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Chandra Observation of the Cluster of Galaxies MS 0839.9+2938 at z = 0.194: The Central Excess Iron and Type Ia Supernova Enrichment
We present the Chandra study of the intermediate-redshift (z=0.194)cluster of galaxies MS 0839.9+2938. By performing both projected anddeprojected spectral analyses, we find that the gas temperature isapproximately constant at about 4 keV within 130-444h-170 kpc. In the inner regions, the gastemperature decreases toward the center, reaching <~3 keV in thecentral 37 h-170 kpc. This implies that the lowerand upper limits of the mass deposit rate are 9-34 and 96-126Msolar yr-1, respectively, within 74h-170 kpc, where the gas is significantly colder.Along with the temperature drop, we detect a significant inward ironabundance increase from about 0.4 Zsolar in the outer regionsto ~=1 Zsolar within the central 37h-170 kpc. Thus, MS 0839.9+2938 is the clustershowing the most significant central iron excess at z>~0.2. We arguethat most of the excess iron should have been contributed by SNe Ia.Using the observed SN Ia rate and stellar mass loss rate, we estimatethat the time needed to enrich the central region with excess iron is6.4-7.9 Gyr, which is similar to those found for nearby clusters.Coinciding with the optical extension of the cD galaxy (up to about 30h-170 kpc), the observed X-ray surface brightnessprofile exhibits an excess beyond the distribution expected by eitherthe β model or the Navarro-Frenk-White (NFW) model and can be wellfitted with an empirical two-β model that leads to a relativelyflatter mass profile in the innermost region.
| A dichotomy in the orientation of dust and radio jets in nearby low-power radio galaxies
We examine the properties of central dust in nearby quiescent and activeearly-type galaxies. The active galaxies are low-power radio galaxieswith Fanaroff & Riley type I or I/II radio jets. We focus on (a) thecomparison of the dust distributions in the active and quiescent galaxysamples; and (b) the relation between the radio jet and dustorientations. Our main observational conclusions are: (i) in line withprevious studies, the dust detection rate is higher in radio-jetgalaxies than in non radio-jet galaxies; (ii) radio galaxies contain ahigher fraction of regular dust “ellipses” compared toquiescent galaxies which contain more often irregular dustdistributions; (iii) the morphology, size and orientation of dustellipses and lanes in quiescent early-types and active early-types withkpc-scale radio jets is very similar; (iv) dust ellipses are alignedwith the major axis of the galaxy, dust lanes do not show a preferredalignment except for large (>kpc) dust lanes which are aligned withthe minor axis of the galaxy; and (v) as projected on the sky, jets donot show a preferred orientation relative to the galaxy major axis (andhence dust ellipses), but jets are preferentially perpendicular to dustlanes. We show that the dust ellipses are consistent with being nearlycircular thin disks viewed at random viewing angles. The lanes arelikely warped dust structures, which may be in the process of settlingdown to become regular disks or are being perturbed by anon-gravitational force. We use the observed dust-jet orientations toconstrain the three-dimensional angle θDJ between jetand dust. For dust-lane galaxies, the jet is approximately perpendicularto the dust structure, while for dust-ellipse galaxies there is a muchwider distribution of θDJ. We discuss two scenariosthat could explain the dust/jet/galaxy orientation dichotomy. If lanesare indeed settling, then the jet orientation apparently is roughlyaligned with the angular momentum of the dust before it settles. Iflanes are perturbed by a jet-related force, it appears that it causesthe dust to move out of its equilibrium plane in the galaxy into a planewhich is perpendicular to the jet.
| 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.
