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Impacts of a Supersonic Shock Front on Star Formation in the Bullet Cluster

We use the Bullet Cluster (1E0657-56) to investigate the extent to which star formation in cluster galaxies is influenced by ram pressure from supersonic gas (Mach 3) during a cluster merger. While the effects of ram pressure have been studied for individual galaxies infalling into galaxy clusters, this system provides a unique opportunity to investigate the impact of dramatic merger events on the cluster galaxy population. In this analysis we use {\it Spitzer} IRAC data to study star formation. At the redshift of the cluster the 6.2 $μ$m PAH feature is redshifted into the 8 $μ$m band, enabling use of the m$_{4.5}$-m$_{8}$ color as a proxy for specific star formation rate. We find that the color distribution on the two sides of the shock differ by less than 2$σ$, and conclude that ram pressure from the shock front has no dramatic, immediate impact on the star formation of cluster galaxies in the Bullet Cluster.