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HI content in galaxies in loose groups
Gas deficiency in cluster spirals is well known and ram-pressurestripping is considered the main gas removal mechanism. In some compactgroups too gas deficiency is reported. However, gas deficiency in loosegroups is not yet well established. Lower dispersion of the membervelocities and the lower density of the intragroup medium in small loosegroups favour tidal stripping as the main gas removal process in them.Recent releases of data from the HI Parkes All-Sky Survey (HIPASS) andcatalogues of nearby loose groups with associated diffuse X-ray emissionhave allowed us to test this notion. In this paper, we address thefollowing questions: (i) do galaxies in groups with diffuse X-rayemission statistically have lower gas content compared to the ones ingroups without diffuse X-ray emission? (ii) does HI deficiency vary withthe X-ray luminosity, LX, of the loose group in a systematicway? We find that (i) galaxies in groups with diffuse X-ray emission, onaverage, are HI deficient, and have lost more gas compared to those ingroups without X-ray emission; the latter are found not to havesignificant HI deficiency; (ii) no systematic dependence of the HIdeficiency with LX is found. Ram-pressure-assisted tidalstripping and evaporation by thermal conduction are the two possiblemechanisms to account for this excess gas loss.
| On the Relevance of the Tremaine-Weinberg Method Applied to an Hα Velocity Field: Pattern Speed Determination in M100 (NGC 4321)
The relevance of the Tremaine-Weinberg (TW) method is tested formeasuring bar, spiral, and inner structure pattern speeds using agaseous velocity field. The TW method is applied to various simulatedbarred galaxies in order to demonstrate its validity in seven differentconfigurations, including star formation and/or dark matter halo. Thereliability of the different physical processes involved and of thevarious observational parameters is also tested. The simulations showthat the TW method could be applied to gaseous velocity fields to get agood estimate of the bar pattern speed, under the condition that regionsof shocks are avoided and measurements are confined to regions where thegaseous bar is well formed. We successfully apply the TW method to theHα velocity field of the Virgo Cluster galaxy M100 (NGC 4321) andderive pattern speeds of 55+/-5 km s-1 kpc-1 forthe nuclear structure, 30+/-2 km s-1 kpc-1 for thebar, and 20+/-1 km s-1 kpc-1 for the spiralpattern, in full agreement with published determinations using the samemethod or alternative ones.
| Photometric properties and origin of bulges in SB0 galaxies
We have derived the photometric parameters for the structural componentsof a sample of fourteen SB0 galaxies by applying a parametricphotometric decomposition to their observed I-band surface brightnessdistribution. We find that SB0 bulges are similar to bulges of theearly-type unbarred spirals, i.e. they have nearly exponential surfacebrightness profiles (< n>=1.48±0.16) and their effectiveradii are strongly coupled to the scale lengths of their surroundingdiscs (< r_e/h>=0.20±0.01). The photometric analysis alonedoes not allow us to differentiate SB0 bulges from unbarred S0 ones.However, three sample bulges have disc properties typical ofpseudobulges. The bulges of NGC 1308 and NGC 4340 rotate faster thanbulges of unbarred galaxies and models of isotropic oblate spheroidswith equal ellipticity. The bulge of IC 874 has a velocity dispersionlower than expected from the Faber-Jackson correlation and thefundamental plane of the elliptical galaxies and S0 bulges. Theremaining sample bulges are classical bulges, and are kinematicallysimilar to lower-luminosity ellipticals. In particular, they follow theFaber-Jackson correlation, lie on the fundamental plane and those forwhich stellar kinematics are available rotate as fast as the bulges ofunbarred galaxies.
| Fast bars in SB0 galaxies
We measured the bar pattern speed in a sample of 7 SB0 galaxies usingthe Tremaine-Weinberg method. This represents the largest sample ofgalaxies for which the bar pattern speed has been measured this way. Allthe observed bars are as rapidly rotating as they can be. We comparedthis result with recent high-resolution N-body simulations of bars incosmologically-motivated dark matter halos, and conclude that these barsare not located inside centrally concentrated halos.
