Title: Black hole accretion in the present-day and early universe 

　　Speaker: Kohei Inayoshi  (KIAA/Peking Univ) 

　　Time: 10:00 am, January 18 (Friday) 

　　Location: Lecture Hall, 3rd floor 

　　Abstract:  

　　Supermassive black holes (SMBHs) are almost ubiquitously harbored at the centers of massive nearby galaxies. The existence of SMBHs is consistent with the number and energetics of bright quasars, which are associated with efficient gas accretion onto SMBHs. Among them, the SMBH population in the early universe (z>6) provides us an important constraint on their formation process and requires rapid growth of their seeds. In the present-day universe, however only a few percent of SMBHs are observed as luminous active galactic nuclei (AGN). A majority of them are nearly quiescent and known as low luminosity AGN. We study the two different accretion domains performing 1D/2D radiation-hydrodynamical simulations. For the higher-rate case, we find the global accretion solutions from outside the Bondi radius at super-Eddington accretion rates (>500 Mdot_Edd), unimpeded by radiation feedback. We apply this result to SMBHs embedded in protogalaxies and discuss their subsequent growth. For the lower-rate case (< Mdot_Edd), the BH accretion is either suppressed due to convective motion (L<10^-7 L_Edd) or led through a cold, geometrically-thin disk (L~10^-3 L_Edd). The transitional behavior of accreting BHs in galactic nuclei naturally explain (1) the reason for the offset between the observed luminosities and theoretical predictions for nearby quiescent SMBHs, and (2) the conditions to fuel gas into the nuclear SMBH.