GALEX Studies of Early-type Galaxies: the UV Rising Flux and Residual Star Formation
We report on studies of early-type galaxies using the Galaxy Evolution Explorer (GALEX) satellite. UV radiation in these galaxies can arise either from hot evolved stars, or by ongoing star formation. GALEX observations have shown that earlier suggestions of a correlation between metallicity and UV rising flux in early-type galaxies are not substantiated in larger samples. The UV excess (UVX) may decline with redshift, the increasing importance of low level star formation makes this a very difficult issue to track. It is possible to match GALEX photometry with that from the Sloan Digital Sky Survey, and to construct NUV-optical color-magnitude diagrams. We see clearly a red sequence of quiescent early type galaxies, and a blue sequence of star forming galaxies. Between the two are found AGN in a Green Valley; there is the suggestion that some galaxies in the star forming blue sequence might transform into red sequence galaxies, perhaps by merging or by the quenching of star formation. We consider these possibilities and report on new observations aimed at further studies of the issue.
KeywordsStar Formation Stellar Population Elliptical Galaxy Galaxy Evolution Main Galaxy Sample
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