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The Relation between Galaxy Activity and the Dynamics of Compact Groups of Galaxies
Using a sample of 91 galaxies distributed over 27 compact groups (CGs)of galaxies, we define an index that allows us to quantify their levelof activity due to an active galactic nucleus (AGN) or star formation.By combining the mean activity index with the mean morphological type ofthe galaxies in a group, we are able to quantify the evolutionary stateof the groups. We find that they span an evolutionary sequence thatcorrelates with the spatial configuration of the galaxies in the CG. Wedistinguish three main configuration types: A, B, and C. Type A CGs showpredominantly low velocity dispersions and are rich in late-type spiralsthat show active star formation or harbor an AGN. Type B groups haveintermediate velocity dispersions and contain a large fraction ofinteracting or merging galaxies. Type C comprises CGs with high velocitydispersions, which are dominated by elliptical galaxies that show noactivity. We suggest that evolution proceeds A==>B==>C. Mappingthe groups with different evolution levels in a diagram of radius versusvelocity dispersion does not reveal the pattern expected based on theconventional fast merger model for CGs, which predicts a direct relationbetween these two parameters. Instead, we observe a trend contrary toexpectation: the evolutionary state of a group increases with velocitydispersion. This trend seems to be related to the masses of thestructures in which CGs are embedded. In general, the evolutionary stateof a group increases with the mass of the structure. This suggestseither that galaxies evolve more rapidly in massive structures or thatthe formation of CGs embedded in massive structures predated theformation of CGs associated with lower mass systems. Our observationsare consistent with the structure formation predicted by the CDM model(or ΛCDM), only if the formation of galaxies is a biased process.
| Near-infrared imaging of ellipticals: surface brightness profiles and photometry
We present near-infrared K-band imaging of a large sample of candidatemerger remnant galaxies and Hickson Compact Group ellipticals. We derivelight profile indices, effective radii and surface brightnesses, as wellas total K-band magnitudes. We find that the light distributions of themerger remnant candidates are consistent with those of `normal'ellipticals, and scatter around a mean profile index of (1/n) = 0.20.Many of our sample galaxies have surface brightness profiles that arenot well described by a de Vaucouleurs law (1/n= 0.25), and we discussthe implications of this on the derived total magnitudes. Comparing thetotal K magnitudes calculated by extrapolating a de Vaucouleurs profileand those derived using a generalized Sérsic form, we find that asignificant bias is introduced if the de Vaucouleurs law is not a gooddescription of the actual light profile.
| 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.
| 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
| Redshift-Distance Survey of Early-Type Galaxies. I. The ENEARc Cluster Sample
This paper presents data on the ENEARc subsample of the larger ENEARsurvey of nearby early-type galaxies. The ENEARc galaxies belong toclusters and were specifically chosen to be used for the construction ofa Dn-σ template. The ENEARc sample includes newmeasurements of spectroscopic and photometric parameters (redshift,velocity dispersion, line index Mg2, and the angular diameterdn), as well as data from the literature. New spectroscopicdata are given for 229 cluster early-type galaxies, and new photometryis presented for 348 objects. Repeat and overlap observations withexternal data sets are used to construct a final merged catalogconsisting of 640 early-type galaxies in 28 clusters. Objectivecriteria, based on catalogs of groups of galaxies derived from completeredshift surveys of the nearby universe, are used to assign galaxies toclusters. In a companion paper, these data are used to construct thetemplate Dn-σ distance relation for early-typegalaxies, which has been used to estimate galaxy distances and derivepeculiar velocities for the ENEAR all-sky sample. Based on observationsat Complejo Astronomico El Leoncito, operated under agreement betweenthe Consejo Nacional de Investigaciones Científicas de laRepública Argentina and the National Universities of La Plata,Córdoba, and San Juan; Cerro Tololo Inter-American Observatory,National Optical Astronomical Observatory, which is operated by theAssociation of Universities for Research in Astronomy, Inc., undercooperative agreement with the National Science Foundation; the EuropeanSouthern Observatory (ESO), partially under the ESO-ON agreement; theFred Lawrence Whipple Observatory; the Observatório do Pico dosDias, operated by the Laboratório Nacional de Astrofísicaand the MDM Observatory at Kitt Peak.
