Home     Getting Started     To Survive in the Universe    
Inhabited Sky
    News@Sky     Astro Photo     The Collection     Forum     Blog New!     FAQ     Press     Login  

NGC 4672



Upload your image

DSS Images   Other Images

Related articles

Ionized gas and stellar kinematics of seventeen nearby spiral galaxies
Ionized gas and stellar kinematics have been measured along the majoraxes of seventeen nearby spiral galaxies of intermediate to latemorphological type. We discuss the properties of each sample galaxy,distinguishing between those characterized by regular or peculiarkinematics. In most of the observed galaxies, ionized gas rotates morerapidly than stars and has a lower velocity dispersion, as is to beexpected if the gas is confined in the disc and supported by rotationwhile the stars are mostly supported by dynamical pressure. In a fewobjects, gas and stars show almost the same rotational velocity and lowvelocity dispersion, suggesting that their motion is dominated byrotation. Incorporating the spiral galaxies studied by Bertola et al.(\cite{Bertola1996}), Corsini et al. (\cite{Corsini1999},\cite{Corsini2003}) and Vega Beltrán et al. (\cite{Vega2001}) wehave compiled a sample of 50 S0/a-Scd galaxies, for which the major-axiskinematics of the ionized gas and stars have been obtained with the samespatial (≈1'') and spectral (≈50 km;s-1) resolution,and measured with the same analysis techniques. This allowed us toaddress the frequency of counter-rotation in spiral galaxies. It turnsout that less than 12% and less than 8% (at the 95% confidence level) ofthe sample galaxies host a counter-rotating gaseous and stellar disc,respectively. The comparison with S0 galaxies suggests that theretrograde acquisition of small amounts of external gas gives rise tocounter-rotating gaseous discs only in gas-poor S0s, while in gas-richspirals the newly acquired gas is swept away by the pre-existing gas.Counter-rotating gaseous and stellar discs in spirals are formed onlyfrom the retrograde acquisition of large amounts of gas exceeding thatof pre-existing gas, and subsequent star formation, respectively.Based on observations carried out at the European Southern Observatory,La Silla (Chile) (ESO 56.A-0684 and 57.A-0569).Tables 3 and 4 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr ( or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/424/447Full Fig. \ref{fig:kinematics} and Figs. \ref{fig:gascomparison} and\ref{fig:starcomparison} are only available in electronic form athttp://www.edpsciences.org

Minor-axis velocity gradients in spirals and the case of inner polar disks
We measured the ionized-gas and stellar kinematics along the major andminor axis of a sample of 10 early-type spirals. Much to our surprise wefound a remarkable gas velocity gradient along the minor axis of 8 ofthem. According to the kinematic features observed in their ionized-gasvelocity fields, we divide our sample galaxies in three classes ofobjects. (i) NGC 4984, NGC 7213, and NGC 7377 show an overall velocitycurve along the minor axis without zero-velocity points, out to the lastmeasured radius, which is interpreted as due to the warped structure ofthe gaseous disk. (ii) NGC 3885, NGC 4224, and NGC 4586 arecharacterized by a velocity gradient along both major and minor axis,although non-zero velocities along the minor axis are confined to thecentral regions. Such gas kinematics have been explained as being due tonon-circular motions induced by a triaxial potential. (iii) NGC 2855 andNGC 7049 show a change of slope of the velocity gradient measured alongthe major axis (which is shallower in the center and steeper away fromthe nucleus), as well as non-zero gas velocities in the central regionsof the minor axis. This has been attributed to the presence of akinematically-decoupled gaseous component in orthogonal rotation withrespect to the galaxy disk, namely an inner polar disk. The case andorigin of inner polar disks are discussed and the list of their hostgalaxies is presented.Based on observations carried out at the European Southern Observatory(ESO 62.A-0463 and 63.N-0305).Tables 3 and 4 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr ( or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/408/873

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 ( or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/386/140

ESO 603-G21: A strange polar-ring galaxy
We present the results of B, V, R surface photometry of ESO 603-G21 - agalaxy with a possible polar ring. The morphological and photometricfeatures of this galaxy are discussed. The central round object of thegalaxy is rather red and presents a nearly exponential surfacebrightness distribution. This central structure is surrounded by a bluewarped ring or disk. The totality of the observed characteristics(optical and NIR colors, strong color gradients, HI and H_2 content, FIRluminosity and star-formation rate, rotation-curve shape, globalmass-to-luminosity ratio, the agreement with the Tully-Fisher relation,etc.) shows that ESO 603-G21 is similar to late-type spiral galaxies. Wesuppose that morphological peculiarities and the possible existence oftwo large-scale kinematically-decoupled subsystems in ESO 603-G21 can beexplained as being a result of dissipative merging of two spiralgalaxies or as a consequence of a companion accretion onto apre-existing spiral host. Based on observations made at theObservatório do Pico dos Dias (OPD), operated by theMCT/Laboratório Nacional de Astrofísica, Brazil.

