J/ApJ/875/85ivo://CDS.VizieR/J/ApJ/875/85doi:10.26093/cds/vizier.18750085CDSLong K.S.Winkler P.F.Blair W.P.2022-04-04T08:56:19Z2020-10-12T08:21:38ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frgalaxiessupernova-remnantsvisible-astronomyh-alpha-photometryspectroscopyThe 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 NGC 6946 surely contains a large number of supernova remnants (SNRs). Here we report a new optical search for these SNRs using narrowband images obtained with the WIYN telescope. We identify 147 emission nebulae as likely SNRs, based on elevated [SII]:H{alpha} ratios compared to HII regions. We have obtained spectra of 102 of these nebulae with Gemini North-GMOS; of these, 89 have [SII]:H{alpha} 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+ (1997ApJS..109..417L) 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]:H{alpha}, of the candidates in NGC 6946 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 NGC 6946 resulted in detections for only two: SN 1980K and SN 2004et. 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.2019ApJ...875...85Lhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/875/85CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toIII/116 : Spectrophotometric Standards (Massey+ 1988)I/284 : The USNO-B1.0 Catalog (Monet+ 2003)VIII/76 : Leiden/Argentine/Bonn (LAB) Survey of Galactic HI (Kalberla+ 2005)J/MNRAS/372/1315 : UBVRI photometry of SN 2004et (Sahu+, 2006)J/ApJS/177/465 : X-ray var. in NGC 6946, NGC 4485/90 (Fridriksson+, 2008)J/ApJS/203/8 : Optical SNR candidates in M83 (Blair+, 2012)J/A+A/545/A43 : HII regions in NGC 628 and NGC 6946 (Cedres+, 2012)J/ApJ/788/55 : HST/WFC3 SNR discoveries in M83 (NGC5236) (Blair+, 2014)J/ApJS/212/21 : A deep Chandra ACIS survey of M83 (Long+, 2014)J/ApJ/839/83 : GMOS spectrosc. obs. of SNR cand. in M83 (Winkler+, 2017)J/ApJ/855/140 : MMT spectra of SNRs and SNR candidates in M33 (Long+, 2018)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/875/85https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/875/85http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/875/85https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/875/85https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/875/85http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/875/85GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJ/875/85/table2 (Supernova remnant (SNR) candidates in NGC 6946)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/875/85/table2?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/875/85/table2?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/875/85/table2?GETtext/xml+votable180.050000true308.562560.17897220.0055555555555555566/15592-15593https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJ/875/85?format=asciiOpticaldefaultJ/ApJ/875/85/table4Emission line fluxes of SNR candidatesNameSource Namemeta.id;meta.maincharu_SIIUncertainty flag on [SII]6716:6731meta.code.errorcharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintFHa[7/2638] H{alpha} flux in 10^-17^erg/s/cm^2^ (1)1e-17mW.m**-2phot.flux;em.line.HalphaintHb[8/117]? H{beta} to H{alpha} ratio (1)phot.flux;arith.ratiointnullableu_Hb[: ] Uncertainty flag on Hb/Hameta.code.errorcharOIII5007[4/518]? [OIII]5007 to H{alpha} ratio (1)phot.flux;arith.ratiointnullableu_OIII5007[:] Uncertainty flag on [OIII]5007meta.code.errorcharOI6300[-357/874]? [OI]6300 to H{alpha} ratio (1)phot.flux;arith.ratiointnullableu_OI6300[:] Uncertainty flag on [OI]6300meta.code.errorcharHa[300] Assumed H{alpha}meta.noteintNII6583[38/739] [NII]6583 to H{alpha} ratio (1)phot.flux;arith.ratiointu_NII6583[:] Uncertainty flag on [NII]6583meta.code.errorcharSII6716[33/368]? [SII]6716 to H{alpha} ratio (1)phot.flux;arith.ratiointnullableu_SII6716[:] Uncertainty flag on [SII]6716meta.code.errorcharSII6731[29/302]? [SII]6731 to H{alpha} ratio (1)phot.flux;arith.ratiointnullableu_SII6731[:] Uncertainty flag on [SII]6731meta.code.errorcharSII/FHa[0.2/2.3]? [SII]:H{alpha} ratiophot.flux;arith.ratiofloatnullableu_SII/FHa[:] Uncertainty flag on [SII]/FHameta.code.errorcharSII[0.7/4.5] [SII]6716 to S[II]6731 ratio (1)phot.flux;arith.ratiofloatFWHM[4/11] Measured FWHM of the lines in the H{alpha}-[N II] complex in Angstroms0.1nmspect.line.widthfloatJ/ApJ/875/85/table2Supernova remnant (SNR) candidates in NGC 6946SimbadSimbad column added by the CDSmeta.ref.urlcharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintNameSource Namemeta.id;meta.maincharprimaryRAJ2000[20] Hour of Right Ascension (J2000)pos.eq.ra;meta.mainDEJ2000[60] Degree of Declination (J2000)pos.eq.dec;meta.mainRgc[0.2/13.3] Galactocentric distance, deprojected (GDC)kpcpos.distance;pos.galactocentricfloatFHa[2/3662] H{alpha} flux in 10^-17^erg/s/cm^2^ (1)1e-17mW.m**-2phot.flux;em.line.HalphaintSII/FHa[0.2/2.5] [SII]:H{alpha} ratiophot.flux;arith.ratiofloatLDisplay the emission line fluxes (link to Table 4)meta.ref.urlcharSpSpectrum used to confirm imaging ratios (2)meta.id;obscharConfSpectroscopic confirmation (3)meta.codecharONameOther Names for the source (4)meta.idchar