Lacerta i and cassiopeia III. Two luminous and distant andromeda satellite dwarf galaxies found in the 3π pan-starrs1 survey

Abstract

We report the discovery of two new dwarf galaxies, Lacerta I/Andromeda XXXI (Lac I/And XXXI) and Cassiopeia III/Andromeda XXXII (Cas III/And XXXII), in stacked Pan-STARRS1 r P1- and i P1-band imaging data. Both are luminous systems (MV -12) located at projected distances of 20.°3 and 10.°5 from M31. Lac I and Cas III are likely satellites of the Andromeda galaxy with heliocentric distances of and , respectively, and corresponding M31-centric distances of 275 ± 7 kpc and . The brightest of recent Local Group member discoveries, these two new dwarf galaxies owe their late discovery to their large sizes ( arcmin or for Lac I; arcmin or 1456 ± 267 pc for Cas III) and consequently low surface brightness (μ0 26.0 mag arcsec-2), as well as to the lack of a systematic survey of regions at large radii from M31, close to the Galactic plane. This latter limitation is now alleviated by the 3π Pan-STARRS1 survey, which could lead to the discovery of other distant Andromeda satellite dwarf galaxies. © 2013. The American Astronomical Society. All rights reserved..