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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.
| The gas content of peculiar galaxies: Strongly interacting systems
A study of the gas content in 1038 interacting galaxies, essentiallyselected from Arp, Arp & Madore, Vorontsov-Velyaminov catalogues andsome of the published literature, is presented here. The data on theinterstellar medium have been extracted from a number of sources in theliterature and compared with a sample of 1916 normal galaxies. The meanvalues for each of the different ISM tracers (FIR, 21 cm, CO lines,X-ray) have been estimated by means of survival analysis techniques, inorder to take into account the presence of upper limits. From the datait appears that interacting galaxies have a higher gas content thannormal ones. Galaxies classified as ellipticals have both a dust and gascontent one order of magnitude higher than normal. Spirals have in mostpart a normal dust and HI content but an higher molecular gas mass. TheX-ray luminosity also appears higher than that of normal galaxies ofsame morphological type, both including or excluding AGNs. We consideredthe alternative possibilities that the molecular gas excess may derivefrom the existence of tidal torques which produce gas infall from thesurrounding regions or from a different metallicity which affects the Xconversion factor between the observed CO line luminosity and the H_2calculated mass. According to our tests, it appears that interactinggalaxies possess a higher molecular mass than normal galaxies but with asimilar star formation efficiency.Table 1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/422/941
| Star-formation in ring galaxies: Multi-band observations
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| Arp 119: A High-Speed Galaxy Collision With Episodic Star Formation
Colliding galaxies are excellent laboratories for studying galacticevolution and global star formation. Computer simulations of galaxycollisions, in which at least one galaxy has a significant gaseouscomponent, show the production of density enhancements and shock wavesin the interstellar medium. These high-density regions coincide with thelocations of recent, large-scale star formation in observations of somereal colliding galaxies. Thus, combined n-body/hydrodynamic computersimulations can be used to explore the history and conditions ofstar-forming regions in colliding galaxies. We compare multiwavelengthobservations of the Arp 119 system with a combined n-body/SPH simulationof colliding galaxies. Most of the observations used here are gleanedfrom the literature. Additionally, we obtained new near-infrared (J- andH-band) observations of this system, using the NIRIM camera at the MountLaguna observatory. These new data add information about the underlying,old stellar population. Arp 119 (CPG 29) is comprised of a southernmember, Arp 119S (Mrk 984), which has an extremely disturbed appearance,and a northern member, Arp 119N, a gas-poor elliptical. The morphologyof both members can be fitted well by a simulation in which a gas-richdisk galaxy has been impacted by an equal-mass elliptical that had atrajectory approximately perpendicular to the plane of the disk andpassed through the disk slightly off-center. From our comparison, wefind that the progression of recent large-scale star formation in thisgalaxy can be accounted for by a single outwardly propagatingcollision-induced density wave in the gas. We deduce that the starformation rate in this density wave was not a smooth function of timebut that, so far, three major episodes of star formation have occurredat roughly 25-30 Myr intervals. An initial burst took place very soonafter the peak of the collision between the two galaxies, and the latestburst is still ongoing. The fit of the simulations to the observationsindicates that this collision occurred approximately 71 Myr ago. At thecurrent, projected separation of 53 kpc (assuming H0=75 kms-1 Mpc-1), we obtain a current relative spacevelocity between the two galaxies of approximately 850 kms-1. This is strong evidence that the collision partner wasArp 119N and not some currently more distant galaxy. Furthermore, thehigh relative velocity of the pair and the paucity of gas currently tobe found in the elliptical may explain the very high velocity gasobserved in the greatly disturbed disk galaxy, Arp 119S.
