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The Complex X-Ray Morphology of NGC 7618: A Major Group-Group Merger in the Local Universe?
We present results from a short Chandra ACIS-S observation of NGC 7618,the dominant central galaxy of a nearby (z=0.017309, d=74.1 Mpc) group.We detect a sharp surface brightness discontinuity 14.4 kpc north of thenucleus subtending an angle of 130° with an X-ray tail extending ~70kpc in the opposite direction. The temperature of the gas inside andoutside the discontinuity is 0.79+/-0.03 and 0.81+/-0.07 keV,respectively. There is marginal evidence for a discontinuous change inthe elemental abundance (Zinner=0.65+/-0.25,Zouter=0.17+/-0.21 at 90% confidence), suggesting that thismay be an ``abundance'' front. Fitting a two-temperature model to theASCA GIS spectrum of the NGC 7618/UGC 12491 pair shows the presence of asecond, much hotter (T=~2.3 keV) component. We consider severalscenarios for the origin of the edge and the tail, including a radiolobe/IGM interaction, nonhydrostatic ``sloshing,'' equal-mass merger andcollision, and ram pressure stripping. In the last case, we consider thepossibility that NGC 7618 is falling into UGC 12491 or that both groupsare falling into a gas-poor cluster potential. There are significantproblems with the first two models, however, and we conclude that thediscontinuity and tail are most likely the result of ram pressurestripping of the NGC 7618 group, as it falls into a larger dark matterpotential.
| Dark matter in early-type galaxies: dynamical modelling of IC 1459, IC 3370, NGC 3379 and NGC 4105
We analyse long-slit spectra of four early-type galaxies which extendfrom ~1 to 3 effective radii: IC 1459; IC 3370; NGC 3379 and NGC 4105.We have extracted the full line-of-sight velocity distribution (in thecase of NGC 3379 we also used data from the literature), which we modelusing the two-integral approach. Using two-integral modelling, we findno strong evidence for dark haloes, but the fits suggest thatthree-integral modelling is necessary. We also find that the inferredconstant mass-to-light ratio in all the four cases is typical forearly-type galaxies. Finally, we also discuss the constraints on themass-to-light ratio, which can be obtained using X-ray haloes in thecase of IC 1459, NGC 3379 and NGC 4105, and compare the estimated valueswith the predictions from the dynamical modelling.
| Multicolor Surface Photometry of Lenticular Galaxies. I. The Data
We present multicolor surface and aperture photometry in the B, V, R,and K' bands for a sample of 34 lenticular galaxies from the UppsalaGeneral Catalogue. From surface photometric analysis, we obtain radialprofiles of surface brightness, colors, ellipticity, position angle, andthe Fourier coefficients that describe the departure of isophotal shapesfrom a purely elliptical form; we find the presence of dust lanes,patches, and ringlike structure in several galaxies in the sample. Weobtain total integrated magnitudes and colors and find that these are ingood agreement with the values from the Third Reference Catalogue.Isophotal colors are correlated with each other, following the sequenceexpected for early-type galaxies. The color gradients in lenticulargalaxies are more negative than the corresponding gradients inelliptical galaxies. There is a good correlation between B-V and B-Rcolor gradients, and the mean gradients in the B-V, B-R, and V-K' colorsare -0.13+/-0.06, -0.18+/-0.06, and -0.25+/-0.11 mag dex-1 inradius, respectively.
| A sample of X-ray emitting normal galaxies from the BMW-HRI Catalogue
We obtained a sample of 143 normal galaxies with X-ray luminosity in therange 1038{-}1043 erg s-1 from thecross-correlation of the ROSAT HRI Brera Multi-scale Wavelet (BMW-HRI)Catalogue with the Lyon-Meudon Extragalactic Database (LEDA). We findthat the average X-ray properties of this sample are in good agreementwith those of other samples of galaxies in the literature. We selected acomplete flux limited serendipitous sample of 32 galaxies from which wederived the log N-log S distribution of normal galaxies in the fluxrange 1.1{-} 110 × 10-14 erg cm-2s-1. The resulting distribution is consistent with theEuclidean -1.5 slope. Comparisons with other samples, such as theExtended Medium Sensitivity Survey, the ROSAT All Sky Survey, theXMM-Newton/2dF survey, and the Chandra Deep Field Survey indicate thatthe log N -log S distribution of normal galaxies is consistent with aEuclidean slope over a flux range of about 6 decades.
