Color separation of galaxy types in the Sloan Digital Sky Survey imaging data

Iskra Strateva, Željko Ivezić, Gillian R. Knapp, Vijay K. Narayanan, Michael A. Strauss, James E. Gunn, Robert H. Lupton, David Schlegel, Neta A. Bahcall, Jon Brinkmann, Robert J. Brunner, Tamás Budavári, István Csabai, Francisco Javier Castander, Mamoru Doi, Masataka Fukugita, Zsuzsanna Gyory, Masaru Hamabe, Greg Hennessy, Takashi IchikawaPeter Z. Kunszt, Don Q. Lamb, Timothy A. McKay, Sadanori Okamura, Judith Racusin, Maki Sekiguchi, Donald P. Schneider, Kazuhiro Shimasaku, Donald York

Research output: Contribution to journalArticlepeer-review


We study the optical colors of 147,920 galaxies brighter than g* = 21, observed in five bands by the Sloan Digital Sky Survey (SDSS) over ∼100 deg2 of high Galactic latitude sky along the celestial equator. The distribution of galaxies in the g*-r* versus u*-g* color-color diagram is strongly bimodal, with an optimal color separator of u*-r* = 2.22. We use visual morphology and spectral classification of subsamples of 287 and 500 galaxies, respectively, to show that the two peaks correspond roughly to early- (E, S0, and Sa) and late-type (Sb, Sc, and Irr) galaxies, as expected from their different stellar populations. We also find that the colors of galaxies are correlated with their radial profiles, as measured by the concentration index and by the likelihoods of exponential and de Vaucouleurs' profile fits. While it is well known that late-type galaxies are bluer than early-type galaxies, this is the first detection of a local minimum in their color distribution. In all SDSS bands, the counts versus apparent magnitude relations for the two color types are significantly different and demonstrate that the fraction of blue galaxies increases toward the faint end.

Original languageEnglish (US)
Pages (from-to)1861-1874
Number of pages14
JournalAstronomical Journal
Issue number4
StatePublished - Oct 2001
Externally publishedYes


  • Galaxies: fundamental parameters

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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