| Companions to Isolated Elliptical Galaxies: Revisiting the Bothun-Sullivan Sample
We investigate the number of physical companion galaxies for a sample ofrelatively isolated elliptical galaxies. The NASA/IPAC ExtragalacticDatabase (NED) has been used to reinvestigate the incidence of satellitegalaxies for a sample of 34 elliptical galaxies, first investigated byBothun & Sullivan using a visual inspection of Palomar Sky Surveyprints out to a projected search radius of 75 kpc. We have repeatedtheir original investigation using data cataloged in NED. Nine of theseelliptical galaxies appear to be members of galaxy clusters; theremaining sample of 25 galaxies reveals an average of +1.0+/-0.5apparent companions per galaxy within a projected search radius of 75kpc, in excess of two equal-area comparison regions displaced by 150-300kpc. This is significantly larger than the +0.12+/-0.42companions/galaxy found by Bothun & Sullivan for the identicalsample. Making use of published radial velocities, mostly availablesince the completion of the Bothun-Sullivan study, identifies thephysical companions and gives a somewhat lower estimate of +0.4companions per elliptical galaxy. This is still 3 times larger than theoriginal statistical study, but given the incomplete and heterogeneousnature of the survey redshifts in NED, it still yields a firm lowerlimit on the number (and identity) of physical companions. An expansionof the search radius out to 300 kpc, again restricted to sampling onlythose objects with known redshifts in NED, gives another lower limit of4.5 physical companions per galaxy. (Excluding five elliptical galaxiesin the Fornax Cluster, this average drops to 3.5 companions perelliptical.) These physical companions are individually identified andlisted, and the ensemble-averaged radial density distribution of theseassociated galaxies is presented. For the ensemble, the radial densitydistribution is found to have a falloff consistent withρ~R-0.5 out to approximately 150 kpc. For non-FornaxCluster companions the falloff continues out to the 300 kpc limit of thesurvey. The velocity dispersion of these companions is found to reach amaximum of 350 km s-1 at around 120 kpc, after which theyfall at a rate consistent with Keplerian falloff. This falloff may thenindicate the detection of a cut-off in the mass-density distribution inthe elliptical galaxies' dark matter halo at ~100 kpc.
| Detailed comparison of the structures and kinematics of simulated and observed barred galaxies
We examine the observable properties of simulated barred galaxies,including radial mass profiles, edge-on structure and kinematics, barlengths and pattern speed evolution for detailed comparison to realsystems. We have run several simulations in which bars are createdthrough inherent instabilities in self-consistent simulations of arealistic disc+halo galaxy model with a disc-dominated, flat rotationcurve. These simulations were run at high (N= 20 million particles) andlow (N= 500000 particles) resolution to test numerical convergence. Wedetermine the pattern speeds in simulations directly from the phaseangle of the bar versus time and the Tremaine-Weinberg method.Fundamental dynamics do not change between the high and low resolution,suggesting that convergence has been reached in this case. We find thatthe higher resolution is needed to simulate structural and kinematicproperties accurately. The edge-on view of the higher-resolution systemshows the bending instability and formation of a peanut-shaped bulgeclearly. We determined bar lengths by different means to determine thatthe simulated bar is fast, with a corotation to bar length ratio ofunder 1.5. Simulated bars in these models form with pattern speedsslower than those observed and slow-down during their evolution.Dynamical friction between the bar and dark halo is responsible for thisdeceleration, as revealed by the transfer of angular momentum betweenthe disc and the halo. However, even though the pattern speed is reducedat later times, the instantaneous scalelength of the disc has grownsufficiently for the bar motion to agree with many observations. Byusing a different model and simulation technique than other authors, weare able to compare the robustness of these methods. An animation of theface-on and edge-on views of the 20-million-particle simulation isavailable at http://www.astro.utoronto.ca/~oneill.
| Secular bar formation in galaxies with a significant amount of dark matter
Using high-resolution N-body simulations of stellar discs embedded incosmologically motivated dark matter haloes, we study the evolution ofbars and the transfer of angular momentum between haloes and bars. Wefind that dynamical friction results in some transfer of angularmomentum to the halo, but the effect is much smaller than previouslyfound in low-resolution simulations and is incompatible with earlyanalytical estimates. After 5 Gyr of evolution the stellar componentloses only 5-7 per cent of its initial angular momentum.Mass and force resolutions are crucial for the modelling of bardynamics. In low-resolution (300-500 pc) simulations we find that thebar slows down and angular momentum is lost relatively fast. Insimulations with millions of particles reaching a resolution of 20-40pc, the pattern speed may not change over billions of years. Ourhigh-resolution models produce bars that are fast rotators, where theratio of the corotation radius to the bar semi-major axis lies in therange , marginally compatible with observational results. In contrast tomany previous simulations, we find that bars are relatively short. As inmany observed cases, the bar semi-major axis is close to the exponentiallength of the disc.The transfer of angular momentum between inner and outer parts of thedisc plays a very important role in the secular evolution of the discand the bar. The bar formation increases the exponential length of thedisc by a factor of 1.2-1.5. The transfer substantially increases thestellar mass in the centre of the galaxy and decreases the dark matterto baryon ratio. As the result, the central 2-kpc region is alwaysstrongly dominated by the baryonic component. At intermediate (3-10 kpc)scales the disc is sub-dominant. These models demonstrate that theefficiency of angular momentum transfer to the dark matter has beengreatly overestimated. More realistic models produce bar structure instriking agreement with observational results.
