Optical Major Axis Research Articles

X-shaped Radio Galaxies: Optical Properties, Large-scale Environment, and Relationship to Radio Structure

Abstract In pursuit of clues to the origin of “winged” or X-shaped radio galaxies (XRGs) we investigate the parent galaxies of a large sample of 106 XRGs for optical–radio axes alignment, interstellar medium, black hole mass, and large-scale environment. For 41 of the XRGs it was possible to determine the optical major axis and the primary radio axis and the strong tendency for the two axes to be fairly close is confirmed. However, several counter-examples were also found and these could challenge the widely discussed backflow diversion model for the origin of the radio wings. Comparison with a well-defined large sample of normal FR II radio galaxies has revealed that: (i) XRGs possess slightly less massive central black holes than the normal radio galaxies (average masses being logM BH ∼ 8.81 M ⊙ and 9.07 M ⊙, respectively); (ii) a much higher fraction of XRGs (∼80%) exhibits red mid-IR colors (W2 − W3 > 1.5), indicating a population of young stars and/or an enhanced dust mass, probably due to relatively recent galaxy merger(s). A comparison of the large-scale environment (i.e., within ∼1 Mpc) shows that both XRGs and FRII radio galaxies inhabit similarly poor galaxy clustering environments (medium richness being 8.94 and 11.87, respectively). Overall, the origin of XRGs seems difficult to reconcile with a single dominant physical mechanism and competing mechanisms seem prevalent.

Evolution of compact groups from intermediate to final stages

Context. Hickson Compact Group (HCG) 16 is a prototypical compact group of galaxies in an intermediate stage of the previously proposed evolutionary sequence, where its galaxies are losing gas to the intra-group medium (IGrM). The group hosts galaxies that are H I-normal, H I-poor, and centrally active with both AGNs and starbursts, in addition to a likely new member and a H I tidal feature of ∼160 kpc in length. Despite being a well-studied group at all wavelengths, no previous study of HCG 16 has focused on its extraordinary H I component. Aims. The characteristics of HCG 16 make it an ideal case study for exploring which processes are likely to dominate the late stages of evolution in compact groups, and ultimately determine their end states. In order to build a coherent picture of the evolution of this group we make use of the multi-wavelength data available, but focus particularly on H I as a tracer of interactions and evolutionary phase. Methods. We reprocess archival VLA L-band observations of HCG 16 using the multi-scale CLEAN algorithm to accurately recover diffuse features. Tidal features and galaxies are separated in three dimensions using the SlicerAstro package. The H I deficiency of the separated galaxies is assessed against the benchmark of recent scaling relations of isolated galaxies. This work has been performed with particular attention to reproducibility and is accompanied by a complete workflow to reproduce all the final data products, figures, and results. Results. Despite the clear disruption of the H I component of HCG 16 we find that it is not globally H I deficient, even though HCG 16a and b have lost the majority of their H I and almost 50% of the group’s H I is in the IGrM. The H I content of HCG 16d shows highly disturbed kinematics, with only a marginal velocity gradient that is almost perpendicular to its optical major axis. The tail of ∼160 kpc in length extending towards the southeast appears to be part of an even larger structure which spatially and kinematically connects NGC 848 to the northwest corner of the group. Conclusions. This study indicates that in the recent past (∼1 Gyr) galaxies HCG 16a and b likely underwent major interactions that unbound gas without triggering significant star formation. This gas was then swept away by a close, high-speed encounter with NGC 848. The starburst events HCG 16c and d, likely initiated by their mutual interaction, triggered galactic winds which, in the case of HCG 16d, appear to have disrupted its H I reservoir. The tidal features still connected to all these galaxies indicate that more H I will soon be lost to the IGrM, while that which remains in the discs will likely be consumed by star-formation episodes triggered by their ongoing interaction. This is expected to result in a collection of gas-poor galaxies embedded in a diffuse H I structure, which will gradually (over several Gyr) be evaporated by the UV background, resembling the final stage of the evolutionary model of compact groups.

