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Dynamical Parameters for AM 0644-741
We present a simulation match to the 2004 Hubble Heritagehigh-resolution optical images of AM 0644-741. In N-body/smoothedparticle hydrodynamics (SPH) simulations of AM 0644-741, we recreate thestar formation features, as well as the underlying kinematics. Oursimulations contain sufficient numerical density to accuratelydistinguish the overlapping/double ring, as well as the off-centernucleus seen in the radio observations of Higdon & Wallin and theyoung stellar features noted in the Space Telescope Science InstituteHeritage observation. Derived star formation rates for the ring andnucleus match the observed star formation features, particularly whenusing a dρ/dt star formation formulation. Kinematic comparison withthe results of Few and collaborators yields a match for the ringvelocities but not necessarily the companion. We note that the gravityand gas dynamics, modeled by N-body plus SPH, dominate over feedbackfrom stellar evolution effects (modeled using a variety of Schmidt-typeparameters), resolving the dilemma posed by Cox and coworkers. Comparingour simulation to reality gives us insight into the ring longevity andlikely generative impact scenario, reaffirming the collisional originsof this ring.
| Rings and Bent Chain Galaxies in the GEMS and GOODS Fields
Twenty-four galaxies with rings or partial rings were studied in theGEMS and GOODS fields out to z~1.4. Most resemble local collisional ringgalaxies in morphology, size, and clumpy star formation. Clump agesrange from 108 to 109 yr, and clump masses go upto several × 108 Msolar, based on colorevolution models. The clump ages are consistent with the expectedlifetimes of ring structures if they are formed by collisions. Fifteenother galaxies that resemble the arcs in partial ring galaxies but haveno evident disk emission were also studied. Their clumps have bluercolors at all redshifts compared to the clumps in the ring and partialring sample, and their clump ages are younger than in rings and partialrings by a factor of ~10. In most respects, they resemble chain galaxiesexcept for their curvature; we refer to them as ``bent chains.'' Severalrings are symmetric with centered nuclei and no obvious companions. Theycould be outer Lindblad resonance rings, although some have no obviousbars or spirals to drive them. If these symmetric cases are resonancerings, then they could be the precursors of modern resonance rings,which are only ~30% larger on average. This similarity in radiussuggests that the driving pattern speed has not slowed by more by ~30%during the last ~7 Gyr. Those without bars could be examples ofdissolved bars.
| Principal component analysis of International Ultraviolet Explorer galaxy spectra
We analyse the UV spectral energy distribution of a sample of normalgalaxies listed in the International Ultraviolet Explorer (IUE) NewlyExtracted Spectra (INES) Guide No. 2 - Normal Galaxies using a principalcomponent analysis. The sample consists of the IUE short-wavelength (SW)spectra of the central regions of 118 galaxies, where the IUE apertureincluded more than 1 per cent of the galaxy size. The principalcomponents are associated with the main components observed in theultraviolet (UV) spectra of galaxies. The first component, accountingfor the largest source of diversity, may be associated with the UVcontinuum emission. The second component represents the UV contributionof an underlying evolved stellar population. The third component issensitive to the amount of activity in the central regions of galaxiesand measures the strength of star-formation events.In all the samples analysed here, the principal component representativeof star-forming activity accounts for a significant percentage of thevariance. The fractional contribution to the spectral energydistribution (SED) by the evolved stars and by the young population aresimilar.Projecting the SEDs on to their eigenspectra, we find that none of thecoefficients of the principal components can outline an internalcorrelation or can correlate with the optical morphological types. In asubsample of 43 galaxies, consisting of almost only compact and BCDgalaxies, the third principal component defines a sequence related tothe degree of starburst activity of the galaxy.
| Mid-Infrared and CO Observations of the Infrared/X-Ray Luminous Seyfert 1 Galaxy NGC 985: The Making or Breaking of a ULIRG?
