- ID:
- ivo://CDS.VizieR/J/ApJ/875/85
- Title:
- Optical search for SNRs in NGC6946 with WIYN & GMOS
- Short Name:
- J/ApJ/875/85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 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]: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.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJS/203/8
- Title:
- Optical SNR candidates in M83
- Short Name:
- J/ApJS/203/8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new optical imaging survey of supernova remnants (SNRs) in M83 (NGC 5236), using data obtained with the Magellan I 6.5m telescope and IMACS instrument under conditions of excellent seeing. Using the criterion of strong [SII] emission relative to H{alpha}, we confirm all but three of the 71 SNR candidates listed in our previous survey, and expand the SNR candidate list to 225 objects, more than tripling the earlier sample. Comparing the optical survey with a new deep X-ray survey of M83 with Chandra, we find that 61 of these SNR candidates have X-ray counterparts. We also identify an additional list of 46 [OIII]-selected nebulae for follow-up as potential ejecta-dominated remnants, seven of which have associated X-ray emission that makes them strong candidates. Some of the other [OIII]-bright objects could also be normal interstellar medium (ISM) dominated SNRs with shocks fast enough to doubly ionize oxygen, but with H{alpha} and [SII] emission faint enough to have been missed. A few of these objects may also be HII regions with abnormally high [OIII] emission compared with the majority of M83 HII regions, compact nebulae excited by young Wolf-Rayet stars, or even background active galactic nuclei. The SNR H{alpha} luminosity function in M83 is shifted by a factor of ~4.5 times higher than for M33 SNRs, indicative of a higher mean ISM density in M83. We describe the search technique used to identify the SNR candidates and provide basic information and finder charts for the objects.
- ID:
- ivo://CDS.VizieR/J/MNRAS/446/943
- Title:
- Optical supernova remnants in nearby galaxies
- Short Name:
- J/MNRAS/446/943
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we present the most up-to-date list of nearby galaxies with optically detected supernova remnants (SNRs). We discuss the contribution of the H{alpha} flux from the SNRs to the total H{alpha} flux and its influence on the derived star formation rate (SFR) for 18 galaxies in our sample. We found that the contribution of SNR flux to the total H{alpha} flux is 5+/-5%. Due to the observational selection effects, the SNR contamination of SFRs derived herein represents only a lower limit.
- ID:
- ivo://CDS.VizieR/J/A+A/484/755
- Title:
- Oxygen recombination lines from Cas A knots
- Short Name:
- J/A+A/484/755
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Fast-moving knots (FMK) in the Galactic supernova remnant Cassiopeia A consist mainly of metals and allow us to study element production in supernovae and to investigate shock physics in great detail. We discuss and suggest observations of a previously unexplored class of spectral lines, the metal recombination lines in optical and near-infrared bands, emitted by the cold ionized and cooling plasma in fast-moving knots.
- ID:
- ivo://CDS.VizieR/J/ApJ/441/307
- Title:
- Proper motions and brightness of Cas A
- Short Name:
- J/ApJ/441/307
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of a multiple-epoch radio study of secular changes in the SNR Cassiopeia A are reported and used to construct a model for the dynamical evolution of diffuse and clumpy ejecta components in the remnant. To quantify the current dynamical status of various ejecta components, the proper motions and brightness evolution of a sample of 304 compact radio features have been accurately determined from high-quality interferometric observations of the remnant at lambda=6 and 20cm, spanning a total time baseline of 12yr. A simple model of homologous expansion does not provide a good fit to the measured proper motions of the radio knots. We find that a single estimate of the ejecta expansion age is not appropriate, as the expansion derived from compact features varies azimuthally and radially in the remnant and differs for subsets of knots segregated by brightness. We verify that the bulk of the radio-emitting plasma in Cas A has indeed been significantly decelerated by the current epoch; bulk expansion ages of 2.5-4 times the actual age of the remnant are measured . Based on these dynamical data, and information on the kinematics of the fast moving optical knots. we synthesize a model that directly relates the dynamics of ejecta components in Cas A to various radiative processes. This model is based on the premise that the emission from Cas A, at a variety of wavelengths, is deceleration-powered. If ejecta components are distributed over a range of internal densities, a sequential "turning-on" of components, in order of increasing density, should be observed. A model for the current emission distribution in Cas A, at radio, X-ray, and optical wavelengths, is outlined in terms of deceleration considerations.
