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|Gas in early-type galaxies: cross-fuelling in late-type-early-type pairs?|
We present 12CO (J= 1-0) and 12CO (J= 2-1)observations of eight early-type galaxies, forming part of a sample ofinteracting galaxies, each consisting of one late- and one early-typesystem. All of the early-type galaxies observed are undetected in CO tolow levels, allowing us to place tight constraints on their moleculargas content. Additionally, we present HI absorption data for one system.The implications for possible gas transfer from the late- to theearly-type galaxy during the interaction are discussed.
|Kinematics of the local universe . XII. 21-cm line measurements of 586 galaxies with the new Nançay receiver|
This paper presents 586 new 21-cm neutral hydrogen line measurementscarried out with the FORT receiver of the meridian transit Nançayradiotelescope in the period July 2000-March 2003. This observationalprogramme is part of a larger project aiming at collecting an exhaustiveand magnitude-complete HI extragalactic catalogue for Tully-Fisherapplications. It is associated with the building of the MIGALEspectroscopic archive and database.Tables 2, 3 and HI-profiles and corresponding comments are onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (220.127.116.11) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/430/373, or directly atour web site http://klun.obs-nancay.fr
|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.
|A Minor-Merger Interpretation for NGC 1097's ``Jets''|
We have conducted a deep search for neutral hydrogen gas associated withthe faint optical ``jets'' of NGC 1097 using the Very Large Array.Measurable H I would have been expected if the jets were tidal in origingiven their moderately blue optical and near-infrared colors. The jetsare free of H I emission to a limiting surface density(ΣHI) of 0.06 Msolar pc-2 (3σ) over a 1102 km s-1 velocity range. We also rule outextended H I emission down to 0.02 Msolar pc-2 (3σ, ΔV=45 km s-1) within a 4' FWHM aperturecentered on the right-angle turn in jet R1. We have detected an H Isource [MHI=(5.1+/-1.0)×106Msolar] coincident with a small edge-on spiral or irregulargalaxy (NGC 1097B) 12' southwest of NGC 1097, situated between two jets.Two other ~106 Msolar H I point sources in thefield are considered marginal detections. Neither are associated withthe optical jets.The jets' radio-X-ray spectral energy distribution is most consistentwith starlight. However, from their morphology, optical/near-infraredcolors, and lack of H I, we argue that the jets are not tidal tailsdrawn out of NGC 1097's disk or stars stripped from the ellipticalcompanion NGC 1097A. We also reject in situ star formation in ancientradio jets as this requires essentially 100% conversion of gas intostars on large scales. Instead, we conclude that the jets represent thecaptured remains of a disrupted dwarf galaxy that passed through theinner few kiloparsecs of NGC 1097's disk.We present N-body simulations of such an encounter that reproduce theessential features of NGC 1097's jets: A long and narrow ``X''-shapedmorphology centered near the spiral's nucleus, right-angle bends, and nodiscernible dwarf galaxy remnant. A series of jetlike distributions areformed, with the earliest appearing ~1.4 Gyr after impact. Well-definedX shapes form only when the more massive galaxy has a strong diskcomponent. Ram-pressure stripping of the dwarf's interstellar mediumwould be expected to occur while passing through NGC 1097's disk,accounting for the jets' lack of H I and H II. The remnants' (B-V) colorwould still agree with observations even after ~3 Gyr of passiveevolution, provided the cannibalized dwarf was low-metallicity anddominated by young stars at impact.
|New Observations of Extra-Disk Molecular Gas in Interacting Galaxy Systems, Including a Two-Component System in Stephan's Quintet|
We present new CO (1-0) observations of 11 extragalactic tails andbridges in nine interacting galaxy systems, almost doubling the numberof such features with sensitive CO measurements. Eight of these 11features were undetected in CO to very low CO/H I limits, with the mostextreme case being the NGC 7714/5 bridge. This bridge contains luminousH II regions and has a very high H I column density(1.6×1021 cm-2 in the 55" CO beam), yet wasundetected in CO to rms T*R=2.4 mK. The H I columndensity is higher than standard H2 and CO self-shieldinglimits for solar-metallicity gas, suggesting that the gas in this bridgeis metal-poor and has an enhancedNH2/ICO ratio compared with theGalactic value. Only one of the 11 features in our sample wasunambiguously detected in CO, a luminous H I-rich star formation regionnear an optical tail in the compact group Stephan's Quintet. We detectCO at two widely separated velocities in this feature, at ~6000 and~6700 km s-1. Both of these components have H I and Hαcounterparts. These velocities correspond to those of galaxies in thegroup, suggesting that this gas is material that has been removed fromtwo galaxies in the group. The CO/H I/Hα ratios for bothcomponents are similar to global values for spiral galaxies.
