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

A multi-wavelength study of Supernova Remnants in six nearby galaxies. I: Detection of new X-ray selected Supernova Remnants with Chandra

We present results from a study of the Supernova Remnant (SNR) population in a sample of six nearby galaxies (NGC 2403, NGC 3077, NGC 4214, NGC 4449, NGC 4395 and NGC 5204) based on Chandra archival data. We have detected 244 discrete X-ray sources down to a limiting flux of 10^{-15} erg/s. We identify 37 X-ray selected thermal SNRs based on their X-ray colors or spectra, 30 of which are new discoveries. In many cases the X-ray classification is confirmed based on counterparts with SNRs identified in other wavelengths. Three of the galaxies in our sample (NGC 4214, NGC 4395 and NGC 5204) are studied for the first time, resulting in the discovery of 13 thermal SNRs. We discuss the properties (luminosity, temperature, density) of the X-ray detected SNRs in the galaxies of our sample in order to address their dependence on their environment. We find that X-ray selected SNRs in irregular galaxies appear to be more luminous than those in spirals. We attribute this to the lower metalicities and therefore more massive progenitor stars of irregular galaxies or the higher local densities of the ISM. We also discuss the X-ray selected SNR populations in the context of the Star Formation Rate of their host galaxies. A comparison of the numbers of observed luminous X-ray selected SNRs with those expected based on the luminosity functions of X-ray SNRs in the MCs and M33 suggest different luminosity distributions between the SNRs in spiral and irregular galaxies with the latter tending to have flatter distributions.Comment: 56 pages, 14 figures, 26 tables. Accepted for publication in Ap

A Search for Radio Supernova Remnants in Four Irregular Galaxies

We survey four nearby irregular galaxies for radio supernova remnants (SNRs) using deep (1 sigma ~ 20 microJy), high resolution (~20 pc) VLA continuum data at 20, 6, and 3.6 cm. We identify discrete sources in these galaxies and use radio spectral indices and H alpha images to categorize them as SNRs, H II regions, or background radio galaxies. Our classifications are generally in good agreement agreement with the literature. We identify a total of 43 SNR candidates: 23 in NGC 1569, 7 in NGC 4214, 5 in NGC 2366, and 8 in NGC 4449. Only one SNR--the well-studied object J1228+441 in NGC 4449--is more luminous at 20 cm than Cas A. By comparing the total thermal flux density in each galaxy to that localized in H II regions, we conclude that a significant fraction must be in a diffuse component or in low-luminosity H II regions.Comment: Accepted by AJ. 17 pages, 9 figures. 23 additional figures will be available in the online version of the Astronomical Journa

Comparing the Water-Tight Closure of Barbed and Conventional Suture Under Static and Dynamic Conditions in an Ex-Vivo Human Knee Arthrotomy Model.

Background: Barbed suture has become popular for closure of the arthrotomy and overlying tissues in total knee arthroplasty. STRATAFIX Symmetric PDS Knotless Tissue Control Device, a unique and novel barbed suture, with barbs formed integral to the suture core provides greater suture strength than the more common cut barbed suture designs. It is the only barbed suture commercially available with an indication in high tension areas, such as fascia. The purpose of this study was to evaluate the use of this novel barbed suture in the formation of a water-tight arthrotomy closure, using a continuous suture pattern, compared to conventional Coated VICRYL (polyglactin 910) Suture, using an interrupted suture pattern, in a cadaveric knee arthrotomy. Methods: Twenty fresh-frozen cadaver knees underwent randomization to provide donor-paired matching of the knee arthrotomy closures using barbed suture in a continuous pattern or conventional suture in an interrupted pattern. Each specimen underwent 5 phases of testing that included 1) predynamic static leak testing; 2) dynamic motion leak testing; 3) postdynamic static leak testing; 4) suture release static leak testing; and 5) postsuture release dynamic motion leak testing, to assess the fluid leak rate. Results: Under the initial static conditions, watertightness was similar for the 2 types of sutures. However, in all subsequent phases of testing, continuous barbed suture created a better watertight closure than interrupted conventional suture. Conclusions: In this study, it was observed that closure of a knee arthrotomy using the novel barbed suture provided improved watertightness compared to conventional interrupted closure under dynamic conditions and suture release

