http://arxiv.org/abs/1702.04962
For 1526 of the sources with redshifts we use radio and X-ray luminosity, optical spectroscopy, mid-infrared colors, and 24$\mu$m and IR to radio flux ratios to search for the presence of an AGN. The analysis reveals a rapid change in the population as flux density decreases from $\sim$500\,$\mu$Jy to $\sim$100\,$\mu$Jy. We find that 80.3\% of the objects show no evidence of AGN and have multi-wavelength properties consistent with radio emission from star forming galaxies (SFG). We classify 11.4\% as Radio Quiet (RQ) AGN and the remaining 8.3\% as Radio Loud (RL) AGN.
The redshift of all populations extends to $z > 3$ with a median of $\sim$1. The median radio and far-IR luminosity increases systematically from SFG, to RQ AGN and RL AGN. The median $q_{\rm 24 \mu m}$ for SFG, $0.89\pm0.01$ is slightly below that for RQ AGN, $1.05\pm0.03$, and both differ substantially from the value for RL AGN of $-0.06\pm0.07$. However, SFG and RQ AGN show no significant difference in far-IR/radio ratios and have statistically indistinguishable star formation rates inferred from radio and far-IR luminosities. We conclude that radio emission from host galaxies of RQ AGN in this flux density regime result primarily from star formation activity.
E. Ocran, A. Taylor, M. Vaccari, et. al.
Fri, 17 Feb 17
43/43
Comments: 15 pages, 15 figures and 6 tables. Accepted for publication in MNRAS