Counts and colours of faint galaxies in the U and R bands

David W. Hogg, Michael A. Pahre, James K. McCarthy, Judith G. Cohen, Roger Blandford, Ian Smail, B. T. Soifer

    Research output: Contribution to journalArticlepeer-review


    Ground-based counts and colours of faint galaxies in the U and R bands in one field at high Galactic latitude are presented. Integrated over flux, a total of 1.2 × 105 source deg-2 are found to U = 25.5 mag and 6.3 × 105 source deg-2 to R = 21 mag, with d log N/dm ∼ 0.5 in the U band and d log N/dm ∼ 0.3 in the R band. Consistent with these number-magnitude curves, sources become bluer with increasing magnitude to median U - R = 0.6 mag at 24 < U < 25 mag and U - R = 1.2 mag at 25 < R < 26 mag. Because the Lyman break redshifts into the U band at z ≈ 3, at least 1.2 × 105 source deg-2 must be at redshifts z < 3. Measurable U-band fluxes of 73 per cent of the 6.3 × 105 source deg-2 suggest that the majority of these also lie at z < 3. These results require an enormous space density of objects in any cosmological model.

    Original languageEnglish (US)
    Pages (from-to)404-410
    Number of pages7
    JournalMonthly Notices of the Royal Astronomical Society
    Issue number2
    StatePublished - 1997


    • Cosmology: observations
    • Galaxies: fundamental parameters
    • Galaxies: photometry
    • Ultraviolet: galaxies

    ASJC Scopus subject areas

    • Astronomy and Astrophysics
    • Space and Planetary Science


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