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|Formation of polar ring galaxies|
Polar ring galaxies are peculiar systems in which a gas-rich, nearlypolar ring surrounds an early-type or elliptical host galaxy. Twoformation scenarios for these objects have been proposed: they arethought to form either in major galaxy mergers or by tidal accretion ofthe polar material from a gas rich donor galaxy. Both scenarios arestudied through N-body simulations including gas dynamics and starformation. Constraints on physical parameters are drawn out, in order todetermine which scenario is the most likely to occur. Polar ringgalaxies from each scenario are compared with observations and wediscuss whether the accretion scenario and the merging scenario accountfor observational properties of polar ring galaxies. The conclusion ofthis study is that the accretion scenario is both the most likely andthe most supported by observations. Even if the merging scenario israther robust, most polar ring galaxies are shown to be the result oftidal gas accretion events.Appendices A and B are only available in electronic form athttp://www.edpsciences.org
|A neutral hydrogen survey of polar ring galaxies. IV. Parkes observations|
A total of 33 polar ring galaxies and polar ring galaxy candidates wereobserved in the 21-cm H I line with the 64-m Parkes radio telescope. Theobjects, selected by their optical morphology, are all south ofdeclination -39o and in only 5 of them H I had been reportedpreviously. H I line emission was detected towards 18 objects, though in3 cases the detection may be confused by another galaxy in the telescopebeam, and one is a marginal detection. Eight objects were detected forthe first time in H I, of which 5 did not have previously knownredshifts. Table 1 is also available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (22.214.171.124) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/386/140
|The dark halo of the Milky Way.|
|Nearby Optical Galaxies: Selection of the Sample and Identification of Groups|
In this paper we describe the Nearby Optical Galaxy (NOG) sample, whichis a complete, distance-limited (cz<=6000 km s-1) andmagnitude-limited (B<=14) sample of ~7000 optical galaxies. Thesample covers 2/3 (8.27 sr) of the sky (|b|>20deg) andappears to have a good completeness in redshift (97%). We select thesample on the basis of homogenized corrected total blue magnitudes inorder to minimize systematic effects in galaxy sampling. We identify thegroups in this sample by means of both the hierarchical and thepercolation ``friends-of-friends'' methods. The resulting catalogs ofloose groups appear to be similar and are among the largest catalogs ofgroups currently available. Most of the NOG galaxies (~60%) are found tobe members of galaxy pairs (~580 pairs for a total of ~15% of objects)or groups with at least three members (~500 groups for a total of ~45%of objects). About 40% of galaxies are left ungrouped (field galaxies).We illustrate the main features of the NOG galaxy distribution. Comparedto previous optical and IRAS galaxy samples, the NOG provides a densersampling of the galaxy distribution in the nearby universe. Given itslarge sky coverage, the identification of groups, and its high-densitysampling, the NOG is suited to the analysis of the galaxy density fieldof the nearby universe, especially on small scales.
|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.
|Cool dense gas in early-type galaxies|
CO observations have shown that many lenticular and elliptical galaxiescontain significant amounts of cool dense gas. This review summarizesthe observational results related to the neutral gas phase and presentsa systematic comparison with other interstellar and stellar data. Thediscovery of very dense molecular gas in the nuclear regions ofearly-type galaxies, the possible existence of a dust component neitherseen optically nor in CO, internal inconsistencies of cooling flowscenarios, the origin of the cool gas, the presence of massive stars,aspects of galaxy evolution, and possibilities for future research arediscussed in the light of the new data.
|An HI survey for protogalaxies in the Centaurus and Fornax galaxy clusters|
The results of 21-cm neutral hydrogen survey observations, made usingthe 64-m Parkes telescope, are presented for two 8 deg by 8 deg fields,centred on the Centaurus and Fornax galaxy clusters, and a smaller 1deg.5 field in Eridanus. The purpose of the observations was to searchfor extended Hi clouds with no clear optical counterparts. 31 previouslycatalogued galaxies were detected, with Hi parameters for 16 beinglisted for the first time. One previously uncatalogued dwarf galaxy(`Wombat I', J0341-3851) was found near the Fornax cluster. AustraliaTelescope Compact Array observations give an Hi mass of 8x10^7 Msolarand a diameter of 4kpc for this object, which is also visible on UKSTsurvey plates. However, no clouds with optically invisible counterpartswere detected. We deduce a 99 per cent confidence limit on the total Hidensity of such objects in the cluster and near-cluster environment ofOmega_HI<10^-2h^-1(deltaV/100kms^-1.
