Deep galaxy counts in the K band with the Keck telescope

S. Djorgovski, B. T. Soifer, M. A. Pahre, J. E. Larkin, J. D. Smith, G. Neugebauer, I. Smail, K. Matthews, D. W. Hogg, R. D. Blandford, J. Cohen, W. Harrison, J. Nelson

    Research output: Contribution to journalArticlepeer-review


    We present deep galaxy counts in the K (λ2.2 μm) band, obtained at the W. M. Keck 10 m telescope. The data reach limiting magnitudes K ∼ 24 mag, about 5 times deeper than the deepest published K-band images to date. The counts are performed in three small (∼1′), widely separated high-latitude fields. Extensive Monte Carlo tests were used to derive the completeness corrections and minimize photometric biases. The counts continue to rise, with no sign of a turnover, down to the limits of our data, with the logarithmic slope of d log N/dm = 0.315 ± 0.02 between K = 20 and 24 mag. This implies a cumulative surface density of ∼5 × 105 galaxies deg-2, or ∼2 × 1010 over the entire sky, down to K = 24 mag. Our counts are in good agreement with, although slightly lower than, those from the Hawaii Deep Survey by Cowie and collaborators; the discrepancies may be due to the small differences in the aperture corrections. The observed field-to-field variations are as expected from the Poissonian noise and galaxy clustering as described by the angular two-point correlation function for faint galaxies. We compare our counts with some of the available theoretical predictions. The data do not require models with a high value of Ω0, but can be well fitted by models with no (or little) evolution, and cosmologies with a low value Ω0. Given the uncertainties in the models, it may be premature to put useful constrains on the value of Ω0 from the counts alone. Optical-to-IR colors are computed, using CCD data obtained previously at Palomar. We find a few red galaxies with (r - K) ≳ 5 mag, or (i - K) ≳ 5 mag; these may be ellipticals at z ∼ 1. While the redshift distribution of galaxies in our counts is still unknown, the flux limits reached would allow us to detect unobscured L* galaxies out to substantial redshifts (z > 3?).

    Original languageEnglish (US)
    Pages (from-to)L13-L16
    JournalAstrophysical Journal
    Issue number1 PART 2
    StatePublished - Jan 1 1995


    • Cosmology: observations
    • Galaxies: evolution
    • Galaxies: photometry

    ASJC Scopus subject areas

    • Astronomy and Astrophysics
    • Space and Planetary Science


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