Alejandro D. Quintero et al. 2004 ApJ 602 190 doi:10.1086/380601
Alejandro D. Quintero1, David W. Hogg1,2, Michael R. Blanton1, David J. Schlegel3, Daniel J. Eisenstein4, James E. Gunn3, J. Brinkmann5, Masataka Fukugita6, Karl Glazebrook7 and Tomotsugu Goto6,8
Show affiliationsTwo different simple measurements of galaxy star formation rate with different timescales are compared empirically on 156,395 fiber spectra of galaxies with r < 17.77 mag taken from the Sloan Digital Sky Survey in the redshift range 0.05 < z < 0.20: a ratio A/K found by fitting a linear sum of an average old stellar population spectrum (K) and average A star spectrum (A) to the galaxy spectrum, and the equivalent width (EW) of the Hα 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 A/K relative to Hα EW. These "K+A" (or "E+A") galaxies must have dramatically decreased their star formation rates over the last ~1 Gyr. The K+A luminosity distribution is similar to that of the total galaxy population. The K+A population appears to be bulge-dominated, but bluer and with 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 ~10-4 h3 Mpc-3 Gyr-1 at redshift z ~ 0.1. These events are taking place in the field; the K+A galaxies found in this study do not primarily lie in the high-density environments or clusters typical of bulge-dominated populations.
galaxies: clusters: general; galaxies: evolution; galaxies: fundamental parameters; galaxies: statistics; galaxies: stellar content; stars: formation
Issue 1 (2004 February 10)
Received 2003 June 10, accepted for publication 2003 October 3
Alejandro D. Quintero et al. 2004 ApJ 602 190
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