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The Effects of Interactions on the Structure and Morphology of Elliptical/Lenticular Galaxies in Pairs
We present a structural and photometric analysis of 42elliptical/lenticular galaxies in E/S0 + S pairs observed in the BVRIcolor bands. The aim of the analysis is to empirically determine theeffects of interactions on the galaxies' morphology, structure, andstellar populations as seen from the CAS parameters (light concentrationC, asymmetry A, and clumpiness S). We further compare these values to acontrol sample of 67 mostly isolated noninteracting E/S0 galaxies. Wefind that the paired E/S0 galaxies occupy more scattered loci in CASspace than noninteracting E/S0s and that the structural effects ofinteractions on E/S0s are minor, in contrast to disk galaxies involvedin interactions. This suggests that observational methods forrecognizing interactions, such the CAS methodology of Conselice, wouldnot detect E/S0s involved in interactions (related to early phases ofthe so-called dry mergers), and that the majority of interactinggalaxies identified at high redshift must be gas-dominated systems.However, we find statistical differences in the asymmetry index whencomparing isolated and interacting E/S0s. On average, paired E/S0galaxies have A-values 2.96+/-0.72 times larger than those ofnoninteracting E/S0s. For the subset of presumably strongly interactingE/S0s, A and S can be several times larger than the typical values ofthe isolated E/S0s. We show that the asymmetries are consistent withseveral internal and external morphological distortions. We concludethat the subsample of interacting E/S0s should be dense, gas-poorgalaxies in systems spanning a wide range of interaction stages, withtypical merging timescales >~0.1-0.5 Gyr. We use the observedphenomenology of this subsample to predict the approximate loci of drypremergers in the CAS parameter space.
| Ultraluminous X-Ray Sources in Nearby Galaxies from ROSAT High Resolution Imager Observations I. Data Analysis
X-ray observations have revealed in other galaxies a class ofextranuclear X-ray point sources with X-ray luminosities of1039-1041 ergs s-1, exceeding theEddington luminosity for stellar mass X-ray binaries. Theseultraluminous X-ray sources (ULXs) may be powered by intermediate-massblack holes of a few thousand Msolar or stellar mass blackholes with special radiation processes. In this paper, we present asurvey of ULXs in 313 nearby galaxies withD25>1' within 40 Mpc with 467 ROSAT HighResolution Imager (HRI) archival observations. The HRI observations arereduced with uniform procedures, refined by simulations that help definethe point source detection algorithm employed in this survey. A sampleof 562 extragalactic X-ray point sources withLX=1038-1043 ergs s-1 isextracted from 173 survey galaxies, including 106 ULX candidates withinthe D25 isophotes of 63 galaxies and 110 ULX candidatesbetween 1D25 and 2D25 of 64 galaxies, from which aclean sample of 109 ULXs is constructed to minimize the contaminationfrom foreground or background objects. The strong connection betweenULXs and star formation is confirmed based on the striking preference ofULXs to occur in late-type galaxies, especially in star-forming regionssuch as spiral arms. ULXs are variable on timescales over days to yearsand exhibit a variety of long term variability patterns. Theidentifications of ULXs in the clean sample show some ULXs identified assupernovae (remnants), H II regions/nebulae, or young massive stars instar-forming regions, and a few other ULXs identified as old globularclusters. In a subsequent paper, the statistic properties of the surveywill be studied to calculate the occurrence frequencies and luminosityfunctions for ULXs in different types of galaxies to shed light on thenature of these enigmatic sources.
| A sample of X-ray emitting normal galaxies from the BMW-HRI Catalogue
We obtained a sample of 143 normal galaxies with X-ray luminosity in therange 1038{-}1043 erg s-1 from thecross-correlation of the ROSAT HRI Brera Multi-scale Wavelet (BMW-HRI)Catalogue with the Lyon-Meudon Extragalactic Database (LEDA). We findthat the average X-ray properties of this sample are in good agreementwith those of other samples of galaxies in the literature. We selected acomplete flux limited serendipitous sample of 32 galaxies from which wederived the log N-log S distribution of normal galaxies in the fluxrange 1.1{-} 110 × 10-14 erg cm-2s-1. The resulting distribution is consistent with theEuclidean -1.5 slope. Comparisons with other samples, such as theExtended Medium Sensitivity Survey, the ROSAT All Sky Survey, theXMM-Newton/2dF survey, and the Chandra Deep Field Survey indicate thatthe log N -log S distribution of normal galaxies is consistent with aEuclidean slope over a flux range of about 6 decades.