The orthogonal gaseous kinematical decoupling in the Sa spiral NGC 2855
We present major and minor-axis kinematics of stars and ionized gas aswell as narrow and broad-band surface photometry of the Sa spiral NGC2855. In the nuclear regions of this unbarred and apparently undisturbedspiral galaxy the gas is rotating perpendicularly to the galaxy disk. Wesuggest that this kinematically-decoupled component is the signature ofan acquisition process in the history of this galaxy. Based onobservations carried out at the Observatorio del Roque de los Muchachos,La Palma (Spain) with the Italian Telescopio Nazionale Galileo and atthe European Southern Observatory, La Silla (Chile) (ESO 62.N-0463 and67.B-0230). Tables 3 and 4 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr ( or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/382/488

Kinematics of the Ionized Gas in the Inner Regions of Disk Galaxies
Not Available

NGC 4672: a new case of an early-type disk galaxy with an orthogonally decoupled core
We report the case of the early-type disk galaxy NGC 4672 as a newexample of a galaxy hosting a bulge and a disk, which are orthogonallydecoupled with respect to one other. The morphological features of thisgalaxy are discussed as well as the velocity curves and velocitydispersions profiles of stars and ionized gas along both its major andminor axis. We concluded that NGC 4672 has structural (i.e. a bulgeelongated perpendicularly to the disk) and kinematical (i.e. a stellarvelocity gradient along the bulge major axis) properties similar tothose of the Sa NGC 4698, in which the orthogonal rotation between theinner bulge and the disk has been recently found by Bertola et al.(1999). This bulge-disk orthogonal decoupling suggests that the diskcomponent is the end result of a second event occurred in the history ofthe galaxy.

How can we gather clues so as to understand structure, formation, andevolution of large stellar systems? This paper addresses three aspectsof this general problem. First we briefly describe a number of recentdevelopements in classical topics of galactic dynamics. Then we reporton studies of the dynamics of galaxies at intermediate redshifts.Finally we address a line of research where distant galaxies are used asa diagnostic tool of weak effects of gravitational lensing and thus helpus pin down the mass distribution of lensing clusters at intermediateredshifts.

The Orthogonal Bulge-Disc Decoupling in NGC 4698
The R-band isophotal map of the Sa galaxy NGC 4698 shows that the innerregion of the bulge is elongated perpendicularly to the major axis ofthe disc. At the same time a central stellar velocity gradient is foundalong the minor axis of the disc. The same properties have also beenrecognized in the Sa galaxy NGC 4672. This remarkable geometric andkinematic decoupling is a direct indication that a second event occurredin the history of these galaxies suggesting that acquisition phenomenacould play a primary role in the formation of early-type spirals.

Kinematical Decouplings in Spiral Galaxies
Like fossils, multiple stellar and gaseous components with a misalignedor even opposite angular momentum with respect to that of their hostconserve memory of processes driving galaxy formation and evolution. Indisk galaxies, apart few cases like polar rings, they usually lurk tomorphological inspection, they are serendipitously discovered bymeasuring detailed kinematics and generally interpreted as the endresult of one or more second events. This is the case of a variety ofkinematically-decoupled components, like the counterrotating gasobserved in several S0's, the counterrotating stellar or gaseous disksfound in a number of early-type spirals, and the orthogonally-rotatingstellar cores we recently discovered in the bulges of two Sa spirals,namely NGC 4698 and NGC 4672. In this contribution we present theresults of a survey aimed to measure the stellar and ionized-gaskinematics in a sample of nearby S0/a's and Sa's, which have beenselected to be morphologically similar to the few spiral galaxieshosting counterrotating stellar and/or gaseous disks. In spite of theirundisturbed appearance, all the sample galaxies host a kinematicallydecoupled gas component since they are characterized by a sharp gasvelocity gradient along their minor axes. In some cases the nuclear gasis even rotating perpendicularly to the galaxy disk. In the pastnumerical experiments predicted that observable consequences of secondevents in disk galaxies (e.g. bulge growing, disk heating) result in achange of the host morphology toward earlier spiral types. Now weattempt to investigate the possible link between morphology and secondevents (unveiled by kinematical decouplings) in early-type spirals.

