2019MNRAS.483..514P

We have observed the environments of a population of 33 heavily dust obscured, ultraluminous, high-redshift galaxies, selected using Wide-Field Infrared Survey Explorer (WISE) and NRAO 1.4 GHz VLA Sky Survey atz > 1.3 with the infrared array camera on the Spitzer Space Telescope over 5.12 arcmin×5.12 arcmin fields. Colour selections are used to quantify any potential overdensities of companion galaxies in these fields. We find no significant excess of galaxies with the standard colour selection for IRAC colours of [3.6] - [4.5] > -0.1 consistent with galaxies at z > 1.3 across the whole fields with respect to wide-area Spitzer comparison fields, but there is a >2σ statistical excess within 0.25arcmin of the central radio-WISE galaxy. Using a colour selection of [3.6]-[4.5]> 0.4, 0.5 magnitudes redder than the standard method of selecting galaxies at z > 1.3, we find a significant overdensity, in which 76 per cent ( 33 per cent) of the 33 fields have a surface density greater than the 3σ ( 5σ) level. There is a statistical excess of these redder galaxies within 0.5arcmin, rising to a central peak ∼2-4 times the average density. This implies that these galaxies are statistically linked to the radio-WISE selected galaxy, indicating similar structures to those traced by red galaxies around radio-loud active galactic nuclei.