Supernova Remnants In M82 Research Articles

Searching for Balmer-dominated Type Ia Supernova Remnants in M33

Abstract We searched for Balmer-dominated Type Ia supernova remnants (SNRs) in M33 by selecting thermal X-ray sources with L X ≥ 5 × 10 35 erg s−1, identifying associated Hα emission features, and checking their [S ii] and [O iii] emission properties. Our search did not find any Balmer-dominated Type Ia SNRs in M33. This result is puzzling because M33 is 2–3 times more massive than the Large Magellanic Cloud (LMC), yet the LMC hosts five Balmer-dominated Type Ia SNRs and M33 has none. We have considered observational biases; interstellar densities and ionization conditions; the Type Ia SN rate expected from the star formation history and Type Ia SN delay time distribution function; and the metallicity effect. None of these can explain the absence of X-ray-bright Balmer-dominated Type Ia SNRs in M33. It is intriguing that the Galaxy has X-ray-bright and thermal Type Ia SNRs (Kepler and Tycho), as well as X-ray-faint and nonthermal Type Ia SNRs (G1.9+0.3, SN1006, and RCW86), while the LMC does not have the X-ray-faint and nonthermal ones and M33 does not have the X-ray-bright and thermal ones.

Supernova remnants in M33: X-ray properties as observed by XMM–Newton

We have carried out a study of the X-ray properties of the supernova remnant (SNR) population in M33 with XMM-Newton, comprising deep observations of 8 fields in M33 covering all of the area within the D$_{25}$ contours, and with a typical luminosity of 7.1$\times$10$^{34}$ erg s$^{-1}$ (0.2-2.0 keV) . Here we report our work to characterize the X-ray properties of the previously identified SNRs in M33, as well as our search for new X-ray detected SNRs. With our deep observations and large field of view we have detected 105 SNRs at the 3$\sigma$ level, of which 54 SNRs are newly detected in X-rays, and three are newly discovered SNRs. Combining XMM-Newton data with deep Chandra survey data allows detailed spectral fitting of 15 SNRs, for which we have measured temperatures, ionization timescales, and individual abundances. This large sample of SNRs allows us to construct an X-ray luminosity function, and compare its shape to luminosity functions from host galaxies of differing metallicities and star formation rates to look for environmental effects on SNR properties. We conclude that while metallicity may play a role in SNR population characteristics, differing star formation histories on short timescales, and small-scale environmental effects appear to cause more significant differences between X-ray luminosity distributions. In addition, we analyze the X-ray detectability of SNRs, and find that in M33 SNRs with higher [SII]/H$\alpha$ ratios, as well as those with smaller galactocentric distances, are more detectable in X-rays.

Size distribution of supernova remnants and the interstellar medium: the case of M 33

The size distribution of supernova remnants (SNRs) can help to clarify the various aspects of their evolution and interaction with the interstellar medium (ISM). Since the observed samples of SNRs are a collection of objects with very different ages and origin that evolve in different conditions of the ISM, statistical Monte Carlo methods can be used to model their statistical distributions. Based on very general assumptions on the evolution, we have modeled samples of SNRs at various initial and environmental conditions, which were then compared with observed collections of SNRs. In the evolution of SNRs the pressure of the ISM is taken into account, which determines their maximum sizes and lifetimes. When comparing the modeled and observed distributions, it is very important to have homogeneous observational data free from selection effects. We found that a recently published collection of SNRs in M33 (Long et al. 2010, ApJS,187,495) satisfies this requirement if we select the X-ray SNRs with hardness ratios in a limited range of values. An excellent agreement between distributions of this subset of SNRs and the subset of modeled SNRs was reached for a volume filling-factor of the warm phase of the ISM (partly ionized gas with $n_{\rm H}\sim 0.2-0.5~ \rm {cm}^{-3}; T \sim 8000-10000~K $) in M33 of $\sim\ 90%$. The statistical distributions constructed in this way, which reproduce practically all the statistical properties of observed SNRs, allowed us to obtain one of the important parameters of M33: the birthrate is one SNR every $ {140} - {150}$ yr, and the total number of SNRs with a shock Mach number $M_{s} \geq 2$ is larger than $\sim 1000$.