We describe Infrared Space Observatory (ISO)1 and BIMA observations of the z=0.04 Seyfert 1ring galaxy NGC 985 which suggest close parallels with some quasar hostgalaxies. NGC 985 contains two closely spaced nuclei embedded in anR1/4-law stellar bulge and an outer ring, evidence of anongoing merger. The system contains ~1.8×1010Msolar of highly disturbed molecular gas which lies in anasymmetric barlike structure with the peak in observed CO columndensities significantly offset from the compact double nucleus. Incontrast to this, the ISO observations show strong dust emissioncentered on the active galactic nucleus (AGN), located in one of the twonuclei. Fainter CO, mid-infrared (MIR), and radio continuum emissionprovides a glimpse of the complexities of star formation in the outerring. An analysis of the kinematics of the main CO emission revealsevidence for two dynamically distinct molecular components within NGC985. The first is a set of isolated supergiant molecular clouds (SGMCs)which are concentrated within 9-10 kpc of the active nucleus. Althoughrandomly distributed about the center, the clouds may form part of aclumpy highly disturbed disk which may be either just forming arounddouble nucleus (the making of an ultraluminous infrared galaxy [ULIRG])or alternatively in the process of being disrupted, perhaps as a resultof a powerful nuclear outflow (the breaking of a ULIRG). A second majorconcentration of CO lies offset from the double nucleus in a dynamicallycoherent ridge of emission in which powerful star formation isoccurring. We tentatively associate CO emission with two out of six UVabsorption lines seen in the blue wing of the very broad Lyαemission. Such an association would imply a complex interrelationshipbetween the nuclear CO cloud population in colliding systems andAGN-driven winds.
| Age Dating Ultraluminous Infrared Galaxies along the Merger Sequence
Imaging spectroscopy using the new Palomar Integral Field Spectrographis presented for the Paα line in four ultraluminous infraredgalaxies. The resulting integral field data cubes reveal line emissionpossessing a wide range of complex spatial morphologies, often quitedifferent from the appearance of the continuum. The velocity fields areequally diverse in nature, often failing to resemble typical modes ofgalactic motion. We see a variety of interesting phenomena in theindividual mergers including star formation rates of 2-5Msolar yr-1 in young tidal tails; a postencounterdisk that obeys the Tully-Fisher relation; a large-scale emission-linenebula possibly associated with a massive outflow; an apparently singlemerging system possessing two distinct kinematical axes belying thepresence of a second galaxy, mostly obscured by its merging companion;and possible formation of tidal dwarf galaxies. In most cases, we areable to establish the geometry of the merger and thus estimate the timein the merger process at which we are viewing the system. The resultingrange in estimated ages, some of which are very young encounters(~5×107 yr), is not predicted by merger models, whichproduce high rates of star formation either 1-2×108 yrafter the first encounter or very late (~109 yr) in themerger process. Even in the very young mergers, despite a sampleselection based on extended line emission, the ultraluminous activityappears to be centrally concentrated on the nucleus of one of theprogenitor galaxies-namely, the galaxy with a prograde orbital geometry.The inferred extinction to these concentrations is high, usually atleast 1 mag at the wavelength of Paα. The presence of asignificant population of very young ultraluminous mergers, togetherwith the majority of ultraluminous infrared galaxies existing in thefinal stages of merger activity, indicates that the ultraluminous galaxyphase is at least bimodal in time. An evolutionary scenario is proposedfor ultraluminous infrared galaxies, wherein the far-infrared luminositymay undergo multiple ultraluminous bursts during the course of theencounter. A substantial fraction of the merger lifetime may be spent ina phase identified with the less powerful luminous infrared galaxyclass.
| The Molecular & Atomic ISM In The Starburst Ring Galaxy AM0644-741
Highly evolved ring galaxies provide unique environments to studystarburst triggering and regulation, yet little is known of themolecular ISM in these objects. We have mapped the large southern ringgalaxy AM0644-741 in the 12CO(2-1) line with the SEST sub-mmtelescope. The 35 kpc diameter starburst outer ring is rich in molecularhydrogen (MH2=1.5x1010Msolar), with only upper-limits in the nucleus and encloseddisk. These data are combined with optical H-alpha images andinterferometric HI & 20cm maps to provide a more complete picture ofthe ISM in a ring galaxy. The collision with the companion hasconcentrated essentially all of the ISM into the expanding ring, andvery high atomic and molecular gas surface densities are derived (peakSHI+H2 = 150 Msolar pc-2, 3 kpcscales). The outer ring is thus far above the threshold for robust starformation as defined by Kennicutt (1989), while star formation istotally quenced in the sub-critical disk. UsingL(H-alpha)/MH2 to measure star formationefficiency, we find values more than an order of magnitude larger thanare commonly found in non-interacting spirals. We also address thequestion of a universal Schmidt Law in the outer ring of this galaxy.Finally, both HI & CO line profiles appear noticeably non-gaussianin parts of the ring. We tentatively attribute this to more complicatedkinematics in a non-planar ``ribbon''-shaped ring (Mihos & Hernquist1994).