The gas content of peculiar galaxies: Counterrotators and polar rings
This paper studies the global ISM content in a sample of 104 accretinggalaxies, including counterrotators and polar rings, which spans theentire Hubble sequence. The molecular, atomic and hot gas content ofaccretors is compared to a newly compiled sample of normal galaxies. Wepresent results of a small survey of the J=1-0 line of 12COwith the 15 m SEST telescope on a sample of 11 accretors (10counterrotators and 1 polar ring). The SEST sample is enlarged withpublished data from 48 galaxies, for which observational evidence ofcounterrotation in the gas and/or the stars has been found. Furthermore,the available data on a sample of 46 polar ring galaxies has beencompiled. In order to explore the existence of an evolutionary pathlinking the two families of accretors, the gas content ofcounterrotators and polar rings is compared. It was found that thenormalized content of cold gas (Mgas/LB) in polarrings is ~ 1 order of magnitude higher than the reference value derivedfor normal galaxies. The inferred gas masses are sufficient to stabilizepolar rings through self-gravity. In contrast, it was found that thecold gas content of counterrotators is close to normal for all galaxytypes. Although counterrotators and polar rings probably share a commonorigin, the gas masses estimated here confirm that light gas ringsaccreted by future counterrotators may have evolved faster than theself-gravitating structures of polar rings. In this scenario, thetransformation of atomic into molecular gas could be enhanced near thetransition region between the prograde and the retrograde disks,especially in late-type accretors characterized by a high content ofprimordial gas. This is tentatively confirmed in this work: the measuredH2/HI ratio seems larger in counterrotators than in normal orpolar ring galaxies for types later than S0s. Based on observationscollected at SEST telescope, European Southern Observatory, La Silla,Chile. Table 1 is only available in electronic form athttp://www.edpsciences.org

Tracing the vertical composition of disc galaxies through colour gradients
Optical observations of a statistically complete sample of edge-ondisc-dominated galaxies are used to study the intrinsic vertical colourgradients in the galactic discs, in order to constrain the effects ofpopulation gradients, residual dust extinction and gradients in themetal abundance of the galaxies. For the majority of our samplegalaxies, the colours and colour gradients in the range1.0hz<=|z|<=3.0hz most likely reflect theintrinsic galactic properties (where hz is the verticalscaleheight). It appears that the intrinsic vertical colour gradientsare either non-existent, or small and relatively constant as a functionof position along the major axes of the galaxies. On average, theearlier-type galaxies exhibit smaller vertical (B-I) gradients than thelater types; our results are consistent with the absence of any verticalcolour gradient in the discs of the early-type sample galaxies. In mostgalaxies small-scale variations in the magnitude and even the directionof the vertical gradient are observed: at larger galactocentricdistances they generally display redder colours with increasing zheight, whereas the opposite is often observed in and near the galacticcentres. For a significant fraction of our sample galaxies anothermechanism in addition to the effects of stellar population gradients isrequired to explain the magnitude of the observed gradients. Thenon-zero colour gradients in a significant fraction of our samplegalaxies are likely to be (at least) partially due to residual dustextinction at these z heights, as is also evidenced from the sometimessignificant differences between the vertical colour gradients measuredon either side of the galactic planes. We suggest that initial verticalmetallicity gradients, if any, have probably not been accentuated byaccretion or merging events over the lifetimes of our sample galaxies.On the other hand, they may have weakened any existing verticalmetallicity gradients, although they also may have left the existingcorrelations unchanged.

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.

