Supernova Remnant In NGC Research Articles

Planetary nebulae and supernova remnants in NGC 4214 from the SIGNALS survey

ABSTRACT Using datacubes from the imaging Fourier transform spectrometer SITELLE at the Canada–France–Hawaii Telescope as part of the star formation, ionized gas, and nebular abundances legacy survey, we identify 15 new planetary nebulae (PNe) as well as five new supernova remnants (SNRs) in the outer parts of the nearby dwarf starburst galaxy NGC 4214. These data also allow us to study the morphology and kinematics of all 18 known SNRs in this galaxy. We highlight the use of a $\xi = \sigma \frac{\rm {[S{\small \,II}]}}{\rm {H\alpha }}$ diagnostic diagram (σ being the velocity dispersion) to separate SNRs from H ii regions and its advantage compared to classical BPT or Sabbadin diagrams. We provide the emission-line flux ([O iii] λ5007, H α, and H β) and radial velocities of all new PNe candidates, as well as those of 12 of the 17 PNe previously discovered in the central part of the galaxy with Hubble Space Telescope (HST) data. Finally, we use the [O iii] emission-line luminosity function of the PNe sample to establish a new velocity-independent distance for NGC 4214: $D = 3.23^{+0.18}_{-0.25}$ Mpc.

Detection of supernova remnants in NGC 4030

ABSTRACT MUSE-based emission-line maps of the spiral galaxy NGC 4030 reveal the existence of unresolved sources with forbidden line emission enhanced with respect to those seen in its own H ii regions. This study reports our efforts to detect and isolate these objects and identify their nature. Candidates are first detected as unresolved sources on an image of the second principal component of the H β, [O iii] 5007, H α, [N ii] 6584, [S ii] 6716, 6731 emission-line data cube, where they stand out clearly against both the dominant H ii region population and the widespread diffuse emission. The intrinsic emission is then extracted accounting for the highly inhomogeneous emission-line ‘background’ throughout the field of view. Collisional to recombination line ratios like [S ii]/H α, [N ii]/H α, and [O i]/H α tend to increase when the background emission is corrected for. We find that many (but not all) sources detected with the principal component analysis have properties compatible with supernova remnants (SNRs). Applying a combined [S ii]/H α and [N ii]/H α classification criterion leads to a list of 59 sources with SNR-like emission lines. Many of them exhibit conspicuous spectral signatures of SNRs around 7300 Å, and a stacking analysis shows that these features are also present, except weaker, in other cases. At nearly 30 Mpc, these are the most distant SNRs detected by optical means to date. We further report the serendipitous discovery of a luminous (MV ∼ −12.5), blue, and variable source, possibly associated with a supernova impostor.

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 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 [S ii]:Hα ratios compared to H ii regions. We have obtained spectra of 102 of these nebulae with Gemini North–GMOS; of these, 89 have [S ii]: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 et al. 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., [N ii]: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.

A SEARCH FOR SUPERNOVA REMNANTS IN NGC 6946 USING THE [Fe II] 1.64 μm LINE

Shock models indicate and observations show that in the infrared (IR), supernova remnants (SNRs) emit strongly in [Fe II] at 1.64 μm. Here, we report the results of a search for SNRs in NGC 6946 relying on [Fe II] 1.64 μm line emission, where we employed an adjacent [Fe II]{sub Off} filter to accurately assess the local continuum levels. For this study, we used the WIYN High Resolution Infrared Camera on the WIYN 3.5 m telescope to image NGC 6946 in broadbands J and H and narrowbands [Fe II], [Fe II]{sub Off}, Paβ, and Paβ{sub Off}. From our search, we have identified 48 SNR candidates (SNRcs), 6 of which are coincident with sources found in prior radio, optical, and/or X-ray studies. The measured [Fe II] fluxes of our SNRcs range from 1.5 × 10{sup –16} to 4.2 × 10{sup –15} erg s{sup –1} cm{sup –2} and are among the highest of previously published extragalactic SNR [Fe II] fluxes. All of the candidates now need to be confirmed spectroscopically. However, the fact that we detect as many objects as we did suggests that [Fe II] can be used as an effective search tool to find extragalactic SNRs.