| Cold gas and star formation in a merging galaxy sequence
We explore the evolution of the cold gas (molecular and neutralhydrogen) and star formation activity during galaxy interactions, usinga merging galaxy sequence comprising both pre- and post-mergercandidates. Data for this study come from the literature, but aresupplemented by some new radio observations presented here. First, weconfirm that the ratio of far-infrared luminosity to molecular hydrogenmass (LFIRM(H2); star formation efficiency)increases close to nuclear coalescence. After the merging of the twonuclei there is evidence that the star formation efficiency declinesagain to values typical of ellipticals. This trend can be attributed toM(H2) depletion arising from interaction induced starformation. However, there is significant scatter, likely to arise fromdifferences in the interaction details (e.g., disc-to-bulge ratio,geometry) of individual systems. Secondly, we find that the centralmolecular hydrogen surface density, ΣH2,increases close to the final stages of the merging of the two nuclei.Such a trend, indicating gas inflows caused by gravitationalinstabilities during the interaction, is also predicted by numericalsimulations. Furthermore, there is evidence for a decreasing fraction ofcold gas mass from early interacting systems to merger remnants,attributed to neutral hydrogen conversion into other forms (e.g., stars,hot gas) and molecular hydrogen depletion resulting from ongoing starformation. The evolution of the total-radio to blue-band luminosityratio, reflecting the total (disc and nucleus) star formation activity,is also investigated. Although this ratio is on average higher than thatfor isolated spirals, we find a marginal increase along the mergingsequence, attributed to the relative insensitivity of disc starformation to interactions. However, a similar result is also obtainedfor the nuclear radio emission, although galaxy interactions arebelieved to significantly affect the activity (star formation, AGN) inthe central galaxy regions. Nevertheless, the nuclear-radio to blue-bandluminosity ratio is significantly elevated compared with that forisolated spirals. Finally, we find that the FIR-radio flux ratiodistribution of interacting galaxies is consistent with star formationbeing the main energizing source.
| Galaxy coordinates. II. Accurate equatorial coordinates for 17298 galaxies
Using images of the Digitized Sky Survey we measured coodinates for17298 galaxies having poorly defined coordinates. As a control, wemeasured with the same method 1522 galaxies having accurate coordinates.The comparison with our own measurements shows that the accuracy of themethod is about 6 arcsec on each axis (RA and DEC).
| On the morphology of peculiar ring galaxies
It is proposed that peculiar ring galaxies can be divided into fiveprincipal types according to the morphology of the ring and bulge, basedon the visual inspection of 489 selected objects. Those objects havebeen named ``peculiar'' following the ``Catalogue of Southern PeculiarGalaxies and Associations'' by \cite[Arp & Madore (1986]{am6}) Table2 with its notes is only available electronically via anonymous ftp130.79.128.5 or http://cdsweb.u-strasbg.fr.
| Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
| The Detection of Massive Molecular Complexes in the Ring Galaxy System ARP 143
We have imaged the kiloparsec-scale distribution of 12CO( J=1--0 )emission in the ring galaxy system Arp 143 (NGC 2444/2445) using theOVRO millimeter array. We find two giant molecular complexes in the ringcomponent (NGC 2445) and a bright central source. The ring complexesrepresent 20%--60% of the detected M _{{H}2} , depending onthe relative ICO- N_{{H}2} for the ring and nucleus. Theirindividual H2 masses and surface densities ( Sigma _{{H}2} )exceed typical spiral arm giant molecular clouds and associationsregardless of the conversion factor. Both are associated with a 6 kpcridge of peak Sigma H I and massive star formation activity. Halpha imaging shows a patchy ring of H II regions situated along theouter edge of the H I ring. The kinematics of the H I ring show clearsigns of expansion. A simple rotating-expanding ring model (V_{{exp}}=118+/-30 {km} {s}^{-1} ) fits the data reasonably well, whichimplies a ring age of 60+/-15 Myr. NGC 2445's ring is able to form verylarge molecular complexes promptly in a metal-poor ISM and triggermassive star formation. Nearly 80% of the detected 12CO(1--0) fluxoriginates in a resolved central source that is slightly offset from NGC2445's starburst nucleus. We find an ordered velocity field in thiscomponent. Assuming an inclined disk, we argue that it is dynamicallystable. The central Sigma _{{H}2} (9 x 10 Msolar pc-2)significantly exceeds Sigma _{{H}2} values commonly found innormal spirals but is much smaller than values derived in similar sizedregions of IR-luminous galaxies. The nuclear H2 may be the result of aprevious encounter with NGC 2444. 12CO(1--0) emission in ring galaxiesmay be dominated by the nucleus, which could bias the interpretation ofsingle-dish measurements.