Wide-field Global VLBI and MERLIN combined monitoring of supernova remnants in M82

From a combination of MERLIN (Multi-Element Radio-Linked Interferometer Network) and global VLBI (Very Long Baseline Interferometry) observations of the starburst galaxy M82, images of 36 discrete sources at resolutions ranging from ~3 to ~80 mas at 1.7 GHz are presented. Of these 36 sources, 32 are identified as supernova remnants, 2 are HII regions, and 3 remain unclassified. Sizes, flux densities and radio brightnesses are given for all of the detected sources. Additionally, global VLBI only data from this project are used to image four of the most compact radio sources. These data provide a fifth epoch of VLBI observations of these sources, covering a 19-yr time-line. In particular, the continued expansion of one of the youngest supernova remnants, 43.31+59.3 is discussed. The deceleration parameter is a power-law index used to represent the time evolution of the size of a supernova remnant. For the source 43.31+59.3, a lower limit to the deceleration parameter is calculated to be 0.53+/-0.06, based on a lower limit of the age of this source.

THE ORTHOGONAL FITTING PROCEDURE FOR DETERMINATION OF THE EMPIRICAL Σ-DRELATIONS FOR SUPERNOVA REMNANTS: APPLICATION TO STARBURST GALAXY M82

The radio surface brightness-to-diameter ({\Sigma} - D) relation for supernova remnants (SNRs) in the starburst galaxy M82 is analyzed in a statistically more robust manner than in the previous studies that mainly discussed sample quality and related selection effects. The statistics of data fits in log {\Sigma} - log D plane are analyzed by using vertical (standard) and orthogonal regressions. As the parameter values of D - {\Sigma} and {\Sigma} - D fits are invariant within the estimated uncertainties for orthogonal regressions, slopes of the empirical {\Sigma} - D relations should be determined by using the orthogonal regression fitting procedure. Thus obtained {\Sigma} - D relations for samples which are not under severe influence of the selection effects could be used for estimating SNR distances. Using the orthogonal regression fitting procedure {\Sigma} - D slope {\beta} \approx 3.9 is obtained for the sample of 31 SNRs in M82. The results of implemented Monte Carlo simulations show that the sensitivity selection effect does not significantly influence the slope of M82 relation. This relation could be used for estimation of distances to SNRs that evolve in denser interstellar environment, with number denisty up to 1000 particles per cm3 .

Chandra ACIS Survey of M33 (ChASeM33): A First Look

We present an overview of the Chandra ACIS Survey of M33 (ChASeM33): A Deep Survey of the Nearest Face-on Spiral Galaxy. The 1.4 Ms survey covers the galaxy out to -->R ≈ 18'(≈ 4 kpc) . These data provide the most intensive, high spatial resolution assessment of the X-ray source populations available for the confused inner regions of M33. Mosaic images of the ChASeM33 observations show several hundred individual X-ray sources as well as soft diffuse emission from the hot interstellar medium. Bright, extended emission surrounds the nucleus and is also seen from the giant H II regions NGC 604 and IC 131. Fainter extended emission and numerous individual sources appear to trace the inner spiral structure. The initial source catalog, arising from ~2/3 of the expected survey data, includes 394 sources significant at the 3 σ confidence level or greater, down to a limiting luminosity (absorbed) of ~ -->1.6 × 1035 ergs s−1 (0.35-8.0 keV). The hardness ratios of the sources separate those with soft, thermal spectra such as supernova remnants from those with hard, nonthermal spectra such as X-ray binaries and background active galactic nuclei. Emission extended beyond the Chandra point-spread function is evident in 23 of the 394 sources. Cross-correlation of the ChASeM33 sources against previous catalogs of X-ray sources in M33 results in matches for the vast majority of the brighter sources and shows 28 ChASeM33 sources within 10 -->'' of supernova remnants identified by prior optical and radio searches. This brings the total number of such associations to 31 out of 100 known supernova remnants in M33.

