Search of Intermediate Mass Black Holes at Low Redshift with Intra-night Variability

TL;DR

This study identifies intermediate-mass black hole candidates through spectral analysis and intra-night optical variability, highlighting 11 promising targets for future detailed mass measurements.

Contribution

It introduces a new method combining spectral features and intra-night variability to select and confirm IMBH candidates from SDSS data.

Findings

11 targets show intra-night variability indicating IMBH activity

Sample includes 25 IMBH candidates with M_BH < 10^6 M_sun

Candidates are suitable for reverberation mapping follow-up

Abstract

We present a sample of intermediate-mass black hole (IMBH) candidates based on the detection of a broad H$\alpha$ emission line and variability, which are selected from the Sloan Digital Sky Survey Data Release 7. By performing spectral decomposition of emission lines as well as visual inspection, we initially identified 131 targets with a broad H$\alpha$ line among a large sample of emission-line galaxies. We further selected 25 IMBH candidates, whose estimated black hole mass (M$_{\rm BH}$) is less than $10^6 \rm M_{\odot}$. To constrain the nature of these candidates, we analyzed X-ray properties and performed an intra-night variability monitoring with optical telescopes. Based on the optical variability analysis, we report a sample of 11 targets with detected intra-night variability as the best IMBH candidates, which are suitable for follow-up observations for accurate M$_{\rm BH}$ determination such as reverberation mapping campaigns.