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The Two-dimensional XMM-Newton Group Survey: z < 0.012 Groups
We present the results of the two-dimensional XMM-Newton Group Survey(2dXGS), an archival study of nearby galaxy groups. In this paper weconsider 11 nearby systems (z<0.012) in Mulchaey et al., which span abroad range in X-ray luminosity from 1040 to 1043ergs s-1. We measure the iron abundance and temperaturedistribution in these systems and derive pressure and entropy maps. Wefind statistically significant evidence for structure in the entropy andpressure of the gas component of seven groups on the 10%-20% level. TheXMM-Newton data for the three groups with best statistics also suggestpatchy metallicity distributions within the central 20-50 kpc of thebrightest group galaxy, probed with 2-10 kpc resolution. This providesinsights into the processes associated with thermalization of thestellar mass loss. Analysis of the global properties of the groupsreveals a subclass of X-ray-faint groups, which are characterized byboth higher entropy and lower pressure. We suggest that the mergerhistory of the central elliptical is responsible for both the source andthe observed thermodynamical properties of the hot gas of theX-ray-faint groups.
| Scaling Mass Profiles around Elliptical Galaxies Observed with Chandra and XMM-Newton
We investigated the dynamical structure of 53 elliptical galaxies usingthe Chandra archival X-ray data. In X-ray-luminous galaxies, temperatureincreases with radius and gas density is systematically higher at theoptical outskirts, indicating the presence of a significant amount ofthe group-scale hot gas. In contrast, X-ray-dim galaxies show a flat ordeclining temperature profile against radius and the gas density isrelatively lower at the optical outskirts. Thus, it is found thatX-ray-bright and faint elliptical galaxies are clearly distinguished bythe temperature and gas density profile. The mass profile is well scaledby a virial radius r200 rather than an optical half-radiusre, is quite similar at (0.001-0.03)r200 betweenX-ray-luminous and dim galaxies, and smoothly connects to those profilesof clusters of galaxies. At the inner region of(0.001-0.01)r200 or (0.1-1)re, the mass profilewell traces a stellar mass with a constant mass-to-light ratio ofM/LB=3-10 Msolar/Lsolar. TheM/LB ratio of X-ray-bright galaxies rises up steeply beyond0.01r200 and thus requires a presence of massive dark matterhalo. From the deprojection analysis combined with the XMM-Newton data,we found that X-ray-dim galaxies NGC 3923, NGC 720, and IC 1459 alsohave a high M/LB ratio of 20-30 at 20 kpc, comparable to thatof X-ray-luminous galaxies. Therefore, dark matter is indicated to becommon in elliptical galaxies; their dark matter distribution, as wellas that of galaxy clusters, almost follows the NFW profile.
| The Luminosity Function of the Fossil Group RX J1552.2+2013
We determine the first fossil group luminosity function based onspectroscopy of the member galaxies. The fossil group RX J1552.2+2013has 36 confirmed members, is at a mean redshift of 0.136, and has avelocity dispersion of 623 km s-1 (or 797 km s-1if four emission-line galaxies in the outskirts of the velocitydistribution are included). The luminosity function of RX J1552.2+2013,measured within the inner region of the system (~1/3Rvir) inthe range -23.5
| Cl 1205+44: A Fossil Group at z = 0.59
This is a report of Chandra, XMM-Newton, Hubble Space Telescope, andAstrophysical Research Consortium telescope observations of an extendedX-ray source at z=0.59. The apparent member galaxies range from spiralto elliptical, and are all relatively red (i'-Ksabout 3). We interpret this object to be a fossil group based on thedifference between the brightness of the first and second brightestcluster members in the i' band, and because the rest-framebolometric X-ray luminosity is about9.2×1043h-270 ergss-1. This makes Cl 1205+44 the highest redshift fossil groupyet reported. The system also contains a central double-lobed radiogalaxy that appears to be growing via the accretion of smaller galaxies.We discuss the formation and evolution of fossil groups in light of thehigh redshift of Cl 1205+44.