- ID:
- ivo://CDS.VizieR/J/MNRAS/246/169
- Title:
- Radio continuum around G 73.9+0.9
- Short Name:
- J/MNRAS/246/169
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A field centered on the galactic supernova remnant (SNR) G073.9+00.9 was mapped in the continuum at 408 and 1420 MHz with the Dominion Radio Astrophysical Observatory (DRAO). The interferometer observations, of resolution 3.4x5.8 arcmin^2^ and 1.0x1.7 arcmin^2^ respectively, were complemented with single-dish data so that the resulting maps are sensitive to all structures down to the synthesized beam. Note that this list is part of the DRAO Penticton P-survey Database (Catalog <VIII/55>)
- ID:
- ivo://CDS.VizieR/J/A+A/241/551
- Title:
- Radio continuum in Cygnus X region
- Short Name:
- J/A+A/241/551
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Cygnus X region has been observed at 408 and 1420 MHz with the Dominion Radio Astrophysical Observatory (DRAO), with an angular resolution of 3.5x5.2 and 1.0x1.5 arcmin.
- ID:
- ivo://CDS.VizieR/J/AJ/137/3869
- Title:
- Radio SNRs in 4 irregular galaxies
- Short Name:
- J/AJ/137/3869
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We survey four nearby irregular galaxies for radio supernova remnants (SNRs) using deep (1{sigma}~20uJy), high-resolution (~20pc) Very Large Array continuum data at 20, 6, and 3.6cm. We identify discrete sources in these galaxies and use radio spectral indices and H{alpha} images to categorize them as SNRs, HII regions, or background radio galaxies. Our classifications are generally in good agreement with the literature. We identify a total of 43 SNR candidates: 23 in NGC 1569, seven in NGC 4214, five in NGC 2366, and eight in NGC 4449. Only one SNR - the well-studied object J1228+441 in NGC 4449 - is more luminous at 20cm than Cas A. By comparing the total thermal flux density in each galaxy with that localized in HII regions, we conclude that a significant fraction must be in a diffuse component or in low-luminosity HII regions.
- ID:
- ivo://CDS.VizieR/J/ApJ/703/370
- Title:
- Radio SNRs in nearby galaxies
- Short Name:
- J/ApJ/703/370
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We compile radio supernova remnant (SNR) samples from the literature for 19 nearby galaxies ranging from the SMC to Arp 220, and use this data to constrain the SNR luminosity function (LF) at 20cm. We find that radio SNR populations are strikingly similar across galaxies. The LF can be described as a power law with constant index and scaling proportional to a galaxy's star formation rate (SFR). Unlike previous authors, we do not find any dependence of SNR luminosity on a galaxy's global interstellar medium density. The observed correlation between the luminosity of a galaxy's brightest SNR and a galaxy's SFR can be completely explained by statistical effects, wherein galaxies with higher SFR more thoroughly sample the high-luminosity end of the SNR LF. The LF is well fitted by a model of SNR synchrotron emission which includes diffusive shock acceleration and magnetic field amplification, if we assume that all remnants are undergoing adiabatic expansion, the densities of star-forming regions are similar across galaxies, and the efficiency of cosmic ray production is constant.
- ID:
- ivo://CDS.VizieR/J/A+AS/115/345
- Title:
- Radio sources in fields near G160.9+2.6 (HB9)
- Short Name:
- J/A+AS/115/345
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalogue of the 408MHz and 1420MHz radio sources in the region centered near Right Ascension 4h58m and Declination 46degrees (epoch 1950), i.e. near the supernova remnant HB9. The observations were made with the Synthesis Telescope at the Dominion Radio Astrophysical Observatory, near Penticton, Canada. 494 sources at 408MHz and 255 sources at 1420MHz were detected. 408-1420MHz spectral indices for 101 common sources were derived. The 408MHz source list was compared with the 4850MHz sources from the Green Bank catalog. Spectral indices were determined for 165 common sources. We also compared the source lists with the IRAS and ROSAT point source catalogs for that region and have identified 16 radio sources with IRAS point sources and 3 radio sources with X-ray sources.
