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The ESO nearby Abell cluster survey. VIII. Morphological and spectral classification of galaxies
We determine the morphological types of 2295 galaxies from the ESONearby Abell Cluster Survey (ENACS) from CCD images obtained with theDutch telescope on La Silla. A comparison with morphological types fromthe literature for 450 of our galaxies shows that the reliability of ourclassification is quite comparable to that of other classifiers. Werecalibrate the ENACS spectral classification with the new morphologicaltypes, and find that early- and late-type galaxies can be distinguishedfrom their spectra with 83% reliability. Ellipticals and S0 galaxies canhardly be distinguished on the basis of their spectra, but late spiralscan be classified from the spectrum alone with more than 70%reliability. We derive pseudo-colors and linestrengths from the ENACSspectra for the galaxies of different morphological types. We considerthe bright (MR ≤ -20) and faint (MR > -20)subsets of the galaxies without emission lines (non-ELG) separately. Wefind a strong and significant correlation between the average color andthe average strength of the metal absorption lines. The averagemetallicity decreases and the average color gets bluer towards laterHubble type. Also, the faint galaxies in each morphological class arebluer and less metal-rich than their brighter counterparts, whichextends the well-established color-magnitude relation of early-typegalaxies to (late) spirals. In view of these very strong global trends,the colors and metallicities of faint S0 galaxies and bright earlyspirals are remarkably similar. The bright early spirals may, onaverage, have somewhat stronger Hδ absorption than the othergalaxies, which could be due to recent starformation. The galaxies withemission lines (ELG) have a bluer spectral continuum than the non-ELG,and the amount of blueing hardly depends on morphological type. Thefraction of ELG depends strongly on morphological type (varying from4±1% for ellipticals to 59±4% for late spirals), but foreach of the morphological types it varies very little with projecteddistance from the cluster center.
| K-band Properties of Galaxy Clusters and Groups: Brightest Cluster Galaxies and Intracluster Light
We investigate the near-infrared K-band properties of the brightestcluster galaxies (BCGs) in a sample of 93 X-ray galaxy clusters andgroups, using data from the Two Micron All Sky Survey. Our clustersample spans a factor of 70 in mass, making it sensitive to any clustermass-related trends. We derive the cumulative radial distribution forthe BCGs in the ensemble and find that 70% of the BCGs are centered inthe cluster to within 5% of the virial radius r200; thisquantifies earlier findings that BCG position coincides with the clustercenter as defined by the X-ray emission peak. We study the correlationsbetween the luminosity of the BCGs (Lb) and the mass and theluminosity of the host clusters, finding that BCGs in more massiveclusters are more luminous than their counterparts in less massivesystems and that the BCGs become less important in the overall clusterlight (L200) as cluster mass increases. By examining a largesample of optically selected groups, we find that these correlationshold for galactic systems less massive than our clusters(<3×1013 Msolar). From the differencesbetween luminosity functions in high- and low-mass clusters, we arguethat BCGs grow in luminosity mainly by merging with other luminousgalaxies as the host clusters grow hierarchically; the decreasing BCGluminosity fraction (Lb/L200) with cluster massindicates that the rate of luminosity growth in BCGs is slow compared tothe rate at which clusters acquire galaxy light from the field or othermerging clusters. Utilizing the observed correlation between the clusterluminosity and mass and a merger tree model for cluster formation, weestimate that the amount of intracluster light (ICL) increases withcluster mass; our calculations suggest that in 1015Msolar clusters more than 50% of total stellar mass is inICL, making the role of ICL very important in the evolution andthermodynamic history of clusters. The cluster baryon fractionaccounting for the ICL is in good agreement with the value derived fromcosmic microwave background observations. The inclusion of ICL reducesthe discrepancy between the observed cluster cold baryon fraction andthat found in hydrodynamical simulations. Based on the observed ironabundance in the intracluster medium, we find that the ICL predicted byour model, together with the observed galaxy light, match the ironmass-to-light ratio expected from simple stellar population models,provided that the Salpeter initial mass function is adopted. The ICLalso makes it easier to produce the ``iron excess'' found in the centralregions of cool-core clusters.
| A Moving Cold Front in the Intergalactic Medium of A3667
We present results from a Chandra observation of the central region ofthe galaxy cluster A3667 with emphasis on the prominent sharp X-raybrightness edge spanning 0.5 Mpc near the cluster core. Our temperaturemap shows large-scale nonuniformities characteristic of the ongoingmerger, in agreement with earlier ASCA results. The brightness edgeturns out to be a boundary of a large cool gas cloud moving through thehot ambient gas, very similar to the ``cold fronts'' discovered byChandra in A2142. The higher quality of the A3667 data allows the directdetermination of the cloud velocity. At the leading edge of the cloud,the gas density abruptly increases by a factor of 3.9+/-0.8, while thetemperature decreases by a factor of 1.9+/-0.2 (from 7.7 to 4.1 keV).The ratio of the gas pressures inside and outside the front shows thatthe cloud moves through the ambient gas at near-sonic velocity,M=1+/-0.2 or v=1400+/-300 km s-1. In front of the cloud, we observe thecompression of the ambient gas with an amplitude expected for such avelocity. A smaller surface brightness discontinuity is observed furtherahead, ~350 kpc in front of the cloud. We suggest that it corresponds toa weak bow shock, implying that the cloud velocity may be slightlysupersonic. Given all the evidence, the cold front appears to delineatethe remnant of a cool subcluster that recently has merged with A3667.The cold front is remarkably sharp. The upper limit on its width, 3.5"or 5 kpc, is several times smaller than the Coulomb mean free path. Thisis a direct observation of suppression of the transport processes in theintergalactic medium, most likely by magnetic fields.