| XMM-Newton and Gemini Observations of Eight RASSCALS Galaxy Groups
We study the distribution of gas pressure and entropy in eight groups ofgalaxies belonging to the ROSAT All-Sky Survey/Center for AstrophysicsLoose Systems (RASSCALS). We use archival and proprietary XMM-Newtonobservations, supplementing the X-ray data with redshifts derived fromthe literature; we also list 127 new redshifts measured with the GeminiNorth telescope. The groups are morphologically heterogeneous in boththe optical and the X-ray, and several suffer from superpositions withbackground galaxies or clusters of galaxies. Nevertheless, they showremarkable self-similarity in their azimuthally averaged entropy andtemperature profiles. The entropy increases with radius; the behavior ofthe entropy profiles is consistent with an increasing broken power lawwith inner and outer slope 0.92+0.04-0.05 and0.42+0.05-0.04 (68% confidence), respectively.There is no evidence of a central, isentropic core, and the entropydistribution in most of the groups is flatter at large radii than in theinner region, challenging earlier reports, as well as theoretical modelspredicting large isentropic cores or asymptotic slopes of 1.1 asr-->&infy;. The pressure profiles are consistent with a self-similardecreasing broken power law in radius; the inner and outer slopes are-0.78+0.04-0.03 and-1.7+0.1-0.3, respectively. The results suggestthat the larger scatter in the entropy distribution reflects the variedgasdynamical histories of the groups; the regularity and self-similarityof the pressure profiles is a sign of a similarity in the underlyingdark matter distributions.Based on observations obtained with XMM-Newton, an ESA science missionwith instruments and contributions directly funded by ESA Member Statesand the US (NASA). The XMM-Newton project is supported by theBundesministerium für Bildung und Forschung/Deutsches Zentrumfür Luft- und Raumfahrt (BMFT/DLR), the Max-Planck Society, and theHeidenhain-Stiftung, and also by PPARC, CEA, CNES, and ASI. Also basedon observations obtained at the Gemini Observatory, which is operated bythe Association of Universities for Research in Astronomy, Inc., under acooperative agreement with the NSF on behalf of the Gemini partnership:the National Science Foundation (US), the Particle Physics and AstronomyResearch Council (UK), the National Research Council (Canada), CONICYT(Chile), the Australian Research Council (Australia), CNPq (Brazil), andCONICET (Argentina).
| An old galaxy group: Chandra X-ray observations of the nearby fossil group NGC 6482
We present the first detailed X-ray observations, using Chandra, of NGC6482 - the nearest known fossil group. The group is dominated by anoptically luminous giant elliptical galaxy and all other known groupmembers are at least two magnitudes fainter. The global X-ray properties(luminosity, temperature, extent) of NGC 6482 fall within the range ofother groups, but the detailed properties show interesting differences.We derive the gas temperature and total mass profiles for the central 30h-170 kpc (~0.1 r200) using ACISspatially resolved spectroscopy. The unusually highLX/Lopt ratio is found to result from a highcentral gas density. The temperature profile shows a continuous decreaseoutward, dropping to 0.63 of its central value at 0.1r200.The derived total mass profile is strongly centrally peaked, suggestingan early formation epoch. These results support a picture in whichfossil groups are old, giving time for the most massive galaxies to havemerged (via the effects of dynamical friction) to produce a centralgiant elliptical galaxy.Although the cooling time within 0.1r200 is less than aHubble time, no decrease in central temperature is detected. The entropyof the system lies toward the low side of the distribution seen in poorgroups and drops all the way into the centre of the system, reachingvery low values. No isentropic core, such as those predicted in simplepre-heating models, is present. Given the lack of any centraltemperature drop in the system, it seems unlikely that radiative coolingcan be invoked to explain this low central entropy. The lack of anysignature of central cooling is especially striking in a system thatappears to be old and relaxed, and to have a central cooling time<=108 yr. We find that the centrally peaked temperatureprofile is consistent with a steady-state cooling-flow solution with anaccretion rate of 2 Msolar yr-1, given the large PdV work arising from the cuspy mass profile. However, solutionsinvolving distributed or non-steady heating cannot be ruled out.
