Reconstructing the Cosmic Evolution of Quasars from the Age Distribution   of Local Early-Type Galaxies
  We use the spectra of 22,000 nearby early-type galaxies from the Sloan Digital Sky Survey (SDSS) to determine the age distribution of these galaxies as a function of their velocity dispersion sigma_v in the range 100 km/s < sigma_v < 280 km/s. We then combine the inferred age-distributions with the local abundance of spheroids, including early-type galaxies and late-type bulges, to predict the evolution of the quasar luminosity function (LF) in the redshift range 0<z<6. We make the following simple assumptions: (i) the formation of stars in each galaxy, at the epoch identified with the mean mass-weighted stellar age, is accompanied by the prompt assembly of the nuclear supermassive black hole (SMBH); (ii) the mass of the SMBH obeys the M_bh-sigma_v correlation observed in nearby galaxies; (iii) the SMBH radiates at a fraction f_Edd of the Eddington limit for a fixed duration t_Q, and is identified as a luminous quasar during this epoch, (iv) the intrinsic dispersions in the Eddington ratio and the M_bh-sigma_v relation produce a combined scatter of Delta(log L_Q) around the mean logarithmic quasar luminosity <log L_Q> at fixed sigma_v. These assumptions require that the SMBH remnants of quasars with bolometric luminosity below L_bol=10^{12.5} f_Edd L_sun reside predominantly in bulges of late type galaxies. We find that evolution of the observed quasar LF can be fit over the entire redshift range in this simple model, 0<z<6 with the choices of Delta(log L_Q)=0.6-0.9, t_Q= (6-8)x10^7 yr, and <f_Edd>=0.3-0.5. We find no evidence that any of the model parameters evolves with redshift, supporting the strong connection between the formation of stars and nuclear SMBHs in spheroids. 
Zoltan Haiman (Columbia), Raul Jimenez (UPenn), Mariangela Bernardi   (UPenn)