Using the catalog of O ’ Neil , Bothun , & Schombert ( 1999 ) , we examine the central surface brightness distribution ( \phi ( \mu _ { B } ( 0 ) ) ) of galaxies in the 22.0 \leq { \mu _ { B } } ( 0 ) \leq 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 bi-variate volume correction to the data and extend the surface brightness distribution function by one magnitude , to 25.0 B mag arcsec ^ { -2 } .
The result is a flat ( slope = 0 ) surface brightness distribution function from the Freeman value of 21.65 \pm 0.30 to the survey limit of 25.0 mag arcsec ^ { -2 } , more than 11 \sigma away .
This indicates that a significant percentage of the baryonic content of the universe is likely in potentials only dimly lit by the embedded galaxy .