| A New Candidate for the Dark Group of Galaxies, RX J0419+0225
The bright extended X-ray source RX J0419 + 0225, first discovered inthe ROSAT All Sky Survey and identified with an S0 galaxy NGC 1550, wasobserved with ASCA for 48ks in 1999 August. The detected diffuse X-rayemission is centered at NGC 1550, whose redshift is 0.0123, extendingout to at least 15', or 210h-175 kpc, whereh75 is the Hubble constant in units of 75 km s-1Mpc-1. The X-ray surface brightness is represented by aβ model with β = 0.47 and a core radius of 15 ± 1h -175 kpc. The temperature and 1-10keV X-rayluminosity (up to 15') of this system were measured as being 1.4keV and4.7 × 1042 h-275 ergs-1, respectively. There is no strong evidence of atemperature gradient. Within a radius of 210h-175, the estimated total mass of the systembecomes 1.5 × 1013 h-175Msolar, which is typical of a galaxy group. With the opticalinformation currently available, there are only two other faintgalaxies. Including their B-band luminosity, the mass-to-light ratio ofthe system comes to 400 h75MsolarLsolar, which is comparable to those ofgalaxy clusters. Therefore, RX J0419 + 0225 can be regarded as a ``darkgroup candidate'' in that it has an unusually high mass-to-light ratiofor its optical luminosity. This object is one of the nearest amongthose ever identified as such candidates.
| Chandra Observations of the NGC 1550 Galaxy Group: Implication for the Temperature and Entropy Profiles of 1 keV Galaxy Groups
We present a detailed Chandra study of the galaxy group NGC 1550. Forits temperature (1.37+/-0.01 keV) and velocity dispersion (~300 kms-1), the NGC 1550 group is one of the most luminous knowngalaxy groups (Lbol=1.65×1043 ergss-1 within 200 kpc, or 0.2rvir). We find thatwithin ~60 kpc, where the gas cooling time is less than a Hubble time,the gas temperature decreases continuously toward the center, implyingthe existence of a cooling core. The temperature also declines beyond~100 kpc (or 0.1rvir). The temperature profile of NGC 1550 isremarkably similar to those of two other 1 keV groups with accuratetemperature determination. The temperature begins to decline at0.07rvir-0.1rvir, while in hot clusters thedecline begins at or beyond 0.2rvir. Thus, there are at leastsome 1 keV groups that have temperature profiles significantly differentfrom those of hot clusters, which may reflect the role ofnongravitational processes in intracluster medium/intergalactic mediumevolution. NGC 1550 has no isentropic core in its entropy profile, incontrast to the predictions of ``entropy floor'' simulations. We comparethe scaled entropy profiles of three 1 keV groups (including NGC 1550)and three 2-3 keV groups. The scaled entropy profiles of 1 keV groupsshow much larger scatter than those of hotter systems, which impliesvaried preheating levels. We also discuss the mass content of the NGC1550 group and the abundance profile of heavy elements.
| Redshift-Distance Survey of Early-Type Galaxies: Spectroscopic Data
We present central velocity dispersions and Mg2 line indicesfor an all-sky sample of ~1178 elliptical and S0 galaxies, of which 984had no previous measures. This sample contains the largest set ofhomogeneous spectroscopic data for a uniform sample of ellipticalgalaxies in the nearby universe. These galaxies were observed as part ofthe ENEAR project, designed to study the peculiar motions and internalproperties of the local early-type galaxies. Using 523 repeatedobservations of 317 galaxies obtained during different runs, the dataare brought to a common zero point. These multiple observations, takenduring the many runs and different instrumental setups employed for thisproject, are used to derive statistical corrections to the data and arefound to be relatively small, typically <~5% of the velocitydispersion and 0.01 mag in the Mg2 line strength. Typicalerrors are about 8% in velocity dispersion and 0.01 mag inMg2, in good agreement with values published elsewhere.
| Star Formation Histories of Early-Type Galaxies. I. Higher Order Balmer Lines as Age Indicators
We have obtained blue integrated spectra of 175 nearby early-typegalaxies, covering a wide range in galaxy velocity dispersion andemphasizing those with σ<100 km s-1. Galaxies havebeen observed both in the Virgo Cluster and in lower densityenvironments. The main goals are the evaluation of higher order Balmerlines as age indicators and differences in stellar populations as afunction of mass, environment, and morphology. In this first paper, ouremphasis is on presenting the methods used to characterize the behaviorof the Balmer lines through evolutionary population synthesis models.Lower σ galaxies exhibit a substantially greater intrinsicscatter, in a variety of line-strength indicators, than do higherσ galaxies, with the large intrinsic scatter setting in below aσ of 100 km s-1. Moreover, a greater contrast inscatter is present in the Balmer lines than in the lines of metalfeatures. Evolutionary synthesis modeling of the observed spectralindexes indicates that the strong Balmer lines found primarily among thelow-σ galaxies are caused by young age, rather than by lowmetallicity. Thus we find a trend between the population age and thecentral velocity dispersion, such that low-σ galaxies have youngerluminosity-weighted mean ages. We have repeated this analysis usingseveral different Balmer lines and find consistent results from onespectral indicator to another.
