Astronomical Institute, School of Science, Tohoku University, Aoba, Sendai 980-8578, Japan
can be made in the heart of ultraluminous infrared
galaxies (ULIGs) during the course of mergers between/among gas rich galaxies.
(a) If one progenitor galaxy had a seed SMBH with mass of 
,
this seed SMBH can grow up to 
due to
efficient Bondi-type gas accretion during the course of merger given a gas
density in the circumnuclear region of 
cm
.
(b) Even if there was no progenitor galaxy with a seed SMBH, star clusters with
compact remnants (neutron stars and/or black holes) produced in the circumnuclear
starbursts can merge into the merger center within a dynamical
time scale of 
years to form a SMBH with 
.
Note, however, that the contribution of compact remnants supplied from
hidden star clusters is necessary to lead to the formation of a SMBH.
In conclusion, the ultraluminous infrared galaxies observed in the local universe
can make a SMBH in their center during the course of merger either by
gas accretion onto a seed SMBH or by dynamical relaxation of compact
remnants made in the violent circumnuclear starbursts.
Therefore, it is quite likely that the ULIGs will finally evolve to optically luminous
quasars as suggested by Sanders et al.