Multiphase ISM in Nearby Early Type Galaxy IC 5063

A multiwavelength study of a nearby dust lane early-type galaxy IC 5063 is presented. The objectives are to investigate dust extinction properties and the association of interstellar dust with other phases of ISM. The color-index maps as well as the extinction maps derived from the analysis of deep CCD observations in optical passbands revealed a prominent dust lane along its optical major axis in the inner region. In addition, two more fainter and extended dust patterns are apparent in the color index map as well as extinction maps. These features are also evident in the smooth model subtracted residual maps. The extinction curve derived for this galaxy revealed that dust grains in it are identical to the canonical grains in the Milky Way with the dust grains little larger than the canonical grains. The total extinction measured in the V band extinction map enabled us to quantify the dust content of this galaxy to be equal to , an order of magnitude shorter than that estimated using the IRAS flux densities at 60 and 100 μm. A Multiphase ISM study revealed a surprising similarity in the morphologies of the Hα emitting ionized gas distribution and X-ray emitting gas. Systematic analysis of high resolution X-ray observations using Chandra telescope enabled us to detect 18 discrete X-ray sources within optical D25 region of IC 5063, out of which 17 sources were separated out as the low mass X-ray binaries and one as the high mass X-ray binary source in the X-ray color-color plot.

The structure of Andromeda II dwarf spheroidal galaxy

We analyze in detail the spatial distribution and kinematic properties of two different stellar populations in Andromeda II (And II) dwarf spheroidal galaxy. We obtained their detailed surface density maps, together with their radial density profiles. The two populations differ not only in age and metallicity, but also in their spatial distribution and kinematics. Old stars ($\gtrsim 11$ Gyr) follow a round distribution well fitted by truncated density profiles. These stars rotate around the projected optical major axis of the galaxy with line-of-sight velocities $v_{los}(r_h) = 16 \pm 3$ km s$^{-1}$ and a velocity gradient of $2.06 \pm 0.21$ km s$^{-1}$ arcmin$^{-1}$. Intermediate-age stars ($\lesssim 9$ Gyr) concentrate in the centre of the galaxy and form an elongated structure extending along the projected optical major axis. This structure appears to rotate with a velocity gradient of $2.24 \pm 0.22$ km s$^{-1}$ arcmin$^{-1}$, and around the optical minor axis. The centres of rotation and kinetic position angles (PA$_{\rm kin}$) of both populations differ. For intermediate-age stars we obtained PA$_{\rm kin} = 18^\circ \pm 2^\circ$ and for the old ones PA$_{\rm kin} = 63^\circ \pm 3^\circ$ in good agreement with photometric PA measured from isopleths fitted to the photometry. We conclude that the two stellar populations may not be fully relaxed and thus be the result of a merger occurred at redshift $z\sim 1.75$.

ALFALFA DISCOVERY OF THE NEARBY GAS-RICH DWARF GALAXY LEO P. V. NEUTRAL GAS DYNAMICS AND KINEMATICS

We present new HI spectral line imaging of the extremely metal-poor, star-forming dwarf irregular galaxy Leo P. Our HI images probe the global neutral gas properties and the local conditions of the interstellar medium (ISM). The HI morphology is slightly elongated along the optical major-axis. We do not find obvious signatures of interaction or infalling gas at large spatial scales. The neutral gas disk shows obvious rotation, although the velocity dispersion is comparable to the rotation velocity. The rotation amplitude is estimated to be V_c = 15 +/- 5 km/s. Within the HI radius probed by these observations, the mass ratio of gas to stars is roughly 2:1, while the ratio of the total mass to the baryonic mass is ~15:1. We use this information to place Leo P on the baryonic Tully-Fisher relation, testing the baryonic content of cosmic structures in a sparsely populated portion of parameter space that has hitherto been occupied primarily by dwarf spheroidal galaxies. We detect the signature of two temperature components in the neutral ISM of Leo P; the cold and warm components have characteristic velocity widths of 4.2 +/- 0.9 km/s and 10.1 +/- 1.2 km/s, corresponding to kinetic temperatures of ~1100 K and ~6200 K, respectively. The cold HI component is unresolved at a physical resolution of 200 pc. The highest HI surface densities are observed in close physical proximity to the single HII region. A comparison of the neutral gas properties of Leo P with other extremely metal-deficient (XMD) galaxies reveals that Leo P has the lowest neutral gas mass of any known XMD, and that the dynamical mass of Leo P is more than two orders of magnitude smaller than any known XMD with comparable metallicity.