| Redshift-Distance Survey of Early-Type Galaxies: Circular-Aperture Photometry
We present R-band CCD photometry for 1332 early-type galaxies, observedas part of the ENEAR survey of peculiar motions using early-typegalaxies in the nearby universe. Circular apertures are used to tracethe surface brightness profiles, which are then fitted by atwo-component bulge-disk model. From the fits, we obtain the structuralparameters required to estimate galaxy distances using theDn-σ and fundamental plane relations. We find thatabout 12% of the galaxies are well represented by a pure r1/4law, while 87% are best fitted by a two-component model. There are 356repeated observations of 257 galaxies obtained during different runsthat are used to derive statistical corrections and bring the data to acommon system. We also use these repeated observations to estimate ourinternal errors. The accuracy of our measurements are tested by thecomparison of 354 galaxies in common with other authors. Typical errorsin our measurements are 0.011 dex for logDn, 0.064 dex forlogre, 0.086 mag arcsec-2 for<μe>, and 0.09 for mRC,comparable to those estimated by other authors. The photometric datareported here represent one of the largest high-quality and uniformall-sky samples currently available for early-type galaxies in thenearby universe, especially suitable for peculiar motion studies.Based on observations at Cerro Tololo Inter-American Observatory (CTIO),National Optical Astronomy Observatory, which is operated by theAssociation of Universities for Research in Astronomy, Inc., undercooperative agreement with the National Science Foundation (NSF);European Southern Observatory (ESO); Fred Lawrence Whipple Observatory(FLWO); and the MDM Observatory on Kitt Peak.
| 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
| The Baryon Mass Distribution for Nearby Galaxy Clusters
Not Available
| 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 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.
| The ROSAT Bright Survey: II. Catalogue of all high-galactic latitude RASS sources with PSPC countrate CR > 0.2 s-1
We present a summary of an identification program of the more than 2000X-ray sources detected during the ROSAT All-Sky Survey (Voges et al.1999) at high galactic latitude, |b| > 30degr , with countrate above0.2 s-1. This program, termed the ROSAT Bright Survey RBS, isto more than 99.5% complete. A sub-sample of 931 sources with countrateabove 0.2 s-1 in the hard spectral band between 0.5 and 2.0keV is to 100% identified. The total survey area comprises 20391deg2 at a flux limit of 2.4 x 10-12 ergcm-2 s-1 in the 0.5 - 2.0 keV band. About 1500sources of the complete sample could be identified by correlating theRBS with SIMBAD and the NED. The remaining ~ 500 sources were identifiedby low-resolution optical spectroscopy and CCD imaging utilizingtelescopes at La Silla, Calar Alto, Zelenchukskaya and Mauna Kea. Apartfrom completely untouched sources, catalogued clusters and galaxieswithout published redshift as well as catalogued galaxies with unusualhigh X-ray luminosity were included in the spectroscopic identificationprogram. Details of the observations with an on-line presentation of thefinding charts and the optical spectra will be published separately.Here we summarize our identifications in a table which contains opticaland X-ray information for each source. As a result we present the mostmassive complete sample of X-ray selected AGNs with a total of 669members and a well populated X-ray selected sample of 302 clusters ofgalaxies with redshifts up to 0.70. Three fields studied by us remainwithout optical counterpart (RBS0378, RBS1223, RBS1556). While the firstis a possible X-ray transient, the two latter are isolated neutron starcandidates (Motch et al. 1999, Schwope et al. 1999).
| Kinematical data on early-type galaxies. V.