| ASCA Compilation of X-Ray Properties of Hot Gas in Elliptical Galaxies and Galaxy Clusters: Two Breaks in the Temperature Dependences
Utilizing ASCA archival data of about 300 objects of ellipticalgalaxies, groups, and clusters of galaxies, we performed systematicmeasurements of the X-ray properties of hot gas in their systems, andcompiled them in this paper. The steepness of the luminosity-temperature(LT) relation, LiX ∝ (kT)α, in therange of kT 1.5 ‑ 15 keV is α = 3.17 ± 0.15,consistent with previous measurements. In the relation, we find twobreaks at around ICM temperatures of 1 keV and 4 keV: α = 2.34± 0.29 above 4 keV, 3.74 ± 0.32 in 1.5-5 keV, and 4.03± 1.07 below 1.5keV. Such two breaks are also evident in thetemperature and size relation. The steepness in the LT relation at kT> 4 keV is consistent with the scale-relation derived from the CDMmodel, indicating that the gravitational effect is dominant in richerclusters, while poorer clusters suffer non-gravity effects. The steep LTrelation below 1keV is almost attributed to X-ray faint systems ofelliptical galaxies and galaxy groups. We found that the ICM mass withinthe scaling radius R1500 follows the relation ofMgas ∝ T2.33±0.07 from X-ray faintgalaxies to rich clusters. Therefore, we speculate that even such X-rayfaint systems contain a large-scale hot gas, which is too faint todetect.
| X-ray scaling properties of early-type galaxies
We present an analysis of 39 X-ray luminous early-type galaxies observedwith the ROSAT PSPC. Using multicomponent spectral and spatial fits tothese data, we have measured halo abundance, temperature, luminosity andsurface brightness profile. We compare these measurements to similarresults from galaxy groups and clusters, fitting a number of relationscommonly used in the study of these larger objects. In particular, wefind that the σ-TX relation for our sample is similarto that reported for clusters, consistent with βspec= 1,and that the LX-TX relation has a steep slope(gradient 4.8 +/- 0.7) comparable with that found for galaxy groups.Assuming isothermality, we construct three-dimensional models of ourgalaxies, allowing us to measure gas entropy. We find no correlationbetween gas entropy and system mass, but do find a trend forlow-temperature systems to have reduced gas fractions. We conclude thatthe galaxies in our sample are likely to have developed their haloesthrough galaxy winds, influenced by their surrounding environment.
| ROSAT HRI Investigation of the NGC 507 X-Ray Halo
We present an X-ray investigation of the elliptical galaxy NGC 507 inthe Pisces cluster. We make use of archival ROSAT HRI and Chandra data,and of previously published PSPC data, to connect the large-scalestructure of the halo to the core morphology. Our analysis, based on abidimensional double beta model of the halo surface brightness, showsthat the halo core (r<2-3re) and the external halo(r>3re) are characterized by different dynamicalproperties and suggests a different origin of the two components. Thehalo core has a complex morphology with a main X-ray emission peak,coincident with the center of the optical galaxy, and several secondarypeaks. The spatial and spectral analysis of the central peak shows thatthis feature is produced by denser hot gas in the galaxy core. Whileboth homogeneous and inhomogeneous cooling flow models predict adeposited mass exceeding the observed amount, our data support thescenario in which the gas is kinetically heated by stellar mass losses.Comparison with previously published studies suggests that the core ofan X-ray extended galaxy is associated with the stellar distribution andhas properties similar to the X-ray halos of compact galaxies. Thesecondary peaks are due instead to interactions between theradio-emitting plasma and the surrounding ISM, producing densityfluctuations in the hot gas. We find that the energy input by thecentral radio source in the ISM is large enough to prevent gas coolingand may explain the failure of the cooling flow models. The total massprofile derived from the bidimensional model shows that a significantamount of dark matter is present at large radii. The dark halo extendson cluster scales and is likely associated with the whole cluster ratherthan with NGC 507. This structure is typical of many X-ray-brightearly-type galaxies and may explain the spatial and spectral differenceswith X-ray compact galaxies largely debated in the literature. Thelarge-scale surface brightness distribution is irregular and moreextended in the northeast direction. The displacement of the clusterhalo from the optical galaxy and the filamentary structures observed inthe halo core further suggest that the galaxy may be slowly movingwithin the group potential. Finally, we found that ~20% of the sourcesdetected by Kim & Fabbiano in the NGC 507 halo are due to pointsources, while the nature of the remaining population is not clear. Ifassociated with NGC 507, they could be either accreting binaries hostinga massive black hole or density clumps of the X-ray halo.
