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|XMM-Newton observations of three poor clusters: Similarity in dark matter and entropy profiles down to low mass|
We present an analysis of the mass and entropy profiles of three poorgalaxy clusters (A1991, A2717 and MKW9) observed with XMM-Newton. Theclusters have very similar temperatures (kT= 2.65, 2.53 and 2.58 keV),and similar redshifts (0.04 z 0.06). We trace the surfacebrightness, temperature, entropy and integrated mass profiles withexcellent precision up to 500 h70-1 kpc(A1991 and A2717) and 350 h70-1 kpc (MKW9).This corresponds to 0.5(0.35) r200, where r200 isthe radius corresponding to a density contrast of 200 with respect tothe critical density at the cluster redshifts. None of the surfacebrightness profiles is well fitted with a single β-model. Doubleisothermal β-models provide reasonable fits, and in all cases thevalue of the external β parameter is consistent with the valuefound for richer clusters. The temperature profiles have central dipsbut are approximately flat at the exterior, up to the detection limit.The integrated mass profiles are very similar in physical units and arereasonably well fitted with the NFW mass model with concentrationparameters in the range c200 =4-6 and M200 =1.2-1.6×1014 h70-1Mȯ. A King model is inconsistent with these mass data.The entropy profiles are very similar at large scale, but there is somescatter in the very central region (r 50 kpc). However, none ofthe clusters has an isentropic core. We then discuss the structural andscaling properties of cluster mass and entropy profiles, includingsimilar quality XMM-Newton data on the slightly cooler cluster A1983(kT= 2.2 keV), and on the massive cluster A1413 (kT= 6.5 keV). We findthat the mass profiles scaled in units of m200 andr200 nearly coincide, with 20 per cent dispersion in theradial range [0.05-0.5] r200, where we could compare theprofiles without excessive extrapolation. We provide a quantitative testof mass profile shapes by combining the concentration parameters ofthese poor clusters with other values of similar precision from theliterature, and comparing with the c200 - M200relation derived from numerical simulations for a ΛCDM cosmology.The data are fully consistent with the predictions, taking into accountthe measurement errors and expected intrinsic scatter, in the mass rangeM200= [1.2 ×1014-1.9 ×1015]h70-1 Mȯ. This excellent agreementwith theoretical predictions - a quasi universal cusped mass profilewith concentration parameters as expected - shows that the physics ofthe dark matter collapse is basically understood. Scaling the entropyprofiles using the self-similar relation S ∝ T, we find a typicalscatter of 30 per cent in scaled entropy in the radial range[0.05-0.5] r200. The dispersion is reduced (22 per cent)if we use the empirical relation S ∝ T0.65. The scatteris nearly constant with radius, indicating a genuine similarity inentropy profile shape. The averaged scaled profile is well fitted by apower law for 0.05
|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 Chandra X-Ray Observation of A1991: The Late Stages of Infall?|
We present results from a 38 ks Chandra X-ray observation of the z=0.059galaxy cluster A1991. The cluster has a bright X-ray core and a centraltemperature gradient that declines inward from 2.7 keV at 130 kpc to~1.6 keV at the cluster center. The radiative cooling time of the gas inthe inner 10 kpc is about 0.5 Gyr, and it rises to 1 Gyr at a radius of20 kpc. The cooling rate of the gas within the latter radius is <~25Msolar yr-1. The Chandra ACIS-S3 image shows thatthe intracluster medium has an asymmetric surface brightnessdistribution with respect to the central galaxy. Bright knots of softX-ray emission embedded in a cometary structure are locatedapproximately 10" north of the optical center of the cD galaxy. Unlikethe structures seen in other cooling flow clusters, the knots have noobvious association with the radio source. The structure's temperatureof 0.83 keV makes it nearly 1 keV cooler than its surroundings, and itsmass is 3.4×109Msolar. Based on itsbow-shaped appearance and modest overpressure with respect to itssurroundings, we interpret the structure as a cool mass concentrationthat is breaking apart as it travels northward through the center of thecluster.
