The Identification of New Stellar Groupings in the M81 Debris Field

Abstract

The 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 M_V ∼ -11 and surface brightnesses μ_V ∼ 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.

This research used the facilities of the Canadian Astronomy Data Centre, operated by the National Research Council of Canada with the support of the Canadian Space Agency.