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D. C. Martin (Caltech), GALEX Science Team
We propose a simple technique for constraining the mass flux density evolving from the blue sequence to the red sequence. We use the volume corrected number density in the extinction-corrected GALEX UV-optical color magnitude distribution, the stellar age indexes H-delta-A and Dn(4000), and a simple prescription for spectral evolution using a quenched/fading star formation history. We exploit the excellent separation of red and blue sequences in the GALEX-SDSS NUV-r band volume-corrected color magnitude diagram. The final value we measure compares favorably with estimates of the average mass flux that we make based on the DEEPII and COMBO-17 surveys. We explore the nature of the galaxies in the transition zone with particular attention to the frequency and impact of AGNs. The AGN fraction peaks in the transition zone. We find circumstantial evidence that the quench rates are higher in higher luminosity AGNs.
GALEX is a NASA Small Explorer mission with contributions from France and South Korea.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.