| Chandra Observation of the Core of the Galaxy Cluster AWM 7
We present results from a Chandra observation of the core region of thenearby X-ray-bright galaxy cluster AWM 7. There are bloblikesubstructures, which are seen in the energy band 2-10 keV, within 10 kpc(20'') of the cD galaxy NGC 1129, and the brightest subpeakhas a spatial extent more than 4 kpc. We also notice that the centralsoft X-ray peak is slightly offset from the optical center by 1 kpc.These structures have no correlated features in optical, infrared, orradio bands. The energy spectrum of the hard subpeak indicates atemperature higher than 3 keV with a metallicity less than 0.3 solar, ora power-law spectrum with photon index ~1.2. A hardness ratio map and anarrow Fe K band image jointly indicate two Fe-rich blobs symmetricallylocated around the cD galaxy, with the direction perpendicular to thesubpeak direction. In larger scales (r<60 kpc), the temperaturegradually drops from 4 to 2 keV toward the cluster center, and the metalabundance rises steeply to a peak of 1.5 solar at r~7 kpc. These resultsindicate that a dynamical process is going on in the central region ofAWM 7, which probably creates heated gas blobs and drives metalinjection.
| A Comparative Study of Globular Cluster Systems in UGC 9799 and NGC 1129
We present a preliminary analysis of HST-WFPC2 observations of globularcluster systems in the two brightest galaxies, UGC 9799 (cD) and NGC1129 (non-cD), located in the center of rich clusters.
| 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.
| Kinematics of AWM and MKW Poor Clusters
We have measured 1365 redshifts to a limiting magnitude of R~15.5 in 15AWM/MKW clusters and have collected another 203 from the literature inMKW 4s, MKW 2, and MKW 2s. In AWM 7 we have extended the redshift sampleto R~18 in the cluster center. We have identified 704 cluster members in17 clusters; 201 are newly identified. We summarize the kinematics anddistributions of the cluster galaxies and provide an initial discussionof substructure, mass and luminosity segregation, spectral segregation,velocity-dispersion profiles, and the relation of the central galaxy toglobal cluster properties. We compute optical mass estimates, which wecompare with X-ray mass determinations from the literature. The clustersare in a variety of dynamical states, reflected in the three classes ofbehavior of the velocity-dispersion profile in the core: rising,falling, or flat/ambiguous. The velocity dispersion of the emission-linegalaxy population significantly exceeds that of the absorption-linegalaxies in almost all of the clusters, and the presence ofemission-line galaxies at small projected radii suggests continuinginfall of galaxies onto the clusters. The presence of a cD galaxy doesnot constrain the global cluster properties; these clusters are similarto other poor clusters that contain no cD. We use the similarity of thevelocity-dispersion profiles at small radii and the cD-like galaxies'internal velocity dispersions to argue that cD formation is a localphenomenon. Our sample establishes an empirical observational baselineof poor clusters for comparison with simulations of similar systems.Observations reported in this paper were obtained at the Multiple MirrorTelescope Observatory, a facility operated jointly by the University ofArizona and the Smithsonian Institution; at the Whipple Observatory, afacility operated jointly by the Smithsonian Astrophysical Observatoryand Harvard University; and at the WIYN Observatory, a joint facility ofthe University of Wisconsin-Madison, Indiana University, YaleUniversity, and the National Optical Astronomy Observatories.
| ASCA Temperature Maps of Three Clusters of Galaxies: Abell 1060, AWM 7, and the Centaurus Cluster
We present two-dimensional temperature maps of three bright clusters ofgalaxies (Abell 1060, AWM 7, and the Centaurus cluster), based onmulti-pointing observations with the ASCA GIS. The temperatures werederived from hardness ratios by taking into account the XRT response.For the Centaurus cluster, we subtracted the central cool componentusing the previous ASCA and ROSAT results, and the metallicity gradientsobserved in AWM 7 and the Centaurus cluster were included in derivingthe temperatures. The intracluster medium in Abell 1060 and AWM 7 isalmost isothermal from the center to the outer regions with temperaturesof 3.3 and 3.9 keV, respectively. The Centaurus cluster exhibitsremarkable hot regions within about 30' from the cluster center, showinga temperature increase of ×0.8 keV from the surrounding level of3.5keV, and the outer cool regions with lower temperatures by -1.3 keV.These results imply that a strong merger has occurred in the Centaurusin the recent 2-3Gyr, and that the central cool component has survivedit. In contrast, the gas in Abell 1060 was well-mixed in an earlyperiod, which probably has prevented the development of a central coolcomponent. In AWM 7, mixing of the gas should have occurred in a periodearlier than the epoch of metal enrichment.