|The QDOT all-sky IRAS galaxy redshift survey|
We describe the construction of the QDOT survey, which is publiclyavailable from an anonymous FTP account. The catalogue consists ofinfrared properties and redshifts of an all-sky sample of 2387 IRASgalaxies brighter than the IRAS PSC 60-μm completeness limit(S_60>0.6Jy), sparsely sampled at a rate of one-in-six. At |b|>10deg, after removing a small number of Galactic sources, the redshiftcompleteness is better than 98per cent (2086/2127). New redshifts for1401 IRAS sources were obtained to complete the catalogue; themeasurement and reduction of these are described, and the new redshiftstabulated here. We also tabulate all sources at |b|>10 deg with noredshift so far, and sources with conflicting alternative redshiftseither from our own work, or from published velocities. A list of 95ultraluminous galaxies (i.e. with L_60μm>10^12 L_solar) is alsoprovided. Of these, ~20per cent are AGN of some kind; the broad-lineobjects typically show strong Feii emission. Since the publication ofthe first QDOT papers, there have been several hundred velocity changes:some velocities are new, some QDOT velocities have been replaced by moreaccurate values, and some errors have been corrected. We also present anew analysis of the accuracy and linearity of IRAS 60-μm fluxes. Wefind that the flux uncertainties are well described by a combination of0.05-Jy fixed size uncertainty and 8per cent fractional uncertainty.This is not enough to cause the large Malmquist-type errors in the rateof evolution postulated by Fisher et al. We do, however, find marginalevidence for non-linearity in the PSC 60-μm flux scale, in the sensethat faint sources may have fluxes overestimated by about 5per centcompared with bright sources. We update some of the previous scientificanalyses to assess the changes. The main new results are as follows. (1)The luminosity function is very well determined overall but is uncertainby a factor of several at the very highest luminosities(L_60μm>5x10^12L_solar), as this is where the remainingunidentified objects are almost certainly concentrated. (2) Thebest-fitting rate of evolution is somewhat lower than our previousestimate; expressed as pure density evolution with density varying as(1+z)^p, we find p=5.6+/-2.3. Making a rough correction for the possible(but very uncertain) non-linearity of fluxes, we find p=4.5+/-2.3. (3)The dipole amplitude decreases a little, and the implied value of thedensity parameter, assuming that IRAS galaxies trace the mass, isΩ=0.9(+0.45, -0.25). (4) Finally, the estimate of density varianceon large scales changes negligibly, still indicating a significantdiscrepancy from the predictions of simple cold dark matter cosmogonies.
|A List of New Blue Galaxies. III|
A list of new fifty-eight blue galaxies identified in three 103aDspectroscopic plates, with 3-image UBV filters obtained with the 48-inSchmidt Camera of Mount Palomar is presented. The fields are centered at(00h 00m, +6o 00'), (00h00m, -12o 00'), and (00h48m, 00o 00') 1950.0 coordinates. These plateswere originally taken for the observational program of faint blue starsin the regions of the South Galactic Pole, by Haro & Luyten (1965).
