Protoquasars: Physical states and observable properties

Based on the radiation hydrodynamic model for black hole (BH) growth and incorporating the chemical evolution of the early-type host galaxy, we construct the coevolution model of the quasar (QSO) BH and host galaxy. As a result, it is found that after a galactic wind epoch, the luminosity is shifted from the host dominant phase to the active galactic nucleus dominant phase (QSO phase) in the timescale of a few 10(8) yr. The former phase corresponds to the early stage of a growing BH and can be regarded as a proto-QSO phase. It has observable characteristic properties as follows: (1) The broad emission lines are narrower than those of ordinary QSOs and are typically less than 1500 km s(-1). (2) The BH-to-bulge mass ratio, M-BH/M-bulge, is in the range of 10(-5.3) to 10(-3.9). (3) Host galaxies are bluer than QSO hosts, by about 0.5 mag in the colors B-V at the rest bands and V-K at the observed bands, with assumed galaxy formation redshifts of z(f)=3-5. (4) The metallicity of gas in the galactic nuclei is similar to8 Z(circle dot) and that of stars weighted by the host luminosity is similar to3 Z(circle dot). (5) The central massive BH (similar or equal to10(7) M-circle dot) is surrounded by a massive dusty disk (>10(8) M-circle dot), which may obscure the nucleus in the edge-on view and make a type 2 nucleus. By comparing these predictions with recent observations, radio galaxies are a possible candidate for proto-QSOs. Also, it is anticipated that the proto-QSO phase is preceded by an optically thick phase, which may correspond to ultra-luminous infrared galaxies (ULIRGs). In this phase, M-BH/M-bulge is predicted to be much less than 10(-3) and to grow with metallicity. Moreover, as precursors of ULIRGs, optically thin star-forming galaxies are predicted. These may be in the assembly phase of Lyman break galaxies (LBGs) or Lyalpha emitters.