Special Astrophysics Seminar

Tracing dusty star formation across redshift and environment with Spitzer/MIPS imaging

Amélie Saintonge

ETH Zürich

Using a large sample of spectroscopically confirmed members in eight massive galaxy clusters at 0.02<z<0.83, we investigate the evolution of the member's mid-infrared (MIR) properties. Combining Spitzer/MIPS and HST imaging, we observe for the first time an increase in the fraction of cluster galaxies with strong, dust-obscured star formation with redshift (i.e. a MIR Butcher-Oemler effect). To test if this increase is driven by environment, we compare our results at z=0.3 to galaxy groups and the field at the same epoch. Galaxies in groups show a measurable excess of MIR sources compared to both the cluster and the field. The fraction of MIR sources in the groups also decreases strongly with increasing local galaxy density, unlike in the cluster where the MIR fraction is uniformly low. Our results highlight the importance of the group environment in transforming the blue, star-forming galaxies in the field to the red early-types that dominate clusters.