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Supernova 2006ax, 2006ay, 2006az
IAUC 8691 available at Central Bureau for Astronomical Telegrams.
| Intragroup diffuse light in compact groups of galaxies: HCG 79, 88 and 95
Deep B and R images of three Hickson Compact Groups, HCG 79, 88 and 95,have been analysed using a new wavelet technique to measure possibleintragroup diffuse light present in these systems. The method used,OV_WAV, is a wavelet technique particularly suitable fordetecting low surface brightness extended structures, down to asignal-to-noise ratio (S/N) = 0.1 per pixel, which corresponds to a5σ detection level in wavelet space. The three groups studied arein different evolutionary stages, as can be judged by their verydifferent fractions of the total light contained in their intragrouphaloes: 46 +/- 11 per cent for HCG 79 and 11 +/- 26 per cent for HCG 95,in the B band, and HCG 88 had no component detected down to a limitingsurface brightness of 29.1B mag arcsec-2. For HCG 95, theintragroup light (IGL) is red, similar to the mean colours of the groupgalaxies themselves, suggesting that it is formed by an old populationwith no significant ongoing star formation. For HCG 79, however, theintragroup material has a significantly bluer colour than the meancolour of the group galaxies, suggesting that the diffuse light may, atleast in part, come from stripping of dwarf galaxies which dissolvedinto the group potential well.
| 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.
| Classifications of the Host Galaxies of Supernovae
Classifications on the DDO system are given for the host galaxies of 177supernovae (SNe) that have been discovered since 1997 during the courseof the Lick Observatory Supernova Search with the Katzman AutomaticImaging Telescope. Whereas SNe Ia occur in all galaxy types, it isfound, at a high level of statistical confidence, that SNe Ib, Ic, andII are strongly concentrated in late-type galaxies. However, attentionis drawn to a possible exception provided by SN 2001I. This SN IInoccurred in the E2 galaxy UGC 2836, which was not expected to harbor amassive young supernova progenitor.
| A Multi-Band Photometric Study of Tidal Debris in a Compact Group of Galaxies: Seyfert's Sextet
In order to investigate the properties of the prominent tidal debrisfeature extending to the northeast of a compact group of galaxies,Seyfert's Sextet, we analyzed multi-band (U, B, V, VR, R, I, J, H, andK') photometric imaging data and obtained the following results: 1) Theradial surface brightness distribution of this tidal debris in Seyfert'sSextet (TDSS) in each band appears to be well approximated by anexponential profile. 2) The observed B-V color of TDSS is similar tothose of dwarf elliptical galaxies in nearby clusters. 3) Comparing thespectral energy distribution (SED) of TDSS with theoretical photometricevolution models and with the SED of the stars in the outer part of HCG79b, we find that its SED is comparable to that of a ~10Gyr-old stellarpopulation with solar metallicity, similar to the stellar population inthe outer part of HCG 79b. This suggests that TDSS consists of starsthat may have been liberated from HCG 79b by strong ga laxyinteractions, not a pre-existing dwarf galaxy as previously thought.
| The Beginning of the End: Hubble Space Telescope Images of Seyfert's Sextet
Hubble Space Telescope (HST) Wide Field Planetary Camera 2 images ofHickson Compact Group (HCG) 79, Seyfert's Sextet, are presented. Bothpoint sources and extended sources detected on the three wide-fieldchips were photometered in four filters: F336W, F439W, F555W, and F814W.Unlike other HCGs that have been imaged with HST, there do not appear tobe any candidate young star clusters among the detected point sources.The majority of the point sources that may be star clusters associatedwith the Sextet have red colors consistent with stellar populationsolder than 1 Gyr. A similar conclusion is drawn with regard to theextended sources. The majority of these appear to be backgroundgalaxies, but a few candidate dwarf galaxies are identified aspotentially associated with Seyfert's Sextet. However, no blue,star-forming objects similar to the tidal dwarf galaxy candidatesidentified in other HCGs are found among the extended objects identifiedin this study. A redshift for one dwarf galaxy candidate was measuredfrom a spectrum obtained with the Hobby-Eberly Telescope, and thisobject was found to have a redshift similar to NGC 6027e, the discordantspiral formerly identified as a member of this compact group. The HSTobservations presented here and previous radio observations of theneutral gas content of this group suggest that the interactions thathave taken place in the Sextet only redistributed the stars from themember galaxies within the group. We speculate that future interactionsmay be strong enough to strip the gas from NGC 6027d and triggerstar-cluster formation.
