Supernova Remnants in M83 as Observed with MUSE

Abstract

Here we describe a new study of the supernova remnants (SNRs) and SNR candidates in nearby face-on spiral galaxy M83, based primarily on MUSE integral field spectroscopy. Our revised catalog of SNR candidates in M83 has 366 objects, 81 of which are reported here for the first time. Of these, 229 lie within the MUSE observation region, 160 of which have spectra with [S ii]:Hα ratios exceeding 0.4, the value generally accepted as confirmation that an emission nebula is shock-heated. Combined with 51 SNR candidates outside the MUSE region with high [S ii]:Hα ratios, there are 211 spectroscopically confirmed SNRs in M83, the largest number of confirmed SNRs in any external galaxy. MUSE’s combination of relatively high spectral resolution and broad wavelength coverage has allowed us to explore two other properties of SNRs that could serve as the basis of future SNR searches. Specifically, most of the objects identified as SNRs on the basis of [S ii]:Hα ratios exhibit more velocity broadening and lower ratios of [S iii]:[S ii] emission than H ii regions. A search for nebulae with the very broad emission lines expected from young, rapidly expanding remnants revealed none, except for the previously identified B12-174a. The SNRs identified in M83 are, with few exceptions, middle-aged interstellar medium (ISM) dominated ones. Smaller-diameter candidates show a larger range of velocity broadening and a larger range of gas densities than the larger-diameter objects, as expected if the SNRs expanding into denser gas brighten and then fade from view at smaller diameters than those expanding into a more tenuous ISM.

High-resolution Spectra of Supernova Remnants in M83

“…We previously reported spectra from many of the SNRs and candidates from our studies using GMOS-S at lower resolution (Winkler et al 2017) and/or MUSE on the VLT (Long et al 2022). There are 58 SNR candidates in our new high-resolution set of GMOS-S spectra that had previously been observed with GMOS-S at lower resolution and 75 that had been observed with MUSE.…”

“…For masks 1 and 2, observed in 2019 and 2020, many of the objects chosen were ones for which our earlier, lowerresolution spectra gave marginal [S II]:Hα ratios, in order to investigate the utility of the velocity width criterion in cases where [S II]:Hα is not definitive. For the final three masks observed in 2021, we concentrated on candidates that at the time of planning had no previous spectra, as well as candidates newly discovered with MUSE (since published by Long et al 2022). We also obtained spectra of several emission nebulae for which images did not indicate an enhanced [S II]:Hα ratio for comparison.…”

“…7 Historically, the most common means for identifying a nebula as an SNR has been through a ratio of [S II] λλ6716, 6731:Hα emission 0.4, the physical basis being that shocks such as present in SNRs produce a long cooling "tail" where S + is abundant, compared with photoionized nebulae, where S is more highly ionized and hence the [S II]:Hα ratio is lower (typically [S II]:Hα ∼0.1). In M83, some 211 objects have previously been spectroscopically confirmed to have [S II] λλ6716, 6731:Hα 0.4, which is more than in any other galaxy to date (Long et al 2022).…”

“…Supernova remnants (SNRs) in the grand-design spiral galaxy M83(NGC 5236, also known as the Southern Pinwheel) have been the subject of several recent studies, and there are currently some 364 cataloged SNRs 6 and candidates (Blair et al 2012;Winkler et al 2017;Williams et al 2019;Long et al 2022, and references in these papers). 7 Historically, the most common means for identifying a nebula as an SNR has been through a ratio of [S II] λλ6716, 6731:Hα emission 0.4, the physical basis being that shocks such as present in SNRs produce a long cooling "tail" where S + is abundant, compared with photoionized nebulae, where S is more highly ionized and hence the [S II]:Hα ratio is lower (typically [S II]:Hα ∼0.1).…”

“…For SNRs the line widths should be comparable to the shock velocity, 100 km s −1 , for all but the most evolved SNRs, compared with the narrow lines expected from photoionized regions, where bulk velocities are typically much smaller. This technique has been used recently by McLeod et al (2021) to confirm SNRs in NGC 300 and by Long et al (2022) to confirm SNRs in the central region of M83, Both of these papers are based on data from the Multi-Unit Spectroscopy Explorer (MUSE) on the Very Large Telescope (VLT).…”