| Detection Rate of Molecular Gas in Elliptical Galaxies: Constraints on Galaxy-Formation Theories
We calculated the detection rate of cold gas in elliptical galaxiesusing a semi-analytic model of galaxy formation, and compared it withobservations. We have shown that a model with a long star-formationtime-scale ( ~ 20 Gyr) is inconsistent with observations. Thus, somemechanisms of reducing the mass of interstellar medium, such as theconsumption of molecular gas by star formation and/or reheating fromsupernovae, are certainly effective in galaxies. Our model predicts thatstar formation is induced when galaxies in a halo collide with eachother and it reduces the cold gas left until the present. However, wefind that the reduction through random collisions of satellite(non-central) galaxies in the mean-free time-scale in a halo is notrequired to explain the observations. For cD galaxies, the predicteddetection rate of cold gas is consistent with observations as long asthe transformation of hot gas into cold gas is prevented in halos whosecircular velocities are larger than 500;km; s-1. Moreover, wefind that the cold gas brought into cDs through capturing gas-richgalaxies is small. We also show that the fraction of galaxies withobservable cold gas should be small for cluster ellipticals incomparison with that for field ellipticals. Our fiducial models and themodels with a large reheating efficiency can reproduce the observationswell, although a comparison with a larger and complete sample ofelliptical galaxies will constrain the physical parameters ingalaxy-formation theories more strictly.
| CO (J = 1-0) Observation of the cD Galaxy of AWM 7: Constraints on the Evaporation of Molecular Gas
We have searched for molecular gas in the cD galaxy of a poor cluster ofgalaxies, AWM 7, using the Nobeyama 45 m telescope. We did not detect COemission in the galaxy. Our limit of molecular gas in the inner 7.5 kpcis M_H_2< 4times 108 MO . We estimate the total mass ofmolecular gas left in the cD galaxy when the gas deposited by a coolingflow once becomes molecular gas and the molecular gas is continuouslyevaporated by the ambient hot gas. The observational limit of moleculargas requires f>~ 10-3, where f is the ratio of the heatconduction rate to that of Spitzer. However, this contradicts recentX-ray observations showing f<10-5. Thus, the non-detectionof CO cannot be explained by evaporation, and most of the cooled gaspredicted by a cooling flow model may not change into molecular gas inthe cD galaxy. Moreover, we estimate the evaporation time of molecularclouds brought to a cD galaxy through the capture of gas-rich galaxiesand find that these clouds should not be evaporated if f<~10-3-10-4. Therefore, the non-detection of CO in acD galaxy could constrain the total mass of the molecular clouds broughtinto it.
| Kinematics and Mass Profile of AWM 7
We have measured 492 redshifts (311 new) in the direction of the poorcluster AWM 7 and have identified 179 cluster members (73 new). We usetwo independent methods to derive a self-consistent mass profile, underthe assumptions that the absorption-line galaxies are virialized andthat they trace an underlying Navarro, Frenk, & White (NFW) dark matterprofile: (1) we fit such an NFW profile to the radial distribution ofgalaxy positions and to the velocity dispersion profile; (2) we applythe virial mass estimator to the cluster. With these assumptions, thetwo independent mass estimates agree to ~15% within 1.7 h-1Mpc, the radial extent of our data; we find an enclosed mass~(3+/-0.5)x1014 h-1 Msolar. The largestpotential source of systematic error is the inclusion of youngemission-line galaxies in the mass estimate. We investigate the behaviorof the surface term correction to the virial mass estimator underseveral assumptions about the velocity anisotropy profile, still withinthe context of the NFW model, and remark on the sensitivity of derivedmass profiles to outliers. We find that one must have data out to alarge radius in order to determine the mass robustly, and that thesurface term correction is unreliable at small radii.
