Search for Intermediate-mass Black Holes at Low Redshift with Intra-night Variability

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 a 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 (BH)) is less than 10(6) M (circle dot). To constrain the nature of these candidates, we analyzed X-ray properties and performed an intra-night variability monitoring campaign 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 (BH) determination such as reverberation mapping campaigns.