| An IRAS High Resolution Image Restoration (HIRES) Atlas of All Interacting Galaxies in the IRAS Revised Bright Galaxy Sample
The importance of far-infrared observations for our understanding ofextreme activity in interacting and merging galaxies has beenillustrated by many studies. Even though two decades have passed sinceits launch, the most complete all-sky survey to date from which far-IRselected galaxy samples can be chosen is still that of the InfraredAstronomical Satellite (IRAS). However, the spatial resolution of theIRAS all-sky survey is insufficient to resolve the emission fromindividual galaxies in most interacting galaxy pairs, and hence previousstudies of their far-IR properties have had to concentrate either onglobal system properties or on the properties of very widely separatedand weakly interacting pairs. Using the HIRES image reconstructiontechnique, it is possible to achieve a spatial resolution ranging from30" to 1.5m (depending on wavelength and detector coverage), whichis a fourfold improvement over the normal resolution of IRAS. This issufficient to resolve the far-IR emission from the individual galaxiesin many interacting systems detected by IRAS, which is very importantfor meaningful comparisons with single, isolated galaxies. We presenthigh-resolution 12, 25, 60, and 100 μm images of 106 interactinggalaxy systems contained in the IRAS Revised Bright Galaxy Sample (RBGS,Sanders et al.), a complete sample of all galaxies having a 60 μmflux density greater than 5.24 Jy. These systems were selected to haveat least two distinguishable galaxies separated by less than threeaverage galactic diameters, and thus we have excluded very widelyseparated systems and very advanced mergers. Additionally, some systemshave been included that are more than three galactic diameters apart,yet have separations less than 4' and are thus likely to suffer fromconfusion in the RBGS. The new complete survey has the same propertiesas the prototype survey of Surace et al. We find no increased tendencyfor infrared-bright galaxies to be associated with other infrared-brightgalaxies among the widely separated pairs studied here. We find smallenhancements in far-IR activity in multiple galaxy systems relative toRBGS noninteracting galaxies with the same blue luminosity distribution.We also find no differences in infrared activity (as measured byinfrared color and luminosity) between late- and early-type spiralgalaxies.
| BVRI surface photometry of mixed morphology pairs of galaxies. II. The second data set
In order to analyze the photometric signature of gravitationalinteractions in spiral and elliptical galaxies, we present results ofmulticolor broad band (BVRI) surface photometry for a second set of 10mixed pairs drawn from the Karachentsev Catalogue of Isolated Pairs ofGalaxies (KPG). We report total magnitudes and colors, as well assurface brightness, color and geometric (ɛ, PA anda4/a) profiles. Most of this subsample have photometricparameters homogeneously derived for the first time. Internal andexternal data comparisons show consistency within the estimated errors.We find 1 true (E+S) pair and 4 probable (E+S) pairs ((E/S0+S) cases) inthe present sample. The remaining objects include 3 lenticular-spiral(S0+S) systems, 1 spiral-spiral (S+S) pair and 1 probable spiral-spiralpair ((S0/Sa+S) case). Four lenticular galaxies show evidence ofunderlying (perhaps induced) structures like bars/arms. Among the spiralcomponents, an over-representation of early (Sa-Sb) types was found. Abrief discussion on the existence of a Holmberg Effect is alsopresented.Based on data obtained at the 0.84 m telescope of the ObservatorioAstronómico Nacional (OAN), San Pedro Mártir, BajaCalifornia, México, operated by the Instituto deAstronomía, UNAM.Tables 1-3 and Figs. 3-12 are only available in electronic form athttp://www.edpsciences.org
| Redshift-Distance Survey of Early-Type Galaxies: Spectroscopic Data
We present central velocity dispersions and Mg2 line indicesfor an all-sky sample of ~1178 elliptical and S0 galaxies, of which 984had no previous measures. This sample contains the largest set ofhomogeneous spectroscopic data for a uniform sample of ellipticalgalaxies in the nearby universe. These galaxies were observed as part ofthe ENEAR project, designed to study the peculiar motions and internalproperties of the local early-type galaxies. Using 523 repeatedobservations of 317 galaxies obtained during different runs, the dataare brought to a common zero point. These multiple observations, takenduring the many runs and different instrumental setups employed for thisproject, are used to derive statistical corrections to the data and arefound to be relatively small, typically <~5% of the velocitydispersion and 0.01 mag in the Mg2 line strength. Typicalerrors are about 8% in velocity dispersion and 0.01 mag inMg2, in good agreement with values published elsewhere.