| 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.
| Spectroscopic study of blue compact galaxies. II. Spectral analysis and correlations
This is the second paper in a series studying the star formation rates,stellar components, metallicities, and star formation histories andevolution of a sample of blue compact galaxies. We analyzed spectralproperties of 97 blue compact galaxies, obtained with the BeijingAstronomical Observatory (China) 2.16 m telescope, with spectral range3580 Å-7400 Å. We classify the spectra according to theiremission lines: 13 of the total 97 BCG sample are non-emission linegalaxies (non-ELGs); 10 have AGN-like emission (AGNs), and 74 of themare star-forming galaxies (SFGs). Emission line fluxes and equivalentwidths, continuum fluxes, the 4000 Å Balmer break index andequivalent widths of absorption lines are measured from the spectra. Weinvestigate the emission line trends in the integrated spectra of thestar-forming galaxies in our sample, and find that: 1) The equivalentwidths of emission lines are correlated with the galaxy absolute bluemagnitude MB; lower luminosity systems tend to have largerequivalent widths. 2) The equivalent width ratio [N II]6583/Hα isanti-correlated with equivalent width Hα; a relationship is giventhat can be used to remove the [N II] contribution from blendedHα+ [N II]6548, 6583. 3) The [O II], Hβ , Hγ andHα fluxes are correlated; those can be used as star formationtracers in the blue. 4) The metallicity indices show trends with galaxyabsolute magnitude and attenuation by dust, faint, low-mass BCGs havelower metallicity and color excess. Tables 1-4, and 6 are only availablein electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/396/503
| Spectroscopic study of blue compact galaxies. I. The spectra
Blue compact galaxies are compact objects that are dominated by intensestar formation. Most of them have dramatically different propertiescompared to the Milky Way and many other nearby galaxies. Using theIRAS, H I data, and optical spectra, we wanted to measure the currentstar formation rates, stellar components, metallicities, and starformation histories and evolution of a large blue compact galaxy sample.We anticipate that our study will be useful as a benchmark for studiesof emission line galaxies at high redshift. In the first paper of thisseries, we describe the selection, spectroscopic observation, datareduction and calibration, and spectrophotometric accuracy of a sampleof 97 luminous blue compact galaxies. We present a spectrophotometricatlas of rest-frame spectra, as well as tables of the recessionvelocities and the signal-to-noise ratios. The recession velocities ofthese galaxies are measured with an accuracy of delta V< 67 kms-1. The average signal-to-noise ratio of sample spectra is ~51. The spectral line strengths, equivalent widths and continuum fluxesare also measured for the same galaxies and will be analyzed in the nextpaper of this series. The atlas and tables of measurements will be madeavailable electronically. Table 3 and Fig. 4 are only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/389/845
| 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.
| Where is the neutral atomic gas in Hickson groups?
