Supergiant Shells Research Articles

The Kinematic Structure of the Supergiant Shell LMC 2

LMC2 was one of the first supergiant shells in the Large Magellanic Cloud (LMC) to be identified, based on the detection of long, curved Hα filaments extending over 900 pc (Goudis & Meaburn 1978). LMC 2 is located to the east of the active star formation region south of 30 Doradus. LMC 2 is a spectacular supergiant shell in the LMC, having the most coherent filamentary structure and the highest X-ray surface brightness. As shown in Fig. 1, the diffuse X-ray emission from LMC 2 is bounded by the Hα filaments in the north and east. A bright X-ray arc is seen in the southwest quadrant, extending from N 158 and N 159.

The Violent Interstellar Medium of Nearby Dwarf Galaxies

AbstractHigh resolution HI observations of nearby dwarf galaxies (most of which are situated in the M81 group at a distance of about 3·2 Mpc) reveal that their neutral interstellar medium (ISM) is dominated by hole-like features most of which are expanding. A comparison of the physical properties of these holes with the ones found in more massive spiral galaxies (such as M31 and M33) shows that they tend to reach much larger sizes in dwarf galaxies. This can be understood in terms of the galaxy's gravitational potential. The origin of these features is still a matter of debate. In general, young star forming regions (OB-associations) are held responsible for their formation. This picture, however, is not without its critics and other mechanisms such as the infall of high velocity clouds, turbulent motions or even gamma ray bursters have been recently proposed. Here I will present one example of a supergiant shell in IC 2574 which corroborates the picture that OB associations are indeed creating these structures. This particular supergiant shell is currently the most promising case to study the effects of the combined effects of stellar winds and supernova explosions which shape the neutral interstellar medium of (dwarf) galaxies.

The UM/CTIO Magellanic Cloud Emission-line Survey

The Magellanic Clouds are unique in providing sites to study the interstellar medium (ISM) and its components at all scales. To promote the pursuit of such studies, we have begun the Magellanic Cloud Emission-line Survey (MCELS), a deep imaging survey of both of these nearby galaxies in the emission of Hα, [S II], and [O III]. The emission-line images will be used in detailed optical and multiwavelength studies of H II regions, supernova remnants, planetary nebulae, superbubbles, and supergiant shells. Together with parallel surveys at other wavelengths, this survey will provide the foundation upon which to build a deeper understanding of the ISM in the Clouds and other galaxies, from small scales (~1 pc) all the way up to global scales. We present a sample of recent and current work using the MCELS dataset.

The Physics of 106 K Gas in LMC Supergiant Shells

We present first results of our study of the interplay between the 106 K, 104 K, 102 K gas phases in the supergiant shell LMC 4.

The Cool Atomic Gas in the Large Magellanic Cloud

Studying the cool atomic phase of the interstellar medium is of special significance as cool atomic clouds can become the raw material for star formation and so determine the evolution of the whole galaxy. The cool atomic interstellar medium of the Large Magellanic Cloud (LMC) seems to be quite different from that in the Milky Way. In three 21 cm absorption line surveys using the Australia Telescope Compact Array (ATCA) the physical properties of the cool atomic hydrogen in the LMC and the halo of the Magellanic Clouds have been studied. Here we present the results of the third HI absorption line survey. A detailed investigation of the cool HI has been done toward the supergiant shell LMC4, the surroundings of 30 Doradus and in the direction of the eastern steep HI boundary. The data have been compared with survey 2 (Dickey et al. 1994) to probe the cool gas fraction for these different regions of the LMC and to study the differences of the cool atomic phase of the LMC and that of the Milky Way.

Bow Shock Induced Star Formation in the LMC

The supergiant shell LMC 4 is known for its ring of HII regions and the deep minimum in HI in the interior (Rohlfs et al. 1984). LMC 4 shows X-ray emission detected by ROSAT and highly ionised gas (C IV) detected with HST (Bomans et al. 1994, 1996). The velocities of its neutral gas indicate it cannot have been formed by the collision with a high velocity cloud (Domgörgen et al. 1995).