Distances to Galaxies from the Correlation between Luminosities and Line Widths. III. Cluster Template and Global Measurement of H0
The correlation between the luminosities and rotation velocities ofgalaxies can be used to estimate distances to late-type galaxies. It isan appropriate moment to reevaluate this method given the great deal ofnew information available. The major improvements described hereinclude: (1) the template relations can now be defined by large,complete samples, (2) the samples are drawn from a wide range ofenvironments, (3) the relations are defined by photometric informationat the B, R, I, and K' bands, (4) the multiband information clarifiesproblems associated with internal reddening, (5) the template zeropoints are defined by 24 galaxies with accurately known distances, and(6) the relations are applied to 12 clusters scattered across the skyand out to velocities of 8000 km s-1. The biggest change fromearlier calibrations are associated with point 5. Roughly a 15% increasein the distance scale has come about with the fivefold increase in thenumber of zero-point calibrators. The overall increase in the distancescale from the luminosity-line width methodology is about 10% afterconsideration of all factors. Modulo an assumed distance to the LargeMagellanic Cloud of 50 kpc and no metallicity corrections to the Cepheidcalibration, the resulting value of the Hubble constant isH0=77+/-8 km s-1 Mpc-1, where the erroris the 95% probable statistical error. Cumulative systematic errorsinternal to this analysis should not exceed 10%. Uncertainties in thedistance scale ladder external to this analysis are estimated at ~10%.If the Cepheid calibration is shifted from the LMC to NGC 4258 with adistance established by observations of circumnuclear masers, thenH0 is larger by 12%.

Box- and peanut-shaped bulges. I. Statistics
We present a classification for bulges of a complete sample of ~ 1350edge-on disk galaxies derived from the RC3 (Third Reference Catalogue ofBright Galaxies, de Vaucouleurs et al. \cite{rc3}). A visualclassification of the bulges using the Digitized Sky Survey (DSS) inthree types of b/p bulges or as an elliptical type is presented andsupported by CCD images. NIR observations reveal that dust extinctiondoes almost not influence the shape of bulges. There is no substantialdifference between the shape of bulges in the optical and in the NIR.Our analysis reveals that 45% of all bulges are box- and peanut-shaped(b/p). The frequency of b/p bulges for all morphological types from S0to Sd is > 40%. In particular, this is for the first time that such alarge frequency of b/p bulges is reported for galaxies as late as Sd.The fraction of the observed b/p bulges is large enough to explain theb/p bulges by bars. Partly based on observations collected at ESO/LaSilla (Chile), DSAZ/Calar Alto (Spain), and Lowell Observatory/Flagstaff(AZ/U.S.A.). Tables 6 and 7 are only available in electronic form at CDSvia anonymous ftp to cdsarc.u-strasbg.fr ( or viahttp://cdsweb.u-strasbg.fr/Abstract.html

A neutral hydrogen survey of polar ring galaxies. III. Nançay observations and comparison with published data
A total of 50 optically selected polar ring galaxies, polar ring galaxycandidates and related objects were observed in the 21-cm H i line withthe Nançay decimetric radio telescope and 31 were detected. Theobjects, selected by their optical morphology, are all north ofdeclination -39o, and generally relatively nearby (V< 8000km s-1) and/or bright (mB< 15.5). The H i linedata are presented for all 74 galaxies observed for the survey with theEffelsberg, Green Bank or Nanç radio telescopes, as well as allother published H i line parameters of these objects. Three objects wereobserved and detected by us at Parkes. A total of 59 objects weredetected. For each object a brief description is given based on aliterature search.

NGC 4672: A new case of an early-type disk galaxy with an orthogonally decoupled core
We report the case of the early-type disk galaxy NGC 4672 as a newexample of a galaxy characterized by the orthogonal geometricaldecoupling between bulge and disk. The morphological features of thisgalaxy are discussed as well as the velocity curves and velocitydispersion profiles of stars and ionized gas along both its major andminor axis. We conclude that NGC 4672 has structural (i.e. a bulgeelongated perpendicularly to the disk) and kinematical (i.e. a stellarcore rotating perpendicularly to the disk) properties similar to thoseof the Sa NGC 4698. The presence of the isolated core suggests that thedisk component is the end result of the acquisition of external materialin polar orbits around a pre-existing oblate spheroid as in the case ofthe ring component of AM 2020-504, the prototype of polar ringellipticals. Based on observations carried out at ESO, La Silla (Chile).Tables 3 to 6 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr ( or viahttp://cdsweb.u-strasbg.fr/Abstract.html.

