The Radio Properties of Type 2 Quasars

TL;DR

This study investigates the radio emission characteristics of optically selected type 2 quasars using high-resolution VLA observations, revealing a high detection rate and a prevalence of radio-intermediate, flat-spectrum sources that challenge simple unification models.

Contribution

First high-resolution, high-sensitivity radio study of optically selected type 2 quasars, providing new insights into their radio properties and spectral characteristics.

Findings

59% detection rate at 8.4 GHz

Approximately 15% are radio-loud

Most sources are radio-intermediate with flat/inverted spectra

Abstract

This paper presents the first high-resolution and high-sensitivity study of the radio properties of optically selected type~2 quasars. We used the Very Large Array at 8.4 GHz to observe 59 sources drawn from the Sloan Digital Sky Survey sample of Zakamska et al. (2003). The detection rate of our survey is 59% (35/59), comparable to the detection rate in FIRST at 1.4 GHz. Ongoing star formation, although present, contributes negligible radio emission at the current sensitivity limit. Comparing the radio powers with the [O III] $\lambda$5007 luminosities, we find that roughly 15%$\pm$5% of the sample can be considered radio-loud. Intriguingly, the vast majority of the detected sources in our sample fall in a region intermediate between those traditionally occupied by radio-loud and radio-quiet quasars. Moreover, most of these "radio-intermediate" sources tend to have flat or inverted radio spectra, which we speculate may be caused by free-free absorption by ionized gas in the narrow-line region. The incidence of flat-spectrum sources in type 2 quasars appears to be much higher than in type 1 quasars, in apparent violation of the simple orientation-based unified model for active galaxies.