A New, Larger Sample of Supernova Remnants in NGC 6946

Abstract

The relatively nearby spiral galaxy NGC~6946 is one of the most actively star forming galaxies in the local Universe. Ten supernovae (SNe) have been observed since 1917, and hence NGC6946 surely contains a large number of supernova remnants (SNRs). Here we report a new optical search for these SNRs using narrow-band images obtained with the WIYN telescope. We identify 147 emission nebulae as likely SNRs, based on elevated [SII]:Halpha ratios compared to HII regions. We have obtained spectra of 102 of these nebulae with Gemini North-GMOS; of these, 89 have [SII]:Halpha ratios greater than 0.4, the canonical optical criterion for identifying SNRs. There is very little overlap between our sample and the SNR candidates identified by Lacey et al. (2001) from radio data. Also, very few of our SNR candidates are known X-ray sources, unlike the situation in some other galaxies such as M33 and M83. The emission line ratios, e.g., [NII]:Halpha, of the candidates in NGC6946 are typical of those observed in SNR samples from other galaxies with comparable metallicity. None of the candidates observed in our low-resolution spectra show evidence of anomalous abundances or significant velocity broadening. A search for emission at the sites of all the historical SNe in NGC6946 resulted in detections for only two: SN1980K and SN2004et. Spectra of both show very broad, asymmetric line profiles, consistent with the interaction between SN ejecta and the progenitor star's circumstellar material, as seen in late spectra from other core-collapse SNe of similar age.

36 pages, 11 figures, accepted for publication in Astrophysical Journal

References in corpus (11)

• High-Resolution Rotation Curves and Galaxy Mass Models from THINGS
• The MAPPINGS III Library of Fast Radiative Shock Models
• Dust and the type II-plateau supernova 2004et
• Photometric and spectroscopic evolution of the type IIP supernova SN 2004et
• HI holes and high-velocity clouds in the spiral galaxy NGC 6946
• A Deep Chandra ACIS Survey of M83
• An Expanded HST/WFC3 Survey of M83: Project Overview and Targeted Supernova Remnant Search
• The Long-Term Variability of the X-Ray Sources in NGC 6946 and NGC 4485/4490
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• A Newly Recognized Very Young Supernova Remnant in M83
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• Kinematics: A Clean Diagnostic for Separating Supernova Remnants from HII Regions in Nearby Galaxies
• Detection of supernova remnants in NGC 4030
• The Supernova Remnant Population of NGC6946 as Observed in [Fe II] 1.644 $\mu$m with HST
• Optical Identification and Spectroscopy of Supernova Remnants in the Galaxy M51
• MaNGA galaxies with off-centered spots of enhanced gas velocity dispersion
• Detection of Late-Time Optical Emission from SN 1941C in NGC 4136
• A Kinematical Study of the Dwarf Irregular Galaxy NGC 1569 and its Supernova Remnants
• The Supernova Remnant Populations of the galaxies NGC 45, NGC 55, NGC 1313, NGC 7793: Luminosity and Excitation Functions
• Optical emission-line Luminosity Function models for populations of Supernova Remnants
• A Search for Supernova Light Echoes in NGC 6946 with SITELLE