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

TL;DR

This study uses ALMA to detect molecular gas in 24 star-forming Brightest Cluster Galaxies across a broad redshift range, revealing consistent gas processing mechanisms over cosmic time.

Contribution

First large, distant sample of molecular gas measurements in star-forming BCGs, showing uniformity in gas processing across different epochs.

Findings

High detection rate of molecular gas in BCGs (~80%)

Gas masses comparable across redshifts, following the main sequence of star formation

Similar gas-SFR correlations at z<0.6 and higher redshifts

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 (SFR) and stellar mass, calculated from existing MIPS 24 $\mu$m and IRAC 3.6 $\mu$m fluxes, respectively. We find these galaxies have molecular gas masses of $0.7-11.0\times 10^{10}\ \mathrm{M}_\odot$, comparable to other BCGs in this redshift range, and specific star formation rates which trace the Elbaz et al. (2011) Main Sequence. We compare our BCGs to those of the lower-redshift, cooling-flow BCG sample assembled by Edge (2001) and find that at z $\lesssim 0.6$ the two samples show very similar correlations between their gas masses and specific SFRs. We suggest that, in this redshift regime, the $\sim10\%$ (Webb et al., 2015) of BCGs that are star-forming process any accreted molecular gas into stars through means that are agnostic to both their redshift and their cluster mass.