Star Formation and Substructure in Galaxy Clusters
  We investigate the relationship between star formation (SF) and substructure
in a sample of 107 nearby galaxy clusters using data from the Sloan Digital Sky
Survey (SDSS). Several past studies of individual galaxy clusters have
suggested that cluster mergers enhance cluster SF, while others find no such
relationship. The SF fraction in multi-component clusters (0.228 +/- 0.007) is
higher than that in single-component clusters (0.175 +/- 0.016) for galaxies
with M^0.1_r < -20.5. In both single- and multi-component clusters, the
fraction of star-forming galaxies increases with clustercentric distance and
decreases with local galaxy number density, and multi-component clusters show a
higher SF fraction than single-component clusters at almost all clustercentric
distances and local densities. Comparing the SF fraction in individual clusters
to several statistical measures of substructure, we find weak, but in most
cases significant at greater than 2 sigma, correlations between substructure
and SF fraction. These results could indicate that cluster mergers may cause
weak but significant SF enhancement in clusters, or unrelaxed clusters exhibit
slightly stronger SF due to their less evolved states relative to relaxed
clusters.