Revealing the Supernova Remnant Population of M33 withChandra

We present results of a search for supernova remnants (SNRs) in archival Chandra images of M33. We have identified X-ray SNRs by comparing the list of Chandra X-ray sources in M33 with tabulations of SNR candidates identified from (1) elevated [S II]/Hα ratios in the optical and (2) radio spectral indices. In addition, we have searched for optical counterparts to soft sources in the Chandra images and X-ray SNR candidates identified in the XMM-Newton survey of M33. Of the 98 optically known SNRs in M33, 22 have been detected at >3 σ level in the soft band (0.35–1.1 keV). At least four of these SNR candidates are spatially extended based on a comparison of the data to simulated images of point sources. Aside from the optically matching SNRs, we have found one soft X-ray source in M33 that exhibits no optical emission and is coincident with a known radio source. The radio spectral index of this source is consistent with particle acceleration in shocks, leading us to suggest that it is a nonradiative SNR. We have also found new optical counterparts to two soft X-ray SNRs in M33. These counterparts exhibit enhanced [S II]/Hα ratios characteristic of radiative shocks. Pending confirmation from optical spectroscopy, the identification of these two optical counterparts increases the total number of known optically emitting SNRs in M33 to 100. This brings the total number of identified SNRs with X-ray counterparts, including those exclusively detected by the XMM-Newton survey of M33, to 37 SNRs. We find that while there are a similar number of confirmed X-ray SNRs in M33 and the LMC with X-ray luminosities in excess of 1035 ergs s-1, nearly 40% of the LMC SNRs are brighter than 1036 ergs s-1, while only 13% of the M33 sample exceed this luminosity. Including X-ray SNR candidates from the XMM-Newton survey (objects lacking optical counterparts) increases the fraction of M33 SNRs brighter than 1036 ergs s-1 to 22%, still only half the LMC fraction. The differences in luminosity distributions cannot be fully explained by uncertainty in spectral model parameters and are not fully accounted for by abundance differences between the galaxies.

Deep Radio Imaging with MERLIN of the Supernova Remnants in M82

SummaryAn 8 day MERLIN deep integration at 5GHz of the central region of the starburst galaxy M82 has been used to investigate the radio structure of a number of supernova remnants in unprecedented detail revealing new shells and partial shell structures for the first time. In addition, by comparing the new deep 2002 image with an astrometrically aligned image from 36 hours of data taken in 1992, it has been possible to directly measure the expansion velocities of 4 of the most compact remnants in M82. For the two most compact remnants, 41.95+575 and 43.31+592, expansion velocities of 2800 ± 300 km s-1 and 8750 ± 400kms-1have been derived. These confirm and refine the measured expansion velocities which have been derived from VLBI multi-epoch studies. For remnants 43.18+583 and 44.01+596, expansion velocities of 10500 ± 750km s-1 and 2400 ± 250 kms-1have been measured for the first time. In addition, the peak of the radio emission for SNR 45.17+612 has moved between the two epochs implying velocities around 7500km s-1. The relatively compact remnants in M82 are thus found to be expanding over a wide range of velocities which appear unrelated to their size. The new 2002 map is the most sensitive high-resolution image yet made of M82, achieving an rms noise level of 17μJy beam-1. This establishes a first epoch for subsequent deep studies of expansion velocities for many SNR within M82.

The impact of supernova remnants on the ISM in Starburst galaxies

We used the near-infrared [Fe II] emission line signature of shock-heating to detect supernova remnants (SNRs) in nearby starburst galaxies. The near-IR narrow-band imaging program has led to the detection of SNR candidates in NGC 1569 and NGC 5253, both host to super-star clusters. A spatially extended component to the [Fe II] line emission dominates the integrated [Fe II] luminosity in the two galaxies. Despite the starburst environment, the [Fe II] luminosity of the individual SNRs is two orders of magnitude lower than the luminosities observed for SNRs in M82. We find that the density and the structure of the interstellar medium is a more important factor than the starburst nature of a galaxy in determining the average [Fe II] luminosity of a SNR. The observations suggest that a significant fraction of the ISM in NGC 1569 and NGC 5253 is under the influence of SNRs. This does not appear to be the case in M82 where the impact of the SNRs is limited to high density knots. To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The [F[CLC]e[/CLC] [CSC]ii[/CSC]] 1.644 Micron Emission in M82 and NGC 253: Is It a Measure of the Supernova Rate?

