Investigating kpc-scale radio emission properties of narrow-line Seyfert 1 galaxies

TL;DR

This study analyzes the kpc-scale radio properties of a large sample of Narrow-Line Seyfert 1 galaxies, revealing insights into their radio emission, jet characteristics, and possible evolutionary stages.

Contribution

It provides the largest analysis of radio properties of NLS1s, highlighting the prevalence of compact, diverse-spectrum radio sources and their potential early or confined jet activity.

Findings

Only about 4.5% of NLS1s are radio-detected, mostly RL-NLS1s.

Most radio-detected NLS1s are compact and exhibit a range of spectral properties.

High-luminosity NLS1s show blazar-like features such as variability and polarization.

Abstract

In recent years, several Radio-Loud Narrow-Line Seyfert 1 galaxies (RL-NLS1) possessing relativistic jets have come into attention with their detections in Very Large Baseline Array (VLBA) and in $\gamma$-ray observations. In this paper we attempt to understand the nature of radio-jets in NLS1s by examining the kpc-scale radio properties of, hitherto, the largest sample of 11101 optically-selected NLS1s. Using 1.4 GHz FIRST, 1.4 GHz NVSS, 327 MHz WENNS, and 150 MHz TGSS catalogues we find the radio-detection of merely $\sim$ 4.5 per cent (498/11101) NLS1s, with majority (407/498 $\sim$ 81.7 per cent) of them being RL-NLS1s. Our study yields the highest number of RL-NLS1s and it can only be a lower limit. We find that the most of our radio-detected NLS1s are compact ($<$ 30 kpc), exhibit both flat as well as steep radio spectra, and are distributed across a wide range of 1.4 GHz radio luminosities (10$^{22}$ $-$ 10$^{27}$ W Hz$^{-1}$). At the high end of radio luminosity our NLS1s often tend to show blazar-like properties such as compact radio-size, flat/inverted radio spectrum, radio variability and polarization. The diagnostic plots based on the mid-IR colours suggest that the radio emission in NLS1s is mostly powered by AGN, while nuclear star-formation may have a significant contribution in NLS1s of low radio luminosities. The radio luminosity versus radio-size plot infers that the radio-jets in NLS1s are either in the early evolutionary phase or possibly remain confined within the nuclear region due to low-power or intermittent AGN activity.