The Space Density of Galaxies through μB(0) = 25.0 Magnitudes per Inverse Arcsecond Squared

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Abstract
Using the catalog of O'Neil, Bothun, & Schombert, we examine the central surface brightness distribution ([μB(0)]) of galaxies in the 22.0 ≤ μB(0) ≤ 25.0 mag arcsec-2 range. Taking advantage of having a catalog in which each galaxy has a known central surface brightness, scale length, and redshift, we apply a bivariate volume correction to the data and extend the surface brightness distribution function by 1 magnitude, to 25.0 B mag arcsec-2. The result is a flat (slope = 0) space density of galaxies as a function of μB(0) from the Freeman value of 21.65 ± 0.30 to the survey limit of 25.0 mag arcsec-2, more than 10 σ away. The galaxies that comprise this sample have scale lengths and circular velocities similar to L* spiral galaxies (i.e., these are not dwarf galaxies). As such, a significant amount of mass is contained in this population. If the baryonic mass fraction of disk galaxies is independent of μB(0), then our results are consistent with a significant percentage of the baryonic content of the universe being contained in potentials only dimly lit by the embedded galaxy.