Shell Of NGC Research Articles

Morpho-kinematic Properties of Wolf–Rayet Planetary Nebulae

The majority of planetary nebulae (PNs) show axisymmetric morphologies, whose causes are not well understood. In this work, we present spatially resolved kinematic observations of 14 Galactic PNs surrounding Wolf–Rayet ([WR]) and weak emission-line stars (wels), based on the Hα and [N ii] emission taken with the Wide Field Spectrograph on the Australian National University 2.3 m telescope. Velocity-resolved channel maps and position–velocity diagrams, together with archival Hubble Space Telescope (HST) and ground-based images, are employed to construct three-dimensional morpho-kinematic models of 12 objects using the program shape. Our results indicate that these 12 PNs mostly have elliptical morphologies, with either open or closed outer ends. The kinematic maps show the on-sky orientations of the interior shells in NGC 6578 and NGC 6629, as well as the compact (≤6″) PNs Pe 1-1, M 3-15, M 1-25, Hen 2-142, and NGC 6567, in agreement with the elliptically symmetric morphologies seen in high-resolution HST images. Point-symmetric knots in Hb 4 exhibit deceleration with distance from the central star, which could be due to shock collisions with the ambient medium. The velocity dispersion maps of Pe 1-1 also disclose the shock interaction between its collimated outflows and the interstellar medium. Collimated bipolar outflows are also visible in the position–velocity diagrams of M 3-30, M 1-32, and M 3-15, which are reconstructed by tenuous prolate ellipsoids extending upward from dense equatorial regions in the kinematic models. The formation of aspherical morphologies and collimated outflows in these PNs could be related to the stellar evolution of hydrogen-deficient [WR] and wels nuclei, which require further investigation.

Deep imaging of the shell elliptical galaxy NGC 3923 with MegaCam

Context. The elliptical galaxy NGC 3923 is known to be surrounded by a number of stellar shells, probable remnants of an accreted galaxy. Despite its uniqueness, the deepest images of its outskirts come from the 1980s. On the basis of the modified Newtonian dynamics (MOND), it has recently been predicted that a new shell lies in this region. Aims. We obtain the deepest image ever of the galaxy, map the tidal features in it, and search for the predicted shell. Methods. The image of the galaxy was taken by the MegaCam camera at the Canada-France-Hawaii Telescope in the g' band. It reached the surface-brightness limit of 29 mag/arcsec2. In addition, we reanalyzed an archival HST image of the galaxy. Results. We detected up to 42 shells in NGC 3923. This is by far the highest number among all shell galaxies. We present the description of the shells and other tidal features in the galaxy. A probable progenitor of some of these features was discovered. The shell system likely originates from two or more progenitors. The predicted shell was not detected, but the new image revealed that the prediction was based on incorrect assumptions and poor data.

A NOVEL APPROACH TO CONSTRAIN THE MASS RATIO OF MINOR MERGERS IN ELLIPTICAL GALAXIES: APPLICATION TO NGC 4889, THE BRIGHTEST CLUSTER GALAXY IN COMA

Minor mergers are thought to be important for the build-up and structural evolution of massive elliptical galaxies. In this work, we report the discovery of a system of four shell features in NGC 4889, one of the brightest members of the Coma cluster, using optical images taken with the Hubble Space Telescope and the Sloan Digital Sky Survey. The shells are well aligned with the major axis of the host and are likely to have been formed by the accretion of a small satellite galaxy. We have performed a detailed two-dimensional photometric decomposition of NGC 4889 and of the many overlapping nearby galaxies in its vicinity. This comprehensive model allows us not only to firmly detect the low-surface brightness shells, but, crucially, also to accurately measure their luminosities and colors. The shells are bluer than the underlying stars at the same radius in the main galaxy. We make use of the colors of the shells and the color-magnitude relation of the Coma cluster to infer the luminosity (or mass) of the progenitor galaxy. The shells in NGC 4889 appear to have been produced by the minor merger of a moderate-luminosity (M_I ~ -18.7 mag) disk (S0 or spiral) galaxy with a luminosity (mass) ratio of ~ 90:1 with respect to the primary galaxy. The novel methodology presented in this work can be exploited to decode the fossil record imprinted in the photometric substructure of other nearby early-type galaxies.

