2017MNRAS.468.4048Z

Modified gravity (MOG) and non-local gravity (NLG) are two alternative theories to general relativity. They are able to explain the rotation curves of spiral galaxies and clusters of galaxies without including dark matter. In the weak-field approximation, these two theories have similar forms, with an effective gravitational potential that has two components: (i) Newtonian gravity with the gravitational constant enhanced by a factor (1 + α) and (ii) a Yukawa-type potential that produces a repulsive force with length-scale 1/µ. In this work, we compare the rotation curves of dwarf galaxies in the LITTLE THINGS catalogue with predictions of MOG, NLG and modified Newtonian dynamics (MOND). We find that the universal parameters of the MOG and NLG theories can fit the rotation curves of dwarf galaxies only at the expense of systematically high stellar mass-to-light ratios at 3.6 µm. For instance, in MOG, half of the galaxies have best-fitting stellar M/L ratios larger than 10. It seems that such a big stellar mass-to-light ratio is in contradiction with observations of nearby stars in the Milky Way and with stellar population synthesis models; however, the stellar mass-to-light ratio of dwarf galaxies is not observed directly by the astrophysical methods. Future observations of binary stars in the dwarf galaxies will identify M/L and consequently examine different modified gravity models.