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Deep optical galaxy counts with the keck telescope

Jun, 1995
7 pages
Published in:
  • Astrophys.J.Lett. 449 (1995) L105
e-Print:
DOI:
Report number:
  • CALTECH-THEORETICAL-ASTROPHYSICS-GRP-405
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Abstract: (arXiv)
We present faint galaxy counts from deep VRIVRI images obtained with the Keck Telescope. These images reach R∼27R\sim27 in median seeing FWHM ∼0.5\sim 0.5--0.6 arcsec and we detect a integrated galaxy number density of 7×1057\times 10^{5} degree−2^{-2}, equivalent to 3×10103\times 10^{10} 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∼24.5R\sim 24.5. Fainter than R∼24.5R\sim24.5, however, the typical \VR\ color becomes redder again, \VI\ remains constant, and \RI\ becomes yet bluer. These trends are consistent with the VRIVRI count slopes, implying a decrease in the VV slope at the faintest levels, which our data supports. 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\sim 0.2 arcsec for a typical R∼25.5R\sim25.5--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 sub-galactic units.