|The Southern Sky Redshift Survey|
We report redshifts, magnitudes, and morphological classifications for5369 galaxies with m_B <= 15.5 and for 57 galaxies fainter than thislimit, in two regions covering a total of 1.70 sr in the southerncelestial hemisphere. The galaxy catalog is drawn primarily from thelist of nonstellar objects identified in the Hubble Space TelescopeGuide Star Catalog (GSC). The galaxies have positions accurate to ~1"and magnitudes with an rms scatter of ~0.3 mag. We compute magnitudes(m_SSRS2) from the relation between instrumental GSC magnitudes and thephotometry by Lauberts & Valentijn. From a comparison with CCDphotometry, we find that our system is homogeneous across the sky andcorresponds to magnitudes measured at the isophotal level ~26 magarcsec^-2. The precision of the radial velocities is ~40 km s^-1, andthe redshift survey is more than 99% complete to the m_SSRS2 = 15.5 maglimit. This sample is in the direction opposite that of the CfA2; incombination the two surveys provide an important database for studies ofthe properties of galaxies and their large-scale distribution in thenearby universe. Based on observations obtained at Cerro TololoInter-American Observatory, National Optical Astronomy Observatories,operated by the Association of Universities for Research in Astronomy,Inc., under cooperative agreement with the National Science Foundation;Complejo Astronomico El Leoncito, operated under agreement between theConsejo Nacional de Investigaciones Científicas de laRepública Argentina and the National Universities of La Plata,Córdoba, and San Juan; the European Southern Observatory, LaSilla, Chile, partially under the bilateral ESO-ObservatórioNacional agreement; Fred Lawrence Whipple Observatory;Laboratório Nacional de Astrofísica, Brazil; and the SouthAfrican Astronomical Observatory.
|Catalogue of HI maps of galaxies. I.|
A catalogue is presented of galaxies having large-scale observations inthe HI line. This catalogue collects from the literature the informationthat characterizes the observations in the 21-cm line and the way thatthese data were presented by means of maps, graphics and tables, forshowing the distribution and kinematics of the gas. It containsfurthermore a measure of the HI extension that is detected at the levelof the maximum sensitivity reached in the observations. This catalogueis intended as a guide for references on the HI maps published in theliterature from 1953 to 1995 and is the basis for the analysis of thedata presented in Paper II. The catalogue is only available inelectronic form at the CDS via anonymous ftp 18.104.22.168 orhttp://cdsweb.u-strasbg.fr/Abstract.html
|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.
|X-ray observations of the interacting system ARP 284|
We discuss the X-ray properties of the interacting system Arp 284,consisting of the active nuclear starburst galaxy NGC 7714 and itspost-starburst companion NGC 7715. A morphological signature of theinteraction, thought to have started <100 Myr ago, is an asymmetricstellar ring dominating the intensity profile of NGC 7714 in the innerdisk ( ~ 2 exponential scale lengths). In agreement to previousEinstein-data our ROSAT PSPC exposure shows the X-ray emission of Arp284 to be confined to NGC 7714. The bulk of the intrinsic X-rayluminosity in the ROSAT 0.1-2.4 keV band can be accounted for by thermalemission from hot ( ~ 5x 10(6) K) gas and amounts to ~ 2-4x 10(41) ergs(-1) . Follow-up observations with the ROSAT HRI revealed two distinctextended emitting regions contributing to the X-ray luminosity in NGC\7714. The more luminous of them (L_Xla 2x 10(41) erg s(-1) ) coincideswith the central starburst nucleus and can be explained this way. Thefainter one (L_X ~ 8x 10(40) erg s(-1) ) is located ~ 20'' off-centerand does not have any conspicuous optical counterpart. It is, likely,located at the borderline between the stellar ring and a massive(>10(9) M_ȯ) H I-bridge further to the east possiblyintersecting NGC 7714. The H I and X-ray morphology and the extensivestarburst nature of the nuclear energy source suggest differentscenarios for the formation of the eastern emission spot. Thepossibilities of (i) collisional heating of the outlying gas by astarburst-driven nuclear wind and (ii) infall of H I-clouds from thebridge onto the disk of NGC 7714 are discussed.
|The Peculiar Morphology of the Irregular Galaxy NGC 1427A|
Multicolor surface photometry and fragmentary low-resolutionspectroscopy of the irregular galaxy NGC 1427A are presented. Thisgalaxy, a member of the Fornax Cluster, has not been studied in detailpreviously. It shows a very distinctive morphology: a low surfacebrightness stellar background with several bright knots forming adistorted ring-like structure. A faint plume and several diffusedfilaments connect the northern part of the main body of the galaxy withan object having elliptical isophotes. The overall aspect of NGC 1427A,then, resembles that of known interacting galaxies. The very blue colorsof the bright knots show that they are composed by young stars, andseveral of them also show emission lines. The northern object, which hasitself a couple of these blue knots, is bluer than the background of themain body of the galaxy. This fact indicates that the star formationhistories in both objects have been different. Morphologically, thenorthern object is similar to the numerous dwarf elliptical or irregulargalaxies that populate the Fornax Cluster. The possibility of aninteraction being the cause of the particular structure of this galaxyis discussed.
