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B. Mobasher, T.H. Puzia, P. Goudfrooij (STScI)
Due to its short lifetime the K+A phenomenon, characterized by strong Balmer absorption with no significant emission lines, marks an important stage during the evolution of spheroidal galaxies. We have developed an efficient photometric technique for identifying K+A galaxy candidates using a combination of photometric redshifts and optical/near-infrared colors. Applying our technique to the GOODS HST/ACS and VLT/ISAAC data we have selected a complete and homogeneous sample of field K+A galaxy candidates and investigate the dependence of their luminosity and color evolution on redshift and galaxy mass. We find evidence for an increasing starburst mass fraction in K+A candidates at higher redshifts, which we interpret in terms of massive field galaxies experiencing more massive/intense starbursts preceding their K+A phase at higher redshifts. Moreover, we find indications for a systematically larger K+A fraction among sub-L\ast/2 early-type galaxies compared to their brighter counterparts. The total K+A fraction among the field early-type galaxies increases with redshift, irrespective of galaxy luminosity. Our results rule are most consistent with galaxy formation scenarios in which massive early-type galaxies are assembled earlier than their low-mass counterparts.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.