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Session 16 - QSOs and Active Galaxies.
Oral session, Monday, June 08

[16.04] The Evolution, Luminosity Function and Luminosity Density of Quasars

A. Maloney, V. Petrosian (Stanford University)

We use several quasar samples (LBQS, HBQS, Durham/AAT and EQS) to determine the density and luminosity evolution of quasars. The luminosity evolution can be found through investigation of the correlation between the bivariate distribution of luminosities and redshifts. Here, one assumes a cosmological model to convert the observed fluxes to luminosities. We used matter dominated models with either zero cosmological constant or zero spatial curvature. These correspond to the cases of Ømega_\Lambda = 0 and Ømega_k = 0, where Ømega_\Lambda = \Lambda / 3 H_o^2 and Ømega_k = 1 - Ømega_\Lambda - \rho / \rho_crit. Here, \Lambda is the cosmological constant, H_o is Hubble's constant, \rho is the matter density and \rho_crit is the critical density. We find that luminosity evolution of the form L \propto e^k t(z) does not describe the data at all luminosities, while evolution L \propto (1+z)^k adequately describes the data, with k = 2.6 ([2.52,3.05] one \sigma region) for the Einstein - de Sitter cosmology.

Using this form of luminosity evolution we determine a global luminosity function and the evolution of the co-moving density. The luminosity function and density function are calculated for the two models. We find that pure luminosity evolution, i.e. constant co-moving density, requires either an empty open universe (for the case Ømega_\Lambda = 0) or a matter density of about 15% of critical (for the case Ømega_k = 0).

>From these we can calculate the quasar luminosity density as a function of redshift. The relationship between this and the variation of the star formation rate will be discussed.

Combining these various samples and accounting for varying selection criteria require new methods for determining the correlation and density function of truncated data, which are presented in the display by Petrosian, Maloney and Efron in these proceedings.

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Program listing for Monday