THE H I CHRONICLES OF LITTLE THINGS BCDs: EVIDENCE FOR EXTERNAL PERTURBATIONS IN THE MORPHOLOGY AND KINEMATICS OF HARO 29 AND HARO 36

We analyze high angular and velocity resolution HI-line data of two LITTLE THINGS (1) blue compact dwarfs (BCDs): Haro 29 and Haro 36. Both of these BCDs are disturbed morphologically and kinematically. Haro 29's HI data reveal a kinematic major axis that is offset from the optical major axis, and a disturbed outer HI component, indicating that Haro 29 may have had a past interaction. Position-velocity diagrams of Haro 36 indicate that it has two kinematically separate components at its center and a likely tidal tail in front of the galaxy. We find that Haro 36 most likely had an interaction in the past, is currently interacting with an unknown companion, or is a merger remnant. (1) "Local Irregulars That Trace Luminosity Extremes The HI Nearby Galaxy Survey" http://www2.lowell.edu/users/dah/littlethings/index.html

FCC046: A CANDIDATE GASEOUS POLAR RING DWARF ELLIPTICAL GALAXY IN THE FORNAX CLUSTER

FCC046 is a Fornax Cluster dwarf elliptical galaxy. Optical observations have shown that this galaxy, besides an old and metal-poor stellar population, also contains a very young centrally concentrated population and is actively forming stars, albeit at a very low level. Here, we report on 21cm observations of FCC046 with the Australia Telescope Compact Array (ATCA) which we conducted in the course of a small survey of Fornax Cluster early-type dwarf galaxies. We have discovered a ~10^7 Mo HI cloud surrounding FCC046. We show that the presence of this significant gas reservoir offers a concise explanation for this galaxy's optical morphological and kinematical properties. Surprisingly, the HI gas, as evidenced by its morphology and its rotational motion around the galaxy's optical major axis, is kinematically decoupled from the galaxy's stellar body. This is the first time such a ring of gaseous material in minor-axis rotation is discovered around a dwarf galaxy.

Dust extinction and X-ray emission from the starburst galaxy NGC 1482

We present the results based on multiwavelength imaging observations of the prominent dust lane starburst galaxy NGC 1482 aimed to investigate the extinction properties of dust existing in the extreme environment. (B–V) colour-index map derived for the starburst galaxy NGC 1482 confirms two prominent dust lanes running along its optical major axis and are found to extend up to ∼11kpc. In addition to the main lanes, several filamentary structures of dust originating from the central starburst are also evident. Though, the dust is surrounded by exotic environment, the average extinction curve derived for this target galaxy is compatible with the Galactic curve, with RV=3.05, and imply that the dust grains responsible for the optical extinction in the target galaxy are not really different than the canonical grains in the Milky Way. Our estimate of total dust content of NGC 1482 assuming screening effect of dust is ∼2.7×105M⊙, and provide lower limit due to the fact that our method is not sensitive to the intermix component of dust. Comparison of the observed dust in the galaxy with that supplied by the SNe to the ISM, imply that this supply is not sufficient to account for the observed dust and hence point towards the origin of dust in this galaxy through a merger like event.Our multiband imaging analysis reveals a qualitative physical correspondence between the morphologies of the dust and Hα emission lines as well as diffuse X-ray emission in this galaxy. Spatially resolved spectral analysis of the hot gas along outflows exhibit a gradient in the temperature. Similar gradient was also noticed in the measured values of metallicity, indicating that the gas in the halo is not yet enriched. High resolution, 2–8keV Chandra image reveals a pair of point sources in the nuclear region with their luminosities equal to 2.27×1039ergs−1 and 9.34×1039ergs−1, and are in excess of the Eddington-limit of 1.5M⊙ accreting source. Spectral analysis of these sources exhibit an absorbed-power law with the hydrogen column density higher than that derived from the optical measurements.

