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Galaxy Interaction and the Starburst-Seyfert Connection
Galaxy interactions are studied in terms of the starburst-Seyfertconnection. The starburst requires a high rate of gas supply. Since theefficiency for supplying the gas is high in a galaxy interaction,although the companion is not necessarily discernible, Seyfert galaxieswith circumnuclear starbursts are expected to be interacting. Since thelarge amounts of circumnuclear gas and dust obscure the broad-lineregion, they are expected to be observed as Seyfert 2 galaxies. Theactive galactic nucleus itself does not require a high rate of gassupply. Seyfert galaxies without circumnuclear starbursts are notnecessarily expected to be interacting even at the highest luminosities.They are not necessarily expected to evolve from Seyfert galaxies withcircumnuclear starbursts. We derive these and other theoreticalexpectations and confirm them with statistics on observational data ofmagnitude-limited samples of Seyfert galaxies.
| 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.
| Sensitive VLBI Continuum and H I Absorption Observations of NGC 7674: First Scientific Observations with the Combined Array VLBA, VLA, and Arecibo
We present phase-referenced VLBI observations of the radio continuumemission from, and the neutral hydrogen 21 cm absorption toward, theluminous infrared galaxy NGC 7674. The observations were carried out at1380 MHz using the VLBA, the phased VLA, and the 305 m Arecibo radiotelescope. These observations constitute the first scientific use of theArecibo telescope in a VLBI observation with the VLBA. The high- andlow-resolution radio continuum images reveal several new continuumstructures in the nuclear region of this galaxy. At ~100 mas resolution,we distinguish six continuum structures extending over 1.4" (742 pc),with a total flux density of 138 mJy. Only three of these structureswere known previously. All these structures seem to be related to activegalactic nucleus (AGN) activity. The overall S-shaped pattern that theradio structures seem to form could be the result of the interstellarmedium diverting the outcoming jets from the central AGN. However, wecannot rule out the possibility of a black hole merger that could resultin a similar structural pattern. At the full resolution of the array(11×5 mas), we detect only two of the six continuum structures.Both are composed of several compact components with brightnesstemperatures on the order of 107 K. While it is possible thatone of these compact structures could host an AGN, they could also beshocklike features formed by the interaction of the jet with compactinterstellar clouds in the nuclear region of this galaxy. Complex H Iabsorption is detected with our VLBI array at both high and low angularresolution. Assuming that the widest H I feature is associated with arotating H I disk or torus feeding a central AGN, we estimate anenclosed dynamical mass of ~7×107 Msolar,comparable to the value derived from the hidden broad Hβ emissionin this galaxy. The narrower H I lines could represent clumpy neutralhydrogen structures in the H I torus. The detection of H I absorptiontoward some of the continuum components and its absence toward otherssuggest an inclined H I disk or torus in the central region of NGC 7674.The overall averaged H I spectrum toward the continuum structures with HI absorption is very consistent with the Arecibo single-dish H Iabsorption spectrum at 3.3′ resolution.
| Dynamical Effects of Interactions and the Tully-Fisher Relation for Hickson Compact Groups
We investigate the properties of the B-band Tully-Fisher (T-F) relationfor 25 compact group galaxies, using Vmax derived fromtwo-dimensional velocity maps. Our main result is that the majority ofthe Hickson Compact Group galaxies lie on the T-F relation. However,about 20% of the galaxies, including the lowest-mass systems, havehigher B luminosities for a given mass, or alternatively, a mass that istoo low for their luminosities. We favor a scenario in which outliershave been brightened because of either enhanced star formation ormerging. Alternatively, the T-F outliers may have undergone truncationof their dark halo due to interactions. It is possible that in somecases both effects contribute. The fact that the B-band T-F relation issimilar for compact group and field galaxies tells us that thesegalaxies show common mass-to-size relations and that the halos ofcompact group galaxies have not been significantly stripped insideR25. We find that 75% of the compact group galaxies studied(22 out of 29) have highly peculiar velocity fields. Nevertheless, acareful choice of inclination, position angle, and center, obtained fromthe velocity field, and an average of the velocities over a large sectorof the galaxy enabled the determination of fairly well-behaved rotationcurves for the galaxies. However, two of the compact group galaxies HCG91a and HCG 96a, which are the most massive members in M51-like pairs,have very asymmetric rotation curves, with one arm rising and the otherone falling, indicating most probably a recent perturbation by the smallclose companions.
