MOND and the Seven Dwarfs

Gerhard has recently analyzed the data on seven dwarf spheroidal galaxies and concluded that these disagree with the predictions of MOND. We contend that this conclusion was premature; with new data for three of the dwarf galaxies, the observations of all dwarfs are in compelling agreement with the predictions of MOND. In most cases, Gerhard found MOND M/L values that fall around a few solar units, as expected if MOND is a valid alternative to dark matter while the Newtonian M/L values are in the range of about 10 to 100 solar units. However, some of Gerhard's MOND M/L values were still outside the range of "reasonable" stellar values, say between 1 and 3 (two were too high about 1(#and one too low). This, we say, was easily attributable to uncertainties in the data and in the assumptions that underlie the analysis. There are now new, much improved determinations of the velocity dispersions for three of the dwarfs, in particular for the two dwarfs for which Gerhard found high MOND M/L values: the preliminary, high value for Leo II has been superseded by a much smaller value (by a factor of 2) that gives a MOND M/L value of about 1.5 (instead of about 9). There is also a new determination of the velocity dispersion of Ursa Minor that brings down the MOND M/L value considerably. The one small MOND M/L value that Gerhard found is also shown to be quite benign. In fact, within just the quoted errors on the velocity dispersions and the luminosities, the MOND M/L values for all seven dwarfs are perfectly consistent with stellar values, with no need for dark matter.