We present Hubble Space Telescope NICMOS [Fe II] 1.644 μm, Paα (1.87 μm), and continuum images of the starburst galaxies M82 and NGC 253 at an unprecedented spatial resolution. In both galaxies we detect [Fe II] compact sources superposed on a diffuse background in the disk of the galaxies, together with a component above and below the plane of the galaxy. The radio and [Fe II] emissions perpendicular to the disk of M82 show a remarkable similarity to each other, suggesting that both emissions originate in shocks from supernova explosions. We find a spatial correspondence between bright compact [Fe II]–emitting regions and the location of radio supernova remnants (SNRs) for approximately 30%–50% of radio SNRs in M82 and NGC 253. This lack of a one-to-one correspondence, more than being indicative of a different origin for the radio and [Fe II] emission in starbursts, suggests two populations of SNRs: an older population (104 yr), traced by the [Fe II] emission, and a younger population (a few hundred years old), traced by the radio SNRs. We therefore conclude that the [Fe II] emission in starburst galaxies provides a good estimate of the supernova activity. Using our newly determined [Fe II] luminosities (corrected for extinction) of M82 and NGC 253, we reevaluate the calibration of the supernova rate in terms of the [Fe II] luminosity for starburst galaxies.

Global very long-baseline interferometry observations of compact radio sources in M82

Observations of the starburst galaxy, M82, have been made with a 20-station global VLBI array at �18cm. Maps are presented of the brightest young supernova remnants (SNR) in M82 and the wide-field mapping techniques used in making images over a field of view of �1 arcminute with 3 milliarcsecond resolution are discussed. A limit has been placed on the power law deceleration of the young SNR, 43.31+592 with an index greater than 0.73 ± 0.11 from observations with the European VLBI Network. Using the global array we have resolved compact knots of radio emission in the source which, with future global observations, will enable better constraints to be placed on the expansion parameters of this SNR. The latest global observations have also provided high resolution images of the most compact radio source in M82, 41.95+575. We determine an upper limit to the radial expansion rate along the major axis of 2000 km s 1 . However, the new images also show structure resembling that of collimated ejection which brings into question the previous explanation of the source as being due to the confinement of a supernova by a high density circumstellar medium. It is apparent that we are now able to image the brightest supernova remnants in M82 with a linear scale which allows direct comparison with galactic SNR such as Cassiopeia A.

Supernova Remnants in the Fossil Starburst in M82

We report the discovery of 10 compact Hα-bright sources in the poststarburst region northeast of the center of M82, called M82 B. These objects have Hα luminosities and sizes consistent with Type II supernova remnants (SNRs). They fall on the same Hα surface brightness–diameter relation (Σ-D) defined by SNRs in other nearby star-forming galaxies, with the M82 candidates lying preferentially at the small-diameter end. These are the first candidates for optically visible SNRs in M82 outside the heavily obscured central starburst within about 250 pc from the galactic center. If these sources are SNRs, they set an upper limit to the end of the starburst in region B2, about 500 pc from the galaxy's core, of about 50 Myr. Region B1, about 1000 pc from the core, lacks good SNR candidates and is evidently somewhat older. This suggests that star formation in the galaxy has propagated inward toward the present-day intense starburst core.

