The Identification of New Stellar Groupings in the M81 Debris Field

TL;DR

This study identifies three new stellar groupings in the M81 debris field using deep imaging, revealing their properties, ages, and potential transient nature due to their proximity to M81 and low masses.

Contribution

The paper reports the discovery and characterization of three new stellar concentrations in the M81 debris field, providing insights into their ages, metallicities, and likely short-lived existence.

Findings

Three new stellar groupings identified within 20 kpc of M81.

The groupings have ages around 30 Myr with evidence of star formation ~ 100 Myr ago.

These structures are likely transient, dissipating within ~ 1 Gyr.

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 ~ 27 - 28 mag per arcsec^2 in V. The main sequence turn-offs 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 HI 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.