The first VLBI image of the young, oxygen-rich supernova remnant in NGC 4449

We report on sensitive 1.4-GHz VLBI radio observations of the unusually luminous supernova remnant SNR 4449-1 in the galaxy NGC 4449, which gave us the first well-resolved image of this object. The remnant's radio morphology consists of two approximately parallel bright ridges, suggesting similarities to the barrel shape seen for many older Galactic supernova remnants or possibly to SN 1987A. The angular extent of the remnant is 65 x 40 mas, corresponding to (3.7 x 2.3) x 10^{18} (D/3.8 Mpc) cm. We also present a new, high signal-to-noise optical spectrum. By comparing the remnant's linear size to the maximum velocities measured from optical lines, as well as using constraints from historical images, we conclude that the supernova explosion occurred between ~1905 and 1961, likely around 1940. The age of the remnant is therefore likely ~70 yr. We find that SNR 4449-1's shock wave is likely still interacting with the circumstellar rather than interstellar medium.

The Nature of the Ultraluminous Oxygen‐Rich Supernova Remnant in NGC 4449

Optical images and spectra, both ground based and taken by Hubble Space Telescope (HST), of the young, luminous O-rich supernova remnant in the irregular galaxy NGC 4449 are presented. HST images of the remnant and its local region were obtained with the ACS/WFC using filters F435W, F555W, F814W (B, V, and I, respectively), F502N ([O III]), F658N (Hα + [N II]), F660N ([N II]), and F550M (line-free continuum). These images show an unresolved remnant (FWHM < 0.05'') located within a rich cluster of OB stars which itself is enclosed by a nearly complete interstellar shell seen best in Hα + [N II] emission approximately 8'' × 6'' (150 pc × 110 pc ) in size. The remnant and its associated OB cluster are isolated from two large nearby H II regions. The ACS [O III] image shows the remnant may be partially surrounded by a clumpy ring of emission approximately 1'' (~20 pc) in diameter. Recent ground-based spectra of the remnant reveal (1) the emergence of broad, blueshifted emission lines of [S II] λλ6716, 6731, [Ar III] λ7136, and [Ca II] λλ7291, 7324 which were not observed in spectra taken in 1978-1980; (2) faint emission at 6540-6605 A centered about Hα and [N II] λλ6548, 6583 with an expansion velocity of 500 ± 100 km s−1; and (3) excess emission around 4600-4700 A suggestive of a Wolf-Rayet population in the remnant's star cluster. We use these new data to re-interpret the origin of the remnant's prolonged and bright luminosity and propose that the remnant is strongly interacting with dense, circumstellar wind loss material from a 20 M☉ progenitor star.

Supernova Remnants and Cosmic‐Ray Acceleration in Nearby Galaxies

Supernova remnants (SNRs) have attracted a considerable amount of interest in modern astrophysics from both observational and theoretical perspectives. SNRs play an integral role in numerous processes associated with the evolution of galaxies, including the injection of significant amounts of kinetic energy and heavy-element–enriched material into the interstellar medium. In addition, SNRs have emerged as the leading candidates for the acceleration of cosmic rays within the disks of galaxies through the proposed diffusive shock acceleration (DSA) mechanism. Observations of SNRs have been conducted at three particular wavelengths, based on distinct processes of energy emission associated with these objects. Thermal bremsstrahlung emission from gas shock-heated to temperatures of 10–10 K, recombination radiation from ionized atomic species such as [S ii], and nonthermal synchrotron emission from relativistic electrons gyrating in the SNR’s magnetic field produce X-ray, optical, and radio emission, respectively. Studies of SNRs within our own Galaxy have been hampered by considerable distance uncertainties and massive extinction along Galactic lines of sight, particularly at the Xray and optical wavelengths. In contrast, the study of SNRs located in nearby galaxies—particularly galaxies located at high Galactic latitudes with face-on or nearly face-on orientations—offers the opportunity to examine equidistant samples of SNRs that are nearly free of obscuration. We present a multiwavelength (X-ray, optical, and radio) study of the resident SNR population of the Sculptor group galaxies NGC 300 and NGC 7793 and the northern granddesign spiral NGC 6946. These three galaxies are nearby (2.1, 3.38, and 5.1 Mpc distant, respectively), are located at high Galactic latitudes, and clearly exhibit extensive massive star formation throughout their disks. We have observed these galaxies at the wavelengths of 6 and 20 cm with the Very Large Array (VLA) and complemented this data with our own Ha images and archived X-ray observations made with the Position Sensitive Proportional Counter instrument aboard the ROSAT satellite. We have searched for X-ray and radio emission from previously known SNRs identified in the optical using the [S ii]/Ha method and searched for new candidate X-ray and radio SNRs. We have found that remarkably few of the optically identified SNRs possess counterparts at either of the other two wavelengths: of the 83 optically identified SNRs in these galaxies, only four (N300-S10, N300-S26, N7793-S26, and NGC 6946-S16) were also detected in the X-ray and the radio. N7793-S26 is a very noteworthy source: in the optical and radio it shows a remarkable filamentary structure approximately 450 pc in size, and its radio emission is nearly twice as luminous as the most radio luminous Galactic SNR, Cassiopeia A. Three other optically identified SNRs, N300-S11, N7793-S11, and NGC 6946-S9, feature strong radio emission but no X-ray emission. Our search for new SNRs in NGC 300 and NGC 7793 has produced 21 candidates: 14 candidate radio SNRs and two candidate X-ray SNRs in NGC 300, and five candidate radio SNRs in NGC 7793. Very limited intersection is seen between the sets of X-ray, optical, and radio-selected SNRs in these two galaxies. These results indicate possible selection effects inherent in these surveys: optical surveys favor the detection of SNRs in low-density regions that are relatively devoid of optical confusion. In contrast, radio and X-ray surveys are biased toward the detection of SNRs in high-density regions where optical surveys are severely impeded. Such selection effects may also indicate selection effects for the type of supernova that parents the SNR: the optical surveys are more likely to detect SNRs produced by the explosion of low-mass stars in Type Ia supernovae, while radio and X-ray surveys are more likely to identify SNRs produced by the explosion of high-mass stars in Type II supernovae. To investigate these selection effects, we have conducted a simulation designed to evaluate the dependence of optical detections of SNRs on distance to the target galaxy. By distributing artificial SNRs within the galaxy at positions corresponding to differing amounts of ambient density and varying the distance to the target galaxy, we find that the detection of SNRs using optical methods becomes increasingly difficult with distance and that SNRs that are embedded in regions of high density are not detected even when the galaxy is rather near. These results indicate the need for a multiwavelength campaign to detect a maximum number of SNRs in a galaxy of interest. A study of the average minimum energies of the radio SNRs in NGC 300, NGC 7793, NGC 6946, and the Local Group spiral M33 (which we have

