Confirmation of intermediate-mass black holes candidates with X-ray observations

TL;DR

This study confirms 15 intermediate-mass black holes using X-ray observations, significantly increasing the known sample and providing new insights into their properties and correlations with optical emission lines.

Contribution

The paper presents a new sample of 15 bona-fide IMBHs confirmed via X-ray data, tripling the known confirmed IMBHs and exploring their luminosity correlations.

Findings

Confirmed 15 new IMBHs, increasing the sample size by 2.5 times.

Found high Eddington ratios close to critical for 30% of objects.

Established correlations between optical emission lines and X-ray luminosity.

Abstract

The origin of supermassive black holes (SMBH) in galaxy centers still remains uncertain. There are two possible ways of their formation - from massive ($10^5 - 10^6 M_{\odot}$) and low-mass ($100 M_{\odot}$) BH nuclei. The latter scenario should leave behind a large number of intermediate mass black holes (IMBH, $10^2 - 10^5 M_{\odot}$). The largest published sample of bona-fide IMBH-powered AGN contains 10 objects confirmed in X-ray. Here we present a new sample of 15 bona-fide IMBHs, obtained by confirming the optically selected IMBH candidates by the presence of radiation from the galactic nucleus in the X-ray range, which increases the number of confirmed IMBHs at the centers of galaxies by 2.5 times. In the same way, 99 black holes with masses of $2\cdot10^5 - 10^6 M_{\odot}$ were confirmed. The sources of X-ray data were publicly available catalogs, archives of data, and our own observations on XMM-Newton, Chandra and Swift. The Eddington coefficients for 30% of the objects from both samples turned out to be close to critical, from 0.5 to 1, which is an unusually high fraction. Also for the first time for light-weight SMBH the correlations between the luminosity in the [OIII] emission line or the broad component of the $H\alpha$ line and the luminosity in the X-ray range were plotted.