We present kinematical data for a sample of 26 galaxies. Rotation curvesand velocity-dispersion profiles are determined for all objects. This isour fifth paper in a series devoted to the presentation of data onelliptical and S0 galaxies, derived from long-slit absorptionspectroscopy; the series now gathers 119 galaxies with homogeneous data.Based on observations collected at the Observatoire de Haute-Provence.Tables 2 and 3 are presented in electronic form only; Tables 1 through 3are available from the CDS, Strasbourg, via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| A new local temperature distribution function for X-ray clusters: cosmological applications
We present a new determination of the local temperature function ofX-ray clusters using a sample of X-ray clusters with fluxes above 2.210-11erg/s/cm2 in the [0.1-2.4] keV band, most ofthese clusters come from the Abell XBAC's sample to which a handful ofknown non-Abell clusters has been added. We estimate this sample to be85% complete, and should therefore provide a useful estimation of thepresent-day number density of clusters. Comprising fifty clusters forwhich the temperature information is available, it is the largestcomplete sample of this kind. It is therefore expected to significantlyimprove the estimation of the temperature distribution function ofclusters. We find that the resulting temperature function is higher thanprevious estimations, but it agrees with the temperature distributionfunction inferred from the BCS and RASS luminosity function (Ebeling etal. 1997; De Grandi et al. 1999a). We have used this sample to constrainthe amplitude of the matter fluctuations sigma_c on cluster's scale of8sqrt [3]{Omega_0 }-1h-1Mpc, assuming amass-temperature relation based on recent numerical simulations. We findsigma_c ~ 0.6+/- 0.02 for an Omega_0 = 1 model (for which sigma_c =sigma_8 ). Our sample provides a useful reference at z ~ 0 to use in theapplication of the cosmological test based on the evolution of X-rayclusters abundance (Oukbir & Blanchard 1992, 1997). We havetherefore estimated the temperature distribution function at z = 0.33using Henry's sample of high-z X-ray clusters (Henry 1997; hereafterH97) and performed a preliminary estimate of Omega_0 . We find that theabundance of clusters at z = 0.33 is significantly smaller, by a factorlarger than 2, which shows that the EMSS sample provides strong evidencefor evolution of the cluster abundance. A likelihood analysis leads to arather high value of the mean density parameter of the universe: Omega_0= 0.92+0.255-0.215 (1 sigma ) for open universesand Omega_0 = 0.865+0.35-0.245 for flat universes,which is consistent with a previous independent estimation based on thefull EMSS sample by Sadat et al. (1998). Some systematic uncertaintieswhich could alter this result are briefly discussed.
| 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.
| A Flux-limited Sample of Bright Clusters of Galaxies from the Southern Part of the ROSAT All-Sky Survey: The Catalog and LOG N-LOG S
We describe the selection of an X-ray flux-limited sample of brightclusters of galaxies in the southern hemisphere, based on the firstanalysis of the ROSAT All-Sky Survey data (RASS1). The sample isconstructed starting from an identification of candidate clusters inRASS1, after which their X-ray fluxes are remeasured using thesteepness-ratio technique. This method is better suited than the RASS1standard algorithm to measuring flux from extended sources. The finalsample is count-rate-limited in the ROSAT hard band (0.5-2.0 keV), sothat as a result of the distribution of N_H, its effective flux limitvaries between ~3 and 4x10^-12 ergs cm^-2 s^-1 over the selected area.This covers the delta<2.5d part of the south Galactic cap region(b<-20^deg), excluding patches of low RASS1 exposure time and of theMagellanic Clouds area, for a total of 8235 deg^2. One hundred andthirty candidate sources fulfill our selection criteria for bona fideclusters of galaxies in this area. Of these, 101 are Abell/ACO clusters,while 29 do not have a counterpart in these catalogs. Of these clusters,126 (97%) have a redshift, and for these we compute an X-ray luminosity.20% of the cluster redshifts come from new observations, as part of theESO Key Program survey of RASS clusters that is currently undercompletion. Considering the intrinsic biases and incompletenessesintroduced by the flux selection and source identification processes, weestimate the overall completeness to be better than 90%. The observednumber count distribution, log N-log S, is well fitted by a power lawwith slope alpha=1.34+/-0.15 and normalization A=11.87+/-1.04 sr^-1(10^-11 ergs cm^-2 s^-1)^alpha, in good agreement with othermeasurements.