| A new catalogue of ISM content of normal galaxies
We have compiled a catalogue of the gas content for a sample of 1916galaxies, considered to be a fair representation of ``normality''. Thedefinition of a ``normal'' galaxy adopted in this work implies that wehave purposely excluded from the catalogue galaxies having distortedmorphology (such as interaction bridges, tails or lopsidedness) and/orany signature of peculiar kinematics (such as polar rings,counterrotating disks or other decoupled components). In contrast, wehave included systems hosting active galactic nuclei (AGN) in thecatalogue. This catalogue revises previous compendia on the ISM contentof galaxies published by \citet{bregman} and \citet{casoli}, andcompiles data available in the literature from several small samples ofgalaxies. Masses for warm dust, atomic and molecular gas, as well asX-ray luminosities have been converted to a uniform distance scale takenfrom the Catalogue of Principal Galaxies (PGC). We have used twodifferent normalization factors to explore the variation of the gascontent along the Hubble sequence: the blue luminosity (LB)and the square of linear diameter (D225). Ourcatalogue significantly improves the statistics of previous referencecatalogues and can be used in future studies to define a template ISMcontent for ``normal'' galaxies along the Hubble sequence. The cataloguecan be accessed on-line and is also available at the Centre desDonnées Stellaires (CDS).The catalogue is available in electronic form athttp://dipastro.pd.astro.it/galletta/ismcat and at the CDS via anonymousftp to\ cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/405/5
| Redshift-Distance Survey of Early-Type Galaxies. I. The ENEARc Cluster Sample
This paper presents data on the ENEARc subsample of the larger ENEARsurvey of nearby early-type galaxies. The ENEARc galaxies belong toclusters and were specifically chosen to be used for the construction ofa Dn-σ template. The ENEARc sample includes newmeasurements of spectroscopic and photometric parameters (redshift,velocity dispersion, line index Mg2, and the angular diameterdn), as well as data from the literature. New spectroscopicdata are given for 229 cluster early-type galaxies, and new photometryis presented for 348 objects. Repeat and overlap observations withexternal data sets are used to construct a final merged catalogconsisting of 640 early-type galaxies in 28 clusters. Objectivecriteria, based on catalogs of groups of galaxies derived from completeredshift surveys of the nearby universe, are used to assign galaxies toclusters. In a companion paper, these data are used to construct thetemplate Dn-σ distance relation for early-typegalaxies, which has been used to estimate galaxy distances and derivepeculiar velocities for the ENEAR all-sky sample. Based on observationsat Complejo Astronomico El Leoncito, operated under agreement betweenthe Consejo Nacional de Investigaciones Científicas de laRepública Argentina and the National Universities of La Plata,Córdoba, and San Juan; Cerro Tololo Inter-American Observatory,National Optical Astronomical Observatory, which is operated by theAssociation of Universities for Research in Astronomy, Inc., undercooperative agreement with the National Science Foundation; the EuropeanSouthern Observatory (ESO), partially under the ESO-ON agreement; theFred Lawrence Whipple Observatory; the Observatório do Pico dosDias, operated by the Laboratório Nacional de Astrofísicaand the MDM Observatory at Kitt Peak.
