An Observational Limit on the Dwarf Galaxy Population of the Local Group

We present the results of an all-sky, deep optical survey for faint LocalGroup dwarf galaxies. Candidate objects were selected from the second Palomarsurvey (POSS-II) and ESO/SRC survey plates and follow-up observations performedto determine whether they were indeed overlooked members of the Local Group.Only two galaxies (Antlia and Cetus) were discovered this way out of 206candidates. Based on internal and external comparisons, we estimate that ourvisual survey is more than 77% complete for objects larger than one arc minutein size and with a surface brightness greater than an extremely faint limitover the 72% of the sky not obstructed by the Milky Way. Our limit ofsensitivity cannot be calculated exactly, but is certainly fainter than 25magnitudes per square arc second in R, probably 25.5 and possibly approaching26. We conclude that there are at most one or two Local Group dwarf galaxiesfitting our observational criteria still undiscovered in the clear part of thesky, and a roughly a dozen hidden behind the Milky Way. Our work places the"missing satellite problem" on a firm quantitative observational basis. Wepresent detailed data on all our candidates, including surface brightnessmeasurements.Comment: 58 pages in AJ manuscript format; some figures at slightly reduced quality; accepted by the Astronomical Journa