# A catalogue sample of low mass galaxies observed in X-rays with central candidate black holes

## TL;DR

This study identifies candidate black holes in low-mass galaxies using X-ray and radio data, estimating their masses and highlighting their potential role in galaxy evolution, while emphasizing the need for follow-up observations.

## Contribution

First systematic cross-correlation of X-ray and radio data to identify candidate black holes in low-mass galaxies, estimating their masses and spatial distribution.

## Key findings

- 37% of low-mass galaxies host X-ray sources with radio counterparts
- Estimated black hole masses range from 10^4 to 2×10^8 solar masses
- Median black hole mass is approximately 3×10^7 solar masses

## Abstract

We present a sample of $X$-ray selected candidate black holes in 51 low mass galaxies with $z\le 0.055$ {and mass up to $10^{10}$ M$_{\odot}$} obtained by cross-correlating the NASA-SLOAN Atlas with the 3XMM catalogue. {We have also searched in the available catalogues for radio counterparts of the black hole candidates and find that 19 of the previously selected sources have also a radio counterpart.} Our results show that about $37\%$ of the galaxies of our sample host { an $X$-ray source} (associated to a radio counterpart) spatially coincident with the galaxy center, in agreement with { other recent works}. For these {\it nuclear} sources, the $X$-ray/radio fundamental plane relation allows one to estimate the mass of the (central) candidate black holes which results to be in the range $10^{4}-2\times10^{8}$ M$_{\odot}$ (with median value of $\simeq 3\times 10^7$ M$_{\odot}$ and eight candidates having mass below $10^{7}$ M$_{\odot}$). This result, while suggesting that $X$-ray emitting black holes in low-mass galaxies may have had a key role in the evolution of such systems, makes even more urgent to explain how such massive objects formed in galaxies. {Of course, dedicated follow-up observations both in the $X$-ray and radio bands, as well as in the optical, are necessary in order to confirm our results