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**Session 25 - Galaxies, Clusters of Galaxies and their Evolution.**

*Oral session, Monday, June 08*

*Presidio, *

## [25.02] A Statistical Approach to Quantifying the Evolution of Galaxies

*R. J. Brunner (Caltech)*

Studies of the distribution and evolution of galaxies are of
fundamental importance to modern cosmology; these studies, however,
are hampered by the complexity of the competing effects of spectral
and density evolution. Constructing a spectroscopic sample that is
able to unambiguously disentangle these processes is excessively
prohibitive. We demonstrate the advantages of adopting a statistical
approach to understanding galaxy evolution. First, statistical
distance indicators provide a redshift estimate that together with an
estimate for the redshift error, allows for the calculation of
astrophysically relevant statistics. Second, incorporating spectral
classifications into the data allows the calculation of these tests to
be done for different spectral types. Taken together, this approach
shows a great deal of promise in disentangling the complicated effects
of galaxy evolution.

We extend and apply this alternative approach that relies on
statistical estimates for both distance (z_P) and spectral type to
a deep multi-band dataset that was obtained for this exact
purpose. These statistical estimates are extracted directly from the
photometric data by capitalizing on the inherent relationships between
flux, redshift, and spectral type. The number of galaxies contained in
our sample is sufficient to construct the multivariate angular
correlation function w(\theta, z_P, Type) and the multivariate
luminosity function \Phi(M_AB, z_P, Type) to z_P
\sim 1.0. With these measurements, we can begin to separate out the
competing
effects of density and spectral evolution, and place constraints on
fundamental cosmological quantities.

**Program
listing for Monday**