| The UZC-SSRS2 Group Catalog
We apply a friends-of-friends algorithm to the combined Updated ZwickyCatalog and Southern Sky Redshift Survey to construct a catalog of 1168groups of galaxies; 411 of these groups have five or more members withinthe redshift survey. The group catalog covers 4.69 sr, and all groupsexceed the number density contrast threshold, δρ/ρ=80. Wedemonstrate that the groups catalog is homogeneous across the twounderlying redshift surveys; the catalog of groups and their membersthus provides a basis for other statistical studies of the large-scaledistribution of groups and their physical properties. The medianphysical properties of the groups are similar to those for groupsderived from independent surveys, including the ESO Key Programme andthe Las Campanas Redshift Survey. We include tables of groups and theirmembers.
| Compact groups in the UZC galaxy sample
Applying an automatic neighbour search algorithm to the 3D UZC galaxycatalogue (Falco et al. \cite{Falco}) we have identified 291 compactgroups (CGs) with radial velocity between 1000 and 10 000 kms-1. The sample is analysed to investigate whether Tripletsdisplay kinematical and morphological characteristics similar to higherorder CGs (Multiplets). It is found that Triplets constitute lowvelocity dispersion structures, have a gas-rich galaxy population andare typically retrieved in sparse environments. Conversely Multipletsshow higher velocity dispersion, include few gas-rich members and aregenerally embedded structures. Evidence hence emerges indicating thatTriplets and Multiplets, though sharing a common scale, correspond todifferent galaxy systems. Triplets are typically field structures whilstMultiplets are mainly subclumps (either temporarily projected orcollapsing) within larger structures. Simulations show that selectioneffects can only partially account for differences, but significantcontamination of Triplets by field galaxy interlopers could eventuallyinduce the observed dependences on multiplicity. Tables 1 and 2 are onlyavailable in electronic at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/391/35
| 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.
| Compact Groups of Galaxies: Evolution of the Stellar Population
We present a study focusing on the nature of compact groups (CGs)through the study of their elliptical (E) galaxies. Parametersdescribing the internal dynamics and the stellar populations of thegalaxies are compared with their counterparts in other environments. Oursample has 24 bright E galaxies located in the core of Hickson CGs and11 bright `bona fide' Es, located in the field or very loose groups.Their spectra were obtained with the 2.1 m Telescope at KPNO and have a4.1 Å resolution over the wavelength range 3500-7000 Å. Wehave found that, from the dynamical point of view, E galaxies in CGs areessentially similar to those in dense clusters. Moreover, the stellarpopulations of Es in CGs seem to be older and less metal rich than thosein the field, behaviour which has also been observed by Rose et al.(1994).
| The Fundamental Plane of Elliptical Galaxies in Compact Groups
We present a study focusing on the nature of compact groups through thestudy of their elliptical galaxies. We determine velocity dispersions(σ) for 18 bright elliptical galaxies located in the core ofHickson compact groups and a control sample of 12 bright bona fideelliptical galaxies located in the field or very loose groups. Severaltests are carried out to avoid sources of systematic effects in σmeasurements. We use these velocity dispersions to compare the positionsof 11 compact group galaxies in the fundamental plane with those of alarge and homogeneous sample of elliptical galaxies. We find that littleor no significant difference exists, as far as the fundamental plane isconcerned, between elliptical galaxies in compact groups and theircounterparts in other environments.
| 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.
| The Nuclear Activity of Galaxies in the Hickson Compact Groups
In order to investigate the nuclear activity of galaxies residing incompact groups of galaxies, we present results of our opticalspectroscopic program made at Okayama Astrophysical Observatory. We haveperformed optical spectroscopy of 69 galaxies belonging to 31 Hicksoncompact groups (HCGs) of galaxies. Among them, three galaxies havediscordant redshifts and, moreover, spectral quality is too poor toclassify another three galaxies. Therefore, we describe our results forthe remaining 63 galaxies. Our main results are summarized as follows:(1) We have found in our sample 28 active galactic nuclei (AGNs), 16 HII nuclei, and 19 normal galaxies showing no emission line. We used thisHCG sample for statistical analyses. (2) Comparing the frequencydistributions of activity types between the HCGs and the field galaxieswhose data are taken from Ho, Filippenko, & Sargent (382 fieldgalaxies), we find that the frequency of H II nuclei in the HCGs issignificantly less than that in the field. However, this difference maybe due to selection bias to the effect that our HCG sample contains moreearly-type galaxies than the field, because it is known that H II nucleiare rarer in early-type galaxies than in later ones. (3) Applying acorrection to this morphological bias to the HCG sample, we find thatthere is no statistically significant difference in the frequency ofoccurrence of emission-line galaxies between the HCGs and the field.This implies that the dense galaxy environment in the HCGs does notaffect the triggering of either the AGN activity and the nuclearstarburst. We discuss some implications on the nuclear activity in theHCG galaxies.
