Prominent Dust Lane Research Articles

AHubble Space TelescopeWFPC2 Investigation of the Disk-Halo Interface in NGC 891

We present deep narrowband observations with high spatial resolution of extraplanar diffuse ionized gas in the halo of NGC 891, obtained with the WFPC2 on board the HST. Our Hα observations, centered on the northern part of NGC 891, reveal an extended gaseous halo, which fills almost the entire field of view of our WFPC2 observation. Whereas NGC 891 has been studied extensively with ground-based telescopes, here the small-scale structure of the extended emission-line gas is presented at a high spatial resolution of 01, corresponding to 4.6 pc at the distance to NGC 891. The majority of the Hα emission is diffuse. Several discrete features (e.g., filaments) are visible as well. Some of the filaments reach distances of up to 2.2 kpc above the galactic plane and are extremely collimated, even at high galactic latitudes. We compare the morphology of these filaments with theoretical models, which describe possible transport mechanisms in a general way. Despite the prominent dust lane, many bubbles, shells, and supershells can be discerned in the midplane. We also investigate extraplanar dust features, which are best visible in unsharp-masked images of our broadband F675W image, and we compare them with the spatial distribution of DIG filaments. The high-|z| dust is detected out to distances of 2.2 kpc above/below the galactic midplane. Individual dust features, however, are not spatially correlated with diffuse ionized gas counterparts, such as individual filaments. Quite interestingly, the orientation of the dust features changes from being mostly aligned perpendicular to the disk at low galactic latitudes to a parallel alignment at high |z|. We compare the diffuse ionized gas distribution to the hot ionized medium, traced by X-ray observations performed by Chandra. There exists a good correlation of the presence of the warm and hot ionized gas: in particular, an X-ray bright region at |z| ~ 1–1.5 kpc fills the entire northern halo region, whereas the intensity in the midplane is considerably depressed. We also compare the sizes of individual Hα emission line features in the midplane of NGC 891 with similar structures that are known in our Milky Way and in the LMC.

Observations of A4059 withChandra,Hubble Space Telescope, and the Very Large Array: Unraveling a Complex Cluster/Radio Galaxy Interaction

We present a detailed reanalysis of Chandra data for the galaxy cluster A4059 and its central radio galaxy, PKS 2354� 35. We also present new 1.4 and 4.7 GHz CnB-array radio data from the Very Large Array, as well as a short archival WFPC2 image from the Hubble Space Telescope. The presence of a strong interaction between this radio galaxy and the intracluster medium (ICM) was suggested by Huang & Sarazin on the basis of a short observation by the High Resolution Imager on ROSATand confirmed in our preliminary analysis of the Chandra ACIS-S data. In particular, X-ray imaging clearly shows two cavities within the ICM that are approximately aligned with the radio galaxy axis. However, using our new radio maps (which are at lower frequencies and better matched to searching for � 1 0 structures than the previous high-quality maps), we fail to find a detailed correspondence between the � 1 0 scale radio lobes and the ICM cavities. This suggests that the cavities are ‘‘ghosts’’ of a previous burst of powerful activity by PKS 2354� 35. This is supported by detailed, spatially resolved X-ray spectroscopy that fails to find any shock-heated ICM, suggesting that the cavities are evolving subsonically. We also examine the nature of the central asymmetric ridge (or bar) of X-ray emission extending for � 30 kpc southwest of the cluster center that has been noted in these previous analyses. We find the ridge to be denser and cooler than, but probably in pressure balance with, its surroundings. The thermal evolution of this structure seems to be dominated by radiative cooling, possibly enhanced by the radio galaxy‐ICM interaction. We discuss several possible models for the formation of this southwest ridge and find none of them to be entirely satisfactory. In our preferred model, the southwest ridge is due to radiative cooling induced by an interaction between a radio galaxy‐driven disturbance and a preexisting bulk ICM flow. The presence of such a bulk flow (with a velocity of � 500 km s � 1 projected on the plane of the sky) is suggested by the off-center nature of the pair of X-ray cavities. Such a bulk flow can be created during a cluster/subcluster merger—the presence of a prominent dust lane in the cD galaxy of A4059, ESO 349� G010, is circumstantial evidence for just such a merger.

