# Using Surface Brightness Fluctuations to Study Nearby Satellite Galaxy Systems: the Complete Satellite System of M101

## TL;DR

This study employs surface brightness fluctuation measurements to determine the distances of low surface brightness dwarf galaxies around M101, effectively identifying true satellites and demonstrating the method's utility with archival data.

## Contribution

It introduces the use of SBF measurements on archival CFHTLS data to confirm satellite memberships of LSB dwarfs around M101, advancing satellite system studies.

## Key findings

- Confirmed two satellites at M101's distance.
- Ruled out 29 candidates as background galaxies.
- Suggested the satellite system is complete down to stellar masses of ~5×10^5 M_sun.

## Abstract

We use surface brightness fluctuation (SBF) measurements to constrain the distance to low surface brightness (LSB) dwarfs in the vicinity of M101. Recent work has discovered many LSB candidate satellite companions of M101. However, without accurate distances, it is problematic to identify these dwarfs as physical satellites of M101. We use CFHT Legacy Survey (CFHTLS) data to measure the SBF signal for 43 candidate dwarfs. The data is deep enough that we constrain 29 of these to be unassociated background galaxies by their lack of SBF. We measure high S/N SBF signals for two of the candidate dwarfs, which are consistent with being at the distance of M101. The remaining candidates are too LSB and/or small for their distances to be constrained. Still, by comparison with Local Group dwarfs, we argue that the M101 satellite system is likely now complete down to stellar masses of $\sim5\times10^5$ M$_\odot$. We also provide a new SBF distance for the nearby dwarf UGC 8882, which suggests that it is significantly outside of the virial radius of M101 and is thus not a physical satellite. By constraining the distances to a majority of the candidates using only archival data, our work demonstrates the usefulness of SBF for nearby LSB galaxies and for studying the satellite systems of nearby massive galaxies.