We use images from the Hubble Space Telescope to determine the distances to a dozen objects with low surface brightness recently observed around the bright nearby spiral M101. Only two dwarf galaxies, M101-DwA and M101-Dw9, turn out to be actual satellites of M101 at distances of about 7 Mpc. The other objects are probably members of a distant group around the S0-galaxies NGC 5485/5473. Based on the radial velocities and projected separations of the 9 satellites, we obtain an estimate of (8.5±3.0)×1011M⊙ for the total mass of M101, which is consistent with a ratio 16±6 for the total mass to the stellar mass of the galaxy.
@article{arxiv.1907.12417,
title = {Dwarf Spheroidal Galaxies in the M101 group and behind it},
author = {I. D. Karachentsev and L. N. Makarova},
journal= {arXiv preprint arXiv:1907.12417},
year = {2019}
}