stellar mass and star formation rate. Although both gas mass ratios and star-forming activity are enhanced in the majority of member galaxies, they appear to follow the same scaling relation as field galaxies. Our results are consistent with the scenario in which the cold gas is efficiently supplied to protocluster cores and to galaxies therein along surrounding filamentary structures, which leads to the high gas mass fractions and thus the elevated star formation activity, but without changing the star formation law.

The VIMOS Ultra Deep Survey: The reversal of the star-formation rate − density relation at 2 <z< 5

“…If such a paucity is pervasive for galaxies in proto-cluster environments at z ∼ 2−2.5, it would help to explain the change in behavior of the SFR−δ gal seen between our higher-and lower-redshift samples. However, such observations remain very sparse even at these redshifts, and the opposite trend (e.g., Gómez-Guijarro et al 2019;Tadaki et al 2019;Aoyama et al 2022) or a flat trend (e.g., Lee et al 2017;Darvish et al 2018) of µ gas with environment is also observed at these redshifts (also see the discussion in §3.4 of Tacconi et al 2020). While it appears likely that in situ gas depletion at z 2.5 and gas enhancement at z 2.5 in highdensity environments helps to drive the behavior of the SFR−δ gal relation seen here, future work with ALPINE and other observations from ALMA and PdBI at these redshifts are required in order to be able to make definitive claims.…”

High-resolution ALMA Study of CO J = 2–1 Line and Dust Continuum Emissions in Cluster Galaxies at z = 1.46

“…For cluster galaxies at z  1.3, submillimeter interferometers have discovered the ubiquity of a large amount of cold molecular gas (M mol gas  10 10 M e ), using mid-/low-J transition lines of carbon monoxide (CO), the second most abundant molecule following molecular hydrogen (H 2 ), or dust continuum emission for substantial samples (e.g., Dannerbauer et al 2017;Lee et al 2017;Noble et al 2017;Webb et al 2017;Rudnick et al 2017;Coogan et al 2018;Miller et al 2018;Oteo et al 2018;Wang et al 2018;Gómez-Guijarro et al 2019;Tadaki et al 2019;Zavala et al 2019;D'Amato et al 2020;Champagne et al 2021;Jin et al 2021;Aoyama et al 2022;Williams et al 2022). These studies have been conducted by observing multiple sources with just a single telescope pointing, allowing an efficient survey of CO line emitters in dense cluster environments.…”

“…Close interactions and mergers of galaxies are often preferentially found in dense environments, and one will naturally predict a shorter gas depletion timescale in cluster galaxies. While several studies report a longer gas depletion timescale for cluster galaxies at high-redshift compared to field galaxies (e.g., Noble et al 2017;Hayashi et al 2018;Tadaki et al 2019;Williams et al 2022), others find it to be consistent (e.g., Gómez-Guijarro et al 2019;Zavala et al 2019;Aoyama et al 2022) or even shorter (Alberts et al 2022). However, these studies are conducted using data with a relatively low angular resolution (1″), and they may just reflect the global properties averaged over the entire galaxy disk.…”

High-resolution ALMA study of CO (2-1) line and dust continuum emissions in cluster galaxies at z = 1.46

“…Noble et al 2017;Hayashi et al 2018;Tadaki et al 2019;Williams et al 2022), others find it consistent (e.g. Gómez-Guijarro et al 2019;Zavala et al 2019;Aoyama et al 2022) or even shorter (Alberts et al 2022). However, these studies are conducted using data with relatively low angular resolution ( 1 ′′ ), and they may just reflect the global properties averaged over the entire galaxy disk.…”

“…For cluster galaxies at z 1.3, submillimeter interferometers have discovered the ubiquity of a large amount of cold molecular gas (M mol gas 10 10 M ⊙ ) using mid-/low-J transition lines of carbon monoxide (CO), the second most abundant molecule following molecular hydrogen (H 2 ), or by dust continuum emission for substantial samples (e.g. Dannerbauer et al 2017;Noble et al 2017;Lee et al 2017;Webb et al 2017;Rudnick et al 2017;Oteo et al 2018;Coogan et al 2018;Wang et al 2018;Miller et al 2018;Tadaki et al 2019;Gómez-Guijarro et al 2019;Zavala et al 2019;D'Amato et al 2020;Champagne et al 2021;Jin et al 2021;Aoyama et al 2022;Williams et al 2022). These studies have been conducted by observing multiple sources with just a single telescope pointing, allowing an efficient survey of CO line emitters in dense cluster environments.…”