We report the discovery of a new dwarf spheroidal satellite of M31 , Andromeda IX , based on resolved stellar photometry from the Sloan Digital Sky Survey ( SDSS ) .
Using both SDSS and public archival data we have estimated its distance and other physical properties , and compared these to the properties of a previously known dwarf spheroidal companion , Andromeda V , also observed by SDSS .
Andromeda IX is the lowest surface brightness galaxy found to date ( \mu _ { V, 0 } \sim 26.8 { mag~ { } arcsec } ^ { -2 } ) , and at the distance we estimate from the position of the tip of Andromeda IX ’ s red giant branch , ( m - M ) _ { 0 } \sim 24.5 ( 805 kpc ) , Andromeda IX would also be the faintest galaxy known ( M _ { V } \sim - 8.3 ) .