Unveiling the submerged part of the iceberg: radio-loud narrow-line Seyfert 1s with SKA

TL;DR

This paper discusses how the upcoming SKA telescope will enable the discovery of a hidden population of radio-loud narrow-line Seyfert 1 galaxies with relativistic jets, which are currently difficult to detect due to their faintness and variability.

Contribution

The study evaluates the potential of SKA to reveal a previously undetectable population of radio-loud NLS1s with relativistic jets, expanding our understanding of AGN diversity.

Findings

SKA's sensitivity will detect fainter RLNLS1s.

Current surveys miss many RLNLS1s due to flux limitations.

SKA will enable studies of jet activity during low-flux states.

Abstract

Narrow-line Seyfert 1 galaxies (NLS1) are active galactic nuclei (AGN) known to have small masses of the central black hole and high accretion rates. NLS1s are generally radio-quiet, but a small part of them (about 7\%) are radio-loud. The recent discovery of powerful relativistic jets in radio-loud NLS1s (RLNLS1s), emitting at high-energy $\gamma$-rays, opened intriguing questions. The observed luminosity of the jet is generally weak, smaller than blazars, although when rescaled for the mass of the central black hole, it becomes of the same order of magnitude of the latter. The weak luminosity, and hence observed flux, resulted in a small number of known RLNLS1. From a recent survey of RLNLS1s, it was found that only 8 out of 42 sources had radio flux density at 1.4 GHz greater than 100 mJy, while 21 out of 42 had flux density smaller than 10 mJy. In addition, given the strong variability at all wavelengths, with present-day facilities RLNLS1s can often only be detected during high activity periods. The Square Kilometer Array (SKA), with its superior sensitivity, will break this limit, allowing us to unveil a relatively unknown population of jetted AGN. We present the results of a study aimed at evaluating the scenario that could emerge after the advent of SKA.