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**Session 16 - QSOs and Active Galaxies.**

*Oral session, Monday, June 08*

*Presidio, *

## [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.

If you would like more information about this abstract, please follow the link to bigbang.stanford.edu/~maloney. This link was provided by the author. When you follow it, you will leave the the Web space for this meeting; to return, you should use the Back button on your browser.The author(s) of this abstract have provided an email address for comments about the abstract: maloney@bigbang.stanford.edu

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