| Star formation in distant starburst galaxies
This paper discusses the stellar population content of distant (5 000 kms^{-1} <== V_R<=16 000 km s^{-1}) galaxies with enhancedstar-formation activity. Distinction is made between isolated galaxiesand galaxies morphologically disturbed, with clear signs of interactionsuch as mergers. In these galaxies the International UltravioletExplorer (M_BoxIUE) large aperture samples most of the galaxy's body.Consequently, the resulting integrated spectra arise primarily from bluestellar populations of different ages together with significantcontributions from intermediate and old age components, subject tovarying reddening amounts. Instead of analysing individual, usually lowSignal-to-Noise ratio (S/N) spectra, our approach is to coadd thespectra of objects with similar spectral properties in the UV,considering as well their properties in the visible/near-infraredranges. Consequently, the resulting high (S/N) template spectra containthe average properties of a rather uniform class of objects, andinformation on spectral features can now be analysed with moreprecision. Three groups have been found for the interacting galaxies,corresponding to a red, blue and very blue continuum. Isolated galaxieshave been separated into two groups, one with a flat/red continuum andthe other with a blue continuum. For comparison, we also include in thepresent analysis two groups of nearby disturbed galaxies. Stellarpopulations are analysed by means of a synthesis algorithm based on starcluster spectral components of different ages which fit the observedspectra both in terms of continuum distribution and spectral features.Flux fractions of the different age groups found in the synthesis havebeen transformed into mass fractions, allowing inferences on the starformation histories. Young stellar populations (age <500 Myr) are themain flux contributors, except for the groups with a red spectrum notdue to extinction, arising from the intermediate (age ~1 - 2 Gyr) andold age populations. We also study the reddening values and theextinction law: a Small Magellanic Cloud-like extinction law isappropriate for all cases. As compared to nearby galaxies with enhancedstar-formation, the distant starburst galaxy spectral groups exhibitlarger contributions from the intermediate and old age populations. Thiseffect is mainly accounted for by the larger spatial area sampled by theM_BoxIUE slit in the distant galaxies, including not only the entirebulge but also evolved disk populations. The present results provide aquantitative measure of the star-forming activity in interactinggalaxies, compared to isolated galaxies. Based upon data collected withthe International Ultraviolet Explorer (IUE) Satellite, supported byNASA, SERC and ESA.
| 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.
| Multiwavelength Observations of Collisional Ring Galaxies.I.Broad-Band Images, Global Properties, and Radial Colors of the Sample Galaxies
This is one of a series of papers discussing the optical, infrared andradio continuum properties of a sample of collisional ring galaxies. Thepresent paper concentrates on the global broad-band optical (B, V and R)and near-IR (J, H and K) images of the galaxies and describe theirglobal properties. An analysis of the colors of the galaxies over avariety of wavelength baselines is described. In the B and V bands, thebluest colors are found in the outer bright ring. The B-V colors of thesample of galaxies are blue, the median value for the sample is B-V =0.60, and V-K= 2.33 mag. The IR morphology of the galaxies is, in mostcases, very similar to that of the B-band data, suggesting that theclumpy appearance of the star formation in the outer rings is real, andnot a result of patchy dust obscuration. Only in one ring (WN1, aSeyfert ring galaxy) was the IR morphology different from the optical,suggesting the presence of significant dust in the disk. In II Hz 4,faint spiral arms are seen within the ring. There is a suggestion thatthe larger rings have redder V-K colors, which may be due to anincreased incidence of nuclear bulges in larger ring galaxies. Radialprofiles of surface brightness and color are presented for fourgalaxies. In all cases, the colors becomes bluer as one proceedsradially outwards, but in two galaxies, the rings redden again outsidethe main ring, suggesting the existence of a red stellar population thatmay have pre-dated the collisions.
| Collisional Ring Galaxies
We review the current state of knowledge of both the observational andtheoretical nature of collisional ring galaxies. Ring galaxies representa class of colliding galaxy in which nearly symmetrical density wavesare driven into a disk as a result of an almost bulls-eye collision withanother galaxy. Since the basic dynamics of the collision is now quitewell understood, the ring galaxies can be used as a form of cosmicperturbation "experiment" to explore various properties of galacticdisks. For example, as the density wave expands into the disk, ittriggers the birth of large numbers of massive stars. This provides uswith an opportunity to study the evolution of stars and star clusters inthe wake of the ring. We review the now extensive observations of ringgalaxies from the early photographic measurements to recent infrared,radio and optical studies. We also present a simple analytical treatmentof the ring-making collisions and compare them to recent N-body andgas-dynamical models. The importance of ring galaxies lies in theirrelative simplicity compared with other colliding systems and thepossibility that low-angular momentum collisions might have been morecommon in the past.
