We have obtained deep Hubble Space Telescope (HST) imaging of 19 dwarf galaxycandidates in the vicinity of M101. Advanced Camera for Surveys HST photometryfor 2 of these objects showed resolved stellar populations and Tip of the RedGiant Branch derived distances consistent with M101 group membership. The other17 were found to have no resolved stellar populations, meaning they arebackground low surface brightness (LSB) galaxies. It is notable that many LSBobjects which had previously been assumed to be M101 group members based onprojection have been shown to be background objects, indicating the need forfuture diffuse dwarf surveys to be careful in drawing conclusions about groupmembership without robust distance estimates. In this work we update thesatellite luminosity function of M101 based on the presence of these newobjects down to M_V=-8.2. M101 is a sparsely populated system with only 9satellites down to M_V~-8, as compared to 26 for M31 and 24.5\pm7.7 for themedian local Milky Way (MW)-mass host. This makes M101 the sparsest groupprobed to this depth, though M94 is even sparser to the depth it has beenexamined (M_V=-9.1). M101 and M94 share several properties that mark them asunusual compared to the other local MW-mass galaxies examined: they have asparse satellite population but also have high star forming fractions amongthese satellites; such properties are also found in the galaxies examined aspart of the SAGA survey. We suggest that these properties appear to be tied tothe galactic environment, with more isolated galaxies showing sparse satellitepopulations which are more likely to have had recent star formation, whilethose in dense environments have more satellites which tend to have no recentstar formation. Overall our results show a level of halo-to-halo scatterbetween galaxies of similar mass that is larger than is predicted in the\LambdaCDM model.

The late assembly of massive galaxies is thought to be dominated by stellaraccretion in their outskirts (beyond 2 effective radii Re) due to dry, minorgalaxy mergers. We use observations of 1010 passive early-type galaxies (ETGs)within z<0.15 from SDSS IV MaNGA to search for evidence of this accretion. Theoutputs from the stellar population fitting codes FIREFLY, pPXF, and Prospectorare compared to control for systematic errors in stellar metallicity (Z)estimation. We find that the average radial logZ/Zsun profiles of ETGs invarious stellar mass (M) bins are not linear. As a result, these profiles arepoorly characterized by a single gradient value, explaining why weak trendsreported in previous work can be difficult to interpret. Instead, we examinethe full radial extent of stellar metallicity profiles and find them to flattenin the outskirts of M>10^{11}Msun ETGs. This is a signature of stellaraccretion. Based on a toy model for stellar metallicity profiles, we infer theex-situ stellar mass fraction in ETGs as a function of M and galactocentricradius. We find that ex-situ stars at 2Re make up 20% of the projected stellarmass of M<10^{10.5}Msun ETGs, rising up to 80% for M>10^{11.5}Msun ETGs.