## Астрофизика высоких энергий сегодня и завтра

### Игорь Чилингарян

##### Смитсонианская Астрофизическая Обсерватория

Популяция черных дыр средних масс, отождествленных как активные галактические ядра низкой светимости
Igor Chilingarian, Ivan Katkov, Ivan Zolotukhin, Kirill Grishin, Yuri Beletsky, Konstantina Boutsia, David Osip

Nearly every massive galaxy harbors a supermassive black hole (SMBH) in its nucleus. SMBH masses are millions to billions $M_{\odot}$, and they correlate with properties of spheroids of their host galaxies. While the SMBH growth channels, mergers and gas accretion, are well established, their origin remains uncertain: they could have either emerged from massive seeds'' ($10^5-10^6 M_{\odot}$) formed by direct collapse of gas clouds in the early Universe or from smaller ($100 M_{\odot}$) black holes, end-products of first stars. The latter channel would leave behind numerous intermediate mass black holes (IMBHs, $10^2-10^5 M_{\odot}$). Although many IMBH candidates have been identified, none is accepted as definitive, thus their very existence is still debated. Using data mining in wide-field sky surveys and applying dedicated analysis to archival and follow-up optical spectra, we identified a sample of 305 IMBH candidates having masses $3\times10^4<M_{\mathrm{BH}}<2\times10^5 M_{\odot}$, which reside in galaxy centers and are accreting gas that creates characteristic signatures of a type~I active galactic nucleus (AGN). We confirmed the AGN nature of ten sources (including five previously known objects which validate our method) by detecting the X-ray emission from their accretion discs, thus defining the first \emph{bona fide} sample of IMBHs in galactic nuclei. The very existence of nuclear IMBHs supports the stellar mass seed scenario of the massive black hole formation.