An Optical Search For Supernova Remnants in Nearby Spiral Galaxies
Session 50 -- Supernova Remnants
Display presentation, Tuesday, 10, 1995, 9:20am - 6:30pm

## [50.08] An Optical Search For Supernova Remnants in Nearby Spiral Galaxies

D.M.Matonick, R.A.Fesen (Dartmouth College), W.P.Blair (Johns Hopkins Univ), K.S.Long (STScI)

Imaging with narrow-band H$\alpha$, [S II], and red continuum filters has been used to distinguish supernova remnant (SNR) candidates from photoionized nebulae in seven nearby spiral galaxies: NGC 2403, NGC 3031 (M81), NGC 5194 (M51), NGC 5204, NGC 5457 (M101), NGC 5585, and NGC 6946. Nebulae which show [S II]/H$\alpha$ $>$ 0.45, indicating shock-heated emission, are identified as SNR candidates. The number of SNRs found in each galaxy using this technique is 3 in NGC 5204, 5 in NGC 5585, 30 in NGC 2403, 32 in M81, 35 in NGC 6946, and 112 in M101. Spectra of some of the emission nebulae have also been obtained, and were used to confirm SNR identifications. Because of its comparatively high radial velocity, M51 could not be examined adequately with our filter set; however, one bright SNR was found and spectroscopically confirmed. In NGC 2403, we obtained spectra on remnant candidates 1 and 2 of D'Odorico et al. (1980, A\&AS, 40, 67), and confirmed them to be SNRs. We also detect the optical SNR identified by Blair \& Fesen (1994, ApJ, 424, L103) in NGC 6946, and find an optical SNR counterpart to the X-ray source S2 identified by Schlegel (1994, ApJ, 424, L99). Sizes of observed SNRs range from unresolved ($<$ 50 pc) to over 300x150 pc for one object in NGC 5585. Although our search technique limits our detection of SNRs embedded in bright H~II regions, in the galaxies with clearly defined spiral arms (i.e NGC 6946, M81, M101), most SNRs appear to trace the spiral arms. Analysis of luminosity functions, diameters, abundances, and distributions of the samples of SNRs will also be discussed.