Detection of the Main Sequence Turn-off of a Newly Discovered Milky Way Halo Structure in the Triangulum-Andromeda Region

摘要: An upper main sequence (MS) and main-sequence turn-off (MSTO) feature appears in the color-magnitude diagram (CMD) of a large area photometric survey southern half M31 stretching to M33. Imaging Washington M,T_2,DDO51 system allows us remove background M31/M33 giants from our CMD more clearly define dwarf star feature, which has an MSTO near M ~ 20.5. The corresponding stellar population shows little density variation over 12 X 6 square degree sky sampled is very low surface brightness, >32 mag/arcsec^2. We show that this not same as previously identified, MS+MSTO foreground Andromeda Galaxy been associated with tidal stream ringing Milky Way disk at less than distance. Thus, new separate, distant entity, perhaps segment debris disrupted satellite galaxy. It most likely related structure similar distance, location uniformity seen excess K Two Micron All-Sky Survey reported companion paper by Rocha-Pinto et al. (2004).