超大質量ブラックホール質量 ： バルジ質量関係の進化と銀河形成過程

Abstract

In the local universe, the mass of supermassive black hole (SMBH), MBH, is proportional to the bulge mass of the host galaxy, Mbluge. We investigate effects of galaxy formation processes on the evolution of the MBH−Mbulge relation, using a semianalytic model of galaxy and SMBH formation. We find that the mass ratio MBH/Mbulge decreases with cosmic time. In our model, the mass growth processes of SMBH are cold gas accretion during starburst and SMBHs coalescence. Bulges grow from stars formed from cold gas during starbursts. Moreover, bulges also grow from stars in progenitor galaxies. Because cold gas in galaxies depleted by star formation, the amounts of cold gas accreted onto SMBH decrease with time. On the other hand, bulges grow from stars in progenitor galaxies during mergers, even at low redshifts. As a result, one should expect the MBH−Mbulge relation to evolve with cosmic time. Comparing these results with observations in a future, we can put a stringent constraint on galaxy and SMBH formation model.