| Wheels of Fire. III. Massive Star Formation in the ``Double-ringed'' Ring Galaxy AM 0644-741
We have used H alpha CCD imaging to map the distribution and intensityof massive star formation (MSF) in AM 0644-741, a large southern ringgalaxy. MSF is restricted to a pair of interlocked 30 kpc diameterrings, with less than 1% contributed by a nuclear point source. Fiftypercent of the total H alpha emission originates in a crescent-shapedregion defining the southwest quadrant of the most prominent ring("A-ring"). North of the nucleus, MSF bifurcates into closely spacedrings of H II complexes. Particularly strong MSF occurs where theyintersect. A broad continuum ring spans the disk south of the nucleus("B-ring"). No diffuse MSF is found over the enclosed disk above an SFRper unit area of 0.15 Mȯ Gyr-1 pc-2 (3 sigma ), which is similar tolimits set in the disks of S0 galaxies. However, low H alpha surfacebrightness ( Sigma H alpha ) complexes are found beyond the southwestA-ring. We derive a total H alpha luminosity (LH alpha ) of 3.0 x 1041ergs s-1 (H0 = 100 km s-1 Mpc-1), and a total SFR of 3 Mȯ yr-1.Both values are significantly larger than those of field spirals andcomparable to those found in interacting disk systems. The integrated Halpha equivalent width (EWH alpha ) is 14 Angstroms, which is similar tovalues derived for noninteracting spirals. Systematic changes in LHalpha and EWH alpha with ring position angle were found in the A-ring,although much less pronounced than the Cartwheel's (Higdon 1995). BothA-rings and B-rings show only small azimuthal changes in red continuum.We have measured LH alpha and EWH alpha for 54 ring H II complexes.While their LH alpha tend to be higher than those commonly found inspiral galaxies, their EWH alpha are very similar. The H II luminosityfunction possesses a flat slope and large peak LH alpha , similar tothose of irregular galaxies. We conclude that MSF in AM 0644-741 hasbeen enhanced (~3x) and redistributed as a result of the intruder'spassage and that the ring galaxy was originally an Sa--Sab spiral. Weinterpret the distribution of Sigma H alpha around the rings and faint Halpha emission beyond the southwest A-ring in terms of MSF triggered onthe outer edge of a primarily gaseous ring density wave. We suggest thatthe unique double-ring structure reflects strong caustics along theinner and outer edges of a single-ring density wave. The much lessextreme MSF properties in AM 0644 relative to the Cartwheel likely arisefrom a combination of a weaker orbit crowding in the ring, highermetallicity, and a thicker precollision disk. We compare our resultswith ring galaxy models, where we find mixed results: the basicdistribution and kinematics of material in ring galaxies appear to bedescribed reasonably well. However, recent models fail to reproduce theobserved distribution of star forming regions.
