Deep images obtained with MegaCam and WIRCam on the Canada-France-Hawaii Telescope ( CFHT ) are used to probe the stellar content outside of the central star-forming regions of M82 .
Stars evolving on the asymptotic giant branch ( AGB ) are traced along the major axis out to projected distances of 12 kpc , which corresponds to 13 disk scale lengths .
The numbers of red supergiants ( RSGs ) and AGB stars normalized to local surface brightness ( the ‘ specific frequency ’ – SF ) is constant when R _ { GC } > 4 kpc , indicating that RSGs and AGB stars are well mixed throughout the disk .
Moreover , the SF of bright AGB stars in the outer disks of M82 and the Sc galaxy NGC 2403 are identical , suggesting that the specific star formation rates ( SFR ) in these galaxies during intermediate epochs were similar .
This similarity in stellar content , coupled with the presence of an extended stellar disk , is consistent with M82 having been a late-type disk galaxy prior to interacting with M81 .
Still , there is a paucity of RSGs in the outer disk of M82 when compared with NGC 2403 , indicating that the SFR in the outer regions of M82 during the past \sim 0.1 Gyr has declined dramatically with respect to that in isolated late-type galaxies .
The stellar content off of the M82 disk plane is also investigated .
A mixture of bright main sequence stars , RSGs , and AGB stars are detected out to minor axis distances of 7 kpc .
These stars , which span a range of ages , are concentrated along the outflow .
The brightest extraplanar AGB stars define a system with an exponential scale height of 1.8 \pm 0.2 kpc , as measured along the minor axis .
It is suggested that the young and intermediate aged stars in the extraplanar regions formed in structures similar to M82 South , and that these were subsequently disrupted by the tidal action of M82 .