AAS 205th Meeting, 9-13 January 2005
Session 94 From Protogalaxies to Large Surveys: Tracing the Galaxy Evolution
Poster, Wednesday, January 12, 2005, 9:20am-6:30pm, Exhibit Hall

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[94.08] The Nature of Blue Cores in Spheroids: a Possible Connection with AGN and Star Formation

F. Menanteau, A. Martel (Johns Hopkins University), P. Tozzi (INAF Osservatorio Astronomico di Trieste, Italy), B. Frye (Princeton U.)

We investigate the physical nature of blue cores in early-type galaxies through the first multi-wavelength analysis of a serendipitously discovered field blue-nucleated spheroid in the background of the deep ACS/WFC griz multicolor observations of the cluster Abell 1689. The resolved g-r, r-i and i-z color maps reveal a prominent blue core identifying this galaxy as a ``typical'' case study, exhibiting variations of 0.5-1.0~mag in color between the center and the outer regions, opposite to the expectations of redded metallicity induced gradients in passively evolved ellipticals. From a Magellan-Clay spectrum we secure the galaxy redshift at z=0.624. We find a strong X-ray source coincident with the spheroid galaxy. Spectral features and a high X-ray luminosity indicate the presence of an AGN in the galaxy. However, a comparison of the X-ray luminosity to a sample derived from the Chandra Deep Field South displays Lx to be comparable to Type~I/QSO galaxies while the optical flux is consistent with a normal star-forming galaxy. We conclude that the galaxy's non-thermal component dominates at high-energy wavelengths while we associate the spheroid blue light with the stellar spectrum of normal star-forming galaxies. We argue about a probable association between the presence of blue cores in spheroids and AGN activity.

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© 2004. The American Astronomical Society.