Stellar population in Cassiopeia III and Perseus I

Our WIYN pODI photometry traces the red giant star population in each galaxy to ~2.5-3 half-light radii from the galaxy center. We use the tip of the red giant branch (TRGB) method to derive distances of (m-M)0=24.62{+/-}0.12mag (839_-45_^+48^kpc, or 156_-13_^+16^kpc from M31) for CasIII and 24.47{+/-}0.13mag (738_-45_^+48^kpc, or 351_-16_^+17^kpc from M31) for Per I. These values are consistent within the errors with TRGB distances derived from a deeper Hubble Space Telescope study of the galaxies inner regions.

For each galaxy, we derive structural parameters, total magnitude, and central surface brightness. We also place upper limits on the ratio of neutral hydrogen gas mass to optical luminosity, confirming the gas-poor nature of both galaxies. We combine our data set with corresponding data for the M31 satellite galaxy LacertaI (AndXXXI) from earlier work and search for substructure within the RGB star populations of CasIII, PerI, and Lac I. We find an overdense region on the west side of Lac I at a significance level of 2.5{sigma}-3{sigma} and a low-significance filament extending in the direction of M31.