A New Sample of Radio‐selected and Optically Confirmed Supernova Remnants in M33

Using radio data to identify and optical data to confirm, we have established the largest and most complete sample of extragalactic radio-bright supernova remnants (SNRs) in the nearby spiral galaxy M33. We have identified 53 radio SNRs, doubling the size of the earlier survey by Duric et al. The increased sample size provides more insight into the nature of SNRs and provides an extensive informational database about SNRs for future studies. The SNR sample was analyzed for statistical trends that relate to the evolution of their radio emission. We report no significant correlation between the radio flux densities and diameters of SNRs in our sample. The absence of a statistically meaningful Σ-D relation is consistent with the view that environmental factors govern the radio evolution of SNRs. A new radio luminosity function for SNRs is presented. Although there appears to be a break in the function, the break is the result of selection effects and not intrinsic to the sample. A comparison of the radio luminosity function with the integrated radio continuum properties of M33 suggests that SNRs may well be the primary source of the relativistic electrons in M33. A histogram of synchrotron spectral indices of the SNRs is presented. Statistical analysis of the spectral index distribution indicates that the mean spectral index of SNRs in M33 is steeper than the mean in samples of SNRs in the Galaxy or the LMC and is consistent with a particle spectrum expected from a diffusive shock acceleration process.

Neutral hydrogen absorption against supernova remnants in M82

We present MERLIN neutral hydrogen absorption measurements against supernova remnants in the central starburst region of M82 with an angular resolution of ∼ 0.4 arcsec. We detect H i absorption or set significant upper limits against 33 supernova remnants from which we have been able to deduce column densities. Hence, using these measurements, we are able to probe the neutral hydrogen distribution and dynamics of the interstellar medium in M82 along 33 lines of sight on linear scales of order 1 pc. Our results show column densities ranging from <1.6 to >30 × 1021 atom cm−2 with the highest values seen towards the edge of the 250-pc ‘ring’. The absorption velocities show a gradient of 7.3 ± 4 km s−1 arcsec−1, consistent with rotation parameters of this ‘ring’ inferred from other measurements. The absorption velocities against individual remnants show deviations of typically 30 km s−1 from simple solid body rotation, and a number show multiple velocity absorption features. Although some of these deviations may be the result of the remnants being embedded at different depths within the neutral gas, the velocities cannot be explained by a simple rotating ring.

A New Optical Sample of Supernova Remnants in M33

We present a new and larger sample of supernova remnants in the nearby spiral galaxy M33. The sample is based upon CCD interference filter observations obtained with the Kitt Peak 4 m telescope and spectroscopic observations obtained with the Multiple Mirror Telescope. Using optical emission-line ratios, supplemented by a radio continuum map of M33 (Duric et al.; Gordon et al.), we have identified 98 supernova remnant (SNR) candidates, of which 53 were previously unknown. We have obtained spectra of 27 SNR candidates, bringing the total number of M33 SNRs for which spectra are available to 72. All the spectra show the characteristic signature of shock-heated gas, which leads us to believe that the rest of the candidates are also supernova remnants. The large sample provides a useful database to investigate the global properties of SNRs. In this paper, we present a new cumulative number-diameter [N(<D)] relation for SNRs. We find that the free expansion model is inconsistent with the observed N(<D) relation and that the Sedov-Taylor (ST) expansion model is a much better fit. The ST expansion model is used to derive a SN rate in M33 of one SN every 360 yr. The spectroscopic sample of SNRs is the largest of its kind in any galaxy. Our investigations show no relation between [N II]:Hα and [S II] λ6717:λ6731. We do, however, find weak trends between the SNR diameter and [N II]:Hα and [S II]:Hα. Further, we find a strong correlation between [N II]:Hα and the galactocentric distance (GCD) indicative of an abundance gradient. There is a large dispersion in the [N II]:Hα ratio at a given GCD that cannot be explained by evolutionary effects and that may be due to a larger abundance dispersion in the inner part of the galaxy.

Low-frequency observations of supernova remnants in M82

We have used MERLIN at 408 MHz to image the central starburst region ofM82 with a resolution of 0.5 arcsec. We detect ~20 supernova remnants at this frequency, which is a much smaller number than we detect at higher frequencies (~50). We attribute this difference to free-free absorption by ionized gas. We find that seven remnants show low-frequency turnovers in their spectra consistent with free-free absorption. These spectra are similarto the spectrum previously obtained for the brightest, youngest supernova remnant, 41.95+57.5. We find a mean optically thin spectral index of -0.6 and emission measures ~ las cm -6 pc for the remnants detected at 408 MHz. These emission measures are an order of magnitude smaller than other published values for the central region of M82 and we therefore suggest that the remnants we detect at 408 MHz are embedded within ionized gas towards the near side of the distribution. In addition to the supernova remnants, we detect the extended background in which several regions attributable to free-free absorption by ionized gas can be seen. The most striking is an extended absorption region (~1 00 pc across) approximately centred on 41.95+57.5 which may be an H II region photoionized by a cluster of early-type stars. The progenitor of 41.95+57.5 may well have been a member of this cluster. We find one source near the dynamical centre of M82, which we speculate could be a possible candidate for an active galactic nucleus.