On Water Masers in Circumstellar Shells

Detection rates for 22 GHz water masers from O-rich circumstellar shells are always less than 100%. This can in part be understood by revisiting high angular-resolution observations of masers in OH 39.7 + 1.5 and red supergiants. The pattern of occurrence for water masers around the pulsation cycle of OH 39.7 + 1.5 suggests that a detectable maser only occurs when it is triggered by a density enhancement with a suitable gain orientation to our line of sight. Enhancements, in effect, break the local symmetry of many otherwise equivalent gain paths to provide a means for focusing emission into a narrow range of rays, which promotes a detectable maser. A brief review of masers in the circumstellar shells of red supergiants shows that water masers exhibit a rich ellipsoidal distribution of emission hot spots. Nevertheless, these usually contain no water masers on the axis of their biconical, higher velocity, lower density, bipolar flows. If many Mira variables and OH/IR stars have important bipolar flows, some will be seen nearly pole-on, and these are less likely to exhibit water masers, even if they host OH masers. The main input of energy (and momentum) to gas in a circumstellar shell comes from friction with dust particles driven through it by radiation pressure. In consequence, the switch between radial-gain masers in OH 39.7 + 1.5 that predominate near maximum light and a tangential-gain maser that can occur near minimum may result entirely from the pulsation-dependent temperature modulation of the shell. However, the fast polar wind in red supergiants is already well developed in the water masing zone, so its causality is probably located within the star itself.

X-Ray Emission from an Expanding Supergiant Shell in IC 2574

We present a multiwavelength study of a supergiant shell within the violent interstellar medium of the nearby dwarf galaxy IC 2574, which is a member of the M81 group of galaxies. Neutral hydrogen (H i) observations obtained with the Very Large Array (VLA) reveal a prominent expanding supergiant H i shell in the northeast quadrant of IC 2574 which is thought to be produced by the combined effects of stellar winds and supernova explosions. It measures roughly pc in size and is expanding at »25 km s 21 . The H i data suggest 1000 # 500 an age of » yr; the energy input must have been of order ergs. Massive star-forming 6 53 1.4 # 10 (2.6 5 1) # 10 regions, as traced by Ha emission, are situated predominantly on the rim of this H i shell. This supports the view that the accumulated H i on the rim has reached densities that are high enough for secondary star formation to commence. VLA radio continuum observations at cm show that these star-forming regions are the main l 5 6 sources of radio continuum emission in this galaxy. This emission is mainly thermal in origin. Soft X-ray emission from within the H i hole is detected by a pointed ROSAT PSPC observation. The emission is resolved, coinciding in size and orientation with the H i shell. These spatial properties suggest that the emission is generated by an X-ray‐emitting plasma located within the H i shell, although a contribution from X-ray binaries cannot be completely ruled out. The X-ray luminosity within the 0.11‐2.4 keV energy range is 38

Multi-wavelength View of the Interstellar Medium in the Large Magellanic Cloud

AbstractThe Large Magellanic Cloud (LMC) has been surveyed in optical emission lines, X-rays, radio continuum, HI, and CO lines. These surveys provide views of the interstellar medium (ISM) in the LMC of unprecedented clarity, allowing us to study astrophysical processes and to examine the relationship among the different phases of the ISM. Multi-wavelength images are used to illustrate the physical structures of supernova remnants, superbubbles, and supergiant shells, as well as the global interstellar structure of the LMC.

HI Supergiant Shells in the Large Magellanic Cloud

AbstractThe recently completed HI mosaic survey of the Large Magellanic Cloud (Kim et al. 1997) reveals complex structure in the interstellar medium, including filaments, arcs, holes and shells. We have catalogued giant and supergiant HI shells and searched for correlations with Hα emission, using a new image taken with a camera lens mounted on the 16-inch telescope at Siding Spring Observatory.

The UM/CTIO Magellanic Cloud Emission-line Survey

AbstractThe Magellanic Clouds are unique in providing us with sites to study the interstellar medium (ISM) and its components at all scales. To promote the pursuit of such studies, we have begun the Magellanic Cloud Emission-line Survey (MCELS), a deep imaging survey of both of these nearby galaxies in the emission of Hα, [S II], and [O III]. The emission-line images will be used in detailed optical and multiwavelength studies of H II regions, supernova remnants, planetary nebulae, superbubbles, and supergiant shells. Together with parallel surveys at other wavelengths, this survey will provide the foundation upon which to build a deeper understanding of the ISM in the Clouds and other galaxies, from small scales (∼1 pc) all the way up to global scales.

Hot Interstellar Gas in the Irregular Galaxy NGC 4449

NGC 4449 is an irregular galaxy with a moderately high star formation activity. The massive stars in NGC 4449 have given rise to many bright HII regions, superbubbles, supergiant shells, and chimney-like radial filaments. ROSAT X-ray observations of NGC 4449 have revealed four point-like sources and a wide-spread diffuse emission. The spectral properties of the diffuse component suggest that the emission originates from hot interstellar gas. We have compared deep ground-based H-alpha images with the X-ray images of NGC 4449 to determine the relationship between the hot (10^6 K) and the warm (10^4 K) components of the interstellar gas. We have also used an archival Hubble Space Telescope WFPC2 image of NGC 4449 taken through the F606W filter to examine the massive stellar content of the X-ray-emission regions. We find that hot interstellar gas exists in (1) active star forming regions, including the giant H II region CM 16, (2) probable outflows from star forming regions, and (3) the supergiant shell SGS2. The X-ray data have been used to derive the rms electron density, mass, and thermal energy of the hot interior of SGS2. Finally we discuss the origin of SGS2 and implications of the detection of diffuse X-rays in irregular galaxies.