The global structure of galactic discs
A statistical study of global galaxy parameters can help to improve ourunderstanding of galaxy formation processes. In this paper we presentthe analysis of global galaxy parameters based on optical andnear-infrared observations of a large sample of edge-on disc galaxies.We found a correlation between the ratio of the radial to vertical scaleparameter and galaxy type: galaxies become systematically thinner whengoing from type S0 to type Sc, whereas the distribution seems to leveloff for later types. The observed scalelength ratios (and thus theradial colour gradients) largely represent the dust content of thegalaxies. On average, the colour gradients indicated by the scalelengthratios increase from type Sa to at least type Sc. For galaxy types laterthan Sc, the average colour gradient seems to decrease again. Thedistribution of K-band (edge-on) disc central surface brightnesses israther flat, although with a large scatter. However, the latest-typesample galaxies (T>6) show an indication that their average disccentral surface brightnesses may be fainter than those of the earliertypes. This effect is probably not the result of dust extinction.

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.

A catalogue of spatially resolved kinematics of galaxies: Bibliography
We present a catalogue of galaxies for which spatially resolved data ontheir internal kinematics have been published; there is no a priorirestriction regarding their morphological type. The catalogue lists thereferences to the articles where the data are published, as well as acoded description of these data: observed emission or absorption lines,velocity or velocity dispersion, radial profile or 2D field, positionangle. Tables 1, 2, and 3 are proposed in electronic form only, and areavailable from the CDS, via anonymous ftp to cdsarc.u-strasbg.fr (to130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html

BVRI and H(alpha) Surface Photometry of the Triple-Ringed Galaxy IC 4214
BVRI and Hα CCD surface photometry is presented for the Sab systemIC 4214, an example of a galaxy with three rings and no conventionalbar. We obtained isophote maps, luminosity profiles, and basicphotometric parameters. The photometry suggests the galaxy has threemajor structural components: the nuclear bulge, the disk, and anon-axisymmetric component that is a mixture of bar, inner ring andlens. The bar is a very weak feature that appears clearly only in the Iband. Even so, the non-axisymmetric component contributes 23% to thetotal I luminosity. The Hα emission is concentrated mostly in thenuclear ring and in the two spiral arms that form the inner ring. Boththe inner ring and nuclear ring are blue compared with theirsurroundings, and must contain regions of star formation mixed withdust. The existence of rings in non-barred and weakly barred galaxies isstill not well explained by theories of ring formation. This galaxyseems to be a case like others that have appeared in the literature,where the bar was stronger in the past, and now is dissolving.

The I band Tully-Fisher relation for cluster galaxies: data presentation.
Observational parameters which can be used for redshift-independentdistance determination using the Tully-Fisher (TF) technique are givenfor \ntot spiral galaxies in the fields of 24 clusters or groups. I bandphotometry for the full sample was either obtained by us or compiledfrom published literature. Rotational velocities are derived either from21 cm spectra or optical emission line long-slit spectra, and convertedto a homogeneous scale. In addition to presenting the data, a discussionof the various sources of error on TF parameters is introduced, and thecriteria for the assignment of membership to each cluster are given.

The z-structure of disk galaxies towards the galaxy planes
We present a detailed study of a statistically complete sample of highlyinclined disk galaxies in the near-infrared K' band. Since the K'-bandlight is relatively insensitive to contamination by galactic dust, wehave been able to follow the vertical light distributions all the waydown to the galaxy planes. The mean levels for the sharpness of theK'-band luminosity peaks indicate that the vertical luminositydistributions are more peaked than expected for the intermediate sech(z)distribution, but rounder than exponential. After fitting a generalizedfamily of fitting functions characterised by an exponent 2/n (n = inftyfor exponential, n = 2 for sech and n = 1 for sech(2) ; van der Kruit1988) we find that the mean value for 2/n in the K' band equals<2/n>_{K'} = 0.538, sigma_ {K'} = 0.198. Since projection of notcompletely edge-on galaxies onto the plane of the sky causes verticalluminosity profiles to become rounder, we have performed simulationsthat show that it is possible that all our galaxies can haveintrinsically exponential vertical surface brightness distributions. Wefind that the profile shape is independent of galaxy type, and varieslittle with position along the major axis. The fact that we observe thisin all our sample galaxies indicates that the formation process of thegalaxy disks perpendicular to the galaxy planes is a process intrinsicto the disks themselves. Based on observations obtained at the EuropeanSouthern Observatory, La Silla, Chile

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.