SK 1: A possible case of triggered star formation in perseus

AbstractAccording to a triggered star formation scenario (e.g. Martin-Pintado & Cernicharo 1987) outflows powered by young stellar objects shape the molecular clouds, can dig cavities, and trigger new star formation. NGC 1333 is an active site of low- and intermediate star formation in Perseus and is a suggested site of self-regulated star formation (Norman & Silk 1980). Therefore it is a suitable target for a study of triggered star formation (e.g. Sandell & Knee 2001, SK1). On the other hand, continuum sub-mm observations of star forming regions can detect dust thermal emission of embedded sources (which drive outflows), and further detailed structures.Within the framework of our wide-field mapping of star formation regions in the Perseus and Orion molecular clouds using SCUBA at 850 and 450 μm, we mapped NCG 1333 with an area of around 14′× 21′. The maps show more structure than the previous maps of the region observed in sub-mm. We have unveiled the known embedded SK 1 source (in the dust shell of the SSV 13 ridge) and detailed structure of the region, among some other young protostars.In agreement with the SK 1 observations, our map of the region shows lumpy filaments and shells/cavities that seem to be created by outflows. The measured mass of SK 1 (~0.07 M) is much less than its virial mass (~0.2-1 M). Our observations support the idea of SK 1 as an event triggered by outflow-driven shells in NGC 1333 (induced by an increase in gas pressure and density due to radiation pressure from the stellar winds that have presumably created the dust shell). This kind of evidences provides a more thorough understanding of the star formation regulation processes.

BV photometry of five shell galaxies

AbstractCurrent views consider shell structures as bona fide signatures of a recent minor/major merging event though also weak interaction models (WIM) could produce long lasting shells on host galaxies possessing a stellar thick disc.We present a B V band photometric study of a sample of 5 shell galaxies belonging to the Malin & Carter (1983) compilation. The structural properties and colors of the galaxies, as well as the colors of their shells are examined in detail.We did not find signatures of the presence of double nuclei. NGC 7585 is the only E galaxy in the sample and has a moderately boxy structure. The other galaxies have either a discy structure or are mixed E/S0 type galaxies. NGC 474 is a true lenticular. NGC 6776 shows a diffuse asymmetric outer structure and a system of tails of the the same color of the galaxy body; but not clear shells. In general, the color of the shells in our sample is similar or slightly redder than that of the host galaxy, whose color, in turn, is typical of the early‐type morphological class. One of the outer shells of NGC 474 is significantly bluer than the body of the galaxy. Since NGC 474 appears to be interacting with NGC 470, the color of this one shell could be explained as result of a recent acquisition of material through tidal interaction.The WIM hypothesis could explain both the red and the blue shells of NGC 474, this latter acquired from the fly‐by of the nearby companion NGC 470, but the lack of the constancy of shell surface brightness as a ratio of the underlying galaxy brightness argues against WIM. We speculate about evidence, which also comes from different observations, that suggests a merging/accretion origin of the shells. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

X-Ray Emission from Expanding Shells in NGC 3077

Deep Chandra observations of NGC 3077, a starburst dwarf galaxy in the M81 triplet, resolve the X-ray emission from several supershells. The emission is brightest in the cavities defined by expanding shells detected previously in Hα emission. Thermal emission models fitted to the data imply temperatures ranging from 1.3 to 4.9 × 106 K. The total 0.3–6.0 keV X-ray luminosity is 2 − 5 × 1039ergs−1 (depending on the selected thermal plasma model). Most (85%) of the X-ray luminosity in NGC 3077 comes from the hot interstellar gas; the remainder comes from six X-ray point sources. The radial density profile of the hot gas is not as steep as that expected in a freely expanding wind (e.g., as seen in the neighboring starburst galaxy M 82) implying that the hot gas is still confined by the Hα shells.

