Supernova remnants in the fossil starburst in M82

We report the discovery of 10 compact Hα-bright sources in the poststarburst region northeast of the center of M82, called M82 B. These objects have Hα luminosities and sizes consistent with Type II supernova remnants (SNRs). They fall on the same Hα surface brightness-diameter relation (Σ-D) defined by SNRs in other nearby star-forming galaxies, with the M82 candidates lying preferentially at the small-diameter end. These are the first candidates for optically visible SNRs in M82 outside the heavily obscured central starburst within about 250 pc from the galactic center. If these sources are SNRs, they set an upper limit to the end of the starburst in region B2, about 500 pc from the galaxy's core, of about 50 Myr. Region B1, about 1000 pc from the core, lacks good SNR candidates and is evidently somewhat older. This suggests that star formation in the galaxy has propagated inward toward the present-day intense starburst core.