Deep optical galaxy counts with the keck telescope

Ian Smail, David W. Hogg, Lin Yan, Judith G. Cohen

    Research output: Contribution to journalArticlepeer-review


    We present faint galaxy counts from deep VRI images obtained with the Keck Telescope. These images reach R i 27 in median seeing FWHM - 0"5-0"6, and we detect a integrated galaxy number density of 7 X 105 deg-2, equivalent to 3 X 1010 galaxies in the observable universe. In addition we present median galaxy colors as a function of magnitude; bluing trends are visible in all colors to R - 24.5. Fainter than R - 24.5, however, the typical V — R color becomes redder again, V — I remains constant, and R — I becomes yet bluer. These trends are consistent with the VRI count slopes, implying a decrease in the V slope at the faintest levels, which our data support. Taking advantage of our good seeing we also present median half-light radii for faint galaxies; these show a steady decline at fainter magnitudes, leading to an intrinsic half-light radius of -0.'2 for a typical R - 26 galaxy. Irrespective of the redshift distribution, the extremely high galaxy surface densities and their small intrinsic sizes are consistent with a scenario in which the majority of the very faint field population are dwarf galaxies or subgalactic units.

    Original languageEnglish (US)
    Pages (from-to)L105-L108
    JournalAstrophysical Journal
    Issue number2
    StatePublished - Aug 20 1995


    • Cosmology: Observations
    • Galaxies: Evolution
    • Galaxies: Photometry

    ASJC Scopus subject areas

    • Astronomy and Astrophysics
    • Space and Planetary Science


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