|New H I Observations of the Prototype Polar Ring Galaxy NGC 4650A|
New, high resolution observations of the \hi\ emission line and 20-cmcontinuum at the Australia Telescope Compact Array (ATCA) for theprototype polar ring galaxy \n4650a\ are presented. We show the presenceof a far more extended \hi\ distribution than previously observed withthe VLA, and a very regular velocity field out to a distance of ~ 50kpc. The combined analysis of the \hi\ data with optical and nearinfrared images argues against previous warp models used to describe thedynamics of this object. A comparison between the high resolution \hi\images and a new B-band image obtained at the ESO NTT further weakensthe interpretation of the optical morphology via warp geometries. Thepresence of two spiral arms stretching out in the polar disk seems torepresent the most likely explanation for the observed morphology andkinematics.
|The visible environment of polar ring galaxies.|
A statistical study of the environment around Polar Ring Galaxies ispresented. Two kinds of search are performed: 1) a study of theconcentration and diameters of all the objects surrounding the PolarRings, within a search field 5 times the ring diameter. New magnitudesfor polar ring galaxies are presented. 2) a search, in a wider field,for galaxies of similar size that may have encountered the polar ringhost galaxy in a time of the order of 1Gyr. Differently from the resultsof similar searches in the fields of active galaxies, the environment ofthe Polar Ring Galaxies seems to be similar to that of normal galaxies.This result may give support to the models suggesting long times forformation and evolution of the rings. If the rings are old (and stableor in equilibrium), no traces of the past interaction are expected intheir surroundings. In addition, the formation of massive polar rings,too big to derive from the ingestion of a present-day dwarf galaxy, maybe easily placed in epochs with a higher number of gas-rich galaxies.
|Metallicity Indices for Multi-Population Models.II.Bulges of Galaxies|
We report metallicity indices in the Lick system (Hβ, Fe52, Fe53,NaD, Mg_2_) for a sample of 45 spiral bulges in the southern hemisphere.The velocity dispersion σ was also derived for each object. Spiralbulges and elliptical galaxies show a continuity in diagrams like theplane Mg_2_- or σ-Mg_2_. Using calibrations derived fromchemical evolutionary models, we estimated metallicities and abundanceratios for those bulges. The sample mean metallicity is [Fe/H]= -0.19+/- 0.27(rmsd), and the mean abundance ratios are [Mg/Fe] = 0.46 +/-0.11 (rmsd) and [Na/Fe] = 0.45 +/- 0.19(rmsd). These abundances suggestthat spiral bulges (like E's) were chemically enriched by type IIsupernovae, and that the main star formation era occurred in a timescale of the order of 1-2 Gyr.
|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.
|On the Usage of Flaring Gas Layers to Determine the Shape of Dark Matter Halos|
I present a new method of deriving the shape of the dark matter (DM)halos of spiral galaxies. The method relies on the comparison of modelpredictions with high spectral and spatial resolution H I observationsof the gas layer. So far, determinations of the flaring of the gas layer(i.e., the increase of the thickness with galactocentric radius) havebeen used to determine the mass-to-light ratio, M/L, of the stellar diskof several edge-on galaxies. In this paper I describe a method which canbe used to determine the shape of DM halos. This technique will beapplied in a forthcoming paper. I show that the model predictions of thegas layer width are best calculated using a global approach, in whichthe potential arising from the total mass distribution of the galaxy isused in the calculation of the vertical distribution of the gas. Ideveloped a new algorithm to calculate the force field of an arbitrary,azimuthally symmetric, density distribution. This algorithm is used tocalculate the forces due to the radially truncated stellar disk as wellas of the flaring gas layer. I use a simple two-parameter family ofdisk-halo models which have essentially the same observed equatorialrotation curve but different vertical forces. This mass model iscomposed of a stellar disk with constant M/L, and a DM halo with a givenaxial ratio (see Sackett & Sparke ApJ, 1990, 361,408). I approximatethe radial force due to the gaseous disk, and iteratively determine thevertical force due to the global distribution of the gas. In agreementwith Maloney (ApJ, 414,41, 1993)1 find that beyond the Holmberg radius,the thickness of the gaseous disk is sensitive to both the flattening ofthe DM halo and the self-gravity of the gas. I also show that theinferred DM-halo flattening is not sensitive to the particular choice ofdisk-halo decomposition. I show that the determination of the thicknessof the gas layer is not restricted to edge-on galaxies, but can bemeasured for moderately inclined systems as well. Thus, in combinationwith detailed modeling, high resolution H I imaging of nearby galaxieswith extended H I envelopes will enable us to determine the shape of theDM halo of these galaxies.