| 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.
| A new measurement of the X-ray temperature function of clusters of galaxies
We present a newly measured X-ray temperature function of galaxyclusters using a complete flux-limited sample of 61 clusters. The sampleis constructed with the total survey area of 8.14 steradians and theflux limit of 1.99x 10-11 ergs s-1 cm-2in the 0.1-2.4 keV band. X-ray temperatures and fluxes of the sampleclusters were accurately measured with ASCA and ROSAT data. The derivedtemperature function covers an unprecedentedly wide temperature range of1.4-11 keV. By fitting these data with theoretically predictedtemperature functions given by the Press-Schechter formalism togetherwith a recent formation approximation and the CDM power spectrum, weobtained tight and individual constraints on Omega_m ,0 and sigma_8 . Wealso employed the Formation-Epoch model in which the distribution in theformation epoch of clusters as well as the temperature evolution aretaken into account, showing significantly different results. Systematicscaused by the uncertainty in the mass-temperature relation are studiedand found to be as large as the statistical errors.
| 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.
| The LX-σ Relation for Galaxies and Clusters of Galaxies
We demonstrate that individual elliptical galaxies and clusters ofgalaxies form a continuous X-ray luminosity-velocity dispersion(LX-σ) relation. Our samples of 280 clusters and 57galaxies have LX~σ4.4 andLX~σ10, respectively. This unifiedLX-σ relation spans 8 orders of magnitude inLX and is fully consistent with the observed and theoreticalluminosity-temperature scaling laws. Our results support the notion thatgalaxies and clusters of galaxies are the luminous tracers of similardark matter halos.
| Metal Abundances in the Hot Interstellar Medium in Early-Type Galaxies Observed with ASCA
We have analyzed ASCA data of 27 early-type galaxies, and studied theproperties of their X-ray emitting ISM (InterStellar Medium) in detail.We found that overlapping lines and free-bound continuum cause strongcoupling in the derived abundances of various elements. The abundancedetermination is also difficult due to the uncertainties in the Fe-Latomic physics, because the Fe-L lines couple with the O and Ne K-lines.However, when the abundances of alpha -elements are fixed, all of theplasma codes give similar Fe abundances with a scattering of only20-30%. To relax the strong coupling among the elements, we included 20%systematic errors in the Fe-L region of the spectra. Then, in X-rayluminous galaxies, the derived abundance of Fe and alpha -elements bothbecame ~ 1 solar within a factor of 2. This result relaxes the previoussevere discrepancy between the ISM and stellar metallicities. The ISMmetallicity in X-ray fainter galaxies is still uncertain, but we can atleast constrain that the contribution from type-Ia SN to the ISMabundance is lower than in X-ray luminous systems. These resultsstrongly suggest that a large fraction of SN Ia products have escapedinto intergalactic space.