We have analyzed the total HI contents of 72 Hickson compact groups ofgalaxies (HCGs) and the detailed spatial distributions and kinematics ofHI within a subset of 16 groups using the high angular resolutionobservations obtained with the VLA in order to investigate a possibleevolutionary scenario for these densest systems in the present daygalaxy hierarchy. For the more homogeneous subsample of 48 groups, wefound a mean HI deficiency of Def_HI = 0.40 +/- 0.07, which correspondsto 40% of the expected HI for the optical luminosities and morphologicaltypes of the member galaxies. The individual galaxies show largerdegrees of deficiency than the groups globally, Def_HI = 0.62 +/- 0.09(24% of the expected HI), due in most cases to efficient gas strippingfrom individual galaxies into the group environment visible in the VLAmaps. The degree of deficiency is found to be similar to the centralgalaxies of Virgo and Coma cluster, and Coma I group, in spite of thesignificantly different characteristics (number of galaxies, velocitydispersion) of these environments. It does not seem plausible that asignificant amount of extended HI has been missed by the observations.Hence phase transformation of the atomic gas should explain the HIdeficiency. The groups richer in early type galaxies or more compactwith larger velocity dispersions show a weak tendency to be more HIdeficient. The detection rate of HCGs at X-ray wavelengths is larger forHI deficient groups, although the hot gas distribution and hence itsorigin is only known for a few cases. In the evolutionary scenario wepropose, the amount of detected HI would decrease further withevolution, by continuous tidal stripping and/or heating. The H_2 contentalso tends to be lower than expected for the galaxies in HI deficientgroups, this may suggest that the HI stripping by frequent tidalinteraction breaks the balance between the disruption of molecularclouds by star formation and the replenishment from the ambient HI. Thiswork is partially based on observations made with the VLA operated bythe National Radio Astronomy Observatory, a facility of the NationalScience Foundation operated under cooperative agreement by AssociatedUniversities, Inc., ALFOSC, which is owned by the Instituto deAstrofísica de Andalucía (IAA, CSIC) and operated at theNordic Optical Telescope (NOT) under agreement between IAA and the NBIfAof the Astronomical Observatory of Copenhagen, and 1.5 m telescope ofthe Observatorio de Sierra Nevada, Granada, Spain, which is operated bythe IAA (CSIC).
| A Chemical Model of the Neutral Envelope of the Planetary Nebula NGC 7027
In response to the recent molecular observations by ISO andmillimeter-wave telescopes, we have developed a spherically symmetric,steady state chemical model for the planetary nebula NGC 7027. In ourmodel, the neutral envelope consists of a geometrically thin,high-density shell of constant density and an outer stellar wind regionwith an inverse-square law density profile. The neutral envelope issubjected to ultraviolet (UV) radiation both from the central star andfrom the external interstellar field. Under an assumed visual extinctionof 4 mag for the neutral envelope, the gas in our model is halfmolecular and half atomic. Simple molecules such as CH, CH+,OH are abundantly formed at an assumed gas temperature of 800 K in thepartially molecular shell. The presence of molecular ions such asHCO+ and CO+ is well explained by photochemistryat high temperatures. The model CN/HCN ratio is almost constant at about30 throughout the wind region and is 1-10 in the dense shell, comparableto observed values in planetary nebulae. Our model suggests thatmolecules are as efficiently formed with timescales shorter than 100 yras they are photodissociated in the neutral envelope of NGC 7027 andprobably in other young planetary nebulae.
| Deep Optical Imaging of a Compact Group of Galaxies: Seyfert's Sextet
To investigate the dynamical status of Seyfert's Sextet (SS), we haveobtained a deep optical (VR+I) image of this group. Our image shows thata faint envelope, down to a surface brightnessμoptical(AB)~=27 mag arcsec-2, surrounds themember galaxies. This envelope is irregular in shape. It is likely thatthis shape is attributed either to recent-past or to ongoing galaxyinteractions in SS. If the member galaxies have experienced a number ofmutual interactions over a long timescale, the shape of the envelopeshould be rounder. Therefore, the irregularly shaped morphology suggeststhat SS is in an early phase of dynamical interaction among the membergalaxies. It is interesting to note that the soft X-ray image obtainedwith ROSAT (Pildis, Bregman, & Evrard) is significantly similar inmorphology. We discuss the possible future evolution of SS briefly.
| 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.