Recalibration of the H-0.5 magnitudes of spiral galaxies
The H-magnitude aperture data published by the Aaronson et al.collaboration over a 10 year period is collected into a homogeneous dataset of 1731 observations of 665 galaxies. Ninety-six percent of thesegalaxies have isophotal diameters and axial ratios determined by theThird Reference Cataloque of Bright Galaxies (RC3; de Vaucouleurs et al.1991), the most self-consistent set of optical data currently available.The precepts governing the optical data in the RC3 are systematicallydifferent from those of the Second Reference Catalogue (de Vaucouleurs,de Vaucouleurs, & Corwin 1976), which were used by Aaronson et al.for their original analyses of galaxy peculiar motions. This in turnleads to systematic differences in growth curves and fiducialH-magnitudes, prompting the present recalibration of the near-infraredTully-Fisher relationship. New optically normalized H-magnitude growthcurves are defined for galaxies of types SO to Im, from which new valuesof fiducial H-magnitudes, Hg-0.5, are measured forthe 665 galaxies. A series of internal tests show that these fourstandard growth curves are defined to an accuracy of 0.05 mag over theinterval -1.5 less than or equal to log (A/Dg) less than orequal to -0.2. Comparisons with the Aaronson et al. values of diameters,axial ratios, and fiducial H-magnitudes show the expected differences,given the different definitions of these parameters. The values ofHg-0.5 are assigned quality indices: a qualityvalue of 1 indicates an accuracy of less than 0.2 mag, quality 2indicates an accuracy of 0.2-0.35 mag, and quality 3 indicates anaccuracy of more than 0.35 mag. Revised values of corrected H I velocitywidths are also given, based on the new set of axial ratios defiend bythe RC3.

A neutral hydrogen survey of polar-ring galaxies, 1: Green Bank observations of the northern sample
We present the results of a neutral hydrogen survey conducted with theGreen Bank 140 foot radio telescope of 47 northern objects in thepolar-ring galaxy atlas of Whitmore et al. (1990). We detected 39 ofthese above our detection limit of 1.7 Jy km/s; the average measuredflux of 21 Jy km/s corresponds to an average neutral hydrogen mass of5.3 x 109 solar mass for a Hubble constant ofHzero = 75 km/s/Mpc. For the polar-ring galaxies in oursample that have also been observed with radio arrays, we find that the21 full width at half maximum (FWHM) Green Bank beam often includes muchmore flux than found by the synthesis instruments for the polar ringsalone; some of these galaxies are known to have gas-rich companions. Wecompare the neutral hydrogen content of the sample to the blueluminosity and Infrared Astronomical Satellite (IRAS) fluxes. The HI-mass-to-blue-light ratios of the confirmed and probable polar ringsare around unity in solar units, indicating that polar-ring galaxies (ortheir environments) are as gas-rich as typical irregular galaxies. Fortheir blue luminosity, the confirmed polar rings are underluminous inthe far infrared, as compared with the rest of the sample. They are alsofar infrared (FIR) underluminous for their H I masses, which suggeststhat most of the gas in the ring may be in stable orbits, rather thanflowing inward to trigger star formation in the central galaxy. The moredisordered class of 'related objects,' which includes a number ofobvious mergers, is highly luminous in the far infrared. Detailed notesfor each galaxy, including information about companions within the GB140 min beam that may contribute to the total H I line integral and itswidth, are contained in the Appendix.

Measuring galaxy distances from optical rotation curves
A distance indicator for spiral galaxies is described using detailedrotation curves derived from H-alpha velocities fields and I band CCDphotometry. Two-dimensional velocity fields are obtained with an imagingFabry-Perot spectrometer, with a velocity accuracy of better than 10km/s. Rotation curves, based upon rotating disks geometries, are fit tothese velocity fields. The I band photometry profiles, and theindividual rotation curves for 75 galaxies are presented. The extractedcircular velocity is combined with I band magnitudes to form aTully-Fisher relation, with a scatter of about 0.25-0.3 mag. As anexample, the data are used to derive the relative distance modulusbetween the Hydra and Antlia clusters, which yields a peculiar motionfor Antlia of 900 +/- 100 km/s. This confirms previous detections oflarge peculiar motions in the Hydra-Centaurus region.

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.

Submit a new article

Related links

  • - No Links Found -
Submit a new link

Member of following groups:

Observation and Astrometry data

Right ascension:12h46m15.50s
Aparent dimensions:2.188′ × 0.832′

Catalogs and designations:
Proper Names   (Edit)
NGC 2000.0NGC 4672

→ Request more catalogs and designations from VizieR