| Gas kinematics of a sample of five Hickson Compact Groups. The data
We present Fabry Perot observations of galaxies in five Hickson CompactGroups: HCG 10, HCG 19, HCG 87, HCG 91 and HCG 96. We observed a totalof 15 galaxies and we have detected ionized gas for 13 of them. We wereable to derive 2D velocity, monochromatic, continuum maps and rotationcurves for the 13 objects. Almost all galaxies in this study arelate-type systems; only HCG 19a is an elliptical galaxy. We can see atrend of kinematic evolution within a group and among different groups -from strongly interacting systems to galaxies with no signs ofinteraction - HCG 10 exhibits at least one galaxy strongly disturbed;HCG 19 seems to be quite evolved; HCG 87 does not show any sign ofmerging but a possible gas exchange between two galaxies; HCG 91 couldbe accreting a new intruder; HCG 96 exhibits past and presentinteractions.Based on observations collected at the European Southern Observatory, LaSilla, Chile and at the Canada-France-Hawaii Observatory, Hawaii, USA.Tables 1 and 2, Figs. 1, 3, 5, 7, 9, 11, 13, 15, 23 are only availablein electronic form at http://www.edpsciences.org
| Sub-arcsecond atomic hydrogen absorption in the Seyfert galaxies NGC 7674 and NGC 7469
Neutral hydrogen has been studied on sub-arcsecond scales in two Seyfertgalaxies, NGC 7469 and NGC 7674. The 1.4-GHz continuum emission fromthese sources agree with higher frequency measurements and shows linear,triple source in NGC 7674 and a compact source surrounded by a weak ringof radio emission in NGC 7469. In both of these sources we detect deeplocalized H I absorption in front of a single continuum component. Inthe case of NGC 7674 the H I absorption is only seen against the centralcomponent and has a peak optical depth of 0.21 +/- 0.03, a linewidth of114 +/- 7 km s-1 and a heliocentric velocity of 8623 +/- 5 kms-1. The integrated H I absorption against the centralcomponent corresponds to a column density of 5.0 +/- 0.7 ×1021 atom cm-2. We interpret the lack of H Iabsorption against the east and west components (τ < 0.07 and0.06) as evidence that the H I is localized within the central fewhundred pc, similar to the H I observed against the nucleus of NGC 4151,and has an upper mass limit of ~4 × 105Msolar. We speculate that this H I may be associated with adusty torus. Giant Meterwavelength Radio Telescope (GMRT) results showextended emission and give a rest velocity of 8699 +/- 20 kms-1. The H I absorption against NGC 7469 shows a single deepfeature against the strong central component. The line has a peakoptical depth 0.25, a linewidth of 65 +/- 6 km s-1 and aheliocentric velocity of 4843 +/- 5 km s-1. The integratedcolumn density is 3.6 +/- 0.4 × 1021 atomcm-2. Unfortunately the other components in NGC 7469 are tooweak to set significant limits to the H I optical depth, and hence,unlike NGC 7674, it is not possible to constrain the size of theabsorbing gas.
| 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 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.
| Optical Spectral Signatures of Dusty Starburst Galaxies
We analyze the optical spectral properties of the complete sample ofVery Luminous Infrared Galaxies presented by Wu et al., and we find ahigh fraction (~50%) of spectra showing both a strong Hδ line inabsorption and relatively modest [O II] emission [e(a) spectra]. Thee(a) signature has been proposed as an efficient method to identifydusty starburst galaxies, and we study the star formation activity andthe nature of these galaxies, as well as the effects of dust on theirobserved properties. We examine their emission-line characteristics, inparticular their [O II]/Hα ratio, and we find this to be greatlyaffected by reddening. A search for AGN spectral signatures reveals thatthe e(a) galaxies are typically H II/LINER galaxies. We compare the starformation rates derived from the FIR luminosities with the estimatesbased on the Hα line and find that the values obtained from theoptical emission lines are a factor of 10-70 (Hα) and 20-140 ([OII]) lower than the FIR estimates (50-300 Msolaryr-1). We then study the morphological properties of the e(a)galaxies, looking for a near companion or signs of a merger/interaction.In order to explore the evolution of the e(a) population, we present anoverview of the available observations of e(a) galaxies in differentenvironments both at low and high redshift. Finally, we discuss the roleof dust in determining the e(a) spectral properties and we propose ascenario of selective obscuration in which the extinction decreases withthe stellar age.