| On position angle errors in the Tremaine-Weinberg method
I show that Tremaine-Weinberg (TW) measurements of bar pattern speedsare sensitive to errors in the position angle of the disc,PAdisc. I use an N-body experiment to measure these errors;for typical random PAdisc errors, the resulting scatter inthe measured values of the dimensionless bar speed parameter (defined asthe ratio of the corotation radius to the bar semi-major axis) is of theorder of the scatter in the observed values.I also consider how the systematic PAdisc errors produced bydisc ellipticities affect TW measurements. The scatter produced by theseerrors may be significant, depending on the ellipticity distribution.Conversely, by using the sample of TW observations, I find that an upperlimit of the typical disc (density) ellipticity is 0.07 at the 90 percent confidence level, which is in good agreement with previousmeasurements.Taken together, the random and systematic scatter suggest that theintrinsic distribution of of gas-poor early-type barred galaxies may beas narrow as that of the gas-rich later types.
| FLASH redshift survey - I. Observations and catalogue
The FLAIR Shapley-Hydra (FLASH) redshift survey catalogue consists of4613 galaxies brighter than bJ= 16.7 (corrected for Galacticextinction) over a 700-deg2 region of sky in the generaldirection of the Local Group motion. The survey region is a70°× 10° strip spanning the sky from the ShapleySupercluster to the Hydra cluster, and contains 3141 galaxies withmeasured redshifts. Designed to explore the effect of the galaxyconcentrations in this direction (in particular the Supergalactic planeand the Shapley Supercluster) upon the Local Group motion, the 68 percent completeness allows us to sample the large-scale structure betterthan similar sparsely-sampled surveys. The survey region does notoverlap with the areas covered by ongoing wide-angle (Sloan or 2dF)complete redshift surveys. In this paper, the first in a series, wedescribe the observation and data reduction procedures, the analysis forthe redshift errors and survey completeness, and present the surveydata.
| Measurement of fast bars in a sample of early-type barred galaxies
We present surface photometry and stellar kinematics of a sample of fiveSB0 galaxies: ESO 139-G009, IC 874, NGC 1308, NGC 1440 and NGC 3412. Wemeasured their bar pattern speed using the Tremaine-Weinberg method, andderived the ratio, , of the corotation radius to the length of the barsemimajor axis. For all the galaxies, is consistent with being in therange from 1.0 to 1.4, i.e. that they host fast bars. This representsthe largest sample of galaxies for which has been measured in this way.Taking into account the measured distribution of and our measurementuncertainties, we argue that this is probably the true distribution of .If this is the case, then the Tremaine-Weinberg method finds adistribution of which is in agreement with that obtained byhydrodynamical simulations. We compare this result with recenthigh-resolution N-body simulations of bars in cosmologically motivateddark matter haloes, and we conclude that these bars are not locatedinside centrally concentrated dark matter haloes.
| Fast bars in early-type barred galaxies
We measured the bar pattern speed of a sample of 6 SB0 galaxies usingthe Tremaine-Weinberg method. We derived the ratio, {cal R}, of thecorotation radius to the length of the bar semi-major axis. For all thegalaxies, {cal R} is consistent with being in the range from 1.0 and1.4, i.e. that they host fast bars. This represents the largest sampleof galaxies for which {cal R} has been measured this way. We comparedthis result with recent high-resolution N-body simulations of bars incosmologically-motivated dark matter halos, and conclude that these barsare not located inside centrally concentrated dark matter halos.
| 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.
| A catalogue of Mg_2 indices of galaxies and globular clusters
We present a catalogue of published absorption-line Mg_2 indices ofgalaxies and globular clusters. The catalogue is maintained up-to-datein the HYPERCAT database. The measurements are listed together with thereferences to the articles where the data were published. A codeddescription of the observations is provided. The catalogue gathers 3541measurements for 1491 objects (galaxies or globular clusters) from 55datasets. Compiled raw data for 1060 galaxies are zero-point correctedand transformed to a homogeneous system. Tables 1, 3, and 4 areavailable in electronic form only at the CDS, Strasbourg, via anonymousftp 130.79.128.5. Table 2 is available both in text and electronic form.
| The fundamental plane of early-type galaxies: stellar populations and mass-to-light ratio.
