J/ApJ/875/85 Optical search for SNRs in NGC6946 with WIYN & GMOS (Long+, 2019)
A new, larger sample of supernova remnants in NGC 6946.
Long K.S., Winkler P.F., Blair W.P.
<Astrophys. J., 875, 85 (2019)>
=2019ApJ...875...85L 2019ApJ...875...85L
ADC_Keywords: Galaxies, nearby; Supernova remnants; Photometry, H-alpha;
Spectra, optical
Keywords: galaxies: individual (NGC 6946) ; ISM: supernova remnants ;
supernovae: individual (SN 1980K, SN 2004et)
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 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]:Hα ratios compared to HII regions.
We have obtained spectra of 102 of these nebulae with Gemini
North-GMOS; of these, 89 have [SII]:Hα 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 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]:Hα, 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.
Description:
We carried out narrowband imaging observations of NGC 6946 from the
3.5m WIYN telescope and MiniMosaic imager on Kitt Peak on the nights
of 2011 June 26-28 (UT). We used interference filters that pass lines
of Hα, [SII]λλ6716,6731, and [OIII]λ5007,
plus red and green narrowband continuum filters so we could subtract
the stars and produce pure emission-line images.
We used the Gemini Multi-Object Spectrograph (GMOS) on the 8.2m
Gemini-North telescope to obtain all the spectra reported here, during
queue-scheduled programs in semesters 2014B (program GN-2014B-Q-83)
and 2015B (program GN-2015B-Q-91). Table 4 lists the information we
obtained for the supernova remnant (SNR) candidates for which we
obtained spectra.
We recovered all of the SNRs that had been identified by
Milisavljevic+ 2008ApJ...677..306M 2008ApJ...677..306M. Of the 147 SNR candidates we
identified, we obtained spectra of 102, and spectroscopically
confirmed 89 of these based on elevated [SII]:Hα ratios.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 83 147 Supernova remnant (SNR) candidates in NGC 6946
table4.dat 64 102 Emission line fluxes of SNR candidates
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See also:
III/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)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- Name Source Name
9- 10 I2 h RAh [20] Hour of Right Ascension (J2000)
12- 13 I2 min RAm [34/35] Minute of Right Ascension (J2000)
15- 19 F5.2 s RAs Second of Right Ascension (J2000)
21 A1 --- DE- [+] Sign of Declination (J2000)
22- 23 I2 deg DEd [60] Degree of Declination (J2000)
25- 26 I2 arcmin DEm [4/13] Arcminute of Declination (J2000)
28- 31 F4.1 arcsec DEs Arcsecond of Declination (J2000)
33- 36 F4.1 kpc Rgc [0.2/13.3] Galactocentric distance,
deprojected (GDC)
38- 41 I4 10-17mW/m2 FHa [2/3662] Hα flux
in 10-17erg/s/cm2 (1)
43- 46 F4.2 --- SII/FHa [0.2/2.5] [SII]:Hα ratio
48- 52 A5 --- Sp Spectrum used to confirm imaging ratios (2)
54- 56 A3 --- Conf Spectroscopic confirmation (3)
58- 83 A26 --- OName Other Names for the source (4)
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Note (1): Hα flux as derived from the emission line images.
Note (2): The spectrum used to measure line fluxes, encoded as Mask.Slitlet,
e.g., 05.18 is mask 5, slitlet 18.
Note (3): Confirmed in the sense that the [SII]:Hα ratio is ≥0.4 in
the spectra that were obtained of the object.
Note (4): Other name initialisms --
MF = Matonick & Fesen (1997ApJS..112...49M 1997ApJS..112...49M ; <[MF97] NGC 6946 NN> in Simbad);
B14 = Bruursema et al. (2014AJ....148...41B 2014AJ....148...41B ; <[BML2014] NN> in Simbad);
F08 = Fridriksson et al. (2008, J/ApJS/177/465 ;
<[FHL2008] NGC 6946 NN> in Simbad);
L97 = Lacey et al. (1997ApJS..109..417L 1997ApJS..109..417L ; <[LDG97] NNN> in Simbad).
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 7 A7 --- Name Source Name
9- 12 I4 10-17mW/m2 FHa [7/2638] Hα flux
in 10-17erg/s/cm2 (1)
14- 16 I3 --- Hb [8/117]? Hβ to Hα ratio (1)
17- 17 A1 --- u_Hb [: ] Uncertainty flag on Hb/Ha
19- 21 I3 --- OIII5007 [4/518]? [OIII]5007 to Hα ratio (1)
22- 22 A1 --- u_OIII5007 [:] Uncertainty flag on [OIII]5007
24- 27 I4 --- OI6300 [-357/874]? [OI]6300 to Hα ratio (1)
28- 28 A1 --- u_OI6300 [:] Uncertainty flag on [OI]6300
30- 32 I3 --- Ha [300] Assumed Hα
34- 36 I3 --- NII6583 [38/739] [NII]6583 to Hα ratio (1)
37- 37 A1 --- u_NII6583 [:] Uncertainty flag on [NII]6583
39- 41 I3 --- SII6716 [33/368]? [SII]6716 to Hα ratio (1)
42- 42 A1 --- u_SII6716 [:] Uncertainty flag on [SII]6716
44- 46 I3 --- SII6731 [29/302]? [SII]6731 to Hα ratio (1)
47- 47 A1 --- u_SII6731 [:] Uncertainty flag on [SII]6731
49- 52 F4.2 --- SII/FHa [0.2/2.3]? [SII]:Hα ratio
53- 53 A1 --- u_SII/FHa [:] Uncertainty flag on [SII]/FHa
55- 58 F4.2 --- SII [0.7/4.5] [SII]6716 to S[II]6731 ratio (1)
59- 59 A1 --- u_SII Uncertainty flag on [SII]6716:6731
61- 64 F4.1 0.1nm FWHM [4/11] Measured FWHM of the lines in the
Hα-[N II] complex in Angstroms
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Note (1): Emission line strengths are listed relative to Hα set to 300.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 07-Sep-2020