| An H_alpha catalogue of galaxies in Hickson compact groups. I. The sample
We present H_alpha photometry for a sample of 95 galaxies in HicksonCompact Groups obtained from observations of 31 groups. The Cataloguelists isophotal and adaptive aperture (Kron aperture) flux measurementsfor about 75% of the accordant galaxies inside the observed HCGs, 22 outof which are upper limits. Non standard data reduction procedures havebeen used to obtain the continuum subtracted H_alpha images for each HCGof the target sample. Flux calibration has also been performed in orderto obtain H_alpha luminosities for the whole sample. Both the datareduction and calibration procedures are carefully described in thispaper. The new data listed in this Catalogue are of great importance inunderstanding the star formation rate inside HCG galaxies and in givingnew insights on its dependence on galaxy interactions. Tables 3 to 10and Figs. 6 to 11 are only available in electronic version athttp://www.edpsciences.com Tables 7, 8, 9 are also available inelectronic version form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Accurate Positions for MCG Galaxies
We have measured accurate celestial coordinates for 4741 extragalacticobjects, primarily drawn from a list of MCG galaxies with no recentlypublished accurate positions. The standard deviations in the newpositions depend slightly on the measurement method but are on the orderof 1.0" to 1.2". Standard deviations in the original MCG positions areconfirmed to be at the 1.5′-2.0′ level. These new positionswere integrated into NED in 1997 December.
| 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.
| Optical colour maps of Seyfert galaxies. II. More Seyfert 2s
We present optical broad band B-I colour maps of a further sample of 10Seyfert 2 galaxies. In these bands, the contribution from emission linesto the total flux is small, and hence the images predominantly trace thecontinuum distribution. As in our earlier colour maps of a sample ofSeyferts type 1 and 2, we detect extended blue continuum components inthe circumnuclear region of several galaxies. These components areeither elongated (in Mkn 533, Mkn 607, Mkn 1066, NGC 5347, NGC 5953 andNGC 7319) or form a double structure across the nucleus (in NGC 5929).They are closely aligned with the radio and emission line axes of thesegalaxies and probably arise from scattering of nuclear continuum lightby extranuclear mirrors. Similar blue elongations (in Mkn 1 and NGC7212) and double structures (in NGC 788) are less well aligned with theradio and line emission, and their relationship with scattering regionsmust be considered uncertain. The colours of the blue maxima areconsistent with those expected from scattering off dust or electrons, aconclusion strengthened by the combined sample of the two papers in thisseries. Our findings thus strongly support the current unified models ofAGN. Based on observations made with the Nordic Optical Telescope,operated on the island of La Palma jointly by Denmark, Finland, Iceland,Norway, and Sweden, in the Spanish Observatorio del Roque de losMuchachos of the Instituto de Astrofisica de Canarias.
