The environments of luminous radio-WISE selected infrared galaxies

Jordan Iain Penney ,Daniel Stern ,N A Hatch ,Mark Lacy ,Anna Sajina ,Sarah Jones ,A Silva ,Stuart I Muldrew ,Amy Kimball ,C J Lonsdale ,Chris Tsai ,M Kim ,T Díaz-Santos ,Dominika Wylezalek ,J J Condon ,Roberto J Assef ,Sara Petty ,A W Blain ,Peter Eisenhardt ,Jinfeng Wu

doi:10.1093/mnras/sty3128

Abstract

We have observed the environments of a population of 33 heavily dust obscured, ultra-luminous, high-redshift galaxies, selected using WISE and NVSS at $z>$1.3 with the Infra-Red Array Camera on the $Spitzer$ Space Telescope over $\rm5.12\,'\times5.12\,'$ 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 $\rm[3.6]-[4.5]>-0.1$ consistent with galaxies at $z>$1.3 across the whole fields with respect to wide-area $Spitzer$ comparison fields, but there is a $\rm>2\sigma$ statistical excess within $\rm0.25\,'$ of the central radio-WISE galaxy. Using a colour selection of $\rm[3.6]-[4.5]>0.4$, 0.5 magnitudes redder than the standard method of selecting galaxies at $z>$1.3, we find a significant overdensity, in which $\rm76\%$ ($\rm33\%$) of the 33 fields have a surface density greater than the $\rm3\sigma$ ($\rm5\sigma$) level. There is a statistical excess of these redder galaxies within $\rm0.5\,'$, rising to a central peak $\rm\sim2$--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 AGN.

Highlights

High-redshift galaxy protoclusters are the largest known cosmological structures, with 90 per cent of their ∼1015 M mass expected within regions spanning ∼35 h−1 Mpc (Chiang, Overzier & Gebhardt 2013; Muldrew, Hatch & Cooke 2015)
Cosmic variance is a significant factor in the comparison fields, expected to scatter the density of galaxies found in 5.12 arcmin × 5.12 arcmin fields by ∼30 per cent (Trenti & Stiavelli 2008), greater than the observed excess in the radio-Wide-Field Infrared Survey Explorer (WISE) selected fields
The results of Spitzer infrared array camera (IRAC) imaging on 5.12 arcmin × 5.12 arcmin fields centred on radio-WISE selected galaxies are as follows: (i) We find that the radio-WISE selected fields have a similar density of IRAC-selected galaxies with colour [3.6] − [4.5] > −0.1 to blank fields, with only a modest 10 per cent overdensity of GroupI selected galaxies

Summary

Introduction

High-redshift galaxy protoclusters are the largest known cosmological structures, with 90 per cent of their ∼1015 M mass expected within regions spanning ∼35 h−1 Mpc (Chiang, Overzier & Gebhardt 2013; Muldrew, Hatch & Cooke 2015). Some luminous IR galaxies harbour luminous active galactic nuclei (AGN), at times placing them in the Ultraluminous Infrared galaxy (ULIRG1) regime (Sanders & Mirabel 1996; Lonsdale, Farrah & Smith 2006; Tsai et al 2015). (DOGs; Dey et al 2008), first uncovered owing to their high 24 μm to. Hot DOGs (Wu et al 2012) are similar but rarer galaxies discovered using the Wide-Field Infrared Survey Explorer (WISE; Wright et al 2010) All-Sky Survey, with red detections in the WISE

Results

Discussion

Conclusion