| Arcsecond Positions of UGC Galaxies
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.
| Old Stellar Populations. VI. Absorption-Line Spectra of Galaxy Nuclei and Globular Clusters
We present absorption-line strengths on the Lick/IDS line-strengthsystem of 381 galaxies and 38 globular clusters in the 4000-6400Angstroms region. All galaxies were observed at Lick Observatory between1972 and 1984 with the Cassegrain Image Dissector Scanner spectrograph,which makes this study one of the largest homogeneous collections ofgalaxy spectral line data to date. We also present a catalog of nuclearvelocity dispersions used to correct the absorption-line strengths ontothe stellar Lick/IDS system. Extensive discussion of both random andsystematic errors of the Lick/IDS system is provided. Indices are seento fall into three families: alpha -element-like indices (including CN,Mg, Na D, and TiO2) that correlate positively with velocity dispersion;Fe-like indices (including Ca, the G band, TiO1, and all Fe indices)that correlate only weakly with velocity dispersion and the alphaindices; and H beta that anticorrelates with both velocity dispersionand the alpha indices. C24668 seems to be intermediate between the alphaand Fe groups. These groupings probably represent different elementabundance families with different nucleosynthesis histories.
| Effects of Interaction-induced Activities in Hickson Compact Groups: CO and Far-Infrared Study
A study of 2.6 mm CO J = 1 --> 0 and far-infrared (FIR) emission in adistance-limited (z < 0.03) complete sample of Hickson compact group(HCG) galaxies was conducted in order to examine the effects of theirunique environment on the interstellar medium of component galaxies andto search for a possible enhancement of star formation and nuclearactivity. Ubiquitous tidal interactions in these dense groups wouldpredict enhanced activities among the HCG galaxies compared to isolatedgalaxies. Instead, their CO and FIR properties (thus, "star formationefficiency") are surprisingly similar to isolated spirals. The CO datafor 80 HCG galaxies presented here (including 10 obtained from theliterature) indicate that the spirals globally show the same H2 contentas the isolated comparison sample, although 20% are deficient in COemission. Because of their large optical luminosity, low metallicity isnot likely the main cause for the low CO luminosity. The CO deficiencyappears linked with the group evolution, and gas exhaustion through paststar formation and removal of the external gas reserve by tidalstripping of the outer H I disk offer a possible explanation. The IRASdata for the entire redshift-limited complete sample of 161 HCG galaxieswere reanalyzed using ADDSCAN/SCANPI, improving the sensitivity by afactor of 3-5 over the existing Point Source Catalog (PSC) and resolvingbetter the contribution from individual galaxies. The new analysis ofthe IRAS data confirms the previous suggestion that FIR emission in HCGgalaxies is similar to isolated, Virgo Cluster, and weakly interactinggalaxies. Their H2 and FIR characteristics yield a star formationefficiency that is similar to that of these comparison samples. A factor2 enhancement in the 25-100 mu m flux ratio among the HCG spirals isfound, which suggests intense localized nuclear starburst activitysimilar to that of H II galaxies. A number of early-type galaxies inHCGs are detected in CO and FIR, lending further support to the ideathat tidal interactions and tidally induced evolution of the groups andmember galaxies are important in our sample.
| The Universality of the Fundamental Plane of E and S0 Galaxies: Spectroscopic Data
We present central velocity dispersion measurements for 325 early-typegalaxies in eight clusters and groups of galaxies, including newobservations for 212 galaxies. The clusters and groups are the A262,A1367, Coma (A1656), A2634, Cancer, and Pegasus Clusters and the NGC 383and NGC 507 Groups. The new measurements were derived frommedium-dispersion spectra that cover 600 Å centered on the Mg I btriplet at lambda ~ 5175 Å. Velocity dispersions were measuredusing the Tonry & Davis cross-correlation method, with a typicalaccuracy of 6%. A detailed comparison with other data sources is made.
