AGN evolution from galaxy evolution viewpoint - II

In order to relate the observed evolution of the galaxy stellar mass function and the luminosity function of active galactic nuclei (AGN), we explore a co-evolution scenario in which AGN are associated only with the very last phases of the star-forming life of a galaxy. We derive analytically the connections between the parameters of the observed quasar luminosity functions and galaxy mass functions. The $(m_{\mathrm{b}\mathrm{h}}\mathrm{/}{m}_{\ast }{)}_{Qing}$ associated with quenching is given by the ratio of the global black hole accretion rate density (BHARD) and star-formation rate density (SFRD) at the epoch in question. Observational data on the SFRD and BHARD suggests $(m_{\rm bh}/m_{}){Qing} \propto (1+z)^{1.5}$ below redshift 2. This evolution reproduces the observed mass-luminosity plane of SDSS quasars, and also reproduces the local $m{\rm bh}/m_{}$relationinpassivegalaxies\mathrm{.}ThecharacteristicEddingtonratio,$\lambda^$,isderivedfromboththeBHARD\mathrm{/}SFRDratioandtheevolving$L^$oftheAGNpopulation\mathrm{.}Thisincreasesupto$z \sim 2$as$\lambda^* \propto (1+z)^{2.5}$butathigherredshifts,$\lambda^*$ stabilizes at the physically interesting Eddington limit, ${\lambda }^{\ast }\sim 1$. The new model may be thought of as an opposite extreme to our earlier co-evolution scenario in Caplar et al. 2015. The main observable difference between the two co-evolution scenarios, presented here and in Caplar et al. 2015, is in the active fraction of low mass star-forming galaxies. We compare the predictions with the data from deep multi-wavelength surveys and find that the “quenching” scenario developed in the current paper is much to be preferred.