What Produced the Ultraluminous Supernova Remnant in NGC 6946?

The ultraluminous supernova remnant (SNR) in NGC 6946 is the brightest known SNR in X-rays, about 1000 times brighter than Cas A. To probe the nature of this remnant and its progenitor, we have obtained high-dispersion optical echelle spectra. The echelle spectra detect Hα, [N II], and [O III] lines and resolve these lines into a narrow (FWHM ~20–40 km s-1) component from unshocked material and a broad (FWHM ~250 km s-1) component from shocked material. Both narrow and broad components have unusually high [N II]/Hα ratios, about 1. Using the echelle observation, archival Hubble Space Telescope images, and archival ROSAT X-ray observations, we conclude that the SNR was produced by a normal supernova whose progenitor was a massive star, either a WN star or a luminous blue variable. The high luminosity of the remnant is caused by the supernova ejecta expanding into a dense, nitrogen-rich circumstellar nebula created by the progenitor.

An Optical Search For Supernova Remnants in NGC 2403

We present the results of an optical search for supernova remnants (SNRs) in the Scd galaxy NGC 2403 using image and spectral observations of a ? 8' ? 8' field covering nearly all of this galaxy. Our SNR identification technique consisted of constructing continuum-subtracted H? and [S II] ??6716, 6731 images, obtaining spectra of a few [S II]-bright emission nebulae found in these images, and then using the [S II]/H? ratios obtained from these spectra to correct the image [S II]/H? ratios. Thirty-five emission nebulae with [S II]/H? ? 0.45 were identified as SNRs and have diameters of 20-200 pc, reddening-corrected H? intensities of 2.2 ? 10-15 to 1.4 ? 10-13 ergs cm-2 s-1, [S II]/H? ratios of 0.45-1.11, and a variety of optical morphologies (shell, arc, and filled). Spectra of 15 of these remnants were obtained and are presented. The two NGC 2403 SNRs previously identified by D'Odorico, Dopita, & Benvenuti were among the 35 SNRs detected. Our final NGC 2403 SNR sample appears biased against detecting large, faint remnants, and no SNRs were detected inside bright H II regions. An examination of the [S II]/H? values for all the nebulae measured in NGC 2403 shows no sharp dividing line between SNRs and H II regions, similar to what was found in M31, NGC 300, and NGC 7793 (Walterbos & Braun; Blair & Long). We estimate roughly that there are about 4 times more SNRs in NGC 2403 than we detected, which, assuming the observable lifetime of a SNR is ~20,000 yr, yields a crude rate of 1 SN in 150 yr. Analysis of the 15 SNR spectra show a detectable nitrogen gradient, a larger scatter in oxygen abundances than in nitrogen, and a lower mean oxygen abundance than from published H II region data, all of which have been seen in previous SNR studies of other galaxies.