| The Northern ROSAT All-Sky (NORAS) Galaxy Cluster Survey. I. X-Ray Properties of Clusters Detected as Extended X-Ray Sources
In the construction of an X-ray-selected sample of galaxy clusters forcosmological studies, we have assembled a sample of 495 X-ray sourcesfound to show extended X-ray emission in the first processing of theROSAT All-Sky Survey. The sample covers the celestial region withdeclination δ>=0deg and Galactic latitude|bII|>=20deg and comprises sources with a countrate >=0.06 counts s-1 and a source extent likelihood ofL>=7. In an optical follow-up identification program we find 378(76%) of these sources to be clusters of galaxies. It was necessary toreanalyze the sources in this sample with a new X-ray sourcecharacterization technique to provide more precise values for the X-rayflux and source extent than obtained from the standard processing. Thisnew method, termed growth curve analysis (GCA), has the advantage overprevious methods in its ability to be robust, to be easy to model and tointegrate into simulations, to provide diagnostic plots for visualinspection, and to make extensive use of the X-ray data. The sourceparameters obtained assist the source identification and provide moreprecise X-ray fluxes. This reanalysis is based on data from the morerecent second processing of the ROSAT Survey. We present a catalog ofthe cluster sources with the X-ray properties obtained as well as a listof the previously flagged extended sources that are found to have anoncluster counterpart. We discuss the process of source identificationfrom the combination of optical and X-ray data. To investigate theoverall completeness of the cluster sample as a function of the X-rayflux limit, we extend the search for X-ray cluster sources to the dataof the second processing of the ROSAT Survey for the northern sky regionbetween 9h and 14h in right ascension. We includethe search for X-ray emission of known clusters as well as a newinvestigation of extended X-ray sources. In the course of this search wefind X-ray emission from 85 additional Abell clusters and 56 veryprobable cluster candidates among the newly found extended sources. Acomparison of the X-ray cluster number counts of the NORAS sample withthe ROSAT-ESO Flux-limited X-Ray (REFLEX) Cluster Survey results leadsto an estimate of the completeness of the NORAS sample of ROSAT All-SkySurvey (RASS) I extended clusters of about 50% at an X-ray flux ofFX(0.1-2.4 keV)=3×10-12 ergs s-1cm-2. The estimated completeness achieved by adding thesupplementary sample in the study area amounts to about 82% incomparison to REFLEX. The low completeness introduces an uncertainty inthe use of the sample for cosmological statistical studies that will becured with the completion of the continuing Northern ROSAT All-Sky(NORAS) Cluster Survey project. Results reported here are based onobservations made with the Multiple Mirror Telescope, a joint facilityof the Smithsonian Institution and the University of Arizona.
| Nearby Optical Galaxies: Selection of the Sample and Identification of Groups
In this paper we describe the Nearby Optical Galaxy (NOG) sample, whichis a complete, distance-limited (cz<=6000 km s-1) andmagnitude-limited (B<=14) sample of ~7000 optical galaxies. Thesample covers 2/3 (8.27 sr) of the sky (|b|>20deg) andappears to have a good completeness in redshift (97%). We select thesample on the basis of homogenized corrected total blue magnitudes inorder to minimize systematic effects in galaxy sampling. We identify thegroups in this sample by means of both the hierarchical and thepercolation ``friends-of-friends'' methods. The resulting catalogs ofloose groups appear to be similar and are among the largest catalogs ofgroups currently available. Most of the NOG galaxies (~60%) are found tobe members of galaxy pairs (~580 pairs for a total of ~15% of objects)or groups with at least three members (~500 groups for a total of ~45%of objects). About 40% of galaxies are left ungrouped (field galaxies).We illustrate the main features of the NOG galaxy distribution. Comparedto previous optical and IRAS galaxy samples, the NOG provides a densersampling of the galaxy distribution in the nearby universe. Given itslarge sky coverage, the identification of groups, and its high-densitysampling, the NOG is suited to the analysis of the galaxy density fieldof the nearby universe, especially on small scales.