The HI Supergiant Shells in the Large Magellanic Cloud

AbstractWe present the result of an HI aperture synthesis mosaic of the Large Magellanic cloud (LMC), made recently with the Australia Telescope Compact Array (ATCA). The resolution of the mosaiced images is l′.0 (15 pc, using a distance to the LMC of 50 kpc). In contrast to its appearance at other wavelengths, the LMC is remarkably symmetrical in HI on the largest scales, with the bulk of the HI residing in a disk of diameter 8.°4 (7.3 kpc). Outer spiral structure is clearly seen, though the features appear to be due to differential rotation, therefore transient in nature. On small to medium scales, the combined action of numerous shells and supershells dominate the structures and motions of the HI gas in the LMC. A good correlation is seen between supershells previously identified in Hα (e.g. Meaburn 1980) and HI structures. We compare the results with a new wide-field Hα image.

An HI Mosaic of the Large Magellanic Cloud

AbstractThe parameters of a new Australia Telescope Compact Array (ATCA) mosaic of the Large Magellanic Cloud (LMC) in the 21-cm line of neutral hydrogen are described. A preliminary peak-brightness-temperature image of the whole of the LMC, and a detailed image of the region around the supergiant shells LMC 4 and 5 is shown.

Supershells and Chimneys: The Giant Ionized Gas Filaments in NGC 1800

view Abstract Citations (10) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Supershells and Chimneys: The Giant Ionized Gas Filaments in NGC 1800 Hunter, Deidre A. Abstract The otherwise unremarkable dwarf galaxy NGC 1800 contains extraordinary structures in its ionized gas including an ∼3 kpc web of filaments, fingers pointing out of the plane of the galaxy, and a supergiant shell, also apparently extending out of the plane. Emission-line ratios of the filamentary structures are similar to those observed in supershells in the LMC and M33, and they are consistent with direct photoionization as the dominant mechanism for ionization. We suggest that the web of filaments is fitted by the model of Mac Low, McCray, & Norman in which supershells from a previous generation of massive stars have expanded out of the disk of the galaxy and fragmented above the plane. The fingers are "chimneys" which provide paths along which UV photons from the current population of massive stars can travel the large distances to the filaments. Structures like these are not often found in late-type galaxies, and so this phenomenon is unlikely to be a common feature of galaxy evolution. Publication: The Astrophysical Journal Pub Date: February 1996 DOI: 10.1086/176762 Bibcode: 1996ApJ...457..671H Keywords: GALAXIES: ISM; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 1800; GALAXIES: STRUCTURE full text sources ADS | data products SIMBAD (7) NED (1)

Supergiant Shells and Hot Gas in NGC 4449

Supergiant shells are the largest interstellar structures in galaxies. They are outlined by long H II filaments enclosing an inner space containing very little warm or cold gas. In the LMC, two supergiant shells have been detected in X-rays indicating the existence of hot gas: LMC 2 (Wang & Helfand 1992) and LMC 4 (Bomans et al. 1994). It is not yet clear whether the hot gas in a galactic halo is supplied by such supergiant shells.

Large scale structure of the ionized gas in the magellanic clouds

view Abstract Citations (123) References (61) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Large Scale Structure of the Ionized Gas in the Magellanic Clouds Kennicutt, Robert C., Jr. ; Bresolin, Fabio ; Bomans, Dominik J. ; Bothun, Gregory D. ; Thompson, Ian B. Abstract Calibrated Hα CCD images taken With the "Parking Lot Camera" are used to investigate the large scale properties of the ionized gas in the Magellanic Clouds. The integrated Hα luminosity, star formation, and the large-scale diffuse emission are studied and compared with other galaxies. The diffuse gas component accounts for 30%-40% of the total Hα emission in both galaxies. The integrated star formation rates and the fraction of diffuse emission are typical for Magellanic irregular galaxies. The Hα maps are used to derive a set of physical parameters for the known supergiant shells in the LMC and SMC. The Hα emission distribution have also been compared to the distribution of HI column density. Evidence for a star formation threshold is discussed. Publication: The Astronomical Journal Pub Date: February 1995 DOI: 10.1086/117304 Bibcode: 1995AJ....109..594K Keywords: Diffuse Radiation; Galactic Structure; H Alpha Line; Ionized Gases; Luminosity; Magellanic Clouds; Star Formation; Astronomical Maps; Charge Coupled Devices; Density Distribution; Hydrogen; Irregular Galaxies; Star Formation Rate; Astronomy; MAGELLANIC CLOUDS; ISM: STRUCTURE full text sources ADS | data products SIMBAD (25) NED (2)