|NGC 1427A - an LMC type galaxy in the Fornax cluster.|
We have discovered that the Fornax irregular galaxy NGC 1427A is in verymany respects a twin of the Large Magellanic Cloud. Based on B, V, I,and Hα images, we find the following. The light of the galaxy isdominated by high surface brightness regions in the south-west that aresuperimposed by a half-ring of OB associations and Hii regionsindicating recent star formation. The colors of the main stellar bodyare (V-I)=0.8mag and (B-V)=0.4mag, comparable to the LMC colors. A lowsurface brightness cloud north of the main body as well as a LSB tail inthe west have colors (V-I =~0.2 mag) that are more typical for bluecompact dwarf galaxies. We identified a system of cluster candidateswith mean ages <=2Gyr (assuming a LMC metallicity) comprising therichest cluster system in an irregular galaxy observed up to now outsidethe Local Group. In X-ray wavelengths NGC 1427A appears with arelatively soft and complex spectrum.
|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.
|An image database. II. Catalogue between δ=-30deg and δ=70deg.|
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
|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.
|Galaxies and Their Environments|
Four questions are asked related to galaxies and their environments inthe context of speculation as to which direction the field may go overthe next decade. These are: What is a galaxy? Where does a galaxy end?Are galaxies open or closed? and How important are interactions? In theprocess, these questions touch upon some of the challenging problemsfacing us today in extragalactic astronomy, such as galaxy formation andevolution, the importance of environemntal effects, and the nature andextent of dark matter. (SECTION: Invited Review Paper)
|A search for CO (1-0) emission from the tidal structures of interacting and merging galaxies|
We have used the National Radio Astronomy Observatory (NRAO) 12 mtelescope to search for CO (J = 1 - 0) emission from the tidal tails ofsix merging or interacting galaxies. Although these plumes are H I-richand several contain star forming regions, they are undetected in CO tolow levels. The lack of strong CO emission from these plumes inconjunction with the presence of massive star formation is reminiscentof the situation in dwarf irregular galaxies, and the CO/H I limits areconsistent with those of dwarfs. The low CO brightness of these plumesmay be due either to a low proportion of molecular gas, or to a highN(H2)/ICO conversion factor.
|The Montreal Blue Galaxy survey. 2: Second list of UV-bright candidates|
We present and discuss the second list of the Montreal Blue Galaxysurvey. Following the inspection of 71 plates, we found 237 newcandidates with B less than 15.5. 73 percent of them are also detectedby Infrared Astronomy Satellite (IRAS). Spectrophotometry was carriedout, at medium resolution, for a subset of 40 objects leading to theidentification of three new AGNs and producing 13 new radial velocities.Spectral classification of our candidates confirms our previous findingthat the majority of our candidates are starburst nucleus galaxiessimilar to the objects studied by Balzano in 1983. Our survey is biasedagainst the high excitation starburst H II galaxies and the LINERgalaxies. Metallicities of our galaxies are found to be from log(O/H)=8.4 to 9.0, which suggests galaxies in advanced stages of chemicalevolution.
|The morphological catalogue of galaxies equatorial survey|
We present 865 redshifts of galaxies located in the equatorial stripdelta between -17.5 deg and -2.5 deg in the right ascension rangebetween 20 h and 5 h. Redshifts have been obtained for the completesample of all 833 galaxies in the Morphological Catalog of Galaxies withmagnitudes brighter than m = 14.5 (corresponding approximately tom(Zwicky) = 15.0). This sample also includes three galaxies from othersources with more reliable magnitudes, satisfying this limit, and 29fainter galaxies, usually companions of the galaxies in the magnitudelimited sample. Our maps of a very large volume of nearby spacedemonstrate a variety of coherent large scale structures which includelarge voids, 20-50/h Mpc in diameter and large walls at least 70/h Mpcacross.