KK 246: A DWARF GALAXY WITH AN EXTENDED H I DISK IN THE LOCAL VOID

We have found that KK 246, the only confirmed galaxy located within the nearby Tully Void, is a dwarf galaxy with an extremely extended H I disk and signs of an H I cloud with anomalous velocity. It also exhibits clear misalignment between the kinematical major and minor axes, indicative of an oval distortion, and a general misalignment between the H I and optical major axes. We measure a H I mass of 1.05 +- 0.08 x 10^8 M_sun, and a H I extent 5 times that of the stellar disk, one of the most extended H I disks known. We estimate a dynamical mass of 4.1 x 10^9 M_sun, making this also one of the darkest galaxies known, with a mass-to-light ratio of 89. The relative isolation and extreme underdense environment make this an interesting case for examining the role of gas accretion in galaxy evolution.

Galaxy shells and the structure of radio galaxies: Clues from Centaurus A (NGC 5128)

We show that the northern middle radio lobe of Cen A, an intriguing and much debated manifestation of radio lobe asymmetry, can be understood in terms of a direct interaction of the northern jet with a gaseous cloud associated with a stellar shell. This same basic mechanism was proposed earlier for the northern inner lobe, but new data allows a more detailed case to be made for the northern middle lobe. Although such an interaction can presently be demonstrated only for Cen A, the nearest radio galaxy, it is likely to be a fairly common occurrence and it provides an alternative to models invoking episodic nuclear activity, possibly accompanied with jet precession, for radio galaxies with multiple lobes and S-shapes. This proposed scenario may also play a key role in the origin of prominent radio galaxy morphological classes, such as the Wide-Angle-Tail sources and the Z-symmetric X-shaped radio sources. The strong tendency for radio lobes to be more distorted in double radio sources with jets that are in closer alignment with the optical major axis of the host elliptical galaxy can likewise be understood in terms of jet–shell interactions. In the frequent cases when jet activity is triggered by mergers of a large elliptical galaxy with a disk galaxy containing cold gas the impact of the gas associated with stellar shells upon the jets is likely to have significant manifestations.

Rotationally Supported Virgo Cluster Dwarf Elliptical Galaxies: Stripped Dwarf Irregular Galaxies?

New observations of 16 dwarf elliptical galaxies (dEs) in the Virgo Cluster indicate that at least seven dEs have significant velocity gradients along their optical major axis, with typical rotation amplitudes of 20–30 km s-1. Of the remaining nine galaxies in this sample, six have velocity gradients of less than 20 km s-1 kpc-1, while the other three observations had too low a signal-to-noise ratio to determine an accurate velocity gradient. Typical velocity dispersions for these galaxies are ~44 ± 5 km s-1, indicating that rotation can be a significant component of the stellar dynamics of Virgo dEs. When corrected for the limited spatial extent of the spectral data, the rotation amplitudes of the rotating dEs are comparable to those of similar-brightness dwarf irregular galaxies (dIs). Evidence of a relationship between the rotation amplitude and galaxy luminosity is found and, in fact, agrees well with the Tully-Fisher relation. The similarity in the scaling relations of dIs and dEs implies that it is unlikely that dEs evolve from significantly more luminous galaxies. These observations reaffirm the possibility that some cluster dEs may be formed when the neutral gaseous medium is stripped from dIs in the cluster environment. We hypothesize that several different mechanisms are involved in the creation of the overall population of dEs and that stripping of infalling dIs may be the dominant process in the creation of dEs in clusters like Virgo.

