ar X iv : a st ro - p h / 97 02 24 1 v 1 2 7 Fe b 19 97 Counts and Colors of Faint Galaxies in the U and R Bands 1
نویسندگان
چکیده
Ground-based counts and colors 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 × 10 sources per square degree are found to U = 25.5 mag and 6.3 × 10 sources per square degree to R = 27 mag, with d logN/dm ∼ 0.5 in the U band and d logN/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× 10 sources per square degree must be at redshifts z < 3. Measurable U -band fluxes of 73 percent of the 6.3 × 10 sources per square degree suggest that the majority of these also lie at z < 3. These results require an enormous space density of objects in any cosmological model. Subject headings: Galaxies: fundamental parameters — Galaxies: photometry — Cosmology: observations — Ultraviolet: galaxies
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