| This dissertation presents the results of an extensive survey of the Leo I group down to MR ∼ -10 dwarf galaxies. This survey is part of a larger effort to measure the faint-end of the galaxy luminosity function in poor groups to faint limiting magnitudes and surface brightnesses. With the KPNO 0.9m+Mosaic we have surveyed over 7 square degrees in the R-band in the Leo I group at 10 Mpc. We have developed a detection method where we complement the standard, thresholding detection procedure with a matched filter technique optimized to enhance low surface brightness features and detect diffuse dwarf galaxies at a distance of 10 Mpc. Our photometric catalog includes morphological membership selection, guided by a representative sample of follow-up distance measurements from redshifts as well as I-band surface-brightness fluctuations of our most diffuse dwarf candidates. We further quantify our selection effects as a function of total R-band magnitude and central surface brightness with extensive Monte Carlo simulations. The resulting selection function we apply to our final luminosity function, weighting each galaxy by its ability to be detected. We find that at the 90% detection limit, we can detect dwarf galaxies similar to Antlia and Sculptor, and at the 50% detection level, dwarfs similar to Tucana and Leo II.;While our method is optimized to find Local-Group-like dwarfs, we also find unusual objects not seen in Local Group. Among our confirmed group members are large scale-length, LSB dwarfs like those seen in Virgo (Impey et al. 1988, ApJ, 330, 634), as well as unusually compact, higher surface brightness dwarfs similar to the recently identified Ultra-Compact Dwarfs (UCDs) of Fornax (Phillipps et al., 2001, ApJ, 560, 201). These objects do not fall on the Local Group magnitude-surface brightness relation, and suggest that using this relation to guide morphological membership classification selects against such unusual objects. From our sub-sample of follow-up observations, we find that 50% of our mu0 > 22 objects are bona fide members, and 11% of our mu0 ≤ 22 objects are members. The majority of back-ground interlopers in our sample are very nearby ( v < 20, 000 km s-1). This fact, coupled with the unexpected object types we find, indicates we require a massive amount of follow-up observations to determine membership for each galaxy individually.;With our current data, we measure a faint-end slope for our completeness-corrected luminosity function of alpha = -1.02 +/- 0.02. If we further correct this for membership completeness as a function of surface brightness, we find a somewhat steeper slope of alpha = -1.17 +/- 0.04. Both of these slopes are rather flat and generally consistent with those measured in the Local Group and other poor groups. We also confirm an unusual gap in the Leo I luminosity function -19.5 < MR < -16 where there appear to be no intermediate luminosity galaxies in Leo I. The presence of UCDs in Leo I, which fall off the high surface brightness, low luminosity envelope of the Local Group's magnitude-surface brightness relation, might indicate a larger population of previously overlooked compact, exponential-profile dwarfs that could contribute significantly to the faint end of the luminosity function. |