Molecular Gas and the Young Starburst in NGC 5253 Revisited

We report the detection of CO(2–1) and 3.1 and 1.3 mm continuum emission toward the extremely young starburst in NGC 5253, with data taken from the Owens Valley Millimeter Array. Faint CO emission originates in five molecular clouds distributed along the prominent dust lane seen in visual images. With the gas, the morphology of NGC 5253 looks much like a dwarf elliptical version of the ‘‘ dust-lane ellipticals ’’ or ‘‘ polar-ring ’’ class of galaxies. The molecular gas resides in GMCs well away from the radio-IR super–star cluster/supernebula seen in the radio and infrared. The millimeter continuum data confirm that the 2 cm flux from the supernebula is optically thick; the Lyman continuum rate derived from the 1.3 mm continuum is NLyc � 6 � 10 52 s � 1 for the central � 20 00 . CO may underestimate the true molecular column density, as expected for a low-metallicity system, although there are regions along the dust lane that appear to have near-Galactic conversion factors. We estimate a total molecular gas mass of MH2 d10 7 M� . The molecular gas in the dust lane is falling into the galaxy, supporting an accretion hypothesis. The dust lane gas cannot therefore be causally associated with the current burst of star formation. A relatively small amount, MH2 d5 � 10 5 M� , of molecular gas is associated with the current starburst. We estimate a star formation efficiency of at least 25% and more likely � 75%, consistent with the formation of a bound cluster. Despite the extreme youth of the starburst, the specific trigger of the starburst remains elusive, although the infall of gas in the dust lane suggests that there is more star formation to come in NGC 5253.

High‐Resolution Near‐Infrared Images and Models of the Circumstellar Disk in HH 30

We present Hubble Space Telescope near-infrared camera and multiobject spectrometer observations of the reflection nebulosity associated with the T Tauri star HH 30. The images show the scattered-light pattern characteristic of a highly inclined, optically thick disk with a prominent dust lane whose width decreases with increasing wavelength. The reflected nebulosity exhibits a lateral asymmetry in the upper lobe on the opposite side to that reported in previously published Wide Field Planetary Camera 2 images. The radiation transfer model that most closely reproduces the data has a flared accretion disk with dust grains larger than standard interstellar medium grains by a factor of approximately 2.1. A single hot spot on the stellar surface provides the necessary asymmetry to fit the images and is consistent with previous modeling of the light curve and images. Photometric analysis results in an estimated extinction of AV ≳ 80; however, since the photometry measures only scattered light rather than direct stellar flux, this a lower limit. The radiative transfer models require an extinction of AV = 7900.

The Magnetic Field Geometry in M82 and Centaurus A

Imaging polarimetry at 1.65 and 2.2 μm is presented for the classic starburst galaxy M82 and the advanced merger system Cen A. Polarimetry at near-IR wavelengths allows the magnetic field geometry in galaxies to be probed much deeper into dusty regions than optical polarimetry. In M82, the magnetic field throughout the nucleus has a polar geometry, presumably due to the massive vertical flow that is a result of the intense star formation there. Fully two-thirds of the line-of-sight dust through to the center of M82 contains a vertical magnetic field. In Cen A, the prominent dust lane shows a normal planar field geometry. There is no indication of significant disturbance in the field geometry in the dust lane and the polarization strength is near normal for the amount of extinction. Either the magnetic field geometry was well maintained during the merger, or it reestablished itself very easily.

