The Stellar Disk of M81

TL;DR

This study uses wide-field optical and near-infrared imaging to analyze the distribution and properties of bright stars in M81's disk, revealing spatial variations in star formation history and stellar populations out to 18 kpc.

Contribution

It provides detailed spatial mapping of bright stars in M81's disk and uncovers radial changes in star formation activity and stellar age distributions.

Findings

Bright main sequence stars and RSGs are observed out to 18 kpc.

The specific star formation rate increases with radius.

A stellar population change occurs near 14 kpc.

Abstract

Wide-field images obtained with the 3.6 meter Canada-France-Hawaii Telescope are used to investigate the spatial distribution and photometric properties of the brightest stars in the disk of M81 (NGC 3031). With the exception of the central regions of the galaxy and gaps between CCDs, the survey is spatially complete for stars with i' < 24 and major axis distances of 18 kpc. A more modest near-infrared survey detects stars with K < 20 over roughly one third of the disk. Bright main sequence (MS) stars and RSGs are traced out to galactocentric distances of at least 18 kpc. The spatial distribution of bright MS stars tracks emission at far-ultraviolet, mid- and far-infrared wavelengths, although tidal features contain bright MS stars but have little or no infrared flux. The specific frequency of bright MS stars and RSGs, normalized to K-band integrated brightness, increases with radius, indicating that during the past 30 Myr the specific star formation rate (SSFR) has increased with increasing radius. The stellar content of the M81 disk undergoes a distinct change near R ~ 14 kpc, and the luminosity-weighted mean age decreases with increasing radius in the outer regions of the M81 disk.