The Complex Neutral Gas Dynamics of the Dwarf Starburst Galaxy NGC 625

We present new multiconfiguration H I aperture synthesis imaging of the nearby dwarf starburst galaxy NGC 625 obtained with the Australia Telescope Compact Array. Total H I column density images show gas well aligned with the optical major axis and low column density H I extending to greater than 6 optical scale lengths. The H I velocity field, on the other hand, is highly disturbed, with neutral gas at nearly all detected velocities within the central region. After considering various interpretations, we find that a blowout scenario most accurately describes the data. Since at our resolution we do not detect any large evacuated holes in the H I disk, we interpret this blowout to be the result of the extended (both spatially and temporally) star formation event that NGC 625 has undergone in the last 100 Myr. This is one of the clearest examples of H I outflow detected in a dwarf galaxy. We find no obvious external trigger for this extended star formation event. We detect strong radio continuum emission from the largest H II regions; comparing to our Hubble Space Telescope and ground-based Hα fluxes suggests either appreciable amounts of extinction toward the star formation regions or the contribution of nonthermal sources to the radio continuum luminosity.

Molecular Gas in Elliptical Galaxies: Distribution and Kinematics

I present interferometric images (∼7'' resolution) of CO emission in five elliptical galaxies and nondetections in two others. These data double the number of elliptical galaxies whose CO emission has been fully mapped. The sample galaxies have 108 to 5 × 109 M⊙ of molecular gas distributed in mostly symmetric rotating disks with diameters of 2–12 kpc. Four out of the five molecular disks show remarkable alignment with the optical major axes of their host galaxies. The molecular masses are a few percent of the total dynamical masses that are implied if the gas is on circular orbits. If the molecular gas forms stars, it will make rotationally supported stellar disks that will be very similar in character to the stellar disks now known to be present in many ellipticals. Comparison of stellar kinematics to gas kinematics in NGC 4476 implies that the molecular gas did not come from internal stellar mass loss because the specific angular momentum of the gas is about 3 times larger than that of the stars.

Radio--optical alignments in a low radio luminosity sample

We present an optically-based study of the alignment between the radio axes and the optical major axes of eight z approximately 0.7 radio galaxies in a 7C sample. The radio galaxies in this sample are approximately 20-times less radio luminous than 3C galaxies at the same redshift, and are significantly less radio-luminous than any other well-defined samples studied to date. Using Nordic Optical Telescope images taken in good seeing conditions at rest-frame wavelengths just longward of the 4000A break, we find a statistically significant alignment effect in the 7C sample. Furthermore, in two cases where the aligned components are well separated from the host we have been able to confirm spectroscopically that they are indeed at the same redshift as the radio galaxy. However, a quantitative analysis of the alignment in this sample and in a corresponding 3C sample from HST (Hubble Space Telescope) archival data indicates that the percentage of aligned flux may be lower and of smaller spatial scale in the 7C sample. Our study suggests that alignments on the 50-kpc scale are probably closely related to the radio luminosity, whereas those on the 15 kpc scale are not. We discuss these results in the context of popular models for the alignment effect.

A search for gravitational lensing in 38 X-ray selected clusters of galaxies

We present the results of a CCD imaging survey for gravitational lensing in a sample of 38 X-ray-selected clusters of galaxies. Our sample consists of the most X-ray luminous (Lx>= 2x10^{44} erg s^{-1}) clusters selected from the Einstein Observatory Extended Medium Sensitivity Survey (EMSS) that are observable from Mauna Kea (dec > -40deg). The sample spans a redshift range of 0.15 0.5. CCD images of the clusters were obtained in excellent seeing. There is evidence of strong gravitational lensing in the form of giant arcs (length l > 8'', axis ratio l/w > 10) in 8 of the 38 clusters. Two additional clusters contain shorter arclets, and 6 more clusters contain candidate arcs that require follow-up observations to confirm their lensing origin. Since the survey does not have a uniform surface brightness limit we do not draw any conclusion based on the statistics of the arcs found. We note, however, that 60% (3 of 5) of the clusters with Lx > 10^{45} erg s^{-1}, and none of the 15 clusters with Lx 10), and are aligned orthogonal to the optical major axes of the clusters, indicate the cluster core mass density profiles must be compact (steeper than isothermal). In several cases, however, there is also some evidence, in the form of possible radial arcs, for density profiles with finite core radii.