| A Test for Large-Scale Systematic Errors in Maps of Galactic Reddening
Accurate maps of Galactic reddening are important for a number ofapplications, such as mapping the peculiar velocity field in the nearbyuniverse. Of particular concern are systematic errors which vary slowlyas a function of position on the sky, as these would induce spuriousbulk flow. We have compared the reddenings of Burstein & Heiles (BH)and those of Schlegel, Finkbeiner, & Davis (SFD) to independentestimates of the reddening, for Galactic latitudes |b|>10^deg. Ourprimary source of Galactic reddening estimates comes from comparing thedifference between the observed B-V colors of early-type galaxies, andthe predicted B-V color determined from the B-V-Mg_2 relation. We havefitted a dipole to the residuals in order to look for large-scalesystematic deviations. There is marginal evidence for a dipolar residualin the comparison between the SFD maps and the observed early-typegalaxy reddenings. If this is due to an error in the SFD maps, then itcan be corrected with a small (13%) multiplicative dipole term. Weargue, however, that this difference is more likely to be due to a small(0.01 mag) systematic error in the measured B-V colors of the early-typegalaxies. This interpretation is supported by a smaller, independentdata set (globular cluster and RR Lyrae stars), which yields a resultinconsistent with the early-type galaxy residual dipole. BH reddeningsare found to have no significant systematic residuals, apart from theknown problem in the region 230^deg
| X-ray luminosities for a magnitude-limited sample of early-type galaxies from the ROSAT All-Sky Survey
For a magnitude-limited optical sample (B_T <= 13.5 mag) ofearly-type galaxies, we have derived X-ray luminosities from the ROSATAll-Sky Survey. The results are 101 detections and 192 useful upperlimits in the range from 10^36 to 10^44 erg s^-1. For most of thegalaxies no X-ray data have been available until now. On the basis ofthis sample with its full sky coverage, we find no galaxy with anunusually low flux from discrete emitters. Below log (L_B) ~ 9.2L_⊗ the X-ray emission is compatible with being entirely due todiscrete sources. Above log (L_B) ~ 11.2 L_osolar no galaxy with onlydiscrete emission is found. We further confirm earlier findings that L_xis strongly correlated with L_B. Over the entire data range the slope isfound to be 2.23 (+/- 0.12). We also find a luminosity dependence ofthis correlation. Below log L_x = 40.5 erg s^-1 it is consistent with aslope of 1, as expected from discrete emission. Above this value theslope is close to 2, as expected from gaseous emission. Comparing thedistribution of X-ray luminosities with the models of Ciotti et al.leads to the conclusion that the vast majority of early-type galaxiesare in the wind or outflow phase. Some of the galaxies may have alreadyexperienced the transition to the inflow phase. They show X-rayluminosities in excess of the value predicted by cooling flow modelswith the largest plausible standard supernova rates. A possibleexplanation for these super X-ray-luminous galaxies is suggested by thesmooth transition in the L_x--L_B plane from galaxies to clusters ofgalaxies. Gas connected to the group environment might cause the X-rayoverluminosity.
| 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.
| Galaxy coordinates. II. Accurate equatorial coordinates for 17298 galaxies
Using images of the Digitized Sky Survey we measured coodinates for17298 galaxies having poorly defined coordinates. As a control, wemeasured with the same method 1522 galaxies having accurate coordinates.The comparison with our own measurements shows that the accuracy of themethod is about 6 arcsec on each axis (RA and DEC).
| Central Mg_2 indices for early-type galaxies
We present 210 new measurements of the central absorption line-strength{Mg_2} index for 87 early-type galaxies drawn from the \cite[Prugniel& Simien (1996)]{PS96} sample. 28 galaxies were not observed before.The results are compared to measurements published previously asavailable in HYPERCAT, and rescaled to the Lick system. The meanindividual internal error on these measurements is 0.009m+/-0.003m andthe mean external error is 0.012m+/-0.002m for this series ofmeasurements. Based on observations collected at the Observatoire deHaute-Provence. Tables 1, 3 and 4 are available in electronic form fromthe CDS, Strasbourg (via anonymous ftp to 130.79.128.5). Tables 1 and 3are available from CDS only.
| The ROSAT Brightest Cluster Sample - I. The compilation of the sample and the cluster log N-log S distribution
We present a 90 per cent flux-complete sample of the 201 X-ray-brightestclusters of galaxies in the northern hemisphere (delta>=0 deg), athigh Galactic latitudes (|b|>=20 deg), with measured redshiftsz<=0.3 and fluxes higher than 4.4x10^-12 erg cm^-2 s^-1 in the0.1-2.4 keV band. The sample, called the ROSAT Brightest Cluster Sample(BCS), is selected from ROSAT All-Sky Survey data and is the largestX-ray-selected cluster sample compiled to date. In addition to Abellclusters, which form the bulk of the sample, the BCS also contains theX-ray-brightest Zwicky clusters and other clusters selected from theirX-ray properties alone. Effort has been made to ensure the highestpossible completeness of the sample and the smallest possiblecontamination by non-cluster X-ray sources. X-ray fluxes are computedusing an algorithm tailored for the detection and characterization ofX-ray emission from galaxy clusters. These fluxes are accurate to betterthan 15 per cent (mean 1sigma error). We find the cumulative logN-logSdistribution of clusters to follow a power law kappa S^alpha withalpha=1.31^+0.06_-0.03 (errors are the 10th and 90th percentiles) downto fluxes of 2x10^-12 erg cm^-2 s^-1, i.e. considerably below the BCSflux limit. Although our best-fitting slope disagrees formally with thecanonical value of -1.5 for a Euclidean distribution, the BCS logN-logSdistribution is consistent with a non-evolving cluster population ifcosmological effects are taken into account. Our sample will allow us toexamine large-scale structure in the northern hemisphere, determine thespatial cluster-cluster correlation function, investigate correlationsbetween the X-ray and optical properties of the clusters, establish theX-ray luminosity function for galaxy clusters, and discuss theimplications of the results for cluster evolution.
