Radio AGNs in Cluster Galaxies

Naveen Reddy

06 January 2003

IRAS FIR versus mid-IR color-color diagram for a sample of galaxies in the most massive and dynamically-relaxed nearby (<100 Mpc) clusters. Large open and filled circles denote early- and late-type galaxies, respectively. Sources showing 5 times excess radio emission than that expected from the linear radio-FIR correlation (i.e., "radio-excess" sources) are shown with large open and filled squares for early- and late-type galaxies, respectively. The small points represent galaxies within 94 Mpc in the IRAS 2 Jy Sample of Yun, Reddy, and Condon (YRC; 2001). A large fraction of radio-excess sources are early-type galaxies, and all show warmer mid-IR colors than the normal population by ~0.5 dex, consistent with a model in which circumnuclear dust is heated by an AGN. Comparison with the YRC field sample reveals that the radio-excess fraction and luminous AGN contribution to the radio luminosity density in clusters is 11 times greater than that of the field.

Collaborator: Min Yun