A blind CO detection of a distant red galaxy in the HS1700+64 protocluster

S C Chapman,R J Ivison,R J Ivison,G R Petitpas,A W Blain,F Bertoldi,Ian Smail,M Gurwell,J E Geach,N Reddy,C C Steidel

doi:10.1093/mnrasl/slv010

Abstract

Abstract We report the blind detection of 12CO emission from a distant red galaxy, HS1700.DRG55. We have used the IRAM Plateau de Bure Interferometer WideX, with its 3.6 GHz of instantaneous dual-polarization bandwidth, to target 12CO(3–2) from galaxies lying in the protocluster at z = 2.300 in the field HS1700+64. If indeed this line in DRG55 is 12CO(3–2), its detection at 104.9 GHz indicates zCO = 2.296. None of the other eight known z ∼ 2.30 protocluster galaxies lying within the primary beam (PB) are detected in 12CO, although the limits are ∼2 × worse towards the edge of the PB where several lie. The optical/near-IR magnitudes of DRG55 (RAB &gt; 27, KAB = 22.3) mean that optical spectroscopic redshifts are difficult with 10-m-class telescopes, but near-IR redshifts would be feasible. The 24-μm-implied star formation rate (210 M⊙ yr−1), stellar mass (∼1011 M⊙) and 12CO line luminosity (3.6 × 1010 K km s−1 pc2) are comparable to other normal12CO-detected star-forming galaxies in the literature, although the galaxy is some ∼2 mag (∼6 ×) fainter in the rest-frame UV than 12CO-detected galaxies at z &gt; 2. The detection of DRG55 in 12CO complements three other 12CO detected UV-bright galaxies in this protocluster from previous studies, and suggests that many optically faint galaxies in the protocluster may host substantial molecular gas reservoirs, and a full blind census of 12CO in this overdense environment is warranted.

Highlights

Massive galaxy clusters at z > 1 show a reversal in the star-formation density relation such that there is an enhancement of activity in the highest density regions (e.g. Elbaz et al 2007, 2011), with observations revealing increasing levels of activity even in the cluster cores (Cooper et al 2008; Chapman et al 2009; Hilton et al 2010; Tran et al 2010; Smail et al 2014)
In this Letter, we describe a blind 3 mm survey for redshifted 12CO(3–2) molecular gas from z ∼ 2.30 galaxies in HS1700+64, a protocluster with a redshift-space galaxy overdensity of δgz ∼ 7 and an estimated matter overdensity which indicates that it will virialize
The 3 mm band provides a reasonably large field of view on the IRAM-Plateau de Bure Interferometer [PdBI; ∼50 arcsec primary beam (PB), ∼0.4 Mpc diameter at z = 2.3], with the strong clustering of galaxies in angular scales and along the line of sight effectively increasing the number of galaxies observed within a single pointing with the PdBI

Summary

INTRODUCTION

Massive galaxy clusters at z > 1 show a reversal in the star-formation density relation such that there is an enhancement of activity in the highest density regions (e.g. Elbaz et al 2007, 2011), with observations revealing increasing levels of activity even in the cluster cores (Cooper et al 2008; Chapman et al 2009; Hilton et al 2010; Tran et al 2010; Smail et al 2014). The gas properties of galaxies in distant clusters remain poorly constrained, despite the fact that they may well elucidate the mechanisms for the increasing SFRs in cores of massive clusters. The 3 mm band provides a reasonably large field of view on the IRAM-Plateau de Bure Interferometer [PdBI; ∼50 arcsec primary beam (PB), ∼0.4 Mpc diameter at z = 2.3], with the strong clustering of galaxies in angular scales and along the line of sight effectively increasing the number of galaxies observed within a single pointing with the PdBI (see Tadaki et al 2014).

O B S E RVAT I O N S

The four archival protocluster PdBI pointings

RESULTS

DISCUSSION AND CONCLUSIONS