| The Universality of the Fundamental Plane of E and S0 Galaxies: Sample Definition and I-Band Photometric Data
As part of a project to compare the fundamental plane and Tully-Fisherdistance scales, we present here I-band CCD photometry for 636early-type galaxies in eight clusters and groups of galaxies. These arethe A262, A1367, Coma (A1656), A2634, Cancer and Pegasus Clusters, andthe NGC 383 and NGC 507 Groups. Sample selection, cluster properties,and cluster membership assignment criteria are discussed. We presentphotometric parameters that are used in the fundamental plane relation,the effective radius r_e, and the effective surface brightness mu_e, asderived from a r^1/4 fit to the observed radial photometric profile ofeach galaxy. A comparison with similar data found in the literature forthe Coma Cluster shows that large systematic uncertainties can beintroduced in the measurement of r_e and mu_e by the particular methodused to derive those parameters. However, the particular combination ofthese two parameters that enters in the fundamental plane relation is aquantity that can be measured with high accuracy.
| Environments of Redshift Survey Compact Groups of Galaxies
Redshift survey compact groups (RSCGs) are tight knots of N >= 3galaxies selected from the CfA2+SSRS2 redshift survey. The selection isbased on physical extent and association in redshift space alone. Wemeasured 300 new redshifts of fainter galaxies within 1 h^-1 Mpc of 14RSCGs to explore the relationship between RSCGs and their environments.Thirteen of 14 RSCGs are embedded in overdense regions of redshiftspace. The systems range from a loose group of five members to an Abellcluster. The remaining group, RSCG 64, appears isolated. RSCGs areisolated and distinct from their surroundings to varying degrees, as arethe Hickson compact groups. Among the 13 embedded RSCGs, three aredistinct from their general environments (RSCG 9, RSCG 11, and RSCG 85).
| Galaxy Alignments in the Pisces-Perseus Supercluster Revisited
A search for preferential galaxy alignments in the Pisces-PerseusSupercluster (PPS) is made using the Minnesota Automated Plate ScannerPisces-Perseus Survey (MAPS-PP). The MAPS-PP is a catalog of ~1400galaxies with a (roughly) isophotal diameter greater than 30"constructed from digitized scans of the blue and red plates of thePalomar Observatory Sky Survey covering the PPS. This is the largestsample of galaxies applied to a search of galaxy alignments in thissupercluster, and it has been used in combination with previouslypublished redshifts to construct the deepest PPS galaxy luminosityfunction to date. While previous studies have relied extensively oncatalogs with visually estimated parameters for both sample selectionand determination of galaxy orientation, the MAPS-PP uses selectioncriteria and measurements that are entirely machine and computer based.Therefore, it is not susceptible to some of the biases, such as thediameter inclination effect, known to exist in some other galaxycatalogs. The presence of anisotropic galaxy distributions is determinedby use of the Kuiper statistic, a robust alternative to the chi^2statistic more traditionally used in these studies. Three statisticallysignificant anisotropic distributions are observed. The reddest galaxiesare observed to be oriented preferentially perpendicular to the locallarge-scale structure. The bluest galaxies near the supercluster planeare observed to have an anisotropic position angle distribution.Finally, a weak trend for the median position angle of color-selectedgalaxy subsamples to ``twist'' with increasing distance from the PPSplane is observed. These position angle distribution anisotropies areweak and are not consistent with any single primordial or modern-eragalaxy alignment mechanism, although a mixture of such mechanisms is notruled out.
| 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.
| 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.
| Galaxy clusters in the Perseus-Pisces region. I - Spectroscopic and photometric data for early-type galaxies
We present new spectroscopic and photometric data for 137 early-typegalaxies in nine clusters and for a set of nearby standard galaxies. Ourspectroscopic data comprise radial velocities, central velocitydispersions, and magnesium line strength indices. We demonstrate thatour new velocity dispersion data can be brought into consistency withthe standard system, to an uncertainty of percent 0.01 dex. From R-bandCCD photometry, we derive the effective diameter, the mean surfacebrightness within the effective diameter, and an R-band diameterequivalent to the Dn parameter of Dressler et al. Internal comparisonsindicate an average error of 0.005 in each measurement of log Dn. Thephotometric data can be brought on to a system consistent with externaldata at the level of 0.5 per cent in distance.
| Observing Hickson galaxy groups.