The Orientation of Extragalactic Radiosources Relative to the Optical Axes of their Host Galaxies

The relative orientation of radio and optical axes of radio-galaxies has been analysed for a sample of about 300 sources. Radio major axes have a tendency to align with optical minor axes of the host galaxies for the more elongated radiosources while they appear correlated with optical major axes for the less elongated radiosources.

A Direct Detection of Dust in the Outer Disks of Nearby Galaxies

We measure the extent of 100 μm galactic emission in two independent galaxy samples using the IRAS 100 μm Sky Survey images and constrain the distribution of dust at large (30 kpc) radii. The first sample consists of 90 nearby (v < 6000 km s-1) galaxies from the Third Reference Catalogue of Bright Galaxies with similar angular sizes and absolute luminosities (5' ≤ D25 ≤ 10' and -22.5 ≤ MB ≤ -18) that are isolated in the 100 μm images. The second sample consists of 24 local galaxies (v < 1500 km s-1, 10' ≤ D25 ≤ 30'). We rescale the 100 μm images of these galaxies using their optical diameters, D25, rotate the images using their optical major-axis position angle, construct the mean and median images, and rebin the final images into polar coordinates to study the 100 μm emission as a function of radius and azimuthal angle. We find that the 100 μm emission extends at least to radii of 33 kpc (2 σ detection) for the typical galaxy in the 5'–10' sample and to 21 kpc (2 σ detection) in the 10'–30' sample (H0 = 75 km s-1 Mpc-1). In both samples, the emission is preferentially elongated along the optical major axis. We fit an exponential to the 100 μm emission along the major axis and measure a scale length of 2.5 ± 0.8 kpc (90% confidence interval). Using a simple model that relates the far-IR emission to the stellar distribution, we examine the range of acceptable dust mass distributions allowed by our data and conclude that the dust is more extended than the starlight.

Neutral hydrogen in M 108 (NGC 3556) and the discovery of HI supershells

We present the first high resolution HI maps of the nearby, edge-on galaxy, M 108 (NGC 3556). This galaxy is known to have a radio continuum thick disk and we have now found HI arcs and extensions protruding from the plane on kpc scales. We interpret two HI loops, positioned at either end of the optical major axis, as expanding supershells. The eastern feature, in particular, has the clear signature of an expanding half-shell and, in the context of an origin from supernovae and stellar winds, the required input energy is > 2.6 × 10 56 erg, making this the most energetic HI supershell yet detected. Since this galaxy is isolated, the supershells are unlikely to have been created through impacting external clouds, yet the required input energy is also greater than that available from the currently observed internal star formation rate. Thus some additional energy enhancement (such as magnetic fields) appears to be important in creating these features. The supershells are so dominant that they distort the outer major axis. Without a knowledge of the resolved structure of these features, the galaxy would be considered warped. We have also modeled the underlying smooth density and velocity distributions of this galaxy by reproducing the line profiles in the HI cube. The rotation curve, as illustrated by a major axis position velocity slice as well as first moment contours, appears to decline at radii > 14 kpc.

