An excellent technical description of M82 can be found in Rob Gendler’s write-up at:
Excerpting from this work, M82 is the prototypical starburst galaxy with a rate of star production 10x of our own, likely due to a close encounter with M81, and is 12 million light years distant. A galactic "super wind" has formed from the outgassing of thousands of new stars and many supernovae, ejecting hydrogen and nitrogen at incredible velocities thousands of light years away from the core. We see this in my image from the HII emission.
I’ve annotated some of the faint background galaxies using TheSky. Many of these range from mag. 17 to 18.1. Click to enlarge.