Dennis Zaritsky

Lick Observatory

Scanning the Sky for Galaxy Clusters


Galaxy clusters provide a key constraint on cosmological models of structure
formation. After briefly discussing how clusters can be used in such an endeavor,
I will focus on our ongoing drift-scan survey of 140 sq. degrees of the sky.
We identify clusters in a unique manner by searching for surface brightness
enhancements rather than as an excess of detected galaxies. This technique
enables us to go to relatively high redshifts (detecting several hundred clusters from
~ 0.3 to 1.1 using images from a 40-inch telescope with exposure times of 3 
minutes!) and provides an independent test on cluster finding algorithms. I 
will discuss the cluster selection algorithm, present results from follow-up observations, 
describe how we estimate redshifts, and how we are attempting to estimate the 
cluster mass. Finally, I will present preliminary results on the cluster distribution 
and implications for cosmological models.