ITAL]HUBBLE SPACE TELESCOPE[/ITAL][ITAL]Hubble Space Telescope[/ITAL] Observations of H[CLC]e[/CLC] 2-10: Outflows and Young Super–Star Clusters

We use Hubble Space Telescope (HST) WFPC2 optical images and GHRS ultraviolet spectroscopy to examine the recent star formation history and properties of the Wolf-Rayet galaxy He 2-10. The high spatial resolution afforded by HST has allowed the identification of a number of starburst knots, or super–star clusters (SSCs). The spatial morphology newly revealed by these HST images exhibits a prominent dust lane between the starburst regions known as A and B and a spur of material to the northwest of the nuclear region. Broadband photometry of the SSCs confirms that these objects have ages as young as a few Myr and masses up to 105 M☉. Narrowband Hα photometry of the SSCs indicates large equivalent widths for nearly half of them, consistent with ages less than 10 Myr. Since an appreciable fraction of SSCs are this young, the star formation history necessarily must be strongly peaked and not continuous. GHRS UV spectra were obtained for sections of the two starburst regions and were used to determine the parameters of the starburst regions. For a stellar population produced in a single burst with stellar masses between 1 and 100 M☉, the UV luminosities indicate regions A and B have masses between 1.6–2.6 × 106 M☉ and 2.6–6.6 × 104 M☉, respectively. The total starburst mass was between 1 and 100 M☉ consistent with the UV luminosity ranges between 1.6 and 2.6 × 106 M☉ and 2.6 and 6.6 × 104 M☉ for regions A and B, respectively. The observed integrated Hα flux is similar to that predicted by the models, implying that the leakage and/or dust absorption of Lyman continuum photons from the starburst regions is small. The integrated Hα equivalent widths of the two regions are substantially smaller than predicted. We attribute this to contamination by the continuum in the starburst regions (the starburst knots do not uniformly fill the GHRS apertures). The UV spectroscopy of starburst region A indicates a large-scale outflow of the interstellar medium of He 2-10 with speeds of at least 360 km s-1 and a total mass of at least 106 M☉. We estimate that the mass in metals which He 2-10 will expel is enough to raise primordial abundances in ≈1 Mpc3 to 10-3 to 10-2 solar.

The Ionization Source in the Nucleus of M84

We have obtained new Hubble Space Telescope (HST) observations of M84, a nearby massive elliptical galaxy whose nucleus contains a approximately 1.5 X 10(exp 9) solar mass dark compact object, which presumably is a supermassive black hole. Our Space Telescope Imaging Spectrograph (STIS) spectrum provides the first clear detection of emission lines in the blue (e.g., [0 II] lambda 3727, HBeta and [0 III] lambda lambda4959,5007), which arise from a compact region approximately 0.28 across centered on the nucleus. Our Near Infrared Camera and MultiObject Spectrometer (NICMOS) images exhibit the best view through the prominent dust lanes evident at optical wavelengths and provide a more accurate correction for the internal extinction. The relative fluxes of the emission lines we have detected in the blue together with those detected in the wavelength range 6295 - 6867 A by Bower et al. indicate that the gas at the nucleus is photoionized by a nonstellar process, instead of hot stars. Stellar absorption features from cool stars at the nucleus are very weak. We update the spectral energy distribution of the nuclear point source and find that although it is roughly flat in most bands, the optical to UV continuum is very red, similar to the spectral energy distribution of BL Lac. Thus, the nuclear point source seen in high-resolution optical images is not a star cluster but is instead a nonstellar source. Assuming isotropic emission from this source, we estimate that the ratio of bolometric luminosity to Eddington luminosity is about 5 x 10(exp -7). However, this could be underestimated if this source is a misaligned BL Lac object, which is a possibility suggested by the spectral energy distribution and the evidence of optical variability we describe.

