Selection and photometric properties of K+A galaxies

Alejandro D. Quintero, David W. Hogg, Michael R. Blanton, David J. Schlegel, Daniel J. Eisenstein, James E. Gunn, J. Brinkmann, Masataka Fukugita, Karl Glazebrook, Tomotsugu Goto

    Research output: Contribution to journalArticlepeer-review


    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 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.

    Original languageEnglish (US)
    Pages (from-to)190-199
    Number of pages10
    JournalAstrophysical Journal
    Issue number1 I
    StatePublished - Feb 10 2004


    • Galaxies: clusters: general
    • Galaxies: evolution
    • Galaxies: fundamental parameters
    • Galaxies: statistics
    • Galaxies: stellar content
    • Stars: formation

    ASJC Scopus subject areas

    • Astronomy and Astrophysics
    • Space and Planetary Science


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