Sensitive radio survey of obscured quasar candidates

Abstract

We study the radio properties of moderately obscured quasars over a range of redshifts to understand the role of radio activity in accretion using the Jansky Very Large Array (JVLA) at 6.0GHz and 1.4GHz. Our z~2.5 sample consists of optically-selected obscured quasar candidates, all of which are radio-quiet, with typical radio luminosities of $\nu L_{\nu}$[1.4 GHz] < $10^{40}$ erg s$^{-1}$. Only a single source is individually detected in our deep (rms~10 $\mu$Jy) exposures. This population would not be identified by radio-based selection methods used for distinguishing dusty star-forming galaxies and obscured active nuclei. In our pilot A-array study of z~0.5 radio-quiet quasars, we spatially resolve four of five objects on scales ~ 5 kpc and find they have steep spectral indices. Therefore, radio emission in these sources could be due to jet-driven or radiatively driven bubbles interacting with interstellar material on the scale of the host galaxy. Finally, we also study the population of ~ 200 faint (~40 $\mu$Jy - 40 mJy) radio sources observed over ~ 120 arcmin$^2$ of our data. 60% of these detections are matched in the SDSS and/or WISE and are, in roughly equal shares, active nuclei at a broad range of redshifts, passive galaxies with no other signs of nuclear activity and IR-bright but optically faint sources. Spectroscopically or photometrically confirmed star-forming galaxies constitute only a small minority of the matches. Such sensitive radio surveys allow us to address important questions of AGN evolution and evaluate the AGN contribution to the radio-quiet sky.