TheHubble Space TelescopeSurvey of BL Lacertae Objects: Gravitational Lens Candidates and Other Unusual Sources

We present Hubble Space Telescope (HST ) observations of seven unusual objects from the HST ii snapshot survey ˇˇ of BL Lacertae objects, of which four are gravitational lens candidates. In three cases a double point source is observed: 0033)595, with separation, and 0502)675 and 1440)122, each 1A with separation. The last two also show one or more galaxies, which could be either host or D0A.3 lensing galaxies. If any are con—rmed as lenses, these BL Lac objects are excellent candidates for measur- ing via gravitational time delay because of their characteristic rapid, high-amplitude variability. An H 0 additional advantage is that, like other blazars, they are likely superluminal radio sources, in which case the source plane is mapped out over a period of years, providing strong additional constraints on the lensing mass distribution. The fourth gravitational lens candidate is 1517)656, which is surrounded by three arclets forming an almost perfect ring of radius If this is indeed an Einstein ring, it is most 2A.4. likely a background source gravitationally lensed by the BL Lac object host galaxy and possibly a sur- rounding group or cluster. In the extreme case that all four candidates are true lenses, the derived fre- quency of gravitational lensing in this BL Lac sample would be an order of magnitude higher than in comparable quasar samples. We also report on three other remarkable BL Lac objects: 0138(097, which is surrounded by a large number of close companion galaxies; 0806)524, whose host galaxy con- tains an uncommon arclike structure; and 1959)650, which is hosted by a gas-rich elliptical galaxy with a prominent dust lane of D5 ) 105 M _ . Subject headings: BL Lacertae objects: generalgalaxies: structuregravitational lensing

Hα Imaging of Early-Type ([CLC]Sa[/CLC]–[CLC]Sab[/CLC]) Spiral Galaxies. I.

Hα and continuum images are presented for 27 nearby early-type (Sa–Sab) spiral galaxies. Contrary to popular perception, the images reveal copious massive star formation in some of these galaxies. A determination of the Hα morphology and a measure of the Hα luminosity suggest that early-type spirals can be classified into two broad categories based on the luminosity of the largest H II region in the disk. The first category includes galaxies for which the individual H II regions have LHα < 1039 ergs s-1. Most of the category 1 galaxies appear to be morphologically undisturbed but show a wide diversity in nuclear Hα properties. The second category includes galaxies that have at least one H II region in the disk with LHα ≥ 1039 ergs s-1. All category 2 galaxies show either prominent dust lanes or other morphological peculiarities such as tidal tails, which suggests that the anomalously luminous H II regions in category 2 galaxies may have formed as a result of a recent interaction. The observations, which are part of an ongoing Hα survey, reveal early-type spirals to be a heterogeneous class of galaxies that are evolving in the current epoch. We have also identified some systematic differences between the classifications of spiral galaxies in the Second General Catalog and the Revised Shapley-Ames Catalog that may be traced to subtle variations in the application of the criteria used for classifying spiral galaxies. An examination of earlier studies suggests that perceptions concerning the Hubble-type dependence of star formation rates among spiral galaxies depends on the choice of catalog.

Dust Properties of NGC 4753

We report on BVR surface photometry of a lenticular galaxy, NGC 4753, with prominent dust lanes. We have used the multicolor broadband photometry to study dust extinction as a function of wavelength and derived the extinction curve. We find the extinction curve of NGC 4753 to be similar to the Galactic extinction curve in the visible region, which implies that the sizes of dust grains responsible for optical extinction are similar to those in our Galaxy. We derive the dust mass from optical extinction as well as from the far-infrared fluxes observed with IRAS. The ratio of the two dust masses, Md,IRAS/Md,optical, is 2.28 for NGC 4753, which is significantly lower than the value of 8.4 ± 1.3 found previously for a large sample of elliptical galaxies. The total mass of the observed dust within NGC 4753 is about a factor of 10 higher than the mass of dust expected from loss of mass from red giant stars and destruction by sputtering and grain-grain collisions in low-velocity shocks and sputtering in supernova-driven blast waves. We find evidence for the coexistence of dust and Hα-emitting gas within NGC 4753. The current star formation rate of NGC 4753, averaged over the past 2 × 106 yr, is estimated to be less than 0.21 M⊙ yr-1. A substantial amount of dust within NGC 4753 exists in the form of cirrus.

