Intermediate-mass black holes (IMBHs; $M_{ BH} <2*10^{ 5} M_{ \odot}$) in galaxy centers are cruciel for painting a coherent picture of the formation and growth of supermassive black holes (SMBHs). Using Big Data analysis, we identified 305 IMBH candidates for IMBH and 1623 candidates of `light-weight' SMBHs ($2 * 10^{ 5} M_{ odot} < M_{ BH} <10^{ 6} M_{ \odot}$). For 35 host galaxies from this combined sample with the X-ray-confirmed active galactic nuclei (AGN) we collected and analyzed optical spectroscopic observations. These data show that bulge stellar velocity dispersions ($\sigma_*$) lie in the range of 24$\dots$118~km/s and do not follow the correlation with $M_{ BH}$ established by larger SMBHs indicating that in the $10^{ 5}-10^{ 6} M_{ \odot}$ range the accretion is the prevailing BH growth channel.
Categories: astro-ph.GA astro-ph.HE