* Astronomy

Title: A Hero's Dark Horse: Discovery of an Ultra-Faint Milky Way Satellite in Pegasus
Author: Dongwon Kim, Helmut Jerjen, Dougal Mackey, Gary S. Da Costa, Antonino P. Milone

We report the discovery of an ultra-faint Milky Way satellite galaxy in the constellation of Pegasus. The concentration of stars was detected by applying our overdensity detection algorithm to the SDSS-DR 10 and confirmed with deeper photometry from the Dark Energy Camera at the 4-m Blanco telescope. Fitting model isochrones indicates that this object, Pegasus III, features an old and metal-poor stellar population ([Fe/H]~-.1) at a heliocentric distance of 205±20 kpc. The new stellar system has an estimated half-light radius of rh=110±6 pc and a total luminosity of MV~ -4.1±0.5 that places it into the domain of dwarf galaxies on the size--luminosity plane. Pegasus III is spatially close to the MW satellite Pisces II. It is possible that the two might be physically associated, similar to the Leo IV and Leo V pair. Pegasus III is also well aligned with the Vast Polar Structure, which suggests a possible physical association.

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