Keck Spectroscopy of Three Gravitational Lens Systems Discovered in the JVAS and CLASS Surveys

We present spectra of three gravitational lens systems taken with the Low Resolution Imaging Spectrograph on the W. M. Keck telescopes. All of the systems were discovered in the JVAS and CLASS radio surveys, which were designed to find lenses suitable for measuring H0. Previous spectra of these systems had low signal-to-noise ratios, and only one of the source redshifts was secure. Our observations provide unambiguous lens and source redshifts for all of the systems, with (zl, zs) = (0.4060, 1.339), (0.5990, 1.535), and (0.4144, 1.589) for B0712+472, B1030+074, and B1600+434, respectively. The observed image splittings in the systems imply that the masses of the lensing galaxies within their Einstein rings are 5.4 × 1010, 1.2 × 1011, and 6.3 × 1010 h-1 M⊙. The resulting V-band mass-to-light ratios for B0712+472 and B1030+074, measured inside their Einstein ring radii, are ~10 h (M/L)⊙,V, slightly higher than values observed in nearby elliptical galaxies. For B1600+434, the mass-to-light ratio is 48 h (M/L)⊙,V. This high value can be explained, at least in part, by the prominent dust lane running through the galaxy. Two of the three lens systems show evidence of variability, so monitoring may yield a time delay and thus a measurement of H0.

Modeling Polarization Maps of External Galaxies.

We extend previous radiation transfer models of disk galaxies to include bulge plus disk systems. The Monte Carlo radiation transfer models include the polarizing effects of dust scattering and transmission through aligned grains. We assume that the dust grains are aligned by large scale toroidal magnetic fields and we model the interstellar polarization using empirical formulae derived for the Milky Way. Although our galaxy models do not include dust or star inhomogeneities arising from clumping or spiral arm structures, they do successfully reproduce the observed dust lanes and polarization patterns and null points. We apply our techniques to NGC 4565 and NGC 891 which are examples of nearly edge-on spiral galaxies with prominent dust lanes. We can successfully model the polarimetric structure of NGC 4565 with uniformly aligned grains and a smooth dust lane. However, our models fail to reproduce the structure within NGC 891's dust lane. This failure is attributed to the striking disk activity present in NGC 891 and the polarimetric evidence for vertical magnetic field structures. The dust lane activity and non-toroidal magnetic fields in NGC 891 appear to break the large scale grain alignment to such an extent that our smooth model is unable to reproduce the flux and polarization maps. Although NGC 891 is often assumed to be very similar to our own Galaxy, our modeling suggests that, polarimetrically at least, NGC 4565 behaves more like the Milky Way than does NGC 891.

A CO Map of the Dwarf Starburst Galaxy NGC 5253

We have mapped CO and 2.6 mm continuum emission in the dwarf galaxy NGC 5253 with the Owens Valley Millimeter Array. CO is detected along the prominent dust lane in the nucleus. The CO emission is extremely weak: NGC 5253 appears to be the most CO-poor starburst known. The CO flux appears to be low by factors of ~100 compared to star-forming regions of similar radio and infrared luminosity in large spiral galaxies and as much as a factor of 10 weaker than those in other metal-poor dwarf galaxies. This unusually weak CO emission, together with the observed morphology of the CO gas and its unusual kinematical properties, lead us to suggest that NGC 5253 has recently accreted gas of extremely low metallicity, significantly lower than that of the galaxy itself.

BVRI imaging polarimetric studies of the galaxy NGC 5128

Multi-colour imaging polarimetry of the galaxy NGC 5128 shows that polarization is present throughout the dust lane with patterns of orientation which are coherent on kpc scale-lengths. In the central regions of the dust lane, within ±0.7 kpc of the projected position of the galactic nucleus, the polarization is oriented parallel to the long axis of the lane and reaches levels up to 5 per cent. At the outer extremities of the the dust lane, higher levels of polarization are found with orientations perpendicular to the axis of the dust lane. In the intermediate regions, null points in the polarization are observed in addition to an unexpected reversal of polarization orientation across the dust lane. We are unable to account for all our observations — polarization maps and the wavelength dependence of polarization in the dust lane — without involving two competing polarizing mechanisms, namely, dichroic extinction and scattering by dust grains. The polarimetric properties of NGC 5128 are very similar to those found in galaxies such as M104, IC 4329A and NGC 2146, and it appears that azimuthal magnetic fields, confined to the equatorial planes of galaxies with prominent dust lanes, are a common occurrence. The nature and origins of these magnetic fields are considered.