| The ESO Nearby Abell Cluster Survey. V. The catalogue: Contents and instructions for use
We present the catalogue resulting from the ESO Nearby Abell ClusterSurvey (the ENACS), which contains redshifts and magnitudes for 5634galaxies in the directions of 107 rich, nearby southern Abell clustercandidates. We describe the contents of the catalogue and discuss theresults of a comparison between the ENACS catalogue and the COSMOSGalaxy Catalogue. When cross-correlating the two catalogues we findthat, at least in the areas of the ENACS clusters, the completeness ofthe COSMOS catalogue is somewhat lower than was estimated previously forthe carefully analyzed and well-calibrated part of the COSMOS catalogueknown as the Edinburgh-Durham Southern Galaxy Survey (EDSGC). The galaxypositions in the COSMOS and ENACS catalogues are found to be on the samesystem to within about one arcsecond. For the clusters for which thephotometry in the ENACS and COSMOS catalogues is based on the samesurvey plates, the two magnitude scales agree very well. We confirm thatthe photometric calibration in the EDSGC subset of the COSMOS catalogueis of higher quality than in the EDSGC complement. The ENACS galaxysamples are unbiased subsets of the COSMOS catalogue as far as theprojected galaxy distribution is concerned, except in only a few cases.We summarize how the ENACS galaxy samples are subsets of the COSMOScatalogues in the ENACS apertures, with respect to magnitude. For theENACS catalogue as a whole, we describe the apparent incompleteness atfaint magnitudes and towards higher redshifts. Finally, we provide somedetailed information about the ENACS catalogue that is essential for itsproper statistical use and we summarize some facts that must beremembered when selecting subsets of galaxies from it. Based onobservations collected at the European Southern Observatory (La Silla,Chile).
| 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.
| Redshifts of 165 Abell and southern rich clusters of galaxies
We present spectroscopic observations and accurate positions for 286galaxies in clusters taken over several observing sessions, mostly withthe DuPont telescope at Las Campanas Observatory. We derive 165redshifts of rich clusters of which 130 are apparently new values.Redhsifts encompass a wide range out to z = 0.27.
| The cluster of galaxies SC2008-57 (A3667)
Results of photometric and spectroscopic observations of the cluster ofgalaxies SC2008-57 (A3667) are presented. The cluster is classified astype L because its galaxy distribution is highly flattened. It shows twostrong concentrations: a main concentration, centered on the clusterbrightest galaxy (a D galaxy) and coincident with the peak of X-rayemission, and a substructure around the second brightest galaxy (also aD galaxy). The extreme flattening of the cluster may be at leastpartially due to the presence of the substructure. The cluster alsoexhibits evidence for luminosity segregation, with the brightestgalaxies being preferentially found in high galaxy density regions. Fromthe fact that most of the luminosity segregation is produced by galaxiesassociated with the two clumps around the D galaxies, it is inferredthat dynamical friction is effective in subclusters with low velocitydispersion and may be associated with the formation of D galaxies.
| EXOSAT observations of clusters of galaxies. I - The X-ray data. II - X-ray to optical correlations
An analysis of the data for all the clusters observed by Exosat ispresented. The spectral and imaging results are given and therelationships between the X-ray properties of clusters are investigated.A significant scatter in the correlation between the X-ray luminosityand temperature, which can be interpreted as variations in the ratio ofthe gas mass to total mass among the clusters, is found. The measurediron abundances are consistent with a 'canonical' average value of 0.3solar. The large majority of clusters are found to be cooling in theircores, indicating that cooling flows are a common phenomenon. Theresults obtained for clusters are compared with the optical, infrared,and radio properties of the clusters taken from the literature. A numberof strong correlations are found. The ratios of the intracluster mediumtemperature and the cluster velocity dispersion are found to have a meanof less than one, in agreement with values obtained from the surfacebrightness distribution of the X-ray emission, thus resolving the 'Betaproblem'.
| The spatial distribution of X-ray clusters of galaxies
A reasonably complete all-sky sample of the 53 X-ray brightest clustersof galaxies is presented. A high frequency of pairs is noted, along withan exceptional concentration in the direction of the 'Great Attractor',but at a much larger distance. The dipole moment of the X-ray clustersdoes not coincide with that of the microwave background dipole. Thetwo-point correlation function of the X-ray clusters is unity on a scaleof about 2000 km/s.
| Southern Galaxy Catalogue.
Not Available
| Optical studies of southern clusters of galaxies. III - Photoelectric photometry of galaxies in 15 clusters
Multiaperture g and r photoelectric photometry is presented for 48galaxies in the clusters: A85, A119, SC0316 - 344, SC0342 - 538, Sersic40/6, SC0626 - 547, A754, A1146, Klemola 21, SC1329 - 314, SC1326 - 311,A2052, SC2008 - 569, SC2059 247, Klemola 44. The data are mainlyintended for the calibration of photographic plates and the existence ofa linear transformation to the UBV system make them useful to workersusing plates taken in the B or V bands. A compilation of publishedphotoelectric photometry on these clusters is given and a detailedcomparison between these and other observations is presented.
| Radio emission from the 2006-56 region
Attention is given to the steep-spectrum radio source 2006-56 that hasbeen mapped with the Fleurs Synthesis Telescope at 1415 MHz with aresolution of 50 arcsec. The radio source is associated with a richirregular cluster; it consists of two possible head-tail objects anddiffuse emission with a size of approximately 2 Mpc (H = 50 km/sec-Mpc).It is pointed out that detection of the new head-tail sources adds tothe unbiased sample of tailed sources needed to examine the importanceof galaxy environment.
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