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

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.