The Dynamical Evolution of Centaurus A

Centaurus A (NGC 5128) is a nearby Giant Elliptical (3.5Mpc, 1012 Solar Masses). It has a prominent dust-lane which has an axis of rotation orientated differently from that of the underlying galaxy. Close to it are two galaxies: NGC 5237 – a dwarf elliptical, and Fourcade-Figueroa – a low surface brightness irregular. We are investigating whether these three objects are the resulting components of a grazing interaction between a Giant Elliptical and a less massive spiral galaxy. We have conducted n-body simulations, modelling all components of the two original interacting galaxies. Preliminary results show that Cen A, its dust-lane, and NGC 5237 are consistent with this simulation model. Centaurus A exhibits many other features which are also indicative of a past interaction.

The distribution of far-infrared light in the 'Dusty Hand' galaxy NGC 2146

The Kuiper Airborne Observatory has been used to obtain high spatial resolution 50 and 100 micron observations of the peculiar galaxy NGC 2146. We find that the far-infrared luminosity of NGC 2146 arises in a 21" x &lt;= 16" (1.5 kpc x &lt;= 1.1 kpc) region (FWHM) elongated along the major axis. This limit is consistent with the size of the central radio continuum and ^12^CO (1-0) sources. The far-infrared distribution is slightly more compact than that of the Hα; this difference is consistent with the observed pattern of extinction in this galaxy. From a study of the energetics in this galaxy, we conclude that young massive stars are largely responsible for powering the far-infrared, luminosity of NGC 2146. The far-infrared and CO (1-0) distributions differ from the reddening morphology as seen in optical images and in the Brγ/Hα ratio. The starlight and the ionized gas appear most highly reddened at the prominent dust lane 15" to the west of the nucleus, while the CO and far- infrared emission peak near the nucleus. This result can be explained by either a high proportion of cold dust and gas at the dust lane, or a geometry in which the dust lane lies in front of the main body of the galaxy.

Kinematics of NGC 4826: A sleeping beauty galaxy, not an evil eye

A recent high resolution H I study of the Sab galaxy NGC 4826 (1992) reveals that the sense of rotation of the neutral gas reverses from the inner to the outer disk. The present paper reports on optical spectra at high velocity resolution in four position angles in NGC 4826, which cover the region of the gas reversal and which reveal a high degree of complexity. In the inner disk, which includes the prominent dusty lane, the stars and gas rotate in concert, and the spiral arms trail (for the adopted geometry). Arcs of ionized gas are observed partially encircling the nucleus; expansion velocities reach 400 km/s. At distances just beyond the prominent dust lane, the ionized gas exhibits a rapid, orderly velocity fall and within 500 parsecs it has reversed from 180 km/s prograde to 200 km/s retrograde; it also has a component radial toward the nucleus of over 100 km/s. The stars, however, continue their prograde rotation. Beyond this transition zone, the neutral gas continues its retrograde rotation, stellar velocities are prograde, but the sense of the almost circular arms is not established. Because of its kinematical complexity as well as its proximity, NGC 4826 is an excellent early-type galaxy in which to observe the long term effects of gas acquistion or a galaxy merger on a disk galaxy.

