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|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.
|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.
|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.
|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 nature of discordant redshift galaxies in compact groups|
We have analysed the sample of 92 compact groups in Hickson's revisedcatalogue to investigate whether the numbers and properties of thediscordant redshift galaxies in these groups are consistent with theprojection hypothesis. The main conclusion of our analysis is that thenumbers, sizes, magnitudes and morphological types of the discordantredshift galaxies in the Hickson compact groups are as expected if theseare due to chance projections of unrelated galaxies on the groups. Thedistribution of positions for the discordant galaxies in quintets,however, is more centrally concentrated than that predicted for auniform distribution of field interlopers. One of the possibleexplanations for this discrepancy is that compact groups can act asgravitational lenses, causing the brightening of background galaxiesthat would otherwise fall below the magnitude cut-off of the group.Distances to two galaxies in the Hickson compact group 61, one of them adiscordant redshift galaxy, have been determined using the Tully-Fisherrelation. Both objects were found to be at distances consistent withtheir redshifts and an expanding Universe. All these results support theview of a cosmological origin for galaxy redshifts.
|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.
|On actual presence of discordant-redshift galaxies in compact groups|
Hickson's compact galaxy groups were classified using the statisticalcriterion which includes the radial velocities of galaxies as well astheir relative positions. These groups on the whole and their componentsare identified as the confident and probable non-chance ones as well asprobable and confident chance ones. All confident chance objects havethe discordant radial velocities with the differences of radialvelocities (DV) Epsilon between 1,000 km/s and 20,000 km/s. The specialclass of objects 'bright discordants' is selected. These galaxies havethe discordant radial velocities with DV Epsilon between 825 km/s and8440 km/s and have a strong tendency to be the brightest components oftheir groups. The lowest difference of radial velocities for the lastclass of objects mean value of DV = (1.0 +/- 0.2) x 103 km/sand we accept this value of DV as the lowest value of discordant radialvelocities. It is found that the biggest part of Hickson's compactgroups consist of non-chance aggregations of galaxies and some of thecases of discordant-redshifts require a special study in order toexplain their origin from a dynamic or some other point of view.
|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.
|The luminosity function of compact groups of galaxies|
An analysis of the luminosity function of 68 compact groups of galaxiescataloged by Hickson (1982) is presented. The luminosities of compactgroup galaxies are consistent with their being drawn from a Schechterluminosity function. Individual morphological-type luminosity functionsare also determined. Both the total and morphological-type specificluminosity functions of compact group galaxies are significantlydifferent from those of field, loose-group, and cluster galaxies. Inparticular, the luminosity function of HCG elliptical galaxies has amean magnitude which is significantly brighter than the mean magnitudeof Virgo cluster elliptical galaxies. The mean luminosity density ofgalaxies in compact groups is estimated. The obtained result isconsistent with the conventional scenario in which compact groups mergeto form elliptical galaxies on a relatively short time scale.
|The plane W(Na I) X W(Mg I) - Effects of interstellar Na I in a sample of southern galaxies|
Galaxy spectra from a subsample of the Southern Sky Redshift Survey databank were used to study the equivalent width plane for the lines Na Ilambda 5893 A vs Mg I lambda 5175 A. An estimate of how important thecontribution of the interstellar gas for the sodium line is compared tothat of the stellar population. The sample is made up of galaxies withmorphological types from E to Sc and are distributed up to radialvelocities of 25,000 km/s, most of them smaller than 15,000 km/s. Mostearly type galaxies with dust lanes, particularly nearly edge-on So's,present an enhancement of the Na I line. Inclined spiral galaxies tendto present enhanced Na I with respect to face-on spirals. This tendency,previously found in a smaller sample of galaxies limited to V equal toor less than 6000 km/s, is now confirmed for more distant ones. In thelarge velocity sample it shows the global bulge rather than the verynucleus; the persistence of the effect suggests that the scale height ofthe gas layer in the central disk can reach a considerable fraction ofthe bulge radius.
|A photometric catalog of compact groups of galaxies|
The paper presents astrometry, photometry, and morphological types,derived from CCD images, for 463 galaxies in the 100 compact groupsselected by Hickson. Some minor revisions to the membership of theoriginal catalog are made, based on these new images. The completenessof the catalog is considered as a function of group magnitude andGalactic latitude. At high Galactic latitude the catalog is estimated tobe 90 percent complete for groups with total B(T) magnitude 13.0 orless. It is less complete at lower Galactic latitude because ofobscuration and high stellar density.
|The Southern Supercluster|
The Southern Supercluster is described using data compiled from fivecatalogs, reduced to a homogeneous system following RC2. In terms ofmass, luminosity, and mass-to-light ratio, the Southern Superclustercompares well with the Coma and Hercules superclusters, but is lessmassive than the Local Supercluster. It is shown that, even though theSouthern Supercluster is the nearest supercluster to the LocalSupercluster, it is well separated from the Local Supercluster. However,there is evidence of a tenuous stream of galaxies connecting theSouthern Supercluster with the Perseus Supercluster.
|Neutral hydrogen in compact groups of galaxies|
Integrated H I profiles were detected for 34 of 51 Hickson compactgroups (HCGs) of galaxies, and sensitive upper limits to the H I fluxdensity were measured for the other 17. About 60 percent of the galaxieswithin compact groups are spirals, and a significant tendency exists forthe fraction of elliptical galaxies to increase with group surfacebrightness. The amount of dark matter within the compact group region isnegligibly small. An HCG on average contains half as much neutralhydrogen as a loose group with a similar spectrum of galaxy luminositiesand morphological types, implying that compact groups are independentdynamical entities and not transient or projected configurations ofloose groups. The observed fraction of galaxies which are luminousenough to be possible merger products of compact groups is smallcompared with the fraction required by the theory of dynamical friction.A clear discrepancy thus exists between solid empirical evidence and astraightforward prediction of Newtonian dynamical theory in a settingwhich does not permit a dark matter explanation.
|Southern Galaxy Catalogue.|
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