| On the Influence of the Environment on the Star Formation Rates of a Sample of Galaxies in Nearby Compact Groups
We present the results of a study of the star formation rates (SFRs) ofa sample of disk galaxies in nearby compact groups compared with theSFRs of a sample of field galaxies. For this purpose, Hαluminosities and equivalent widths were derived for the galaxies of oursample. A direct comparison of the equivalent widths and Hαluminosities, normalized to the B luminosities and estimated area of thegalaxies of both samples, yields the result that the median values ofthese quantities are almost identical for both samples, although thedistributions for the compact-group sample are broader around the meanvalue than was found in the field galaxy sample. This result can beexplained by assuming that although interactions between galaxies incompact groups can alter the SFRs, the median value of the normalizedSFRs is preserved, being almost indistinguishable from the correspondingvalue for field galaxies. Measuring the global L_Hα/L_B of thegroups, including early-type galaxies, we find that most of the groupsthat show the highest level of L_Hα/L_B with respect to a set ofsynthetic groups built out of field galaxies show tidal features in atleast one of their members. Finally, we have explored the relationshipbetween the ratio L_Hα/L_B and several relevant dynamicalparameters of the groups: velocity dispersion, crossing time, radius,and the mass-to-luminosity ratio, finding no clear correlation. Thissuggests that the exact dynamical state of a group does not control theSFR of the group as a whole. Our results are compatible with a scenariofor compact groups of galaxies in which the dark matter of the group isarranged in a common halo, therefore preventing a fast collapse of thegalaxies.
| Kinematics of early-type galaxies in compact groups. HCG 67, HCG 74, and HCG 79
We present measurements of stellar kinematics for seven early-typegalaxies in HCG 67, HCG 74, and HCG 79. These data are aimed at studyingthe relation between the environment and the dynamics, structure andstellar content of early-type galaxies. In the present three groups, thekinematic features we observed cannot be associated unambiguously tophysical interactions. Visible morphological peculiarities do not appearcorrelated with kinematical perturbations. Table \ref{Tab3} and Table 4are available from the CDS, Strasbourg, via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html Based in part on observationsobtained at the Observatoire de Haute-Provence.
| 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
| Atlas of H alpha Emission of a Sample of Nearby Hickson Compact Groups of Galaxies
H alpha and adjacent continuum images are presented for a sample ofnearby groups of galaxies extracted from the Atlas of Compact Groups ofGalaxies. Also, more detailed H alpha maps of the most remarkablegalaxies are shown in this paper. A short description of the H alphaemission for each of the galaxies with accordant redshift is presentedtogether with a morphological classification of the accordant galaxiesin the sample. A large fraction of ellipticals and lenticulars weredetected in H alpha . Also, clear signs of interactions were found inseven of the groups, but in only in three of them was H alpha emissiondetected along the tidal features. Candidates of dwarf galaxies werefound at the tips of the tidal tails developed during the interactionsin these three groups.
| Enhanced Hα Emission in Early-Type Galaxies Belonging to Compact Groups
The results of Hα photometry of a sample of early-type galaxiesbelonging to nearby compact groups are presented. Over 75% of thegalaxies in the sample were detected in Hα, a result that we haveinterpreted as proof of the presence of a warm interstellar mediumwithin them. Comparing the Hα luminosities of the galaxies in oursample with those of a sample of early-type galaxies from the field, wehave found that field early-type galaxies are systematically fainter inHα than the compact group ones for a given B absolute magnitude byDeltalog(L_Hα/L_B)~0.5. We suggest that the excess in the Hαemission within the groups is due to photoionization of gas by Lymancontinuum photons emitted by massive stars. Recent massive starformation would be a consequence of the accretion by early-type galaxiesof gas from the outer envelopes of gas-rich galaxies experiencing closepassages across the group.
| 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.
| Catalogue of HI maps of galaxies. I.