| 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.
| Detailed Surface Photometry of Dwarf Elliptical and Dwarf S0 Galaxies in the Virgo Cluster
We analyze new V-band images of 14 dwarf S0 galaxies and 10 dwarfelliptical galaxies in the Virgo Cluster, in combination with R-bandimages of 70 dwarf elliptical galaxies from an earlier paper. We computethe intensity-weighted mean ellipticity, the mean deviations fromelliptical isophotes, and a newly defined parameter to measure isophotaltwists. We also fit each major-axis profile to a power lawSigma(a)~exp[-(a/a_s)^n], where n is allowed to vary. Consistent withother studies of the Virgo dwarf ellipticals, we find that the profileshapes for the entire sample is strongly peaked near n=1 (exponentialprofiles) and that no galaxies have n=1/4 (de Vaucouleurs profile). Thefaintest galaxies all have nearly exponential profiles, while thebrighter ones on average have n<1. The correlation betweenellipticity and the boxy/disky parameter is similar to that of largeelliptical galaxies, suggesting that dwarfs may also be divided into twogroups with differing internal dynamics. The Virgo dEs also show agreater degree of isophotal twisting than more luminous ellipticalgalaxies. There does not seem to be any combination of parameters fromthe surface photometry that statistically correlates with the dE/dS0designation: in particular, the dS0 galaxies do not, on average, havemore pointed (disky) isophotes than the dEs.
| A Photometric and Kinematic Study of AWM 7
We have measured redshifts and Kron-Cousins R-band magnitudes for asample of galaxies in the poor cluster AWM 7. We have measured redshiftsfor 172 galaxies; 106 of these are cluster members. We determine theluminosity function (LF) from a photometric survey of the central 1.2 x1.2 h^-1 Mpc. The LF has a bump at the bright end and a faint-end slopeof alpha = -1.37 +/- 0.16, populated almost exclusively byabsorption-line galaxies. The cluster velocity dispersion is lower inthe core (~530 km s^-1) than at the outskirts (~680 km s^-1), consistentwith the cooling flow seen in the X-ray. The cold core extends ~150 h^-1kpc from the cluster center. The Kron-Cousins R-band mass-to-light ratioof the system is 650 +/- 170 h M_ȯ/L_ȯ, substantially lower thanprevious optical determinations, but consistent with most previous X-raydeterminations. We adopt H_0 = 100 h km s^-1 Mpc^-1 throughout thispaper; at the mean cluster redshift (5247 +/- 76 km s^-1), 1 h^-1 Mpcsubtends 65.5′.
| 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.
| ASCA Observation of the Poor Cluster of Galaxies AWM 7: Evidence of an Abundance Increase in the Intra-Cluster Medium at the Center
We present the results of the ASCA central-pointing observation of thepoor cD cluster AWM 7. The Performance Verification phase data of GIS 2,GIS 3, SIS 0 chip 1, and SIS 1 chip 3 were used to study the propertiesof the intra-cluster medium (ICM) within 16' around the X-ray centroid.We found that, compared with the outer regions, the equivalent width ofthe Fe-K lines increases in the central 4' ( ~ 123 h(-1_{50) kpc)}region by a factor of ~ 1.5. Although the ICM temperature tends todecrease in the same region, the observed increase in the Fe-K lineequivalent width cannot be explained away by a possible temperaturedrop. The model fitting indicates that the abundance increases from ~0.4 solar outside 4' to ~ 0.6 solar at the center. Thus, after theCentaurus cluster and the Virgo cluster, AWM 7 is the third poor cDcluster confirmed to show an abundance increase in the central region.The 0.5--3 keV flux of the cool emission within 4' is constrained to be<8*E(42) h(-2}_{50) erg s(-1) , or <21% of the total 0.5--3 keVflux from the same spatial region. We discuss possible relations ofthese phenomena to the cD galaxy.
