TRGB Distances to the Andromeda Dwarf Satellites from the INT Monitoring Survey

Abstract

We measure tip of the red giant branch (TRGB) distances to 17 dwarf satellites of M31 from Sloan $i$-band photometry of the Isaac Newton Telescope (INT) monitoring survey of Local Group dwarf galaxies, and add the distances of And I, And VII and And IX from earlier papers of the survey. We locate the tip with a Sobel edge-detection filter applied to the luminosity function of stars within two half-light radii of each galaxy. The distance moduli range from $23.38 \pm 0.06$ mag (And XVI, 474 kpc) to $25.35 \pm 0.06$ mag (And XVIII, 1177 kpc), and 15 of the 20 satellites lie between 650 and 850 kpc. For most galaxies, our distance agrees with at least one published value. Compared with Conn et al. (2012), our tip is brighter for 12 of the 18 galaxies in common, by up to 0.39 mag, possibly because of crowding in the central regions. And XII lies at $844^{+40}_{-38}$ kpc, about 60 kpc behind M31, consistent with a first infall into the Local Group. And XXII lies at $753^{+28}_{-27}$ kpc, closer than all earlier estimates, and about 59 kpc from M33 in three dimensions (for an M33 distance of 794 kpc), consistent with an association with M33. And XVIII lies about 400 kpc behind M31, too far for a secure association with M31.