Optically Identified Supernova Remnants in the Nearby Spiral Galaxies NGC 5204, NGC 5585, NGC 6946, M81, and M101

We present the results of an optical search for supernova remnants (SNRs) in the spiral galaxies NGC 5204, NGC 5585, NGC 6946, M81, and M101. Using the criterion that emission nebulae with [S II]/Hα ≥ 0.45 are identified as SNRs, we found three SNRs in NGC 5204, five in NGC 5585, 27 in NGC 6946, 41 in M81, and 93 in M101. Including the 35 SNRs recently detected in NGC 2403 by Matonick et al., we have doubled the current number of galaxies that have been well searched for SNRs and increased the number of known extragalactic SNRs by about 50%. Since no SNRs were detected inside H II regions and because our optical search appears biased against detecting large, faint SNRs, we estimate that there could be 4 times more SNRs in each of our target galaxies than we detected. Statistical analysis of the spatial distribution of detected SNRs indicates that those in NGC 2403, M81, and M101 are associated with star-forming regions (e.g., H II regions, spiral arms, and molecular clouds), suggesting that a significant fraction of the detected SNRs are the result of SN II or SN Ib/c explosions. Thirty-one SNRs found in these six galaxies have estimated diameters greater than 100 pc, which is larger than is possible for a single SNR in an interstellar medium of density ~0.1-1 cm-3. Such objects are probably combinations of multiple SNRs and massive stellar winds. We present an overview of extragalactic SNR searches, combining our SNR samples with published results of optical SNR searches in the Large and Small Magellanic Clouds and in M31, M33, NGC 300, and NGC 7793 to create an ensemble of 12 SNR samples. From these data, we find that an important selection effect is the apparent trend for higher L(Hα)mode with increasing galaxy distance because intrinsically fainter SNRs are more difficult to detect in more distant galaxies. In addition, several physical trends were found in the SNR ensemble, including a constant value of Dmode ≈ 40 pc for the SNR samples in these galaxies, suggesting that a significant fraction of the detected SNRs are in a similar evolutionary stage.

The radio counterpart to the luminous X-ray supernova remnant in NGC 6946

view Abstract Citations (27) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Radio Counterpart to the Luminous X-Ray Supernova Remnant in NGC 6946 van Dyk, Schuyler D. ; Sramek, Richard A. ; Weiler, Kurt W. ; Hyman, Scott D. ; Virden, Rachel E. Abstract We report detection from VLA observations of the radio counterpart to the very luminous X-ray and optical supernova remnant in the galaxy NGC 6946 (Schlegel 1994; Blair & Fesen 1994). We find it to be a very luminous radio source, being ~3 times more powerful than Cas A and within an order of magnitude of the extraordinarily powerful supernova remnant in NGC 4449. We suggest that the NGC 6946 supernova remnant is analogous to the NGC 4449 supernova remnant, but is probably much older. The high luminosity at radio wavelengths for the NGC 6946 supernova remnant likely results from interaction with a dense local environment. Publication: The Astrophysical Journal Pub Date: April 1994 DOI: 10.1086/187314 Bibcode: 1994ApJ...425L..77V Keywords: Radio Astronomy; Radio Sources (Astronomy); Spiral Galaxies; Supernova Remnants; Very Large Array (Vla); Cassiopeia A; Centimeter Waves; Decimeter Waves; Stellar Luminosity; Superhigh Frequencies; Ultrahigh Frequencies; X Ray Sources; Astronomy; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 6946; RADIO CONTINUUM: GALAXIES; RADIO CONTINUUM: ISM; ISM: SUPERNOVA REMNANTS full text sources ADS | data products SIMBAD (6) NED (2)