We analyse the residuals to the fundamental plane (FP) of ellipticalgalaxies as a function of stellar-population indicators; these are basedon the line-strength parameter Mg_2_ and on UBVRI broad-band colors, andare partly derived from new observations. The effect of the stellarpopulations accounts for approximately half the observed variation ofthe mass-to-light ratio responsible for the FP tilt. The residual tiltcan be explained by the contribution of two additional effects: thedependence of the rotational support, and possibly that of the spatialstructure, on the luminosity. We conclude to a constancy of thedynamical-to-stellar mass ratio. This probably extends to globularclusters as well, but the dominant factor would be here the luminositydependence of the structure rather than that of the stellar population.This result also implies a constancy of the fraction of dark matter overall the scalelength covered by stellar systems. Our compilation ofinternal stellar kinematics of galaxies is appended.
| A Catalog of Stellar Velocity Dispersions. II. 1994 Update
A catalog of central velocity dispersion measurements is presented,current through 1993 September. The catalog includes 2474 measurementsof 1563 galaxies. A standard set of 86 galaxies is defined, consistingof galaxies with at least three reliable, concordant measurements. It issuggested that future studies observe some of these standard galaxies sothat different studies can be normalized to a consistent system. Allmeasurements are reduced to a normalized system using these standards.
| 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.
| 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.
| 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.
| New velocity dispersions and photometry for E and S0 galaxies in the great attractor
New spectroscopy and photometry have been obtained for 136 ellipticaland S0 galaxies in the direction of the large-scale streaming flowattributed to the great attractor. Measurements of central velocitydispersion (sigma), total B magnitudes B(T), the photometric parameterDn, and the absorption-line index Mg2 are presented. Both internal andexternal comparisons indicate that measurements of log sigma areaccurate to 0.05 dex, B(T) to 0.15 mag, Dn to 0.015 dex, and Mg2 to0.017 mag. These data have been used by Dressler and Faber (1990) toestimate distances for these galaxies via the Dn-sigma relation. It isshown in this paper that the Dn-Mg2 relation also predicts the sametrends of peculiar velocity with distance, but with less accuracy. Therelative accuracy of other distance indicators for elliptical galaxiesis also discussed.
| The plane W(Na I) X W(Mg I) - Effects of interstellar Na I in a sample of southern galaxies
Galaxy spectra from a subsample of the Southern Sky Redshift Survey databank were used to study the equivalent width plane for the lines Na Ilambda 5893 A vs Mg I lambda 5175 A. An estimate of how important thecontribution of the interstellar gas for the sodium line is compared tothat of the stellar population. The sample is made up of galaxies withmorphological types from E to Sc and are distributed up to radialvelocities of 25,000 km/s, most of them smaller than 15,000 km/s. Mostearly type galaxies with dust lanes, particularly nearly edge-on So's,present an enhancement of the Na I line. Inclined spiral galaxies tendto present enhanced Na I with respect to face-on spirals. This tendency,previously found in a smaller sample of galaxies limited to V equal toor less than 6000 km/s, is now confirmed for more distant ones. In thelarge velocity sample it shows the global bulge rather than the verynucleus; the persistence of the effect suggests that the scale height ofthe gas layer in the central disk can reach a considerable fraction ofthe bulge radius.
| A southern redshift survey. I - Accurate redshifts for 500 galaxies observed at SAAO
Radial velocities are presented for about 500 galaxies observed with anintensified Reticon photon-counting detector attached to the 1.9 mtelescope at the Sutherland field station of SAAO. The velocities weredetermined by cross correlation with standard velocity templates, fromthe measured wavelengths of emission lines, or from both techniques,with spectra covering the wavelength range from 3700 to 5400 A. Thefinal velocities appear to have the same zero point as H I radiovelocities, and have standard deviations of the order of 35 km/s, thoughcross-correlation velocities on their own may have significantly largererrors.
| Redshifts for galaxies in southern clusters
Redshifts for galaxies, including the clusters ZW 9-19 and Klemola 27,in the ESO/SRC survey field 444 are presented based on observationscarried out in May 1980 and April 1981 with the 1.52-m ESO telescope inLa Silla. Satisfactory agreement is found with previous data. Thesurveyed sky area contains the Hydra/Centaurus supercluster with meanradial velocities between 3000 and 5000 km/s, behind which seems to be alarge empty space extending out to a redshift of about 9000 km s.
| Static properties of galaxies in the Shapley-Centaurus cluster. I - The catalogue
A catalogue of the positions, sizes, orientations, ellipticities, andmorphological descriptions of 127 galaxies measured in the Southern SkySurvey Field 444 is given. The measurement errors, both internal andexternal, are discussed.
| Redshift observations in the Centaurus-Hydra supercluster region. I
The paper presents 111 new redshifts in the region of theCentaurus-Hydra supercluster. Also presented is the growth of theHydra-Centaurus structures as a function of the percolation vector, thesurface distribution of galaxies in this region, and the distribution inredshift of the observed galaxies.
| Southern Galaxy Catalogue.
Not Available
| Redshifts in Klemola 27
Observational data for galaxies in the galaxy cluster Klemola 27gathered over the last few years are presented. These are mostly newredshifts and further, accurate coordinates and morphological types fora large number of 'prominent' galaxies in the ESO/SRC-Survey fields 444and 445. A few preliminary H I radial velocities are also reported. Thedata available for this cluster are briefly discussed.
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