| X-ray spectral analysis of elliptical galaxies from ASCA: the Fe abundance in a multiphase medium
We present spectral analysis of ASCA data of 17 elliptical and threelenticular galaxies most of which have high L_x/L_B. Single-temperaturemodels (mekal and Raymond-Smith) give unacceptable fits(chi^2_red>1.5 in most cases and, in agreement with previous studies,give very subsolar abundances, =0.19+/-0.12 Zsolar (mekal). Thespectra for approximately half the sample are fitted better by acooling-flow model, which in three cases gives a substantially betterfit. The abundances derived from the cooling-flow model are alsosignificantly larger, =0.6+/-0.5 Zsolar. We empirically testedthe reliability of the plasma codes in the Fe L region and found noevidence for serious problems with the determined temperatures andabundances. Two-temperature models give substantially better fits thatare formally acceptable (chi^2_red~1.0) in all but a few cases. Thehighest signal-to-noise ratio galaxies (which also have highest L_x/L_B)have fitted temperatures <2 keV for both components consistent witheach being distinct phases of hot gas. The lowest signal-to-noise ratiogalaxies (which also have lowest L_x/L_B) generally have a hot componentwith temperature, T_H>~5 keV, which is consistent with emission fromdiscrete sources. (We discuss the origin of these two components fromanalysis of L_x-L_B and L_x/L_B.) The abundances of thesetwo-temperature models are approximately solar, =0.9+/-0.7Zsolar (mekal), consistent with a recent multiphase model for theevolution of hot gas in ellipticals. Finally, for several galaxies wefind evidence for absorption in excess of the Galactic value and discussits implications.
| Old Stellar Populations. VI. Absorption-Line Spectra of Galaxy Nuclei and Globular Clusters
We present absorption-line strengths on the Lick/IDS line-strengthsystem of 381 galaxies and 38 globular clusters in the 4000-6400Angstroms region. All galaxies were observed at Lick Observatory between1972 and 1984 with the Cassegrain Image Dissector Scanner spectrograph,which makes this study one of the largest homogeneous collections ofgalaxy spectral line data to date. We also present a catalog of nuclearvelocity dispersions used to correct the absorption-line strengths ontothe stellar Lick/IDS system. Extensive discussion of both random andsystematic errors of the Lick/IDS system is provided. Indices are seento fall into three families: alpha -element-like indices (including CN,Mg, Na D, and TiO2) that correlate positively with velocity dispersion;Fe-like indices (including Ca, the G band, TiO1, and all Fe indices)that correlate only weakly with velocity dispersion and the alphaindices; and H beta that anticorrelates with both velocity dispersionand the alpha indices. C24668 seems to be intermediate between the alphaand Fe groups. These groupings probably represent different elementabundance families with different nucleosynthesis histories.