| Redshift-Distance Survey of Early-Type Galaxies: Circular-Aperture Photometry
We present R-band CCD photometry for 1332 early-type galaxies, observedas part of the ENEAR survey of peculiar motions using early-typegalaxies in the nearby universe. Circular apertures are used to tracethe surface brightness profiles, which are then fitted by atwo-component bulge-disk model. From the fits, we obtain the structuralparameters required to estimate galaxy distances using theDn-σ and fundamental plane relations. We find thatabout 12% of the galaxies are well represented by a pure r1/4law, while 87% are best fitted by a two-component model. There are 356repeated observations of 257 galaxies obtained during different runsthat are used to derive statistical corrections and bring the data to acommon system. We also use these repeated observations to estimate ourinternal errors. The accuracy of our measurements are tested by thecomparison of 354 galaxies in common with other authors. Typical errorsin our measurements are 0.011 dex for logDn, 0.064 dex forlogre, 0.086 mag arcsec-2 for<μe>, and 0.09 for mRC,comparable to those estimated by other authors. The photometric datareported here represent one of the largest high-quality and uniformall-sky samples currently available for early-type galaxies in thenearby universe, especially suitable for peculiar motion studies.Based on observations at Cerro Tololo Inter-American Observatory (CTIO),National Optical Astronomy Observatory, which is operated by theAssociation of Universities for Research in Astronomy, Inc., undercooperative agreement with the National Science Foundation (NSF);European Southern Observatory (ESO); Fred Lawrence Whipple Observatory(FLWO); and the MDM Observatory on Kitt Peak.
| A new catalogue of ISM content of normal galaxies
We have compiled a catalogue of the gas content for a sample of 1916galaxies, considered to be a fair representation of ``normality''. Thedefinition of a ``normal'' galaxy adopted in this work implies that wehave purposely excluded from the catalogue galaxies having distortedmorphology (such as interaction bridges, tails or lopsidedness) and/orany signature of peculiar kinematics (such as polar rings,counterrotating disks or other decoupled components). In contrast, wehave included systems hosting active galactic nuclei (AGN) in thecatalogue. This catalogue revises previous compendia on the ISM contentof galaxies published by \citet{bregman} and \citet{casoli}, andcompiles data available in the literature from several small samples ofgalaxies. Masses for warm dust, atomic and molecular gas, as well asX-ray luminosities have been converted to a uniform distance scale takenfrom the Catalogue of Principal Galaxies (PGC). We have used twodifferent normalization factors to explore the variation of the gascontent along the Hubble sequence: the blue luminosity (LB)and the square of linear diameter (D225). Ourcatalogue significantly improves the statistics of previous referencecatalogues and can be used in future studies to define a template ISMcontent for ``normal'' galaxies along the Hubble sequence. The cataloguecan be accessed on-line and is also available at the Centre desDonnées Stellaires (CDS).The catalogue is available in electronic form athttp://dipastro.pd.astro.it/galletta/ismcat and at the CDS via anonymousftp to\ cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/405/5
| A catalogue and analysis of X-ray luminosities of early-type galaxies
We present a catalogue of X-ray luminosities for 401 early-typegalaxies, of which 136 are based on newly analysed ROSAT PSPC pointedobservations. The remaining luminosities are taken from the literatureand converted to a common energy band, spectral model and distancescale. Using this sample we fit the LX:LB relationfor early-type galaxies and find a best-fit slope for the catalogue of~2.2. We demonstrate the influence of group-dominant galaxies on the fitand present evidence that the relation is not well modelled by a singlepower-law fit. We also derive estimates of the contribution to galaxyX-ray luminosities from discrete-sources and conclude that they provideLdscr/LB~=29.5ergs-1LBsolar-1. Wecompare this result with luminosities from our catalogue. Lastly, weexamine the influence of environment on galaxy X-ray luminosity and onthe form of the LX:LB relation. We conclude thatalthough environment undoubtedly affects the X-ray properties ofindividual galaxies, particularly those in the centres of groups andclusters, it does not change the nature of whole populations.
