A CO Survey of SpARCS Star-forming Brightest Cluster Galaxies: Evidence for Uniformity in BCG Molecular Gas Processing across Cosmic Time

Delaney A Dunne,Tracy M A Webb,Christopher Lidman,H K C Yee,Heath Shipley,Adam Muzzin,Allison Noble,Gillian Wilson

doi:10.3847/2041-8213/abeb6f

Abstract

Abstract We present ALMA CO (2-1) detections of 24 star-forming brightest cluster galaxies (BCGs) over 0.2 < z < 1.2, constituting the largest and most distant sample of molecular gas measurements in BCGs to date. The BCGs are selected from the Spitzer Adaptation of the Red-Sequence Cluster Survey (SpARCS) to be IR-bright and therefore star-forming. We find that molecular gas is common in star-forming BCGs, detecting CO at a detection rate of 80% in our target sample of 30 objects. We additionally provide measurements of the star formation rate and stellar mass, calculated from existing MIPS 24 μm and IRAC 3.6 μm fluxes, respectively. We find these galaxies have molecular gas masses of 0.7–11.0 × 1010 M ⊙, comparable to other BCGs in this redshift range, and specific star formation rates that trace the main sequence of Elbaz et al. We compare our BCGs to those of the lower-redshift, cooling-flow BCG sample assembled by Edge and find that at z ≲ 0.6 the two samples show very similar correlations between their gas masses and specific SFRs. We suggest that, in this redshift regime, the ∼10% of BCGs that are star-forming process accreted molecular gas into stars through means that are agnostic to both their redshift and their cluster mass.

Highlights

Galaxy clusters are extreme examples of hierarchical structure formation, forming the largest overdensities in the primordial universe
We indicate the two other Brightest Cluster Galaxies (BCGs) selected from SpARCS with confident molecular gas detections — SpARCS1049 (Webb et al 2017), whose gas has recently been shown to be fed by a massive cooling flow (Hlavacek-Larrondo et al 2020)
We find that 80% of our BCGs are detected in CO, suggesting that molecular gas is common in star-forming BCGs at high redshifts

Summary

Introduction

Galaxy clusters are extreme examples of hierarchical structure formation, forming the largest overdensities in the primordial universe. Brightest Cluster Galaxies (BCGs), as massive galaxies residing in the dense, violent centers of galaxy clusters, evolve through pathways that are a direct result of this environment In the latter stage of their evolution (after z ∼ 1), the stellar mass of BCGs roughly doubles (Lidman et al 2012). While this is expected to be mostly a dry process, done primarily through gasless mergers of the BCG with infalling cluster galaxies (De Lucia & Blaizot 2007), some (∼10%, based on a 24 μm flux ≥ 100μJy; Webb et al 2015) BCGs do show star formation at these redshifts. Either major or minor, of the BCG with gas-rich infalling cluster galaxies, or large-scale ‘cooling flows’ of gas from the intracluster medium (ICM) onto the BCG

Objectives

Results

Discussion

Conclusion