| Discovery of a Large-Scale Abundance Gradient in the Cluster of Galaxies AWM 7 with ASCA
A large-scale gradient in the metal abundance has been detected withASCA from an X-ray bright cluster of galaxies, AWM 7. The metalabundance shows a peak of 0.5 solar at the center and smoothly declinesto <~0.2 solar at a radius of 500 kpc. The gas temperature is foundto be constant at 3.8 keV. The radial distribution of iron can be fittedwith a beta model with beta ~ 0.8 assuming the same core radius (115kpc) as that of the intracluster medium. The metal distribution in AWM 7suggests that the gas injected from galaxies is not efficiently mixed inthe cluster space and traces the distribution of galaxies.
| The Effects of Dust on Broadband Color Gradients in Elliptical Galaxies
In order to examine the possibility that dust effects cause colorgradients in elliptical galaxies, we have constructed a set ofelliptical galaxy models spanning a wide range of dust properties,including mass, spatial distribution, and spectral properties. Thesemodels are spherically symmetric and include the effects of scattering.We have calculated the emergent broadband colors from the far-UV bandsthrough K. These results were then compared with the color propertiesfor a sample of 52 galaxies taken from the literature. In the optical,we can reproduce the magnitude, morphology, and color gradient ratios[i.e., {DELTA}U - R)/{DELTA}(B - R)] observed in many of the galaxies.The best fits are found for distributions with ρ_d_ ~ r^-1^ andτT ~ 1, which corresponds to dust masses on the order of 10^6^M_sun_ within the central 10-30 kpc. More condensed dust profiles alsoproduce strong color gradients, but only in the central regions (r <0.5 kpc). For many of the objects in this sample, the implied dustmasses are in reasonable agreement with the dust masses inferred fromIRAS observations, although a number of objects require significantlyhigher dust masses than their IRAS observations imply if their colorproperties are to be attributed solely to reddening by dust. Our modelssuggest that a simple dusty elliptical galaxy scenario can reproduce themagnitude, morphology, and ratios of observed broadband color gradientsin many ellipticals. We find that currently available color gradientmeasurements are consistent with our model results but that thesemeasurements are not precise enough in many objects to provide tightconstraints on the models. Extended dust distributions will greatlycomplicate the interpretation of all broadband data. Any broadbandanalysis hindered by age-metallicity degeneracy will also be hindered bydust effects. In effect, all broadband observations of ellipticalgalaxies may be age-metallicity-dust degenerate. We also consider theeffects of dust on several global relationships in ellipticals, such asthe color-magnitude relation and various distance indicators.
| 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.
| A Catalog of Stellar Velocity Dispersions. II. 1994 Update
A catalog of central velocity dispersion measurements is presented,current through 1993 September. The catalog includes 2474 measurementsof 1563 galaxies. A standard set of 86 galaxies is defined, consistingof galaxies with at least three reliable, concordant measurements. It issuggested that future studies observe some of these standard galaxies sothat different studies can be normalized to a consistent system. Allmeasurements are reduced to a normalized system using these standards.