Not Available
| Photoelectric UBV Photometry of 179 Bright Galaxies
This paper presents photoelectric UBV multiaperture photometry of 179bright galaxies that was used to compute total magnitudes and colorindices published in the Third Reference Catalog of Bright Galaxies(RC3). The observations were made at the McDonald Observatory from 1983December to 1986 September with an Amperex 56-DVP photometer attached tothe 0.76 and 0.91 m telescopes. The observations can also be used tocalibrate CCD images.
| 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.
| Far infrared properties of Hickson compact groups of galaxies. I. High resolution IRAS maps and fluxes.
The Far Infrared (FIR) properties of galaxies which are members ofcompact groups bear relevant information on the dynamical status and thephysical properties of these structures. All studies published so farhave been undermined by the poor sensitivity and spatial resolution ofthe IRAS-PSC and IRAS Sky Survey data. We used the HIRAS softwareavailable at the IRAS server at the Laboratory for Space Research inGroningen to fully exploit the redundancy of the IRAS data and toapproach the theoretical diffraction limit of IRAS. Among the 97 groupswhich were observed by IRAS, 62 were detected in at least one band,while reliable upper limits were derived for all the others. Among thedetected groups, 49 were fully or partially resolved, i.e. it waspossible to discriminate which member or members emit most of the FIRlight. At 60μm, for instance, 87 individual sources were detected in62 groups. In order to ease the comparison with data obtained at otherwavelengths - and in particular in the X and radio domains - we giveco-added and HIRAS maps for all the detected groups.
| 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.
| ROSAT observations of compact groups of galaxies
We have systematically analyzed a sample of 13 new and archival ROSATPosition Sensitive Proportional Counter (PSPC) observations of compactgroups of galaxies: 12 Hickson compact groups plus the NCG 2300 group.We find that approximately two-thirds of the groups have extended X-rayemission and, in four of these, the emission is resolved into diffuseemission from gas at a temperature of kT approximately 1 keV in thegroup potential. All but one of the groups with extended emission have aspiral fraction of less than 50%. The baryon fraction of groups withdiffuse emission is 5%-19%, similar to the values in clusters ofgalaxies. However, with a single exception (HCG 62), the gas-to-stellarmass ratio in our groups has a median value near 5%, somewhat greaterthan the values for individual early-type galaxies and two orders ofmagnitude than in clusters of galaxies. The X-ray luminosities ofindividual group galaxies are comparable to those of similar fieldgalaxies, although the LX-LB relation forearly-type galaxies may be flatter in compact groups than in the field.
| Deep Optical Observations of Compact Groups of Galaxies
Compact groups of galaxies appear to be extremely dense, making themlikely sites of intense galaxy interaction, while their smallpopulations make them relatively simple to analyze. In order to searchfor optical interaction tracers such as diffuse light and galaxy tidalfeatures in Hickson compact groups (HCGs), we carried out deepphotometry in three filters on a sample of HCGs with ROSAT observations.Using a modeling procedure to subtract the light of bright early-typegalaxies, we found shell systems and extended envelopes around many, butnot all, of those galaxies. Only one group in our sample, HCG 94, hasdiffuse light in the group potential (with a luminosity of 7 L^*^); theother groups do not contain more than 113 L^*^ in diffuse light. Withthe exception of HCG 94 (which is the most x-ray-luminous HCG), we foundno correlation between the presence of shells or other tidal featuresand the x-ray luminosity of a group. Better predictors of detectablegroup x-ray emission are a low spiral fraction and belonging to a largergalaxy condensation-neither of which are correlated with opticaldisturbances in the group galaxies. No elliptical galaxies that areextremely optically luminous but x-ray faint are found to have shellsand very complex color structures. This is likely due to recent infallof gas-rich material into the galaxies, which would produce both thedisruption of stellar orbits and a significant amount of star formation.
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