|The peculiar motions of early-type galaxies in two distant regions - II. The spectroscopic data|
We present the spectroscopic data for the galaxies studied in the EFARproject, which is designed to measure the properties and peculiarmotions of early-type galaxies in two distant regions. We have obtained1319 spectra of 714 early-type galaxies over 33 observing runs on 10different telescopes. We describe the observations and data reductionsused to measure redshifts, velocity dispersions and the Mgb and Mg_2Lick linestrength indices. Detailed simulations and intercomparison ofthe large number of repeat observations lead to reliable error estimatesfor all quantities. The measurements from different observing runs arecalibrated to a common zero-point or scale before being combined,yielding a total of 706 redshifts, 676 velocity dispersions, 676 Mgblinestrengths and 582 Mg_2 linestrengths. The median estimated errors inthe combined measurements are Delta cz=20 km s^-1, Delta sigma sigma=9.1 per cent, Delta Mgb Mgb=7.2 per cent and Delta Mg_2=0.015 mag.Comparison of our measurements with published data sets shows nosystematic errors in the redshifts or velocity dispersions, and onlysmall zero-point corrections to bring our linestrengths on to thestandard Lick system. We have assigned galaxies to physical clusters byexamining the line-of-sight velocity distributions based on EFAR andZCAT redshifts, together with the projected distributions on the sky. Wederive mean redshifts and velocity dispersions for these clusters, whichwill be used in estimating distances and peculiar velocities and to testfor trends in the galaxy population with cluster mass. The spectroscopicparameters presented here for 706 galaxies combine high-quality data,uniform reduction and measurement procedures, and detailed erroranalysis. They form the largest single set of velocity dispersions andlinestrengths for early-type galaxies published to date.
|Arcsecond Positions of UGC Galaxies|
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.
|Spectral gradients in central cluster galaxies: further evidence of star formation in cooling flows|
We have obtained radial gradients in the spectral features of thelambda4000-Angstroms break (D_4000) and Mg_2 for a sample of 11 centralcluster galaxies (CCGs): eight in clusters with cooling flows and threein clusters without. After careful removal of the emission lines foundwithin the D_4000 and Mg_2 bandpasses for some objects, the new datastrongly confirm the correlations between line-strength indices and thecooling flow phenomenon found in our earlier study. We find that suchcorrelations depend on the presence and characteristics of emissionlines in the inner regions of the CCGs. The nuclear indices arecorrelated with the mass deposition rate (M^.) only when emission linesare found in the central regions of the galaxies. The central D_4000 andMg_2 indices in cooling flow galaxies without emission lines arecompletely consistent with the indices measured in CCGs in clusterswithout cooling flows. CCGs in cooling flow clusters exhibit a clearsequence in the D_4000-Mg_2 plane, with a neat segregation depending onemission-line type and blue morphology. This sequence can be modelled,using stellar population models with a normal initial mass function(IMF), by a recent (~0.1 Gyr old) burst of star formation, althoughmodel uncertainties do not allow us to completely discard continuousstar formation or a series of bursts over the last few Gyr. In CCGs withemission lines, the gradients in the spectral indices are flat orpositive inside the emission-line regions, suggesting the presence ofyoung stars. Outside the emission-line regions, and in cooling flowgalaxies without emission lines, gradients are negative and consistentwith those measured in CCGs in clusters without cooling flows and giantelliptical galaxies. Index gradients measured exclusively in theemission-line region correlate with M^.. Using the same populationmodels we have estimated the radial profiles of the mass transformedinto new stars. The derived profiles are remarkably parallel to theexpected radial behaviour of the mass deposition rate derived from X-rayobservations. Moreover, a large fraction ( probably most) of the coolingflow gas accreted into the emission-line region is converted into stars.In the light of these new data, we discuss the evolutionary sequencesuggested by McNamara, in which radio-triggered star formation burststake place several times during the lifetime of the cooling flow. Weconclude that this scenario is consistent with the availableobservations.
