Optical Spectroscopy of Supernova Remnants in M81 and M82

Abstract

We present spectroscopy of 28 SNR candidates as well as one H II region in M81, and two SNR candidates in M82. Twenty six out of the M81 candidates turn out to be genuine SNRs, and two in M82 may be shocked condensations in the galactic outflow or SNRs. The distribution of [N II]/Hα ratios of M81 SNRs is bimodal. M81 SNRs are divided into two groups in the spectral line ratio diagrams: an [O III]-strong group and an [O III]-weak group. The latter have larger sizes, and may have faster shock velocity. [N II]/Hα ratios of the SNRs show a strong correlation with [S II]/Hα ratios. They show a clear radial gradient in [N II]/Hα and [S II]/Hα ratios: dLog ([N II]/Hα)/dLog R = -0.018 {\pm} 0.008 dex/kpc and dLog ([S II]/Hα)/dLog R = -0.016 {\pm} 0.008 dex/kpc where R is a deprojected galactocentric distance. We estimate the nitrogen and oxygen abundance of the SNRs from the comparison with shock-ionization models. We obtain a value for the nitrogen radial gradient, dLog(N/H)/dLogR = -0.023 {\pm} 0.009 dex/kpc, and little evidence for the gradient in oxygen. This nitrogen abundance shows a few times flatter gradient than those of the planetary nebulae and H II regions. We find that five SNRs are matched with X-ray sources. Their X-ray hardness colors are consistent with thermal SNRs.

19 pages, 24 figures, 5 tables, ApJ accepted

References in corpus (8)

• The MAPPINGS III Library of Fast Radiative Shock Models
• The SAMI Galaxy Survey: Shocks and Outflows in a normal star-forming galaxy
• The oxygen abundance in the inner HII regions of M101. Implications for the calibration of strong-line metallicity indicators
• HST/STIS Spectroscopy of Five Super Star Clusters in the Starburst Galaxy M82
• A New Optical Survey of Supernova Remnant Candidates in M31
• Properties of Optically Selected Supernova Remnant Candidates in M33
• The radial metallicity gradient and the history of elemental enrichment in M81 through emission-line probes
• A new method to estimate local pitch angles in spiral galaxies: Application to spiral arms and feathers in M81 and M51

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• Optical Identification and Spectroscopy of Supernova Remnants in the Galaxy M51
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• The Supernova Remnant Populations of the galaxies NGC 45, NGC 55, NGC 1313, NGC 7793: Luminosity and Excitation Functions
• Calibrating X-ray binary luminosity functions via optical reconnaissance II. The high-mass XLF and globular cluster population of X-ray binaries in the low star-forming spiral M81