Presentation #309.03 in the session AGN, QSOs, and Galactic Evolution.
The origin of supermassive black holes (SMBHs) in galaxy centers remains one of the major unsolved mysteries of modern astrophysics. Were SMBH seeds ‘light’ (<100 MSun), that is the remnants of first stars, or ‘massive’ (>105 MSun) originating from direct collapse of gas clouds in the early Universe? An elusive population of intermediate-mass black holes (IMBHs, 100<MBH<105 MSun) holds an answer to the question of SMBH origin: their very existence would strongly argue for the ‘light seeds’ scenario. In our multi-wavelength observational campaign we confirmed in X-ray 30 active IMBHs in galaxy nuclei, and over a hundred of ‘light-weight’ SMBHs (MBH<106 MSun), re-measured masses of dozens of them using intermediate-resolution optical spectra collected with 6.5-10m class telescopes, and obtained structural properties from Hubble Space Telescope images. We constructed scaling relations between SMBHs and their host galaxies (MBH-σ and MBH-Mbulge) in the light-weight regime suggesting that the bulge and SMBH growth is not as tightly connected as for ‘normal’ more massive SMBHs. We identified a sub-population of Eddington-limited IMBHs/LWSMBHs and also an active binary IMBH with the estimated mass ratio of ~10:1, which proves that both BH growth channel play their roles in the low-mass regime. However, the high abundance of high-Eddington sources (~1/3 of the total sample) suggests that the accretion is the dominant growth mechanism.