|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 catalogue of spatially resolved kinematics of galaxies: Bibliography|
We present a catalogue of galaxies for which spatially resolved data ontheir internal kinematics have been published; there is no a priorirestriction regarding their morphological type. The catalogue lists thereferences to the articles where the data are published, as well as acoded description of these data: observed emission or absorption lines,velocity or velocity dispersion, radial profile or 2D field, positionangle. Tables 1, 2, and 3 are proposed in electronic form only, and areavailable from the CDS, via anonymous ftp to cdsarc.u-strasbg.fr (to18.104.22.168) or via http://cdsweb.u-strasbg.fr/Abstract.html
|The peculiar motions of early-type galaxies in two distant regions. III - The photometric data|
We present R-band CCD photometry for 776 galaxies observed in the EFARproject. The photometry is compared with photoelectric data, showingthat a common zero-point good to better than 1 per cent and a precisionof 0.03 mag per zero-point have been achieved. We give the circularlyaveraged surface brightness profiles and the photometric parameters ofthe 762 program galaxies, D(n) diameters, half-luminosity radii, totalmagnitudes, and average effective surface brightnesses. More than 80percent of the profiles have a global S/N ratio larger than 300. Theextrapolation needed to derive total magnitudes is less than 10 percentfor 80 percent of the fits. More than 80 percent of the galaxies havemean effective surface brightness larger than the observed skybrightness. In 90 percent of the profiles the estimate of thecontamination of the sky by the galaxy light is less than 1 percent. Wederive total magnitudes and half-luminosity radii to better than 0.15mag and 25 percent, respectively, for 90 percent of our sample. Incontrast, external comparisons show that data in the literature can bestrongly affected by systematic errors due to large extrapolations,small radial range, sky subtraction errors, seeing effects, and the useof a simple R exp 1/4 fit. The resulting errors can easily amount tomore than 0.5 mag in the total magnitudes and 50 percent in thehalf-luminosity radii.
|The Peculiar Motions of Early-Type Galaxies in Two Distant Regions. I. Cluster and Galaxy Selection|
The EFAR project is a study of 736 candidate elliptical galaxies in 84clusters lying in two regions, toward Hercules-Corona Borealis andPerseus-Pisces-Cetus, at distances cz ~ 6000-15,000 km s^-1^. In thispaper (the first of a series), we present an introduction to the EFARproject and describe in detail the selection of the clusters andgalaxies in our sample. Fundamental data for the galaxies and clustersare given, including accurate new positions for each galaxy andredshifts for each cluster. The galaxy selection functions aredetermined by using diameters measured from Schmidt sky survey imagesfor 2185 galaxies in the cluster fields. Future papers in this serieswill present the spectroscopic and photometric observations of thissample, investigate the properties of the fundamental plane forelliptical galaxies, and determine the large- scale peculiar velocityfields in these two regions of the universe.
|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.
|Structures of small-size radio galaxies in clusters|
We present high resolution maps of a sample of radio galaxies belongingto Abell clusters, showing linear size less than or approximately 20kpc, i.e. completely embedded within the optical galaxy. These radiogalaxies were unresolved or only sligtly resolved in previousinterferometric observations. Most of the sources are resolved at thepresent resolution. Radio maps of all the resolved sources are given.The correlation of the linear size versus the total radio power at 1.4GHz is derived for radio galaxies belonging to clusters and is comparedwith the results found in a non-cluster sample. The size of clustersources is slightly smaller on average than that of non-cluster ones,but the difference is not statistically significant. The tailedstructure, typical of cluster radio galaxies of large size, found inapproximately 24% of the sources of the present sample. This percentageis higher than in a non-cluster sample, but lower than ina clustersample of radio galaxies with larger size. Tailed radio galaxies aremostly located at the cluster centers, the smallest ones beingidentified with the brightest cluster member. Stripping of the hotinterstellar medium is suggested to be present in these galaxies.