|Dynamics of interacting galaxies|
The dynamics of interacting galaxies as observed in the present epoch isreviewed. Topics discussed include numerical methods for modelinggalactic interactions, the signatures of interacting galaxies due totidal forces, and events that add mass to a galaxy. The review alsocovers major mergers between systems of comparable mass, forms ofactivity triggered or induced by galactic interactions, and galaxies'return to normality and related cosmological issues. Finally, somequestions that yet have to be answered are examined.
|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.
|Hydroxyl in galaxies. I - Surveys with the NRAO 300 FT telescope|
Results are presented of a search for 1667- and 1665-MHz mainline OHtransitions for 321 galaxies, which were observed during four separatesessions at the NRAO 300-ft telescope in the period 1984-1987. Threedetections of OH megamasers are reported, as well as detections of threenew OH absorption sources. The observational sample contains sourcesfrom a variety of catalogs and represents different criteria. Theresults for the whole sample confirm that FIR luminosity and colorcriteria used for these surveys are indeed optimized for findingmegamasers. The results also confirm that detecting distant highluminosity OH megamasers is considerably more successful than findingnearby weak masers.
|Astronomical imaging with infrared array detectors|
Advances in astronomy which have resulted from the use of IR-sensitivetwo-dimensional array detectors are reviewed. The technological aspectsof IR array detectors are discussed. Observations of star formationregions, planetary nebulae, the Galactic center, activity in othergalaxies, and the collision of two galaxies are examined. Picturesillustrating IR imagery from various observatories are presented.
|The genesis of the ring galaxy ARP 144 (NGC 7828/29)|
Multicolor near-infrared images have been obtained for the 'folded ring'galaxy Arp 144 (NGC 7828/29). About 10 to the 10th solar mass stellarnuclei associated with both NGC 7828 and NGC 7829 are found, indicatingthat this system is the result of an interaction between two similarlymassive galaxies. The galaxy/intergalactic H I cloud collision modelproposed by Freeman and de Vaucouleurs (1974) appears to be untenable,since it unequivocally predicts the existence of a single evolvedstellar nucleus.
|Neutral hydrogen observations of ARP 144|
A search was made for the giant intergalactic neutral hydrogen cloud(IGC) proposed by Freeman and de Vaucouleurs (1974) to be responsiblefor the peculiar galaxy system Arp 144. VLA 21 cm D-configurationobservations disclosed the presence of a total of 5.6 x 10 to the 9th/sqh solar masses of neutral hydrogen - nearly half of which resides in twomain structures extending as far as 98/h kpc from Arp 144. An additionalamount of H I flux resides outside the velocity range covered by theseobservations. The overall H I distribution is consistent with theFreeman and de Vaucouleurs model. It may be possible to identify one ofthe large neutral hydrogen features as part of the IGC, with the otherarising from tidal forces. An alternate hypothesis which views Arp 144as an ongoing merger between the galaxies NGC 7828 and NGC 7829 is alsoconsidered.
|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.
|The nuclear activity of interacting galaxies|
A search for active galactic nuclei among interacting galaxies isreported. A sample of 167 systems of interacting and asymmetric galaxieswas observed spectrophotometrically in the spectral range 4700-7100 A.The results are compared with a sample of isolated galaxies. It is foundthat (1) there are no Seyfert nuclei in elliptical or dwarf irregulargalaxies of the sample; (2) there is an excess of Seyfert nuclei amonginteracting spirals, but it is only at the 90 percent confidence level;(3) this excess becomes statistically significant (98 percent) when onlystrongly interacting spirals are included (four new Seyfert nuclei arepresented); (4) in the subgroup of galaxies with extreme tidaldistortions, no Seyfert nuclei were found.
|TAURUS observations of the ring galaxy in VELA|
Two-dimensional velocity field mapping of the ring galaxy in Vela (1008- 3814) is reported. TAURUS, an imaging Fabry-Perot interferometer,attached to the Cassegrain focus of the AAT and employing the IPCS as anarea detector, was used to obtain the data. The resultant velocity fieldis found to be incompatible with the simple expanding, rotating ringanticipated from previous ring galaxy studies. The appearance andkinematics favours a folded ring structure, similar to, but not asextreme as, the classic folded ring, Arp 144. The relevance to ringgalaxy formation is discussed.
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