| Kinematics and dynamics of the MKW/AWM poor clusters
We report 472 new redshifts for 416 galaxies in the regions of the 23poor clusters of galaxies originally identified by Morgan, Kayser, andWhite (MKW), and Albert, White, and Morgan (AWM). Eighteen of the poorclusters now have 10 or more available redshifts within 1.5/h Mpc of thecentral galaxy; 11 clusters have at least 20 available redshifts. Basedon the 21 clusters for which we have sufficient velocity information,the median velocity scale is 336 km/s, a factor of 2 smaller than foundfor rich clusters. Several of the poor clusters exhibit complex velocitydistributions due to the presence of nearby clumps of galaxies. We checkon the velocity of the dominant galaxy in each poor cluster relative tothe remaining cluster members. Significantly high relative velocities ofthe dominant galaxy are found in only 4 of 21 poor clusters, 3 of whichwe suspect are due to contamination of the parent velocity distribution.Several statistical tests indicate that the D/cD galaxies are at thekinematic centers of the parent poor cluster velocity distributions.Mass-to-light ratios for 13 of the 15 poor clusters for which we havethe required data are in the range 50 less than or = M/LB(0)less than or = 200 solar mass/solar luminosity. The complex nature ofthe regions surrounding many of the poor clusters suggests that thesegroupings may represent an early epoch of cluster formation. Forexample, the poor clusters MKW7 and MKWS are shown to be gravitationallybound and likely to merge to form a richer cluster within the nextseveral Gyrs. Eight of the nine other poor clusters for which simpletwo-body dynamical models can be carried out are consistent with beingbound to other clumps in their vicinity. Additional complex systems withmore than two gravitationally bound clumps are observed among the poorclusters.
| ROSAT observations of the galaxy group AWM 7.
We present results of ROSAT/PSPC and HRI observations of the AWM 7 groupof galaxies, which is a poor galaxy cluster and forms part of thePerseus-Pisces filament. The X-ray emission originates from intraclustergas at temperatures of 1.7 to 4.5keV. The cluster obviously iselliptical with a position angle perpendicular to the position angle ofthe dominant elliptical galaxy NGC 1129, which is offset from thecluster X-ray centre by 30kpc. The analysis of the PSPC imaging andspectral data yield a gravitational mass of2-5x10^14^Msun_within a radius of 1.2Mpc and a cooling flowwith a mass deposition rate of up to 60-66Msun_/yr.
| IRAS CPC Observations of Galaxies - Part One - Catalog and Atlas
. - We present the results of far-infrared imaging observations of 258regions of 12' x9' each centered on a selected individual galaxy, aclose pair, or a compact group of galaxies mapped at 50 and 100 micronwavelength with the CPC instrument of the IRAS satellite. The CPCinstrument has a significantly better resolution than the IRAS Surveyinstrument at these wavelengths, i.e. a round beam with a FWHM of about80" at 50 microns and 95" at 100 microns, respectively, intended to bematched to the diffraction limit of the telescope at 100 microns. Themaps were made using a new algorithm to correct for gain variations,which gives better results than the one used previously for the imagesmade available on tape in 1985. Of 262 objects observed, 167 and 188were detected at 50 and 100 microns, respectively, about 85% of thegalaxies from the same sample listed as detected by the Surveyinstrument in the IRAS Point Source Catalog. For all 55 galaxiesresolved (i.e. with a FWHM major axis diameter exceeding 1.6 times thebeam FWHM and/or extended lower-level emission) by the CPC we alsopresent the averaged maps at 50 and 100 microns. These 55 objectsinclude 35 for which there are no published maps obtained with the IRASSurvey instrument. We rescaled the flux densities of the published CPCmaps using the more accurate IRAS Survey instrument data, since theabsolute flux density calibration of the CPC is only accurate to about+/-60%. We also present images of a triplet of galaxies associated witha single Survey point source, which were resolved into separate sourcesby the CPC.
| Groups of galaxies within 80 Mpc. II - The catalogue of groups and group members
This paper gives a catalog of the groups and associations obtained bymeans of a revised hierarchical algorithm applied to a sample of 4143galaxies with diameters larger than 100 arcsec and redshifts smallerthan 6000 km/s. The 264 groups of galaxies obtained in this way (andwhich contain at least three sample galaxies) are listed, with the looseassociations surrounding them and the individual members of eachaggregate as well; moreover, the location of every entity among 13regions corresponding roughly to superclusters is specified. Finally,1729 galaxies belong to the groups, and 466 to the associations, i.e.,the total fraction of galaxies within the various aggregates amounts to53 percent.
| 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.