|2.1 μm images of the evolved stellar disk and the morphological classification of spiral galaxies|
Near-infrared images confirm that the Hubble classification of spiralgalaxies does not constrain the morphology of their stellar PopulationII disk, since galaxies on opposite ends of the spiral sequence candisplay remarkably similar evolved disk morphologies. Thus, the gasdominated Population I component determines the types (a, b, c),decoupled from the Population II. The underlying mass distributionsobserved in the infrared are exceptionally regular, suggesting thatlarge scale spiral structure is principally intrinsic, as argued by themodal theory. Moreover, single arms, bisymmetric arms, lopsidednessand/or bars dominate the old stellar disk. The absence of infraredmultiple-armed structure is attributed to the efficiency of InnerLindblad Resonance absorption in the evolved Population II disk. Theseobservations support a coherent framework for galaxy classificationbased on three parameters: stellar disk "temperature", gas content andactive disk mass.
|Particle orbits in triaxial potentials of two ellipsoidal bodies.|
|General study of group membership. II - Determination of nearby groups|
We present a whole sky catalog of nearby groups of galaxies taken fromthe Lyon-Meudon Extragalactic Database. From the 78,000 objects in thedatabase, we extracted a sample of 6392 galaxies, complete up to thelimiting apparent magnitude B0 = 14.0. Moreover, in order to considersolely the galaxies of the local universe, all the selected galaxieshave a known recession velocity smaller than 5500 km/s. Two methods wereused in group construction: a Huchra-Geller (1982) derived percolationmethod and a Tully (1980) derived hierarchical method. Each method gaveus one catalog. These were then compared and synthesized to obtain asingle catalog containing the most reliable groups. There are 485 groupsof a least three members in the final catalog.
|Groups of galaxies within 80 Mpc. II - The catalogue of groups and group members|
This paper gives a catalog of the groups and associations obtained bymeans of a revised hierarchical algorithm applied to a sample of 4143galaxies with diameters larger than 100 arcsec and redshifts smallerthan 6000 km/s. The 264 groups of galaxies obtained in this way (andwhich contain at least three sample galaxies) are listed, with the looseassociations surrounding them and the individual members of eachaggregate as well; moreover, the location of every entity among 13regions corresponding roughly to superclusters is specified. Finally,1729 galaxies belong to the groups, and 466 to the associations, i.e.,the total fraction of galaxies within the various aggregates amounts to53 percent.
|The supergalactic plane redshift survey|
Redshift measurements, about 1000 of which are new, are presented for1314 galaxies in a survey toward the apex of the large-scale streamingflow for ellipticals. The velocity histogram shows that the excess ingalaxy number counts in this area is due to a substantial concentrationof galaxies with discrete peaks at V about 3000 km/s and V about 4500km/s. After correction for the sampling function, the centroid of thedensity distribution is found to be near V about 4500 km/s.Normalization to the more extensive SSRS survey, which was selected bythe same criteria, shows that the region studied contains a considerableoverdensity of galaxies from 2000 to 6000 km/s. This result is in goodagreement with the 'great attractor' model suggested by Lynden-Bell etal. (1988) which attributes the peculiar motions of elliptical galaxiesover a large region of space to an extensive mass overdensity whichincludes the Hydra-Centaurus and Pavo-Indus superclusters. The centroidof the density enhancement is also consistent with new data by Dresslerand Faber (1990) of peculiar motions of elliptical and spiral galaxies,both of which show a zero crossing of the Hubble line at approximately4500-5000 km/s.
|Surface photometry of barred spiral galaxies|
Detailed surface photometry has been made for six early-type barredspiral galaxies using high-resolution photographic plates. Azimuthalluminosity profiles are extracted and analyzed in detail. Radialluminosity profiles of the bars and underlying disk components arestudied, and the bar components are extracted and their structurestudied in detail. The observed properties are compared with results ofnumerical simulations of a stellar disk.
|Le ballet des galaxies.|
|Southern Galaxy Catalogue.|
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