| IUE Spectra of Selected Ring Galaxies
A ``ring'' galaxy is thought to result from the nearly head-on collisionbetween an intruder galaxy and a spiral. During this collision, anexpanding density wave sweeps disk material into a ring form in thetarget galaxy. The cloud-cloud collisions in the nucleus of the targetgalaxy result in starburst activity. We present IUE spectra for a sampleof 11 ``ring'' galaxies selected on the basis of their morphology andIRAS detections. The remnant nuclei of the target galaxies were observedwith the SWP camera. The IUE observations reveal diverse results; i.e.,starburst activity (NGC 7714), elevated UV continuum (Arp 144), andLy-alpha emission with no other UV features (Arp 147). Presumably, theUV activity is dependent upon the dynamics of the initial collision, thestrength and duration of the nuclear starburst, and the elapsed timesince the collision.
| Large-Scale Structures in the Zone of Avoidance: The Galactic Anticenter Region
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...449..527L&db_key=AST
| Self-Consistent Evolution of Ring Galaxies
Ring galaxies are commonly known as objects where a burst of starformation was triggered by a close encounter with an intruder, maybe asatellite galaxy. BVRI CCD observations of five ring galaxies have beenperformed. Here we present the results of a self-consistent approach toreproduce their observed morphology and spectral energy distributionusing updated N-body simulations and evolutionary population synthesismodels extending from UV to far-IR wavelengths. Some suggestions aboutthe evolutionary properties of these starburst galaxies are thenderived.
| The CO emission of ring galaxies.
Using the 15m SEST and 30m IRAM telescope we have observed 16 ringgalaxies in the 2CO10 transition and detected 14. Six ring galaxies havebeen detected in the ^12^CO(2-1) line. The Cartwheel, often consideredas the prototype of ring galaxies, has not been detected. We suggestthat the weak CO emission of this galaxy is due to its low metallicity.The observations do not exclude the possibility that the Cartwheel maybe H_2_rich and actively forming stars. We also present new HIdetections of six rings. We have compared the CO emission of the ringgalaxies with that of the distance-limited sample of Sage (1993a,b) andfound that ring galaxies are bright in CO compared to normal galaxies.If the standard conversion factor from CO emissivities into H_2_columndensities holds for ring galaxies, this suggests that a large amount ofmolecular gas is available for star formation and that ring galaxies areactively forming stars. This result is in agreement with the highfar-infrared luminosities of ring galaxies. We have also observed twoHoag-type objects in CO but have detected neither of them.
| Galactic scale gas flows in colliding galaxies: 3-dimensional, N-body/hydrodynamics experiments
We present some results from three dimensional computer simulations ofcollisions between models of equal mass galaxies, one of which is arotating, disk galaxy containing both gas and stars and the other is anelliptical containing stars only. We use fully self consistent models inwhich the halo mass is 2.5 times that of the disk. In the experiments wehave varied the impact parameter between zero (head on) and 0.9R (whereR is the radius of the disk), for impacts perpendicular to the diskplane. The calculations were performed on a Cray 2 computer using acombined N-body/smooth particle hydrodynamics (SPH) program. The resultsshow the development of complicated flows and shock structures in thedirection perpendicular to the plane of the disk and the propagationoutwards of a density wave in both the stars and the gas. Thecollisional nature of the gas results in a sharper ring than obtainedfor the star particles, and the development of high volume densities andshocks.
| An interaction model for the formation of dwarf galaxies and 10 exp 8 solar mass clouds in spiral disks
Ten H I clouds with masses larger than 10 exp 8 solar masses in theinteracting galaxies IC 2163/NGC 2207 are identified. Twenty-eight otherinteracting pairs of galaxies with large knots or star formationstructures in their optical images are also tabulated. It is suggestedthat interactions can lead to the formation of greater than 10 solarmass clouds and young stellar regions in the outer parts of galacticdisks, and that some of these regions may become gravitationally bounddwarf galaxies if they are ejected in tidal arms. It is proposed thatthe key to the origin of clouds of greater than 10 exp 8 solar mass ininteracting systems lies in the high velocity dispersion of theinterstellar gas. Numerical N-body simulations of the interactinggalaxies suggest that the complete detachment of an unbound dwarf galaxyrequires a companion mass comparable to or larger than the galaxy mass.