| Wheels of Fire. II. Neutral Hydrogen in the Cartwheel Ring Galaxy
The VLA was used to investigate the distribution and kinematics ofneutral hydrogen, and the relation between massive star formation (MSF)and gas surface density, in the Cartwheel ring galaxy. Over 85% of theCartwheel's H I resides in the outer ring, with a low surface densitycomponent filling much of the interior. Analysis of the H I velocityfield indicates that the outer ring is expanding at V_exp_ = 53 +/- 9 kms^-1^, and that ~300 Myr have elapsed since the intruder's passage.Changes in V_exp_ with radius show that gas is beginning to leave theouter ring and is infalling for R <~ 8 kpc. H I is accumulating justbeyond the inner ring, though optical (V - R) maps show gas and dustcrossing the ring and flowing into the nucleus along two streams. No H Ianalogs of the optical "spokes" are found. The ring's surface brightnessin Hα ({SIGMA}_Hα_) and 20 cm continuum ({SIGMA}_20 cm_) areidentical, showing that peculiar extinction is not responsible for theobserved crescent of MSF. Only the two most luminous H II complexes aredetected at 6 cm and are characterized by nonthermal spectra(α^bar^ = - 0.65) and low 6 cm- Hα extinction (A^bar^_V_ =1.7 mag). The 20 cm continuum-derived Type II SN rate (0.1 +/- 0.02yr^-1^) is consistent with the lower bound of optical estimates. H I andHα are both concentrated and anticorrelated in the outer ring. MSFappears to take place on the H I ring's leading edge throughout thestarburst quadrant, where a disturbed H I component is found. TheCartwheel's gas consumption time-scale is 290 Myr. If the inner ringtriggers a second sustained starburst, a significant fraction of theremaining gas supply may be converted into stars. The globaldistribution of MSF can be understood in terms of a critical surfacedensity ({SIGMA}_crit_; reported by Kennicutt in 1989): Only in theouter ring does the atomic gas surface density ({SIGMA}_ag_) exceed{SIGMA}_crit_ when averaged over a full range in azimuth. At smallerradii, {SIGMA}_ag_/{SIGMA}_crit_ <= 0.5. The absence of strong shocksin the outer ring argue against MSF induced by high-velocity cloudcollisions (as discussed by Olson & Kwan in 1990). The ringstarburst appears to be the result of very massive cloud complexesformed through agglomeration at low velocities. Feedback and systematicvariations in collision rates/speeds likely influence MSF on kiloparsecscales in the ring itself. Large departures from Schmidt law behaviorare found. H I is detected in two companion galaxies. Mass estimatesusing their H I line widths yield values <~ 6% of the Cartwheel'sdisk + halo. A broad and massive (2 x 10^9^ M_sun_) H I plume projects82 kpc from the ring to the northeast. It is argued that this H I"splash" resulted from the passage of G3 through the Cartwheel's disk~300 Myr ago. Much of this material will escape the ring galaxy.
| Briefly noted: Irish astronomy (poem)
Not Available
| The Catalog of Southern Ringed Galaxies
The Catalog of Southern Ringed Galaxies (CSRG) is a comprehensivecompilation of diameters, axis ratios, relative bar position angles, andmorphologies of inner and outer rings, pseudorings, and lenses in 3692galaxies south of declination -17 deg. The purpose of the catalog is toevaluate the idea that these ring phenomena are related to orbitalresonances with a bar or oval in galaxy potentials. The catalog is basedon visual inspection of most of the 606 fields of the Science ResearchCouncil (SRC) IIIa-J southern sky survey, with the ESO-B, ESO-R, andPalomar Sky surveys used as auxiliaries when needed for overexposed coreregions. The catalog is most complete for SRC fields 1-303 (mostly southof declination -42 deg). In addition to ringed galaxies, a list of 859mostly nonringed galaxies intended for comparison with other catalogs isprovided. Other findings from the CSRG that are not based on statisticsare the identification of intrinsic bar/ring misalignment; bars whichunderfill inner rings; dimpling of R'1pseudorings; pointy, rectangular, or hexagonal inner or outer ringshapes; a peculiar polar-ring-related system; and other extreme examplesof spiral structure and ring morphology.
| Candidates for a southern extension of the Karachentsev catalogue of isolated pairs of galaxies.
Not Available
| Massive Star Formation and Gas Threshold Effects In Ring Galaxies: The Cartwheel and AM0644-741
Ring galaxies are formed when a companion galaxy passes through the diskof a gas rich spiral along its rotation axis. Models indicate thatstrong orbit crowding forces much of the spiral's ISM into a series ofexpanding rings, while significantly reducing the gas surface densityover the remainder of the disk. The large differences in surface densitybetween the rings and disk that arise make these systems valuable testcases for gas threshold models of Massive Star Formation (MSF) ingalaxies. We have combined aperture synthesis HI maps with Hα CCDimages of two large southern ring galaxies, the Cartwheel andAM0644-741, in order to map the distributions of neutral atomic gas andMSF, and to determine the threshold surface density for star formationthroughout each system. We find that the neutral atomic gas surfacedensity equals or exceeds the critical value only in the outer rings,where MSF is restricted. The regions interior to the starburst rings aresignificantly below threshold and show no evidence of Hα emission.These results support the idea of a gas surface density threshold forstar formation on large scales, although the situation is morecomplicated in the rings themselves.