| 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.
| An X-Ray Survey of Galaxies in Pairs
Results are reported from the first survey of X-ray emission fromgalaxies in pairs. The sample consists of 52 pairs of galaxies from theCatalog of Paired Galaxies whose coordinates overlap the ROSAT PositionSensitive Proportional Counter pointed observations. The mean observedlogl_X for early-type pairs is 41.35+/-0.21, while the mean logl_Xpredicted using the l_X-l_b relationship for isolated early-typegalaxies is 42.10+/-0.19. With 95% confidence, the galaxies in pairs areunderluminous in the X-ray, compared with isolated galaxies, for thesame l_b. A significant fraction of the mixed pair sample also appearssimilarly underluminous. A spatial analysis shows that the X-rayemission from pairs of both types typically has an extent of ~10-50 kpc,much smaller than the group intergalactic medium, and thus likelyoriginates from the galaxies. CPG 564, the most X-ray luminousearly-type pair, 4.7x10^42 ergs s^-1, is an exception. The extent of itsX-ray emission, greater than 169 kpc, and HWHM, ~80 kpc, is comparableto that expected from an intergalactic medium. The sample shows only aweak correlation, ~81% confidence, between l_X and l_b, presumably dueto variations in gas content within the galaxies. No correlation betweenl_X and the pair velocity difference (Deltav), separation (Deltar), orfar-infrared luminosity (l_fir) is found, although the detection rate islow, 22%.
| 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.
| 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.
| Seyfert Galaxies With Companions: Orbital and Kinematic Clues to AGN Triggering
This paper presents imaging and optical spectroscopy of paired Seyfertgalaxies and their companions. The aim is to seek common properties ofSeyfert galaxies in interacting systems, which might provide evidence ofAGN triggering in a way independent of the usual two-sample statisticswhich have proven ambiguous on this issue. Three kinds of comparisonhave been made-the kinds of interactions involving Seyfert galaxies, therelative luminosities of the Seyferts and their companions, and thelevel of kinematic disturbance as measured from rotation curves. (1)Dynamics and tidal features have been used to determine (or at leastlimit) the sense of orbital motion (direct/retrograde/polar with respectto the Seyfert galaxy's disk) for many of these pairs. There is noobviously preferred kind of interaction-direct, polar, and retrogradeencounters are all well represented, despite the gross differences indynamical response of a disk to these various kinds of encounter. To theextent that triggering of Seyfert nuclei occurs due to tidal encounters,the existence of a perturbation seems more important than its exactduration or detailed effects on the disk. However, the ratio of mergingto paired Seyferts is higher than for disk galaxies in general,consistent with more effective triggering of AGN in this specific phase;the implied time scale for enhanced occurrence during mergers is thesame as the timescape for merger remnants to appear as such, a fewdisk-edge crossing times (typically several times 10^8^ yr). (2) Seyfertnuclei occur preferentially in the brighter members of galaxy pairs, bya median of 0.93 mag after making the maximal correction forcontaminating nonstellar light in the nuclei. Only about 1/3 of thiseffect can be accounted for by the known tendency of Seyfert nuclei tooccur in more luminous galaxies. Enhancement of AGN by interactions isevidently more effective for more luminous galaxies (though this willalso be the case if both star formation and AGN occurrence are enhancedin the same galaxies). (3) The rotation curves of the paired Seyfertsshow systematically small regions of rising or solid-body rotationcompared to the disk radius, as a group comparable to Sa but verydifferent from Sb or Sc galaxies (even for Seyfert galaxies with Hubbletype later than Sa). There is weak evidence that this difference is alsopresent with respect to more isolated Seyfert galaxies. Despite theobvious utility of a dynamically disturbed disk for transport of angularmomentum and "feeding the monster," Seyfert galaxies in pairs actuallyhave smaller kinematic disturbances (measured by the maximum departurefrom a symmetric rotation curve, normalized to the full rotationamplitude) than found in a complete sample of non-Seyfert spirals inpairs.