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| A near-infrared imaging survey of interacting galaxies - The small angular-size ARP systems
Near-IR images of a large sample of interacting galaxies selected fromthe Atlas of Peculiar Galaxies by Arp (1966) have been obtained.Approximately 180 systems have been imaged in at least two, and usuallythree of the standard JHK bands. The survey and the observing and datareduction procedures, are described, and contour plots and aperturephotometry are presented. Future papers will analyze the imaging data bygroupings based on interaction type, stage, and progenitors. The goalsof the analysis are to explore the relationships between galaxyinteractions, activity, and morphology by studying the structure of thenear-IR luminosity distribution, where extinction effects are muchreduced relative to the optical and the major stellar mass component ofgalaxies dominates the observed light.
| A model for ring galaxies - ARP 147-like systems
The galaxy Arp 147 belongs to a class of objects believed to have formeda ring as a result of a collision with a second galaxy. We have produceda combined stellar and gasdynamical computer model of a pair ofinteracting galaxies which exhibits many of the features seen in Arp147. In our model, the ring forms in a disk galaxy following the passageof an equal-mass elliptical galaxy approximately perpendicular throughthe disk, about two radial scale lengths from the center. Some genericfeatures of this type of collision are that (1) 'hot spots' of increasedgas density and shocks occur on opposite sides of the ring, away fromthe nucleus; (2) an incomplete ring forms, with the disk galaxy'sremnant nucleus offset from the center and no longer in the plane of thedisk; and (3) this nucleus can appear buried in one edge of the ringdepending on the orientation relative to the observer.
| A Model for Ring Galaxies: Arp 147-Like Systems
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| IUE Spectra of the Ring Galaxy ARP 147
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| The peculiar, off-centered ring of the SA galaxy NGC 3611
The discovery of a faint ring of 30 kpc diameter and absolute magnitude-15.8 + or - 1 surrounding the northeastern end of the relativelyisolated, but disturbed-looking, Sa galaxy NGC 3611 is reported. Thisring appears centered approximately on the edge of the main disk of NGC3611, at 8 kpc projected distance from the nucleus. If intrinsicallynear circular, the ring is oriented roughly perpendicular to that disk.Four different hypotheses concerning the nature and origin of thispuzzling structure are discussed. Various arguments favor the hypothesisthat the ring is a classical ring galaxy formed when a small diskcompanion was disrupted by a near-central collision with NGC 3611itself.
| An extragalactic database. I - The Catalogue of Principal Galaxies
The Catalogue of Principal Galaxies is described, which lists equatorialcoordinates (for the equinoxes 1950 and 2000) and cross-identificationsfor 73,197 galaxies. The 40,932 coordinates have standard deviationssmaller than 10 arcsec. A total of 131,601 names from the 38 most commonsources are listed. In addition, mean data for each object are givenwhen available: 49,102 morphological descriptions, 52,954 apparent majorand minor axes, 67,116 apparent magnitudes, 20,046 radial velocities and24,361 position angles. This information was used for facilitatingproper identification. Finally, distribution options are explained.
| Near-Infrared Imaging of Ring Galaxies
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| Models of ring galaxies. I - The growth and disruption of clouds in the expanding density wave
Cloud-fluid models of the growth and evolution of density waves in acolliding ring galaxy with a low mass companion are studied. It is foundthat, if the ring expands and grows on a time scale comparable with thecollision time between interstellar clouds in the disk galaxy, bothenhancement and suppression of star formation can occur. A second ringshould form after the first wave has become well developed. This ring islikely to be more strongly compressed than the first, leading togenerally stronger star formation. The infall of gas onto a nucleuscapable of nonthermal activity at the ring center appears to beinevitable during most of the lifetime of the ring phenomenon.
| 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.
| X-ray observations of ring galaxies with the Einstein Observatory
Nine ring-type galaxies and the compact blue galaxy II Zw 40 wereobserved with the Einstein Observatory. Only NGC 985, with a Seyfertnucleus, was detected. Its nonthermal X-ray source is clearly located inthe nucleus, and its luminosity is typical of Seyfert galaxies. Theother observed galaxies are no brighter in the X-ray than other samplesof peculiar and interacting galaxies. A model of thermal X-ray emissiondue to shock waves resulting from galaxy collisions is presented whichpredicts emission of similar luminosity to that from a combination ofdiscrete sources.
| A new ring galaxy in Canes Venatici
A new object, tentatively identified as a ring galaxy, has been found 23arcsec away from the 9.5 mag SAO44762 star. It resembles a face-on ring,almost fully circular, with a single bright knot on the side away fromthe star. Further observations are urged to establish the extragalacticnature of this object and its relation to neighbouring galaxies.
| 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
| Anuclear ring galaxies.
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| Ring galaxies
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