Big fish, small fish: Two New Ultra-Faint Satellites of the Milky Way

摘要

We report the discovery of two new Milky Way satellites in the neighboringconstellations of Pisces and Pegasus identified in data from the Sloan DigitalSky Survey. Pisces II, an ultra-faint dwarf galaxy lies at the distance of ~180kpc, some 15 degrees away from the recently detected Pisces I. Segue 3, anultra-faint star cluster lies at the distance of 16 kpc. We use deep follow-upimaging obtained with the 4-m Mayall telescope at Kitt Peak NationalObservatory to derive their structural parameters. Pisces II has a half-lightradius of ~60 pc, while Segue 3 is twenty times smaller at only 3pc.