| A statistical study of the spectra of very luminous IRAS galaxies. II. Spectral and environmental analysis
Spectroscopic observations of a sample of 73 very luminous IRAS galaxies(log(LIR/Lsun)>=11.5 for H0=50 km\s(-1) ; Mpc(-1) ,q0=0.5) from the 2 Jy redshift surveycatalogue were carried out using the 2.16 m telescope at the BeijingAstronomical Observatory. The observational data, including the opticalimages (extracted from Digital Sky Survey) and spectra for thesegalaxies, are presented in Paper I \cite[(Wu et al. 1998)]{wu98}. Inthis paper, we give the spectral and morphological classifications forthese very luminous IRAS galaxies (VLIRGs). We show that about 60% ofVLIRGs exhibit AGN-like spectra (Seyfert 1s, Seyfert 2s, LINER-likegalaxies). This fraction goes up to 82% for the ultraluminous IRASgalaxies (ULIRGs) subsample (Log(LIR/Lsun) >=12.0). 56% of the VLIRGs show strong interaction or merging signatures;this fraction rises to 91% for the ULIRGs. These statistical resultsstrongly suggest that interaction triggers nuclear activities andenhances the infrared luminosity. We find that LINER and a mixture typewhich have optical properties of both HII galaxies and LINERs could beat the transition stage from infrared luminous HII galaxies to AGNs;their main energy production is from starbursts as well as AGNs. Bothinfrared luminosities and Hα equivalent widths increasedramatically as nuclear separations between VLIRGs and their nearestneighbors decrease. There is little doubt that strong starbursts happenin the nuclei of VLIRGs. Assuming class 0 as advanced merger, weconstruct a simple merger sequence, from morphological classes 1 to 4(with near or far companions), to class 5 and 6 (interacting pairs andmergers) and then to class 0 (isolated galaxies). Along this sequence,VLIRGs evolve from HII galaxies to AGNs. Table 1 is only available atthe CDS via anonymous ftp 130.79.128.5 or http://cdsweb.u-strasbg.fr
| Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
| A statistical study of the spectra of very luminous IRAS galaxies. I. Data
This paper presents the results of spectral observations for the largestcomplete sample of very luminous IRAS galaxies obtained to date. Thesample consists of those 73 objects for which log(L_IR/Lsun)>= 11.5 (H0=50;km; s(-1) Mpc(-1) , q0=0.5) andmag <= 15.5 , and was extracted from the 2 Jy IRAS redshift catalog.All the spectra were obtained using the 2.16 m telescope of BeijingAstronomical Observatory during the years 1994-1996. A total of 123galaxy spectra were obtained with spectral ranges of 4400;Angstroms to7100;Angstroms and 3500;Angstroms to 8100;Angstroms at resolutions of11.2;Angstroms and 9.3;Angstroms respectively. In addition to the 73spectra for sample galaxies, we also present spectra for ten non-samplegalaxies and a further 40 for the companions of sample galaxies. Thedata presented include nuclear spectrum and the parameters describingthe emission lines, absorption lines and continua as well as DSS imagesand environmental parameters. Table 1 is also available in electricform, Table 2-4 are only available in electronic form form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130. 79.128.5) or via http:cdsweb.u-strasbg.fr/Abstract.html. Figures 4 and 9 are published in theon-line version of A&A..
| Hickson 96: a physical compact group.
We analyze the morphology and dynamics of the galaxies of the Hickson 96compact group by means of deep CCD images in the B, V and R photometricbands and long-slit spectroscopy. The four galaxies of this spiral richgroup show signs of gravitational interaction. Two long tails come outfrom the contact region of the close pair H96ac. It is also there whereboth galaxies, bi-symmetrical in their inner parts, loose one of theirarms. Moreover, both the photometric and kinematical center of H96a aredisplaced relative to the center of the disk. H96b, a giant ellipticalgalaxy, shows significant deviations from a r^1/4^ law at the innerparts and small rotation along its major axis. We find at the centre ofthe galaxy an elongated component which is kinematically decoupled. Awide faint plume seems to emerge from this galaxy. H96d, the smallestgalaxy of the group, seems to be influenced by the bigger members, asindicated by three prominent knots of recent bursts of star formation inits blue disk, and by hints of optical bridges joining H96d with H96aand b. Finally the group has a low velocity dispersion (160km/s) and iswell isolated - no galaxies with comparable magnitude to H96a or H96bare found in its neighborhood. All these results lead us to concludethat Hickson 96 constitutes a real physical system.
| Observing Hickson galaxy groups.
