Deep Optical Galaxy Counts with the Keck Telescope

We present faint galaxy counts from deep $VRI$ images obtained with the KeckTelescope. These images reach $R\sim27$ in median seeing FWHM $\sim 0.5$--0.6arcsec and we detect a integrated galaxy number density of $7\times 10^{5}$degree$^{-2}$, equivalent to $3\times 10^{10}$ galaxies in the observableUniverse. In addition we present median galaxy colors as a function ofmagnitude; bluing trends are visible in all colors to $R\sim 24.5$. Fainterthan $R\sim24.5$, however, the typical \VR\ color becomes redder again, \VI\remains constant, and \RI\ becomes yet bluer. These trends are consistent withthe $VRI$ count slopes, implying a decrease in the $V$ slope at the faintestlevels, which our data supports. Taking advantage of our good seeing we alsopresent median half-light radii for faint galaxies, these show a steady declineat fainter magnitudes, leading to an intrinsic half-light radius of $\sim 0.2$arcsec for a typical $R\sim25.5$--26 galaxy. Irrespective of the redshiftdistribution, the extremely high galaxy surface densities and their smallintrinsic sizes are consistent with a scenario in which the majority of thevery faint field population are dwarf galaxies or sub-galactic units.Comment: 7 pages plus four figures in a self-unpacking uuencoded tar file. Accepted for publication, ApJ Letter