Protoquasars: Physical States and Observable Properties

Abstract

Based on the radiation hydrodynamical model for the black hole (BH) growth, incorporated with the chemical evolution of the early-type host galaxy, we construct the coevolution model of a QSO BH and the 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 AGN-dominant phase (QSO phase) in the timescale of a few 10 8 years. The former phase corresponds to the early stage of growing BH, and can be regarded as a "proto-QSO" phase. It has observable characteristic properties as follows: (1) The width of broad emission line is narrower than that of ordinary QSOs, and it is typically less than 1500km/s. (2) The BH-to-bulge mass ratio, M BH /M bulge , is in the range of 10 −5.3 − 10 −3.9 . (3) Host galaxies are bluer compared to QSO hosts, by about 0.5 magnitude in the colors of (B − V ) at the rest bands and (V − K ) at the observed bands, with assuming galaxy formation redshifts of z f = 3 − 5. (4) The metallicity of gas in galactic nuclei is ∼ 8Z ⊙ , and that of stars weighted by the host luminosity is ∼ 3Z ⊙ . (5) The central massive BH (≃ 10 7 M ⊙ ) is surrounded by a massive dusty disk (> 10 8 M ⊙ ), 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 ULIRGs. In this phase, M BH /M bulge is predicted to be much less than 10 −3 and 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 Lyα emitters.

A Physical Model for the Coevolution of QSOs and Their Spheroidal Hosts

“…One mechanism yielding such proportionality has been discussed by Umemura (2001), Kawakatu & Umemura (2002), and Kawakatu, Umemura, & Mori (2003). In the central regions of protogalaxies the drag due to stellar radiation may result in a loss of angular momentum of the gas at a rate that in a clumpy medium is well approximated by…”

The Coevolution of Supermassive Black Holes and Massive Galaxies at High Redshift

“…Several physical mechanisms can cause a fraction of the gas in galaxies to lose angular momentum and to pile up in the very central regions. A non exhaustive list includes gas drag, dynamical friction of gas plus star clumps, tidal fields, spiral waves, winds and bars, radiation drag (e.g., Norman & Scoville 1988;Shlosman et al 1989Shlosman et al , 1990Shlosman & Noguchi 1993;Hernquist & Mihos 1995;Noguchi 1999;Umemura 2001;Kawakatu & Umemura 2002;Kawakatu et al 2003;Thompson et al 2005;Bournaud et al 2007Bournaud et al , 2011, 2011. In general the presence of clumps, which may be generated by fragmentation of gas already organized in an unstable disc or by inflow of gas and star subclumps, tends to increase the efficiency of such mechanisms.…”

Metallicity Evolution of AGNs

“…As theoretically predicted by Kawakatu et al (2003) and Granato et al (2004), QSOs reach their maximum luminosity at the final stage of their evolutionary history, where their chemical properties are expected to be mature. Therefore we have to carry out deeper QSO surveys than SDSS to search for fainter QSOs that may be in an evolving phase of their chemical evolution (Juarez et al 2009).…”

“…Note that evolving QSOs are accompanied by active star formation, and thus such QSOs may be obscured by dust. As a result, we could be missing evolving QSOs (Kawakatu et al 2003(Kawakatu et al , 2008. Next-generation QSO surveys with deeper limiting magnitudes will identify such evolving QSOs (with low luminosity, probably).…”