|Photoelectric and CCD photometry of E and S0 galaxies|
We present BR photoelectric photometry for 352 E and S0 galaxies thatare part of a large survey of the properties and peculiar motions ofgalaxies in distant clusters. Repeat measurements show our internalerrors to be 2-3 percent in B and R and 1-2 percent in B-R. Comparisonsof BR and BVR reductions for 10 galaxies also observed in V show smallsystematic errors due to differences between the spectral energydistributions of stars and galaxies. External comparisons with B-Vcolors in the literature confirm that these colors are good to 1percent. We also describe R-band CCD observations for 95 of the galaxiesand place these on a BR photometric system for photoelectric and CCDphotomerry, with a common zero-point good to better than 1 percent. Wefind the rms precision of both our photoelectric and CCD R magnitudes tobe 2-3 percent for galaxies as faint as R = 15.
|H I absorption toward cooling flows in clusters of galaxies|
An H I survey of 14 cooling flow clusters and two noncooling flowclusters was conducted, and H I absorption features were detectedagainst the nuclear radio continuum sources of two cooling flow dominant(CFD) galaxies, 2A 0335 + 096 and MKW3s. The absorption features arebroad and redshifted with respect to the stellar absorption-linevelocity of the CFDs by 90-225 km/s. This indicates that the H I isfalling onto, and is probably gravitationally bound to, the CFDs. Thekinematics of the H I clouds suggest a possible kinematic link betweenthe warm and cold phases of the intracluster medium. The clouds areorders of magnitude smaller in radius and mass and larger in densitythan Galactic H I clouds. The detected CFDs have mass-accretion ratesthat are about 2.5 times larger than the CFDs that were not detected.
|A 20 CM VLA survey of Abell clusters of galaxies. I - Distance class of not greater than 3 clusters|
Nearby Abell clusters of distance class of not greater than 3 arestudied based on 20-cm VLA observations, Westerbork Synthesis RadioTelescope results, and Einstein Observatory X-ray data. No significantcorrelation is found between the 20-cm radio power and X-ray luminosity,and no evidence is found that regular-type clusters are statisticallymore likely to be radio loud than irregular-type clusters. A weakcorrelation is noted between X-ray-cooling mass-accretion rates andradio powers for central dominant galaxies in cooling-flow clusters,suggesting that either cooling accretion directly fuels the centralengine and/or cooling flows strongly interact with the radio plasma.
|Narrow-angle tail radio sources and the distribution of galaxy orbits in Abell clusters|
The present data on the orientations of the tails with respect to thecluster centers of a sample of 70 narrow-angle-tail (NAT) radio sourcesin Abell clusters show the distribution of tail angles to beinconsistent with purely radial or circular orbits in all the samples,while being consistent with isotropic orbits in (1) the whole sample,(2) the sample of NATs far from the cluster center, and (3) the samplesof morphologically regular Abell clusters. Evidence for very radialorbits is found, however, in the sample of NATs near the cluster center.If these results can be generalized to all cluster galaxies, then thepresence of radial orbits near the center of Abell clusters suggeststhat violent relaxation may not have been fully effective even withinthe cores of the regular clusters.
|WSRT radio observations at 1.4 GHz of 32 Abell clusters of distance class 3 and 4|
A survey of 61 Abell clusters was carried out at 1.4 GHz with theWesterbork Synthesis Radio Telescope. In this paper radio and opticaldata on 23 clusters of distance class 3 and on 9 clusters of distanceclass 4 are presented. Only the radio sources identified with galaxieslikely to be cluster members are considered here. A finding chart foreach radio galaxy and contour maps for the interesting structures areprovided.
|A catalog of morphological types in 55 rich clusters of galaxies|
Data are presented from a study of 55 rich clusters of galaxies. Thedata include positions, morphological types, estimated total magnitudes,bulge sizes, and ellipticities for about 6000 galaxies, as determinedfrom high scale photographic plates. Data reduction procedures aredescribed, and a brief analysis of cluster richness, which indicatesthat Abell richness classes are only rough indicators of total clustermembership, is included.
|Atlas of interacting galaxies, Part. II and the concept of fragmentation of galaxies.|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977A&AS...28....1V&db_key=AST
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