Imaging and spectroscopy of ionized shells in M33 and M31

This paper extends an examination of the spectral signature of the interaction of massive stars with the surrounding interstellar medium to the nearby spiral galaxies M33 and M31. H-alpha images and low-dispersion spectra have been obtained for eight giant ionized shell structures in M33 and two in M31. These structures are believed to be the result of the encircled groups of stars blowing holes in the gas through winds and supernova explosions. The emission-line ratios are compared to those of giant and supergiant shells in the Large Magellanic Cloud (LMC). Generally, the shells in M33 and M31 follow the same trend lines outlined by the shells and H II regions in the LMC with the M31 shells being offset to higher metallicity. However, unlike shells in the LMC, the M33 shells have some emission-line ratios that are not particularly distinct from those of H II regions in the same galaxy. Nevertheless, like the shells in the LMC, the emission-line ratios imply that the emission from the shells in M33 and M31 is dominated by photoionization processes. Upper limits to (O I)/H-alpha are consistent with this in most cases.

Ultraviolet interstellar absorption lines in the LMC: Searching for hidden SNRs

Strong x-ray emission detected in Large Magellanic Cloud (LMC) superbubbles has been explained as the result of interior supernova remnants (SNRs) hitting the dense superbubble shell. Such SNRs cannot be found using conventional criteria. We thus investigate the possibility of using the interstellar absorption properties in the ultraviolet (UV) as a diagnostic of hidden SNR shocks. The International Ultraviolet Explorer (IUE) archives provide the database for this pilot study. They contain high-dispersion spectra of several stars in x-ray bright superbubbles. To distinguish the effects of SNR shocks from those of local stellar winds and a global hot halo around the LMC, we included control objects in different environments. We find that almost all interstellar absorption properties can be explained by the interstellar environment associated with the objects. Summarizing the two most important results of this study: (1) a large velocity shift between the high-ionization species (C IV and Si IV) and the low-ionization species (S II, Si II, and C II*) is a diagnostic of hidden SNR shocks; however, the absence of a velocity shift does not preclude the existence of SNR shocks; (2) there is no evidence that the LMC is uniformly surrounded by hot gas; hot gas is preferentially found associated with large interstellar structures like superbubbles and supergiant shells, which may extend to large distances from the plane.

Kinematic structure of the 30 Doradus giant H II region

We have used the echelle CCD spectrograph on the Cerro Tololo Inter-American Observatory (CTIO) 4 m telescope to map the nebular velocity field in the 30 Doradus giant H II region. The kinematics of 30 Dor are very complex. The outer regions are charaterized by a smooth velocity field, but its turbulent velocity, 30-40 km/s Full Width Half Maximum (FWHM), is considerably higher than those in most smaller H II regions. In the central 9 min core, multiple velocity components are observed at most positions. The velocity field is dominated by a large number of expanding structures, ranging in size from 1 to 100 pc and expansion velocities of 20-200 km/s, and often organized into large hierarchical networks. The integral of these complex expanding structures in 30 Dor produces a surprisingly simple profile with a broad Gaussian core and faint extended wings. Several fast-expanding shells, with diameters of 2-20 pc, expansion velocities of 100-300 km/s, and kinetic energies of 0.5-10 x 10(exp 50) ergs have been identified. The large fast-expanding shells and networks are coincident with extended X-ray sources and are probably associated with supernova remnants embedded in supershells produced by the combined effects of stellar winds and supernovae from OB associations. We have used the intensity-calibrated echelle spectra to determine the basic physical and dynamical properties of the kinematic features in 30 Dor. The expanding shells contain roughly half of the kinetic energy in the 30 Dor complex, and this energy is several times higher than the gravitational binding energy of the region. The energetic requirements of the gas are consistent with the observed stellar content of 30 Dor, if the gas is accelerated by a combination of stellar winds and supernovae. Extrapolating the current energy injection rate in the nebula over the lifetime of the OB complex suggest that 30 Dor and its vicinity will evolve into a supergiant shell as seen in the LMC and other nearby galaxies.