The Mid-Infrared Environments of High-Redshift Radio Galaxies

TL;DR

This study uses Spitzer mid-infrared data to identify and analyze the environments of high-redshift radio galaxies, revealing that most are located in medium to dense galaxy regions, including known and new cluster candidates.

Contribution

It introduces a simple IRAC color criterion to efficiently identify high-redshift galaxy environments and demonstrates their prevalence around radio galaxies at z>1.2.

Findings

73% of fields are denser than average

Successfully rediscovered known clusters and protoclusters

Discovered new galaxy cluster candidates at z>1.2

Abstract

Taking advantage of the impressive sensitivity of Spitzer to detect massive galaxies at high redshift, we study the mid-infrared environments of powerful, high-redshift radio galaxies at 1.2<z<3. Galaxy cluster member candidates were isolated using a single Spitzer/IRAC mid-infrared color criterion, [3.6]-[4.5]>-0.1 (AB), in the fields of 48 radio galaxies at 1.2<z<3. This simple IRAC color selection is effective at identifying galaxies at z>1.2. Using a counts-in-cell analysis, we identify a field as overdense when 15 or more red IRAC sources are found within 1arcmin (i.e.,~0.5Mpc at 1.2<z<3) of the radio galaxy to the 5sigma flux density limits of our IRAC data (f3.6=11.0uJy, f4.5=13.4uJy). We find that radio galaxies lie preferentially in medium to dense regions, with 73% of the targeted fields denser than average. Our (shallow) 120s data permit the rediscovery of previously known clusters and protoclusters associated with radio galaxies as well as the discovery of new promising galaxy cluster candidates at z>1.2.