| The Universality of the Fundamental Plane of E and S0 Galaxies: Spectroscopic Data
We present central velocity dispersion measurements for 325 early-typegalaxies in eight clusters and groups of galaxies, including newobservations for 212 galaxies. The clusters and groups are the A262,A1367, Coma (A1656), A2634, Cancer, and Pegasus Clusters and the NGC 383and NGC 507 Groups. The new measurements were derived frommedium-dispersion spectra that cover 600 Å centered on the Mg I btriplet at lambda ~ 5175 Å. Velocity dispersions were measuredusing the Tonry & Davis cross-correlation method, with a typicalaccuracy of 6%. A detailed comparison with other data sources is made.
| The Universality of the Fundamental Plane of E and S0 Galaxies: Sample Definition and I-Band Photometric Data
As part of a project to compare the fundamental plane and Tully-Fisherdistance scales, we present here I-band CCD photometry for 636early-type galaxies in eight clusters and groups of galaxies. These arethe A262, A1367, Coma (A1656), A2634, Cancer and Pegasus Clusters, andthe NGC 383 and NGC 507 Groups. Sample selection, cluster properties,and cluster membership assignment criteria are discussed. We presentphotometric parameters that are used in the fundamental plane relation,the effective radius r_e, and the effective surface brightness mu_e, asderived from a r^1/4 fit to the observed radial photometric profile ofeach galaxy. A comparison with similar data found in the literature forthe Coma Cluster shows that large systematic uncertainties can beintroduced in the measurement of r_e and mu_e by the particular methodused to derive those parameters. However, the particular combination ofthese two parameters that enters in the fundamental plane relation is aquantity that can be measured with high accuracy.
| Environments of Redshift Survey Compact Groups of Galaxies
Redshift survey compact groups (RSCGs) are tight knots of N >= 3galaxies selected from the CfA2+SSRS2 redshift survey. The selection isbased on physical extent and association in redshift space alone. Wemeasured 300 new redshifts of fainter galaxies within 1 h^-1 Mpc of 14RSCGs to explore the relationship between RSCGs and their environments.Thirteen of 14 RSCGs are embedded in overdense regions of redshiftspace. The systems range from a loose group of five members to an Abellcluster. The remaining group, RSCG 64, appears isolated. RSCGs areisolated and distinct from their surroundings to varying degrees, as arethe Hickson compact groups. Among the 13 embedded RSCGs, three aredistinct from their general environments (RSCG 9, RSCG 11, and RSCG 85).
| ROSAT observations of X-ray-faint S0 galaxies - NGC 1380
We used the ROSAT Position Sensitive Proportional Counter (PSPC) toobtain a 13 ks exposure and the ROSAT HRI to obtain a 42.5 ks exposureof the faint S0 galaxy NGC 1380. We show that the PSPC spectrum can bemodeled as a thermal spectrum with kT 0.5 keV, which is consistent withemission from a hot interstellar medium. We do not detect any emissionfrom a hard component; the 90 percent upper limit is consistent with thetrend for the scaled-up luminosities of X-ray-emitting point sources.The radial profiles from the PSPC and HRI data support the spectralfitting, because each profile is more sharply concentrated than theoptical light (which reflects the stellar distribution), in contrast toother E/S0 galaxies. The PSPC radial profile is consistent with emissionfrom a point source, because of the larger point-spread function; theHRI profile reveals the presence of extended hot gas. We also extend theLX-LB plane, described by Matsumoto et al. in the range log L(B) between10.8 and 11.3, to log L(B) 10.5. We extend this plane separately for thehard discrete and the soft thermal components and show that the scalingrelation for the hard component continues to at least log L(B) about10.5.
| A catalogue of Mg_2 indices of galaxies and globular clusters
We present a catalogue of published absorption-line Mg_2 indices ofgalaxies and globular clusters. The catalogue is maintained up-to-datein the HYPERCAT database. The measurements are listed together with thereferences to the articles where the data were published. A codeddescription of the observations is provided. The catalogue gathers 3541measurements for 1491 objects (galaxies or globular clusters) from 55datasets. Compiled raw data for 1060 galaxies are zero-point correctedand transformed to a homogeneous system. Tables 1, 3, and 4 areavailable in electronic form only at the CDS, Strasbourg, via anonymousftp 130.79.128.5. Table 2 is available both in text and electronic form.
| 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.
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