paper

Selection and photometric properties of K+A galaxies

arXiv:astro-ph/0307074 · doi:10.1086/380601

Abstract

Two different simple measurements of galaxy star formation rate with different timescales are compared empirically on fiber spectra of galaxies with mag taken from the Sloan Digital Sky Survey in the redshift range : a ratio $\Aamp / \Kamp$ found by fitting a linear sum of an average old stellar poplulation spectrum (\Kamp) and average A-star spectrum (\Aamp) to the galaxy spectrum, and the equivalent width (EW) of the $\Halpha$ emission line. The two measures are strongly correlated, but there is a small clearly separated population of outliers from the median correlation that display excess $\Aamp /\Kamp$ relative to \Halpha EW. These ``K+A'' (or ``E+A'') galaxies must have dramatically decreased their star-formation rates over the last Gyr. The K+A luminosity distribution is very similar to that of the total galaxy population. The K+A population appears to be bulge-dominated, but bluer and higher surface-brightness than normal bulge-dominated galaxies; it appears that K+A galaxies will fade with time into normal bulge-dominated galaxies. The inferred rate density for K+A galaxy formation is at redshift . These events are taking place in the field; K+A galaxies don't primarily lie in the high-density environments or clusters typical of bulge-dominated populations.

arXiv commentsubmitted to ApJ

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