A catalogue is presented of galaxies having large-scale observations inthe HI line. This catalogue collects from the literature the informationthat characterizes the observations in the 21-cm line and the way thatthese data were presented by means of maps, graphics and tables, forshowing the distribution and kinematics of the gas. It containsfurthermore a measure of the HI extension that is detected at the levelof the maximum sensitivity reached in the observations. This catalogueis intended as a guide for references on the HI maps published in theliterature from 1953 to 1995 and is the basis for the analysis of thedata presented in Paper II. The catalogue is only available inelectronic form at the CDS via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| 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.
| A multiparametric analysis of the Einstein sample of early-type galaxies. 1: Luminosity and ISM parameters
We have conducted bivariate and multivariate statistical analysis ofdata measuring the luminosity and interstellar medium of the Einsteinsample of early-type galaxies (presented by Fabbiano, Kim, &Trinchieri 1992). We find a strong nonlinear correlation betweenLB and LX, with a power-law slope of 1.8 +/- 0.1,steepening to 2.0 +/- if we do not consider the Local Group dwarfgalaxies M32 and NGC 205. Considering only galaxies with logLX less than or equal to 40.5, we instead find a slope of 1.0+/- 0.2 (with or without the Local Group dwarfs). Although E and S0galaxies have consistent slopes for their LB-LXrelationships, the mean values of the distribution functions of bothLX and LX/LB for the S0 galaxies arelower than those for the E galaxies at the 2.8 sigma and 3.5 sigmalevels, respectively. We find clear evidence for a correlation betweenLX and the X-ray color C21, defined by Kim,Fabbiano, & Trinchieri (1992b), which indicates that X-rayluminosity is correlated with the spectral shape below 1 keV in thesense that low-LX systems have relatively large contributionsfrom a soft component compared with high-LX systems. We findevidence from our analysis of the 12 micron IRAS data for our samplethat our S0 sample has excess 12 micron emission compared with the Esample, scaled by their optical luminosities. This may be due toemission from dust heated in star-forming regions in S0 disks. Thisinterpretation is reinforced by the existence of a strongL12-L100 correlation for our S0 sample that is notfound for the E galaxies, and by an analysis of optical-IR colors. Wefind steep slopes for power-law relationships between radio luminosityand optical, X-ray, and far-IR (FIR) properties. This last point arguesthat the presence of an FIR-emitting interstellar medium (ISM) inearly-type galaxies is coupled to their ability to generate nonthermalradio continuum, as previously argued by, e.g., Walsh et al. (1989). Wealso find that, for a given L100, galaxies with largerLX/LB tend to be stronger nonthermal radiosources, as originally suggested by Kim & Fabbiano (1990). We notethat, while LB is most strongly correlated withL6, the total radio luminosity, both LX andLX/LB are more strongly correlated with L6CO, the core radio luminosity. These points support the argument(proposed by Fabbiano, Gioia, & Trinchieri 1989) that radio cores inearly-type galaxies are fueled by the hot ISM.
| 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.
| Corrections and additions to the third reference catalogue of bright galaxies
List of corrections and additions to the Third Reference Catalogue ofBright Galaxies (RC3) are given. The corrected version of the catalogue(RC3.9b), dated April 1994, is currently available through the nationaldata centers.
| Galaxy structures in the Hercules region
216 redshifts have been obtained in a region of 981 sq deg south of theHercules supercluster. 172 of these redshifts are of galaxies withmpg less than or equal to 15.1, 110 of which had no previousvelocity measurement. 44 new redshifts are of galaxies fainter thanmpg = 15.1. With these new data we have been able to define asample in a vast region (approximately 1700 sq deg) around Herculeslimited to mpg less than or equal to 15.1 with a velocitycompleteness of 81.5%. 189 galaxies have been morphologically classifiedso that all galaxies in the sample with known velocity now also haveknown morphology. The magnitude limited sample, including 556 galaxies,is then used to identify and describe galaxy structures in the region.We find that the overdense volume is small, that its overall appearanceis that of a coral branch floating in a sea of nothing and that earlyand late type galaxies defined different structures.
| 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 wonderful world of galaxies.
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| 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.
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