An X-ray View of Star Formation in the Central 3 kpc of NGC 2403

Archival Chandra observations are used to study the X-ray emission associated with star formation in the central region of the nearby SAB(s)cd galaxy NGC 2403. The distribution of X-ray emission is compared to the morphology visible at other wavelengths using complementary Spitzer, GALEX, and ground-based Halpha imagery. In general, the brightest extended X-ray emission is associated with HII regions and to other star-forming structures but is more pervasive; existing also in regions devoid of strong Halpha and UV emission. This X-ray emission has the spectral properties of diffuse hot gas (kT ~ 0.2keV) whose likely origin is in gas shock-heated by stellar winds and supernovae with < 20% coming from faint unresolved X-ray point sources. This hot gas may be slowly-cooling extra-planar remnants of past outflow events, or a disk component that either lingers after local star formation activity has ended or that has vented from active star-forming regions into a porous interstellar medium.Comment: 25 pages, accepted to A

Physical Structure and Nature of Supernova Remnants in M101

Supernova remnant (SNR) candidates in the giant spiral galaxy M101 have been previously identified from ground-based H-alpha and [SII] images. We have used archival Hubble Space Telescope (HST) H-alpha and broad-band images as well as stellar photometry of 55 SNR candidates to examine their physical structure, interstellar environment, and underlying stellar population. We have also obtained high-dispersion echelle spectra to search for shocked high-velocity gas in 18 SNR candidates, and identified X-ray counterparts to SNR candidates using data from archival observations made by the Chandra X-ray Observatory. Twenty-one of these 55 SNR candidates studied have X-ray counterparts, although one of them is a known ultra-luminous X-ray source. The multi-wavelength information has been used to assess the nature of each SNR candidate. We find that within this limited sample, ~16% are likely remnants of Type Ia SNe and ~45% are remnants of core-collapse SNe. In addition, about ~36% are large candidates which we suggest are either superbubbles or OB/HII complexes. Existing radio observations are not sensitive enough to detect the non-thermal emission from these SNR candidates. Several radio sources are coincident with X-ray sources, but they are associated with either giant HII regions in M101 or background galaxies. The archival HST H-alpha images do not cover the entire galaxy and thus prevents a complete study of M101. Furthermore, the lack of HST [SII] images precludes searches for small SNR candidates which could not be identified by ground-based observations. Such high-resolution images are needed in order to obtain a complete census of SNRs in M101 for a comprehensive investigation of the distribution, population, and rates of SNe in this galaxy.Comment: 37 pages, 4 Tables, 7 Figures, accepted for publication in the Astronomical Journa

Multiwavelength study of the nuclei of a volume-limited sample of galaxies I: X-ray observations

We discuss ROSAT HRI X-ray observations of 33 very nearby galaxies, sensitive to X-ray sources down to a luminosity of approximately 10^38 erg/s. The galaxies are selected from a complete, volume limited sample of 46 galaxies with d<7 Mpc for which we have extensive multi-wavelength data. For an almost complete sub-sample with M_B<-14 (29/31 objects) we have HRI images. Contour maps and source lists are presented within the central region of each galaxy, together with nuclear upper limits where no nuclear source was detected. Nuclear X-ray sources are found to be very common, occurring in ~35% of the sample. Nuclear X-ray luminosity is statistically connected to host galaxy luminosity - there is not a tight correlation, but the probability of a nuclear source being detected increases strongly with galaxy luminosity and the distribution of nuclear luminosities seems to show an upper envelope that is roughly proportional to galaxy luminosity. While these sources do seem to be a genuinely nuclear phenomenon rather than nuclear examples of the general X-ray source population, it is far from obvious that they are miniature Seyfert nuclei. The more luminous nuclei are very often spatially extended, and HII region nuclei are detected just as often as LINERs. Finally, we also note the presence of fairly common super-luminous X-ray sources in the off-nuclear population - out of 29 galaxies we find 9 sources with a luminosity larger than 10^39 erg/s. These show no particular preference for more luminous galaxies. One is already known to be a multiple SNR system, but most have no obvious optical counterpart and their nature remains a mystery.Comment: Accepted for publication in MNRAS. 26 pages, 47 figures (figures 1-29,31 and 38 as separate, low resolution files; full resolution files are available at http://www.star.le.ac.uk/~plt

