SIMBAD references

We present panoramic Spitzer MIPS 24 µm observations, covering ∼9x9 Mpc² (25'x25') fields around two massive clusters, Cl 0024+16 and MS 0451-03, at z=0.39 and z=0.55, respectively, reaching a 5 σ flux limit of ∼200 µJy. Our observations cover a very wide range of environments within these clusters, from high-density regions around the cores out to the turnaround radius. Cross-correlating the mid-infrared catalogs with deep optical and near-infrared imaging of these fields, we investigate the optical/near-infrared colors of the mid-infrared sources. We find excesses of mid-infrared sources with the optical/near-infrared colors expected of cluster members in the two clusters and test this selection using spectroscopically confirmed 24 µm members. The much more significant excess is associated with Cl 0024+16, whereas MS 0451-03 has comparatively few mid-infrared sources. The mid-infrared galaxy population in Cl 0024+16 appears to be associated with dusty star-forming galaxies (typically redder than the general cluster population by up to A_V∼1-2 mag) rather than emission from dusty tori around active galactic nuclei in early-type hosts. We compare the star formation rates derived from the total infrared (8-1000 µm) luminosities for the mid-infrared sources in Cl 0024+16 with those estimated from a published Hα survey, finding rates ≳5 times those found from Hα, indicating significant obscured activity in the cluster population. Compared to previous mid-infrared surveys of clusters from z∼0-0.5, we find evidence for strong evolution of the level of dust-obscured star formation in dense environments to z=0.5, analogous to the rise in the fraction of optically selected star-forming galaxies seen in clusters and the field out to similar redshifts. However, there are clearly significant cluster-to-cluster variations in the populations of mid-infrared sources, probably reflecting differences in the intracluster media and recent dynamical evolution of these systems.