| The visual appearance of the nuclei of ring-shaped galaxies as an alternative classification criterion
A new criterion is introduced for the classification of the apparentring-shaped galaxies on the basis of the morphology of the main bodies.For this purpose, a list of probable ring-shaped galaxies was preparedbased on visual inspection of 56 film copies of the J SRC/ESO survey.The objects found were also classified according to the Few and Madore(1986) subdivision system.
| An interacting galaxy in the Klemola 11 group
Photographic and spectroscopic data of the galaxy group Klemola 11, arepresented. The central galaxy is shown to be an S0 which exhibits mildemission at H-alpha and Forbidden S II and has a well developed dustlane. The overall spectral type indicates ongoing star formation and thegalaxy has an estimated Mv = -21.6. The galaxy has a large semicirculararm wrapped to form an incomplete ring, and evidence for its formationvia collision and merger or some internal mechanism are discussed. Thereis evidence in the image of a slight ripple and it is argued that thematerial, gas and dust have been provided by a cannibalistic merger witha dwarf member of the group.
| Two-dimensional caustics in disturbed galaxy disks
Interacting galaxies show a variety of exotic morphologies besides thewell-known rings, spirals, and bars. It is proposed that many of thesecan be identified with nonlinear, caustic structures that are known fromsingularity theory to be generic in collisionless dynamics. A simplekinematical model for stellar orbits is used to study the development ofcaustic waveforms in galaxy disks following impulsive, nonaxiallysymmetric (collisional) disturbances. It appears that all of thecaustics known from singularity theory to be generic in two dimensionsdevelop as transient forms in at least some moderately off-centercollisions. The more complex, higher-order caustics appear mostprominently in the more off-center and larger amplitude disturbances. Itis further suggested that the highly nonlinear caustic waves may play animportant role in interaction-induced star formation.
| Interacting galaxies
Present knowledge of interacting galaxies is reviewed. The structures ofundisturbed galaxies are described, and the effects of galacticinteractions on those structures are addressed. How the distortionscaused by the interactions give rise to bursts of star formation isconsidered.
| Star formation rates in ring galaxies from IRAS observations
IRAS and optical data for a sample of 26 ring galaxies are analyzed, andit is found that: (1) relatively high average values of far-infraredluminosity L(FIR), infrared to blue luminosity ratio L(FIR)/L(B), andcolor temperature compared to normal galaxies, implying a high recentstar formation rate; (2) evidence that a large fraction of the youngstars are located in the rings, indicating a very extended, coherentstarburst; and (3) a possible trend of the dispersion of L(FIR) amongrings as a function of ring diameter. Thus, within the uncertaintiesinherent in the study of this relatively small sample, it appears thatring galaxies represent a unique class of nonnuclear coherentstarbursts.
| Southern Galaxy Catalogue.
Not Available
| Shells and rings around galaxies
It is pointed out that the outer parts of galaxies often exhibitdistinct surface brightness enhancements. The development of rings andshells around galaxies has been ascribed to mechanisms in which theinteraction of a galaxy with its neighbors plays a key role. Accordingto some concepts, the big events, such as those leading to the formationof ring galaxies, are interspersed with an entire set of smaller ones.In particular, small galaxies in a group are inclined to fall into theirbigger neighbors without affecting the latter very much. After theevent, the big galaxy is provided with certain features, taking intoaccount ellipticals with shells, and S0s with polar rings. A review isconducted of the properties of these types of galaxies, insofar as theiroutskirts have identifiable shells or rings. Attention is given to ringgalaxies, outer rings around spirals and S0s, polar ring galaxies, andshells around elliptical galaxies.
| Ring galaxies. I - Kinematics of the southern ring galaxy AM 064-741
New photometric and spectroscopic data are presented for the southernring galaxy AM 064-741. The ring nucleus has a systemic velocity of 6749+ or - 67 km/s and shows rapid rotation both in the emission- andabsorption-line spectrum; however, the gas appears to be rotating afactor of three times faster than the stellar component. Twenty-tworadial velocity measurements of H II regions around the ring show thatthe ring is rotating at 311 + or - 19 km/s and expanding/contracting at128 + or - 14 km/s. A companion near an extension of the minor axis ofthe ring is identified as the intruder responsible for the ringformation.
| Atlas of interacting galaxies, Part. II and the concept of fragmentation of galaxies.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977A&AS...28....1V&db_key=AST
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