2003/07/03 by Alejandro D. Quintero, David W. Hogg, Michael R. Blanton +8 · 7 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Galaxies: Formation, Evolution, Phenomena #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/380601
published as Astrophys.J.602:190-199,2004 · submitted to ApJ
arxiv created 2003/07/03 · openalex publication_date 2004/02/10 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/01
Two 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 h 3 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.