The Identification of New Stellar Groupings in the M81 Debris Field1,1Based on observations obtained with the MegaPrime/MegaCam, a joint project of the CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l’Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and

Abstract

ABSTRACTThe stellar content of the debris field around M81 is investigated using deep images obtained with MegaCam on the Canada-France-Hawaii Telescope. Three new concentrations of bright main-sequence stars and red supergiants are identified within ∼20 kpc of M81. These systems have integrated brightnesses MV ∼ -11 and surface brightnesses μV ∼ 27–28 mag arcsec-2. The main-sequence turnoffs are consistent with an age of ∼30 Myr, while the presence of a well-developed red supergiant plume indicates that their stellar content is not coeval, as they also formed stars ∼100 Myr in the past. The photometric properties of the red supergiants indicate that the young stars in these systems have metallicities that are comparable to those of other objects in the debris field. The H I density near these groupings comfortably exceeds the threshold required to trigger star formation. Based on the close proximity of these objects to M81, coupled with their extended sizes and low inferred masses, it is argued that they will not be long-lived structures, but will probably dissipate within the next ∼1 Gyr.