# Uncovering the host galaxy of the $\gamma$-ray-emitting narrow-line Seyfert 1 galaxy FBQS J1644+2619

## TL;DR

This study uses near-infrared imaging to analyze the host galaxy of the gamma-ray-emitting NLSy1 galaxy FBQS J1644+2619, revealing an elliptical host and estimating a black hole mass consistent with radio-loud AGN.

## Contribution

First detailed near-infrared structural analysis of this gamma-ray-emitting NLSy1 galaxy's host, linking its properties to elliptical galaxy characteristics and black hole mass estimates.

## Key findings

- Host galaxy is elliptical with Sersic index n=3.7.
- Black hole mass estimated at approximately 2.1 x 10^8 solar masses.
- Host galaxy properties align with known elliptical galaxy correlations.

## Abstract

The discovery of $\gamma$-ray emission from radio-loud narrow-line Seyfert 1 (NLSy1) galaxies has questioned the need for large black hole masses (> 10$^8$ M$_{\odot}$) to launch relativistic jets. We present near-infrared data of the $\gamma$-ray-emitting NLSy1 FBQS J1644+2619 that were collected using the camera CIRCE (Canarias InfraRed Camera Experiment) at the 10.4-m Gran Telescopio Canarias to investigate the structural properties of its host galaxy and to infer the black hole mass. The 2D surface brightness profile is modelled by the combination of a nuclear and a bulge component with a S\'ersic profile with index $n$ = 3.7, indicative of an elliptical galaxy. The structural parameters of the host are consistent with the correlations of effective radius and surface brightness against absolute magnitude measured for elliptical galaxies. From the bulge luminosity, we estimated a black hole mass of (2.1$\pm$0.2) $\times$10$^8$ M$_{\odot}$, consistent with the values characterizing radio-loud active galactic nuclei.