On the Origin of the Ultraviolet Continuum Emission from the High-Redshift Radio Galaxy 3C 256

view Abstract Citations (74) References (85) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the Origin of the Ultraviolet Continuum Emission from the High-Redshift Radio Galaxy 3C 256 Dey, Arjun ; Cimatti, Andrea ; van Breugel, Wil ; Antonucci, Robert ; Spinrad, Hyron Abstract We report spectropolarimetric observations obtained with the W. M. Keck Telescope of the high-redshift (z = 1.824) aligned radio galaxy 3C 256. Our observations confirm that the spatially extended UV continuum emission from this galaxy is polarized (P_V_ ~ 10.9% +/- 0.9%) with the electric vector perpendicular to the aligned radio and optical major axes (θ_V_ ~ 48.0^deg^ + 2.4^deg^). This strongly suggests that a significant fraction of the rest frame UV continuum emission from the galaxy is not starlight, but is instead scattered light from a powerful active galactic nucleus that is hidden from our direct view. The narrow emission lines, including Mg II, are unpolarized. The percentage polarization of the continuum emission and the polarization position angle are roughly constant as a function of wavelength. Although the present data do not permit us to discriminate between cool electrons and dust as the origin of the scattering, scattering by a population of hot (T ~> 10^7^ K) electrons cannot be the dominant process, since such a population would overproduce X-ray emission. A large population of cooler electrons (T ~ 10^4^ K) could be responsible for both the line emission and the scattered light, but would require that the dust-to-gas ratio in the scattering cones is 10^-3^ times smaller than that in our Galaxy and would imply that a large fraction of the baryonic mass in the galaxy is in the ionized component of its interstellar medium. Dust scattering is more efficient, but would result in detectable extinction of the emission-line spectrum unless the dust distribution is more highly clumped than the line emitting gas. Finally, we detect a strong (W^rest^lambda_ ~ 12 A) broad (FWHM ~ 6500 km s^-1^) absorption line centered at λ_rest_ ~ 1477 A. We discuss several possibilities for its origin and conclude that the most likely candidate is absorption by a high-velocity broad absorption line cloud near the nucleus of 3C 256. Publication: The Astrophysical Journal Pub Date: July 1996 DOI: 10.1086/177409 arXiv: arXiv:astro-ph/9601099 Bibcode: 1996ApJ...465..157D Keywords: GALAXIES: ACTIVE; GALAXIES: INDIVIDUAL ALPHANUMERIC: 3C 256; GALAXIES: ISM; POLARIZATION; SCATTERING; ULTRAVIOLET: GALAXIES; Astrophysics E-Print: Uu-encoded compressed gzip tarfile containing 41 page LaTex file, 10 postscript figs, and AASTex style files. To appear in July 1, 1996 ApJ vol. 465 full text sources arXiv | ADS | data products SIMBAD (11) NED (1)

The Peculiar H [CSC]i[/CSC] Kinematics of the Wolf-Rayet Starburst Galaxy NGC 5253

We report the discovery of a peculiar H I velocity field in the nearby amorphous dwarf starburst galaxy NGC 5253 which indicates that the bulk of the neutral atomic gas rotates about the galaxy's optical major axis. There is also weak evidence for a second H I dynamical component rotating about the optical minor axis. We estimate the dynamical mass at 3 × 108/sin2 i M☉. The gasdynamics in NGC 5253 are vaguely reminiscent of what is seen in polar ring galaxies and dust lane ellipticals, but the large gas mass fraction (~0.6 for i = 50°), young starburst population, irregular optical morphology, lack of a stellar ring, and lack of stellar rotation (≤ 7 km s-1) are inconsistent with either type of object. NGC 5253's unique gasdynamics and current star formation activity may be either (1) the result of an interaction with the nearby spiral M83 ~109 yr ago or (2) due to the disruption and accretion of a gas-rich companion on a highly inclined orbit. A combination of wide-field, high-sensitivity H I mapping and new optical spectra measuring the stellar kinematics along the minor axis could discriminate between these two possible interaction scenarios and constrain the original, preinteraction nature of NGC 5253. It is possible that NGC 5253 will later develop into a polar ring galaxy and that we are observing it during its period of ring formation.