ABSTRACT We report on observations of redshifted CO(1–0) line emission and observed-frame $\rm \sim 30\,$GHz radio continuum emission from five ultra-luminous, mid-IR selected hot, Dust-Obscured Galaxies (Hot DOGs) at $z\rm \gtrsim 3$ using the Karl G. Jansky Very Large Array. We detect CO(1–0) line emission in all five Hot DOGs, with one of them at high signal-to-noise ratio. We analyse FIR-radio spectral energy distributions, including dust, free–free, and synchrotron emission for the galaxies. We find that most of the $\rm 115\,$ GHz rest-frame continuum is mostly due to synchrotron or free–free emission, with only a potentially small contribution from thermal emission. We see a deficit in the rest-frame $\rm 115\,$ GHz continuum emission compared to dusty star-forming galaxies and sub-millimetre galaxies (SMGs) at high redshift, suggesting that Hot DOGs do not have similar cold gas reserves compared with star-forming galaxies. One target, W2305−0039, is detected in the FIRST $\rm 1.4\, GHz$ survey, and is likely to possess compact radio jets. We compare to the FIR–radio correlation, and find that at least half of the Hot DOGs in our sample are radio-quiet with respect to normal galaxies. These findings suggest that Hot DOGs have comparably less cold molecular gas than star-forming galaxies at lower, $z\rm \sim 2$ redshifts, and are dominated by powerful, yet radio-quiet AGN.

We have observed the environments of a population of 33 heavily dust obscured, ultraluminous, high-redshift galaxies, selected using WISE and NVSS at z >1.3 with the Infra-Red Array Camera on the Spitzer Space Telescope over 5.12 ×5.12 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 [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 0.25 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% (33%) of the 33 fields have a surface density greater than the 3σ (5σ) level. There is a statistical excess of these redder galaxies within 0.5 , 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 AGN.

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