The Central Region of NGC 1365. SEST and VLA Observations of CO and the Radio Continuum

The barred spiral Seyfert galaxy NGC 1365 has been observed in the radio continuum at wavelengths of 2, 6 and 20 cm, using scaled arrays of the VLA, and complete maps have been made in the J = 1–0 and J = 2–1 CO emission lines using the SEST. MEM maps of the 6 and 20 cm emission, as well as a spectral index map, have been produced with a resolution of 2″.3 × 0″.9, and the 2-cm map has a resolution of 0″.25 ×0″.10. The dominant continuum features are a number of unresolved sources with relatively flat non-thermal spectral indices (−0.3 to −0.5), immersed in an incomplete circumnuclear ring, which is superimposed upon a background that extends into the bar along the prominent dust lanes. The ring has angular dimensions of 8″ × 20″, which corresponds to a linear dimension of the order of 1 kpc. There is clear evidence of a jet, about 5″ long, originating at the position of the Seyfert nucleus and extending in a southeastern direction, closely along the minor axis of the galaxy. The jet has a steep non-thermal spectral index (–1.0) and is aligned along the axis of a conical shell of [OIII] emission. The CO molecular gas peaks at the nucleus and is strongly concentrated to the nucleus and bar regions with a certain enhancement along the bar. The total molecular hydrogen gas mass in the observed region is 2 × 1010M⊙, with 6 × 109M⊙ lying within 2.2 kpc of the nucleus. A full presentation of the results will be published in Astronomy and Astrophysics in 1994.

The highly enriched planetary nebula BV-1

view Abstract Citations (13) References (45) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Highly Enriched Planetary Nebula BV-1 Kaler, James B. ; Chu, You-Hua ; Jacoby, George H. Abstract BV-1 is a Type I planetary nebula, highly enriched in nitrogen and helium with N/O = 1.5 and He/H = 0.17, powered by an exceeingly hot star. Imaging in: (1) [N II] (20% contamined by Hα) shows an elongated 54×32 arcsec (diameter) structure with a bright thin central bar and faint extensions, which the authors classify on Balick's system as middle-to-late butterfly; (2) [O III] shows a prominent dust lane; (3) the yellow continuum reveals no central star, and yields a lower (bright) limit to V(star) of 21.5. Kinematics, structure, distance, age and properties of the central star are discussed in detail. Publication: The Astronomical Journal Pub Date: October 1988 DOI: 10.1086/114890 Bibcode: 1988AJ.....96.1407K Keywords: H Alpha Line; Hot Stars; Planetary Nebulae; Stellar Luminosity; Stellar Mass; Stellar Temperature; Giant Stars; Helium; Nitrogen; Radial Velocity; Stellar Cores; Astrophysics; NEBULAE: PLANETARY full text sources ADS | data products SIMBAD (4)

Molecular spiral structure in M51

view Abstract Citations (56) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Molecular Spiral Structure in M51 Lo, K. Y. ; Ball, R. ; Masson, C. R. ; Phillips, T. G. ; Scott, S. ; Woody, D. P. Abstract Observations of CO emission at 7 arcsec resolution from the central 2 arcmin x 1 arcmin of M51 show directly that molecular gas, probably complexes of relatively warm giant molecular clouds, is strongly confined to spiral arms outlined by prominent dust lanes and radio continuum ridges. Molecular clouds must also populate fairly uniformly the interarm regions. The arm-to-interarm N(H2) ratio, averaged over 300 pc, is at least three. These observations suggest that in the inner region of M51 molecular clouds coalesce to form bigger complexes in the presence of a spiral gravitational potential, and that such complexes are redispersed into molecular clouds upon leaving the arms. The spiral arm molecular cloud complexes last at most 50 million yr, the arm crossing time, and molecular clouds probably last as long as the interarm crossing time which is at most 100 million yr at 45 arcsec (2.2 kpc) from the center. Publication: The Astrophysical Journal Pub Date: June 1987 DOI: 10.1086/184913 Bibcode: 1987ApJ...317L..63L Keywords: Carbon Monoxide; Galactic Structure; Molecular Clouds; Spiral Galaxies; Astronomical Maps; Coalescing; Galactic Nuclei; Interferometry; Interstellar Gas; Astrophysics; GALAXIES: STRUCTURE; INTERSTELLAR: MOLECULES full text sources ADS | data products SIMBAD (1) NED (1)