The multiple-shell structure of the planetary nebula NGC 6751

An intriguing bipolar mass outflow and a faint envelope were detected spectroscopically in the planetary nebula NGC 6751 by Gieseking and Solf (1986). To study the physical structure, deep CCD images of this nebula have been obtained which detect not only the morphological counterparts of the aforementioned features but also additional faint halos extending out to a much larger radius. Long-slit echelle spectra are obtained to determine the internal motion and radial velocity, as well as low-dispersion spectra to determine the physical condition and abundances of each feature in the whole nebula. NGC 6751 is apparently a multiple-shell nebula moving through a gas-rich environment. An He abundance difference between the planetary nebula and the ambient medium and an N/O abundance ratio enhancement in the forbidden N II-bright knots in the main nebula are found. From the physical structure of the shells in NGC 6751, information is derived about the average mass-loss rates at various stages. 32 refs.

Heiles shells in NGC 3079

view Abstract Citations (30) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Heiles Shells in NGC 3079 Irwin, Judith A. ; Seaquist, E. R. Abstract C array VLA H I observations have been made of the active radio lobe spiral galaxy, NGC 3079. We observe numerous H I arcs and filaments extending away from the plane of this edge-on galaxy which appear to be unrelated to the nuclear activity. The distribution, sizes, and energies of these features are similar to those of Galactic Heiles shells, and may be produced by star-forming activity in the disk. Publication: The Astrophysical Journal Pub Date: April 1990 DOI: 10.1086/168635 Bibcode: 1990ApJ...353..469I Keywords: Active Galactic Nuclei; Galactic Structure; H I Regions; Radio Sources (Astronomy); Spiral Galaxies; H Ii Regions; Interstellar Gas; Very Large Array (Vla); Astrophysics; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 3079; GALAXIES: INTERSTELLAR MATTER; GALAXIES: STRUCTURE; RADIO SOURCES: GALAXIES; RADIO SOURCES: 21 CM RADIATION full text sources ADS | data products SIMBAD (2) NED (1)

Dust and Ionized Gas in Active Radio Elliptical Galaxies

AbstractWe present broad and narrow bandwidth imaging of three southern elliptical galaxies which have flat-spectrum active radio cores (NGC 1052, IC 1459 and NGC 6958). All three contain dust and extended low excitation optical line emission, particularly extensive in the case of NGC 1052 which has a large Hα + [Nil] luminosity. Both NGC 1052 and IC 1459 have a spiral morphology in emission-line images. All three display independent strong evidence that a merger or infall event has recently occurred, i.e., extensive and infalling HI gas in NGC 1052, a counter-rotating core in IC 1459 and Malin-Carter shells in NGC 6958. This infall event is the most likely origin for the emission-line gas and dust, and we a currently investigating possible excitation mechanisms (Sparks et al. 1990).

Spectrophotometry of Shell Galaxies

Low dispersion spectra of two shell galaxies, NGC 3923 and NGC 3051, have been obtained covering the 5300Å to 10000Å spectral range. These long-slit spectra go through the nucleus of each galaxy and also through 12 shells in NGC 3923 and through 3 shells in NGC 3051. the main results are:1) In NGC 3051 the surface brightness of the 2 inner shells is nearly constant with radius. These plateaus of luminosity have very abrupt outer cutoffs but have no detectable inner limits.

Spectrophotometry of shell galaxies

Low dispersion spectra of two shell galaxies, NGC 3923 and NGC 3051, have been obtained covering the 5300A to 10000A spectral range. These long-slit spectra go through the nucleus of each galaxy and also through 12 shells in NGC 3923 and through 3 shells in NGC 3051.