Sensitive radio survey of obscured quasar candidates

We study the radio properties of moderately obscured quasars in samples at both low (z ~ 0.5) and high (z ~ 2.5) redshift to understand the role of radio activity in accretion, using the Karl G. Jansky Very Large Array (VLA) at 6.0 GHz and 1.4 GHz. Our z ~ 2.5 sample consists of optically selected obscured quasar candidates, all of which are radio-quiet, with typical radio luminosities of vL_v [1.4 GHz] ≲ 10⁴⁰ erg s^-1. Only a single source is individually detected in our deep (rms~10 μJy) 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 with an average value of α = -0.75. 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 additional population of ~200 faint (~40 μJy-40 mJy) field radio sources observed over ~120 arcmin² of our data. 60 per cent of these detections (excluding our original targets) are matched in the Sloan Digital Sky Survey (SDSS) and/or Wide-Field Infrared Survey Explorer (WISE) and are, in roughly equal shares, active galactic nuclei (AGN) at a broad range of redshifts, passive galaxies with no other signs of nuclear activity and infrared-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.