Kiloparsec-scale Radio Structure in z ∼ 0.25 Radio-quiet QSOs

Abstract

We present analysis of a homogeneous, optically selected, volume-limited (0.2 < z < 0.3) sample of 128 radio-quiet quasi-stellar objects (QSOs) recently observed at 6 GHz with the Very Large Array (VLA) in A configuration (∼0.″33 resolution). We compare these new results to earlier (2010–2011) 6 GHz observations with the VLA in C configuration (∼3.″5). While all of these radio-quiet QSOs (RQQs) were unresolved on a 3.″5 scale (∼14 kpc at z = 0.25), we resolve notable complex subgalactic structures in about half of the RQQs at 0.″33 resolution (∼1.3 kpc at z = 0.25). By comparison of flux density measurements between the two sets of observations, we demonstrate that significant sub-galactic-scale radio structure is present in at least 70% of the RQQ population and that the central component accounts for an average of ≈65% of the total detected radio power. One RQQ, J0935+4819, shows striking symmetric, double-lobed morphology and appears to be the first identified example of a radio-quiet QSO with FR II type morphology on ∼arcsec scale (projected size of ≳6 kpc). In addition to revealing RQQ subgalactic morphology, we employ counterparts from legacy (FIRST at 1.4 GHz) and recent (VLA Sky Survey at 3 GHz) VLA surveys to investigate radio spectral indices and potential variability over decades-long timescales for a subset of the RQQs and for the cores of radio-intermediate and radio-loud sources in the parent sample of 178 QSOs. These results support the growing notion that the RQQ population is not a monolithic phenomenon but instead consists of a mixture of mainly starburst-powered and jet-powered galaxies.