| 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.
| A comparative study of morphological classifications of APM galaxies
We investigate the consistency of visual morphological classificationsof galaxies by comparing classifications for 831 galaxies from sixindependent observers. The galaxies were classified on laser print copyimages or on computer screen using scans made with the Automated PlateMeasuring (APM) machine. Classifications are compared using the RevisedHubble numerical type index T. We find that individual observers agreewith one another with rms combined dispersions of between 1.3 and 2.3type units, typically about 1.8 units. The dispersions tend to decreaseslightly with increasing angular diameter and, in some cases, withincreasing axial ratio (b/a). The agreement between independentobservers is reasonably good but the scatter is non-negligible. In spiteof the scatter, the Revised Hubble T system can be used to train anautomated galaxy classifier, e.g. an artificial neural network, tohandle the large number of galaxy images that are being compiled in theAPM and other surveys.
| Integrated photoelectric magnitudes and color indices of bright galaxies in the Johnson UBV system
The photoelectric total magnitudes and color indices published in theThird Reference Catalogue of Bright Galaxies (RC3) are based on ananalysis of approximately equals 26,000 B, 25,000 B-V, and 17,000 U-Bmultiaperture measurements available up to mid 1987 from nearly 350sources. This paper provides the full details of the analysis andestimates of internal and external errors in the parameters. Thederivation of the parameters is based on techniques described by theVaucouleurs & Corwin (1977) whereby photoelectric multiaperture dataare fitted by mean Hubble-type-dependent curves which describe theintegral of the B-band flux and the typical B-V and U-B integrated colorgradients. A sophisticated analysis of the residuals of thesemeasurements from the curves was made to allow for the random andsystematic errors that effect such data. The result is a homogeneous setof total magnitudes BTA total colors(B-V)T and (U-B)T, and effective colors(B-V)e and (U-B)e for more than 3000 brightgalaxies in RC3.
| 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 distribution of galaxies around NGC 5846
The present study investigates the 3D distribution of galaxies in aregion surrounding the chain of galaxies in the NGC 5846 group bysubjective and objective tests for clustering. The results of anautomated search, in which a percolation algorithm is applied to aredshift sample complete in magnitude not greater than 14.9, arecompared with those of the subjective impressions. At a number densityenhancement of 20 over the mean background, eight large groups whichwere not affected by incompleteness at very low declinations areidentified. Four of these groups - the Virgo II cloud, the NGC 5846group, and groups 139 and 148 from the list of GH - are nearby. VirgoIII is loose and irregular whereas NGC 5846 is dense and symmetric. Theother two groups are small compact clumps. The conclusions are inagreement with a study by Tully (1982) that these four nearby groupsform a prolate cloud with an overall density contrast over the mean ofabout 10, and that this cloud lies out of the supergalactic plane andpoints toward the Virgo cluster.
| The influence of environment on gas and dust in S0 galaxies
Consideration is given to the effect of local environemnt on the gas anddust content of S0 galaxies relative to other spiral systems in theLocal Supercluster. The optical properties, H I content, and FIRcontinuum properties of a complete sample of Local Supercluster S0galaxies are analyzed. The characteristics of S0 galaxies are comparedwith those of Sa and Sc galaxies. It is concluded that, like otherspiral galaxies, S0's undergo continuing gas removal when they passthrough high-density regions.