The optical counterpart to the luminous X-ray supernova remnant in NGC 6946

view Abstract Citations (33) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Optical Counterpart to the Luminous X-Ray Supernova Remnant in NGC 6946 Blair, William P. ; Fesen, Robert A. Abstract We identify a high surface brightness optical supernova remnant (SNR) in NGC 6946 that is coincident with a bright soft X-ray point source detected in a ROSAT PSPC image of this galaxy (Schlegel 1994). Optical CCD/interference filter images and spectra show the object to have an observed Hα flux of 1.9 x 10^-14^ ergs cm^-2^ s^-1^, corresponding to an intrinsic Hα luminosity of 2 x 10^38^ (d/5.1 Mpc)^2^ ergs s^- 1^. A moderate-resolution optical spectrum shows normal SNR line emissions, with no high velocities (V <400 km s^-1^) or relative line strengths indicative of enriched heavy element abundances. This suggests a relatively old SNR, a conclusion supported by the presence of an emission nebula at its position on photographic plates dating back to at least 1921. With both an optical line flux and soft X-ray flux exceeding those of other luminous extragalactic SNRs, this object may have an optical luminosity near the maximum limit for SNRs. Assuming current flux levels, we estimate the SNR's age to be <= 3500 yr and suggest its unusual luminosity is due to both its expansion into dense surroundings and a relatively low column density along our line of sight. Publication: The Astrophysical Journal Pub Date: April 1994 DOI: 10.1086/187285 Bibcode: 1994ApJ...424L.103B Keywords: Balmer Series; Data Reduction; H Alpha Line; Light (Visible Radiation); Optical Emission Spectroscopy; Supernova Remnants; X Ray Sources; Charge Coupled Devices; Line Of Sight; Luminosity; Photographic Plates; Rosat Mission; Astrophysics; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 6946; ISM: SUPERNOVA REMNANTS full text sources ADS | data products SIMBAD (6) NED (1) HEASARC (1)

The very luminous supernova remnant in NGC 6946

In this paper, I discuss an extremely luminous X-ray source found on the northern arm of the nearly face-on spiral galaxy NGC 6946. The source was originally discovered in an Einstein observation, but the poor spatial resolution prevented an accurate identification. Here, Roentgen Satellite (ROSAT) data provide a position to approximately 5 sec - 10 sec. The spectrum is rather soft, and moderately absorbed. The source appears to be local to NGC 6946 and a supernova remnant, based upon the positional coincidence with an optical counterpart. The luminosity, assuming a distance to NGC 6946 of 5.1 Mpc, is 2.8 x 10(exp 39) erg/s, among the highest known X-ray luminosities of a remnant. The optical counterpart is at least 100 years old.

High-resolution imaging of forbidden Fe II 1.64 microns, Brackett-gamma, and H2 1-0 S(1) emission in the starburst galaxy NGC 253

We present 1" resolution imaging of the nuclear region of the starburst galaxy NGC 253 in the near-infrared lines of [Fe II] 1.64 microns, Brackett-γ, and H_2_ 1-0 S(1), together with the adjacent continuum. The data reveal an emission region extended some 10" northeast of the nucleus, with several embedded compact peaks or hot spots. The continuum and the three spectral lines have the same general distribution but differ in detail. The line emission from H_2_ and Brγ are closely matched in the circumnuclear region. However, the H_2_ emission reveals wispy structures which are more prominent to the northwest of the nucleus. We propose that the Brγ and H_2_ emission lines are excited in star formation regions and that the [Fe II] emission traces the distribution of supernova remnants. The hot spots are compact (&lt;= 12 pc) circumnuclear star formation regions containing a mixture of H II regions, supernova remnants, and supergiants. There is evidence that many of the supernova remnants in NGC 253 may be more luminous than their counterparts in the Galaxy. These observations constrain the stellar populations in the circumnuclear region and indicate that the radio emission is dominated by nonthermal emission processes.

The extraordinary extragalactic supernova remnant in NGC 4449. II - X-ray and optical investigations

X-ray observations with the Einstein Observatory show that the supernova remnant (SNR) in the galaxy NGC 4449 is the most luminous known X-ray SNR - a distinction it already holds at optical and radio wavelengths. New optical spectroscopy and the X-ray data indicate that the extraordinary luminosity is due to chemically enriched material at unusually high densities. A model in which the remnant resulted from the explosion of a massive star in a medium of density near 25 cm<SUP>-3</SUP> about 100 years ago is consistent with all of the data. In this picture the X-rays stem from chemically enriched supernova ejecta heated by a reverse shock.

VLA observations of the luminous supernova remnant in NGC 4449

VLA observations of the luminous supernova remnant in NGC 4449

IUE observations of supernova remnants

Ultraviolet spectra of supernova remnants obtained with the IUE satellite provide unique information concerning the shock conditions and elemental abundances in the optically bright filaments. High temperature species such as N V provide diagnostics for shock velocities above 100 km s−1, and strong lines of carbon and silicon in the IUE spectral range make it possible to study the destruction of refractory grains in shocked interstellar gas. Observations of a non-radiative shock at the edge of the Cygnus Loop provide constraints on the physics of the shock front itself. Most of the very young remnants whose optical spectra show anomalous elemental abundances are too highly reddened for IUE observations, but extensive observations of the Crab Nebula and a spectrum of the supernova remnant in NGC 4449 yield carbon to oxygen ratios from which the mass of the progenitor may be estimated.