Spitzer Observations of MF 16 Nebula and the associated Ultraluminous X-ray Source

We present Spitzer Infrared Spectrograph (IRS) observations of the ultra-luminous X-ray source (ULX) NGC 6946 X-1 and its associated nebula MF 16. This ULX has very similar properties to the famous Holmberg II ULX, the first ULX to show a prominent infrared [O IV] emission line comparable to those found in AGN. This paper attempts to constrain the ULX Spectral Energy Distribution (SED) given the optical/UV photometric fluxes and high-resolution X-ray observations. Specifically, Chandra X-ray data and published Hubble optical/UV data are extrapolated to produce a model for the full optical to X-ray SED. The photoionization modeling of the IR lines and ratios is then used to test different accretion spectral models. While either an irradiated disk model or an O-supergiant plus accretion disk model fit the data very well, we prefer the latter because it fits the nebular parameters slightly better. In this second case the accretion disk alone dominates the extreme-UV and X-ray emission, while an O-supergiant is responsible for most of the far-UV emission.Comment: 26 pages, 7 figures, accepted by Ap

Black Hole Powered Nebulae and a Case Study of the Ultraluminous X-ray Source IC342 X-1

We present new radio, optical, and X-ray observations of three Ultraluminous X-ray sources (ULXs) that are associated with large-scale nebulae. We report the discovery of a radio nebula associated with the ULX IC342 X-1 using the Very Large Array (VLA). Complementary VLA observations of the nebula around Holmberg II X-1, and high-frequency Australia Telescope Compact Array (ATCA) and Very Large Telescope (VLT) spectroscopic observations of NGC5408 X-1 are also presented. We study the morphology, ionization processes, and the energetics of the optical/radio nebulae of IC342 X-1, Holmberg II X-1 and NGC5408 X-1. The energetics of the optical nebula of IC342 X-1 is discussed in the framework of standard bubble theory. The total energy content of the optical nebula is 6 x 10^52 erg. The minimum energy needed to supply the associated radio nebula is 9.2 x 10^50 erg. In addition, we detected an unresolved radio source at the location of IC342 X-1 at VLA scales. However, our Very Long Baseline Interferometry (VLBI) observations using the European VLBI Network likely rule out the presence of any compact radio source at milli-arcsecond (mas) scales. Using a simultaneous Swift X-ray Telescope measurement, we estimate an upper limit on the mass of the black hole in IC342 X-1 using the "fundamental plane" of accreting black holes and obtain M_BH < (1.0\pm0.3) x 10^3 M_Sun. Arguing that the nebula of IC342 X-1 is possibly inflated by a jet, we estimate accretion rates and efficiencies for the jet of IC342 X-1 and compare with sources like S26, SS433, IC10 X-1.Comment: 11 pages, 8 figures, accepted for publication in Ap

Kinematics of the Ionised Gas in the Spiral Galaxy NGC 2403

We present a study of the kinematics of the ionised gas in the nearby spiral galaxy NGC 2403 using deep long-slit spectra obtained with the 4.2-m William Herschel Telescope. The data show the presence of a halo component of ionised gas that is rotating more slowly than the gas in the disk. The kinematics of this ionised halo gas is similar to that of the neutral halo gas. On small scales, broad line profiles (up to 300 km/s wide) indicate regions of fast outflows of ionised gas. We discuss these new results in the context of galactic fountain models.Comment: 17 pages, 10 figures, accepted for publication in A&