The Faint End of the Luminosity Function and Low Surface Brightness
  Galaxies
  SHELS (Smithsonian Hectospec Lensing Survey) is a dense redshift survey
covering a 4 square degree region to a limiting R = 20.6. In the construction
of the galaxy catalog and in the acquisition of spectroscopic targets, we paid
careful attention to the survey completeness for lower surface brightness dwarf
galaxies. Thus, although the survey covers a small area, it is a robust basis
for computation of the slope of the faint end of the galaxy luminosity function
to a limiting M_R = -13.3 + 5logh. We calculate the faint end slope in the
R-band for the subset of SHELS galaxies with redshif ts in the range 0.02 <= z
< 0.1, SHELS_{0.1}. This sample contains 532 galaxies with R< 20.6 and with a
median surface brightness within the half light radius of SB_{50,R} = 21.82 mag
arcsec^{-2}. We used this sample to make one of the few direct measurements of
the dependence of the faint end of the galaxy luminosity function on surface
brightness. For the sample as a whole the faint end slope, alpha = -1.31 +/-
0.04, is consistent with both the Blanton et al. (2005b) analysis of the SDSS
and the Liu et al. (2008) analysis of the COSMOS field. This consistency is
impressive given the very different approaches of th ese three surveys. A
magnitude limited sample of 135 galaxies with optical spectroscopic reds hifts
with mean half-light surface brightness, SB_{50,R} >= 22.5 mag arcsec^{-2} is
unique to SHELS_{0.1}. The faint end slope is alpha_{22.5} = -1.52+/- 0.16.
SHELS_{0.1} shows that lower surface brightness objects dominate the faint end
slope of the l uminosity function in the field, underscoring the importance of
surface brightness limits in evaluating measurements of the faint end slope and
its evolution.