| The environment and the origin of twisting in early-type galaxies
The effects of random collisions in groups or clusters on thedevelopment of isophotal twisting (IT) in early-type galaxies areinvestigated. The maximum ellipticity and IT in each galaxy is estimatedon the basis of published observational data and correlated with thegalaxy number density. The proportions of S0 and elliptical (E) galaxieswith IT are found to be independent of local environmental density. CCDobservations of six isolated nonhierarchical pairs containing early-typegalaxies, obtained at the Cassegrain focus of the 1.82-m telescope atAsiago Observatory, are then used to study tidal interactions ingalaxies with normal morphology; the data are presented in tables andgraphs and examined in detail. It is shown that mutual tidalperturbations alone cannot explain the IT phenomena: S0 galaxies areless twisted than Es in all density regimes, and the proportion oftwisted Es in E+E pairs is similar to that in the overall sample.
| A search for features in early-type galaxies
Using data from the CCD surface-photometry survey of Djorgovski (1985),images of 159 galaxies were examined for the presence of dust lanes,incipient stellar disks, bars, shells, and other features that signifydeviations from elliptical symmetry. The sample contained 116 ellipticalgalaxies, 33 SO galaxies and 10 intermediate galaxies. It was found thatforty-two of the ellipticals either definitely or very likely containdust, either in patches or in well-defined lanes or rings. Five of theE/SO galaxies also show possible or definite dust, as do 15 of the SOs.Three of the elliptical galaxies definitely contain stellar disks, withseveral more possible candidates. The presence of these features inalmost half of the elliptical galaxies studied demonstrates thatelliptical galaxies are not the featureless objects they were oncethought to be. Moreover, the finding of weak stellar disks in some ofthem further blurs the distinction between ellipticals and SOs.
| Mass-to-Light Ratios of Binary Galaxies. III. Analysis
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1987ApJS...64..427S&db_key=AST
| JHK colours of 'ordinary' galaxies
Accurate JHK photometry is presented for 19 elliptical, 10 lenticular,29 'ordinary' spiral galaxies, and 1 Im type on the SAAO photometricsystem which has well-defined transformations to the Caltech/CTIO andAAO systems. The groups having the highest degree of color uniformityare the ellipticals and lenticulars. 'Ordinary', or inactive spirals,show slightly more scatter; late types are bluer than average in J-H andemission-line galaxies are redder in H-K. In general, the infrared andV-K colors determined here agree well with previous work. However, noevidence for significant change of infrared color with radius has beenseen, in contrast to the results of some other workers.
| Neutral hydrogen in elliptical radio galaxies
A well defined sample of radio-emitting ellipticals has been observed todiscover if these galaxies contain unusual amounts of neutral hydrogen.At a detection limit of 300 million solar masses, independent ofdistance, at most 4 galaxies in 22 were detected. There is statisticallyweak evidence that these galaxies are more luminous at 5.0 GHz than theundetected ones, but any correlation between radio luminosity and H Icontent must be extremely loose.
| Redshifts for 115 galaxies near the equator
New redshifts for 115 bright galaxies located near the celestial equatorare reported. The spectra were observed with a blue-sensitivephoton-counting Reticon on the 100-in. DuPont telescope, and theredshifts were derived using the data-analysis system developed for theCfA Redshift Survey. Comparisons with other measured redshifts suggestthat these data are similar in quality to the redshifts measured at Mt.Hopkins for the CfA Redshift Survey; the velocity zero point is good to10 or 15 km/s, with a typical error of 35 km/s for the individualmeasurements.
| A 5-GHz survey of bright Southern elliptical and S0 galaxies
The Parkes 64-m telescope has been used in a 5.0-GHz survey of 181Southern E and S0 galaxies from the Reference catalogue of brightgalaxies. Of the 39 detections above the nominal limit of 12 mJy, 15 arenew, several have radio spectra indicating membership in the activeclass, and two have shown intensity variations at centimeterwavelengths. The results of this survey combined with results fromearlier surveys of lower sensitivity suggest that only about 40 per centof the E/S0 galaxies in the Reference catalogue have a flux density at 5GHz exceeding 1 mJy.
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