Spectroscopic Confirmation of a Large AGN Population in Clusters of Galaxies

Martini, P., Kelson, D.D., Kim, E., Mulchaey, J.S., and Athey, A.A. 2006, ApJ, 644, 116

We have completed a spectroscopic survey of X-ray point sources in eight low-redshift clusters of galaxies (0.0510^{41}) ~ 5%. We stress that additional, lower-luminosity AGN are expected to be present in the M_R < -20 mag cluster members. Our data unambiguously demonstrate that cluster galaxies host AGN more frequently than previously expected. Only four of these galaxies have obvious visible-wavelength AGN signatures, even though their X-ray luminosities are too high for their X-ray emission to be due to populations of low-mass X-ray binaries or hot, gaseous halos. We attribute the significant difference in visible and X-ray AGN identification to dilution of low-luminosity AGN spectral signatures by host galaxy starlight and/or obscuration of accretion onto the central, supermassive black hole.

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