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

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 γ-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 radiodetection of merely ∼ 4.5 per cent (498/11101) NLS1s, with majority (407/498 ∼ 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.

TXS 2116−077: A Gamma-Ray Emitting Relativistic Jet Hosted in a Galaxy Merger

“…The age will be even shorter for the larger jet velocity/viewing angle. This finding suggests a 'young' jet in TXS 2116−077, which is in line with the hypothesis that NLSy1 jets are likely to be in the early phase of evolution (Singh & Chand 2018). Note that the radio emission in NLSy1 galaxies could be originated from the star-formation activities and/or due to non-relativistic kiloparsec-scale outflows (Gallimore et al 2006).…”

Deep GMRT 610 MHz observations of the ELAIS N1 field: catalogue and source counts

“…Narayan & Yi 1994). Thus, radio spectra are useful in unveiling the physical processes in radio sources (Prandoni et al 2010;Singh & Chand 2018).…”

Gamma-ray emitting narrow-line Seyfert 1 galaxies: Past, present, and future

“…Moreover, the Doppler factor, or equivalently bulk Lorentz factor Γ, of the γ-NLSy1 jets is reported to be smaller with respect to blazar jets (Paliya et al 2019a). Radio observations of these sources also support this finding (Angelakis et al 2015; Gu et al 2015;Fuhrmann et al 2016;Singh & Chand 2018). A smaller Doppler factor implies a relatively mild boosting which explains the scarcity of the NLSy1 galaxies in the Fermi-LAT catalogs.…”