Measuring the Total Ultraviolet Light from Galaxy Clusters at z=0.5-1.6: The Balance of Obscured and Unobscured Star-Formation

Abstract

Combined observations from UV to IR wavelengths are necessary to fully account for the star-formation in galaxy clusters. Low mass log M/M * < 10 galaxies are typically not individualy detected, particularly at higher redshifts (z ∼ 1 − 2) where galaxy clusters are undergoing rapid transitions from hosting mostly active, dust-obscured starforming galaxies to quiescent, passive galaxies. To account for these undetected galaxies, we measure the total light emerging from GALEX/N U V stacks of galaxy clusters between z = 0.5 − 1.6. Combined with existing measurements from Spitzer, WISE, and Herschel, we study the average UV through far-infrared (IR) spectral energy distribution (SED) of clusters. From the SEDs, we measure the total stellar mass and amount of dust-obscured and unobscured star-formation arising from all cluster-member galaxies, including the low mass population. The relative fraction of unobscured star-formation we observe in the UV is consistent with what is observed in field galaxies. There is tentative evidence for lower than expected unobscured star-formation at z ∼ 0.5, which may arise from rapid redshift evolution in the low mass quenching efficiency in clusters reported by other studies. Finally, the GALEX data places strong constraints on derived stellar-to-halo mass ratios at z < 1 which anti-correlate with the total halo mass, consistent with trends found from local X-ray observations of clusters. The data exhibit steeper slopes than implementations of the cluster star-formation efficiency in semi-analytical models.