Study of Milli-Jansky Seyfert Galaxies with Strong Forbidden High-Ionization Lines Using the Very Large Array Survey Images

TL;DR

This study investigates the radio properties of Seyfert galaxies with strong forbidden high-ionization lines using VLA images, revealing low detection rates, nuclear-dominated radio emission, and support for the unified scheme hypothesis.

Contribution

It provides the first large-scale radio analysis of FHIL Seyfert galaxies, showing their radio emission characteristics and absorption effects, and supports the unified model of AGN.

Findings

Radio detection rate is 49%, lower than other Seyfert samples.

Radio emission is dominated by the active nucleus with minimal thermal contribution.

Approximately 8% of sources are radio-intermediate, most are radio-quiet.

Abstract

We study the radio properties at 1.4 GHz of Seyfert galaxies with strong forbidden high-ionization lines (FHILs), selected from the Sloan Digital Sky Survey - a large-sized sample containing nearly equal proportion of diverse range of Seyfert galaxies showing similar redshift distributions compiled by Gelbord et al. (2009) using the Very Large Array survey images. The radio detection rate is low, 49%, which is lower than the detection rate of several other known Seyfert galaxy samples. These galaxies show low star formation rates and the radio emission is dominated by the active nucleus with $\le$10% contribution from thermal emission, and possibly, none show evidence for relativistic beaming. The radio detection rate, distributions of radio power, and correlations between radio power and line luminosities or X-ray luminosity for narrow-line Seyfert 1 (NLS1), Seyfert 1 and Seyfert 2 galaxies are consistent with the predictions of the unified scheme hypothesis. Using correlation between radio and [O\,III]\,$\lambda$ \,5007\,\AA\ luminosities, we show that $\sim$8% sample sources are radio-intermediate and the remaining are radio-quiet. There is possibly an ionization stratification associated with clouds on scales of 0.1-1.0 kpc, which have large optical depths at 1.4 GHz, and it seems these clouds are responsible for free-free absorption of radio emission from the core, hence, leading to low radio detection rate for these FHIL-emitting Seyfert galaxies.