| CCD surface photometry of galaxies with dynamical data. II - UBR photometry of 39 elliptical galaxies
Intrinsic properties of elliptical galaxies and the mechanisms of theirformation and evolution are discussed on the basis of high-precision,multicolor, surface photometry of 39 elliptical galaxies andmeasurements of rotation curves and velocity dispersion profiles. Usingthe data collected, a number of correlations between the characteristicparameters of the stellar population of the galaxies have been made toexplore their structure and kinematics. The luminosity dependence ofcolor gradients is a good discriminant among various models of galaxyformation. The lowest luminosity galaxies in the sample do not show anycolor gradients. They have boxy isophotes, and are also rotationallyflattened. These properties may be related to the fact that they arecompanions of larger ellipsoidal systems and it could also provide animportant clue to the formation of ellipticals.
| Star formation in cooling flows in clusters of galaxies
Spectrophotometry (wavelength = 3400-5100 A) has been obtained for thenuclei of 13 cD galaxies in cooling flows. Spectral anomalies are foundin 8 of the objects, consisting of abnormally strong forbidden O IIemission or excess flux effects. Consideration is given to metallicityeffects, the relationship between UV excesses and the presence ofmassive OB stars formed from the cooling flows, and low-level effectsrelated to accretion.
| The structure of brightest cluster members. II - Mergers
Surface photometry of 342 bright elliptical galaxies in 103 clusters isanalyzed for evidence of mergers. Structural differences betweenbrightest cluster members (BCMs) and normal ellipticals can besummarized as having enlarged characteristic radii and shallow profileslopes (beta greater than -1.7). Profile morphology criteria for theelliptical types gE, D, and cD are outlined. Comparison of observationswith numerical simulations of mergers strongly suggests a past historyof dynamical growth for BCMs. Weak correlations of global clusterproperties to BCMs supports the hypothesis proposed by Merritt (1984)that mergers are important in early subgroups before virialization andformation of a cluster identity.
| Spectroscopy and photometry of elliptical galaxies. III - UBV aperture photometry, CCD photometry, and magnitude-related parameters
Photoelectric aperture photometry of nearly 2000 individual observationsof 449 elliptical galaxies combined with published measurements usingthe self-consistent UVB color catalog developed by Burstein et al.(1987) are presented. The data are placed on a standard magnitude andcolor system, and 'total' magnitudes and effective diameters are derivedby comparison with the standard elliptical magnitude growth curve. Agraphical representation of the standard growth curve and the residualsfrom it for each galaxy are given, and a new diameter measurement Dn ispresented which can be measured reliably for elliptical galaxies andserves as an accurate distance indicator when combined with centralvelocity dispersion. Individual magnitudes, surface brightnesses,effective diameters, and values of Dn are summarized for each galaxy incatalog form.
| Structure of superclusters and supercluster formation. V - Spatial correlation and voids
The galaxian spatial correlation function is calculated for variousobservational samples having different sample volume. It is demonstratedthat the correlation length increases with sample volume. For volumesconsiderably smaller than the size of the Local Supercluster thecorrelation length is about half the conventional value, 5/h Mpc, whichcorresponds to sizes of intermediate samples, containing the wholesupercluster. Samples containing several superclusters have correlationlengths twice the conventional one. Similar calculations have beencarried out for various theoretical models. Samples representingluminous matter in a neutrino-dominated universe and having differentsample volumes have correlation length which increases with volume untilthe sample size reaches the average size of voids. Further increase inthe sample size does not change the correlation length, indicating thatfair samples of the model universe have been reached. These calculationsand simple theoretical estimates indicate that the value of thecorrelation length reflects the filling factor of the sample and thepresence of large voids in galaxy distribution. The observed correlationfunction of galaxies reflects the distribution of luminous matter. Aftercorrecting for the difference between the correlation functions of truemass and galaxies, the correlation length for a fair sample of theuniverse is estimated to be 10/h Mpc.
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