A NEW MILKY WAY DWARF SATELLITE IN CANES VENATICI

摘要

In this Letter, we announce the discovery of a new dwarf satellite of the Milky Way, located in the constellation Canes Venatici. It was found as a stellar overdensity in the north Galactic cap using Sloan Digital Sky Survey Data Release 5 (SDSS DR5). The satellite's color-magnitude diagram shows a well-defined red giant branch as well as a horizontal branch. As judged from the tip of the red giant branch, it lies at a distance of ～220 kpc. Based on the SDSS data, we estimate an absolute magnitude of M_v～ -7.9, a central surface brightness of μ_(0,v) ～ 28 mag arcsec~(-2), and a half-light radius of ～8.5′(～550 pc at the measured distance). The outer regions of Canes Venatici appear extended and distorted. The discovery of such a faint galaxy in proximity to the Milky Way strongly suggests that more such objects remain to be found.