Not Available
| 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.
| The Nature of Seyfert 2 Galaxies with Obscured Broad-Line Regions. II. Individual Objects
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...440..578T&db_key=AST
| The Nature of Seyfert 2 Galaxies with Obscured Broad-Line Regions. I. Observations
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...440..565T&db_key=AST
| Morphology of galaxies in compact groups
We present the results of an isophotal analysis of 140 early-typegalaxies and a visual inspection of images of an additional 202 galaxiesin compact groups. This is essentially the entire sample of galaxies inthe subset of 92 Hickson compact groups which have at least threeaccordant members. About 12% of the elliptical galaxies have largercharacteristic radii and shallower surface brightness profiles thangalaxies of the same luminosity in less dense environments. The averageellipticity of elliptical galaxies in compact groups is a slowlyincreasing function of the metric radius, as it is for field andloose-group galaxies. No alignment is found among the major axes of thegalaxies and the major axis of the group. When combined with previouslypublished morphological, kinematic, radio, infrared, and colorinformation on the same galaxies, our data show that 43% of the galaxiesin the compact group sample show morphological and/or kinematicaldistortions indicative of interactions and/or mergers. About 32% of thegroups have three or more galaxies which show some sign of interaction.This is a lower limit, since for the great majority of the galaxies inthe groups, only imaging and low-resolution spectra are available. Forthe subsample of 16 groups for which published detailed kinematical dataare also available, the fraction of groups with three or more galaxiesin interaction is 75%. No correlation is found between the number ofinteracting galaxies in a group and the group velocity dispersion orcrossing time. These observations strongly support the view that compactgroups are systems of physically associated galaxies and not chancealignments of field, loose-group, or cluster galaxies. They also confirmthe importance of compact groups for studies of interactions and galaxyevolution. While the lack of a good control sample makes it difficult tomake quantitative comparisons for some aspects of this study, it isclear that the fraction of galaxies showing evidence of interactions ismuch higher in compact groups than in other environments.
| New evidence for mergers in compact groups of galaxies
In the (logR_e_, μ_e_) plane defined by the logarithm of theeffective radius and the effective surface brightness, ellipticalgalaxies that are members of Hickson's compact groups turn out to belongto the bright family, thus suggesting that most of them have likelyexperiences subtantial secondary evolution.
| The Structure and Dynamics of Elliptical Galaxies in Compact Groups
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993ApJ...418...72Z&db_key=AST
| Dynamical properties of compact groups of galaxies
Radial velocities are presented for 457 galaxies in the 100 Hicksoncompact groups. More than 84 percent of the galaxies measured havevelocities within 1000 km/s of the median velocity in the group.Ninety-two groups have at least three accordant members, and 69 groupshave at least four. The radial velocities of these groups range from1380 to 42,731 km/s with a median of 8889 km/s, corresponding to amedian distance of 89/h Mpc. The apparent space density of these systemsranges from 300 to as much as 10 exp 8 sq h/sq Mpc, which exceeds thedensities in the centers of rich clusters. The median projectedseparation between galaxies is 39/h kpc, comparable to the sizes of thegalaxies themselves. A significant correlation is found between crossingtime and the fraction of gas-rich galaxies in the groups, and a weakanticorrelation is found between crossing time and the luminositycontrast of the first-ranked galaxy.
| Bayesian deconvolution in optical astronomy
Bayesian methods and spatial stochastic processes are used here in thedeconvolution of images of galaxies. Under very simple but realisticprior assumptions about the true underlying image of a galaxy theBayesian framework is put to work. The method is tested in CCD images ofextragalactic objects of different morphological types and an analysisof the deconvolutions obtained is performed emphasizing the comparisonwith other observational results.
| Optical colors of early-type galaxies in compact groups
UBVRI colors of a sample of 55 elliptical galaxies as well as 21 S0galaxies in Hickson compact groups are presented. Four of the ellipticalgalaxies and one of the S0 galaxies in the compact groups aresignificantly bluer than normal for early-type galaxies of theirluminosity. A population of elliptical galaxies with blue optical colorsis predicted by standard models of the evolution of galaxies in compactgroups because of the favorable conditions for interactions and mergersin these regions. The brightest of the blue elliptical galaxies has anextensive shell system; however, the other two blue elliptical galaxiesfor which there is sufficient spatial resolution show no unusualmorphological features such as tails or shells. In addition to theircolor, the primary distinguishing feature of the blue ellipticalgalaxies is their color gradient, as they tend to be bluer in the centerthan at large radii, which is contrary to the usual trend in ellipticalgalaxies.
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