# Dwarf Spheroidal Galaxies in the M101 group and behind it

## TL;DR

This study uses Hubble Space Telescope images to identify and analyze dwarf spheroidal galaxies around M101, estimating the galaxy's total mass and satellite membership.

## Contribution

It provides new distance measurements for low surface brightness objects and refines the mass estimate of M101 based on satellite dynamics.

## Key findings

- Only two dwarf galaxies are confirmed as M101 satellites.
- The total mass of M101 is estimated at approximately 8.5 x 10^{11} solar masses.
- The mass-to-stellar mass ratio of M101 is about 16.

## Abstract

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 $(8.5\pm3.0)\times 10^{11} M_{\odot}$ for the total mass of M101, which is consistent with a ratio $16\pm6$ for the total mass to the stellar mass of the galaxy.