Infrared Fabry‐Perot Imaging of M82 [Feii] Emission. II. Tracing Extragalactic Supernova Remnants

We report high spatial and spectral resolution [Fe II] 1.644 μm Fabry-Perot imaging observations of M82. We present extinction-corrected [Fe II] images and discuss the nature of compact [Fe II] emission regions revealed by these new data. We conclude that these [Fe II] sources trace a population of supernova remnants in M82 that are substantially older than those revealed previously on 6 cm radiographs. In addition, we find that M82 contains a distributed [Fe II] emission component that is extended along the southern minor axis and that accounts for 90% of the galaxy's [Fe II] luminosity. We interpret this extended emission as tracing disk material entrained in a super wind that has broken out of the galactic disk to the south. We find that the [Fe II]/Brγ line ratio throughout M82 correlates with the age of the starburst as reflected by the color of the photospheric emission from the galaxy's stars. This correlation suggests that the [Fe II] emission regions in M82 are colocated with a post-main-sequence stellar population. The engineering details of our Fabry-Perot imaging methodology are also discussed.

Spectral index evolution of young shell supernova remnants in the milky way and other galaxies

Abstract We show that the radio spectral index of young shell supernova remnants evolvs differently in galaxies with and without a star burst (M82, NGC253 and the Galaxy, M31, M33, LMC, SMC). This is explained by the difference in gas density, which determines the dynamic evolution of shell supernova remnants in these galaxies (ρM82/ρGal ≈ 150). The spectral index – diameter dependence is suggested to be used for the estimation of a typical initial mass, M 0, of a shell supernova remnant. For shells in M82, it is estimated as M 0 = 2.3 ± 1.1M[odot]. This is the first known estimate of this kind for the remnants in M82, as well as the kinetic energy of the shell 41.9+58, 1051 ergs. We conclude that the unusually high radio brightness of supernova remnants in M82 is a consequence of only the interaction with ambient medium.

Forbidden Fe+ emission from supernova remnants in M33

Supernovae remnants are known to be luminous sources of infrared [FeII] emission. By studying how the luminosity scales with age, environment and other relevant factors, we can construct an [FeII] luminosity function for supernovae remnants. This will enable us to predict supernovae rates in starburst galaxies that are too distant for individual remnants to be resolved. First, however, we require accurate luminosities for a sample of remnants of varying ages, and in varying physical environments. As part of this project we have carried out an initial study of a small sample of evolved (ages greater than a few thousand years) remnants in M33. From these data we tentatively conclude that there is evidence for the peak luminosity in the [FeII] lines of these sources to arise in a narrow range of ages. In other respects, the M33 remnants are similar to their galactic and Magellanic Cloud counterparts in the observed peak luminosity. From this, and internal evidence as to the environment present in these regions, we conclude that the luminosity of evolved remnants is only marginally dependent on density and metallicity.

The structure of young supernova remnants in M82

We have used the enhanced MERLIN at 5 GHz to image the central 700 pc of the nearby starburst galaxy M82. We detect in excess of 40 discrete sources, all of which are resolved by the MERLIN 50-mas (0.75-pc) beam. The observations confirm that most of the discrete sources are supernova remnants. Several show complete shells, and many more show structure consistent with partial shells. We have measured the sizes, flux densities and radio brightnesses of 23 of the sources, and show that they follow a surface brightness/diameter relation consistent with that found in the LMC and Galactic remnants. The cumulative number as a function of diameter appears to increase linearly to diameters of at least 3 pc, and indicates a supernova rate of 0.05 per year if the shells are expanding at 5000 km s −1