| Fundamental plane distances to early-type field galaxies in the South Equatorial Strip. I. The spectroscopic data
Radial velocities and central velocity dispersions are derived for 238E/S0 galaxies from medium-resolution spectroscopy. New spectroscopicdata have been obtained as part of a study of the Fundamental Planedistances and peculiar motions of early-type galaxies in three selecteddirections of the South Equatorial Strip, undertaken in order toinvestigate the reality of large-scale streaming motion; results of thisstudy have been reported in Müller et al. (1998). The new APM SouthEquatorial Strip Catalog (-17fdg 5 < delta < +2fdg 5) was used toselect the sample of field galaxies in three directions: (1) 15h10 -16h10; (2) 20h30 - 21h50; (3) 00h10 - 01h30. The spectra obtained have amedian S/N per Å of 23, an instrumental resolution (FWHM) of ~ 4Å, and the spectrograph resolution (dispersion) is ~ 100 kms-1. The Fourier cross-correlation method was used to derivethe radial velocities and velocity dispersions. The velocity dispersionshave been corrected for the size of the aperture and for the galaxyeffective radius. Comparisons of the derived radial velocities with datafrom the literature show that our values are accurate to 40 kms-1. A comparison with results from Jo rgensen et al. (1995)shows that the derived central velocity dispersion have an rms scatterof 0.036 in log sigma . There is no offset relative to the velocitydispersions of Davies et al. (1987).
| 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.
| 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.
| Large-Scale Structure at Low Galactic Latitude
We have extended the CfA Redshift Survey to low galactic latitudes toinvestigate the relation between the Great Wall in the North GalacticCap and the Perseus-Pisces chain in the South Galactic Cap. We presentredshifts for 2020 galaxies in the Catalogue of Galaxies and of Clustersof Galaxies (Zwicky et al. 1961-68, CGCG) in the following regions: 4^h^<= α <= 8^h^, 17^h^ <= α <= 20^h^, 0^deg^ <=δ <= 45^deg^. In these regions, the redshift catalogue includes1664 galaxies with B(0) <= 15.5 (of which 820 are newly measured) andis 97% complete. We also include redshifts for an additional 356galaxies in these regions with B(O) > 15.5; of these, 148 werepreviously unmeasured. The CGCG samples the galaxy distribution down tob_II_ = 10^deg^. In this paper, we discuss the acquisition and reductionof the spectra, and we examine the qualitative features of the redshiftdistribution. The Great Wall and the Perseus-Pisces chain are not simplyconnected across the Zone of Avoidance. These structures, which at firstappear to be coherent on scales of ~100 h^-1^ Mpc or more, actually formthe boundaries of neighboring voids of considerably smaller scale,approximately 50h^-1^ Mpc. The structures delineated by ouroptically-selected sample are qualitatively similar to those detected bythe far-infrared-selected IRAS 1.2 Jansky Survey (Fisher et al. 1995).Although the IRAS survey probes more deeply into the Zone of Avoidance,our optically-selected survey provides better sampling of structures atb_II_ >= 10^deg^.
| An image database. II. Catalogue between δ=-30deg and δ=70deg.
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
| Integrated photoelectric magnitudes and color indices of bright galaxies in the Johnson UBV system
The photoelectric total magnitudes and color indices published in theThird Reference Catalogue of Bright Galaxies (RC3) are based on ananalysis of approximately equals 26,000 B, 25,000 B-V, and 17,000 U-Bmultiaperture measurements available up to mid 1987 from nearly 350sources. This paper provides the full details of the analysis andestimates of internal and external errors in the parameters. Thederivation of the parameters is based on techniques described by theVaucouleurs & Corwin (1977) whereby photoelectric multiaperture dataare fitted by mean Hubble-type-dependent curves which describe theintegral of the B-band flux and the typical B-V and U-B integrated colorgradients. A sophisticated analysis of the residuals of thesemeasurements from the curves was made to allow for the random andsystematic errors that effect such data. The result is a homogeneous setof total magnitudes BTA total colors(B-V)T and (U-B)T, and effective colors(B-V)e and (U-B)e for more than 3000 brightgalaxies in RC3.
| General study of group membership. II - Determination of nearby groups
We present a whole sky catalog of nearby groups of galaxies taken fromthe Lyon-Meudon Extragalactic Database. From the 78,000 objects in thedatabase, we extracted a sample of 6392 galaxies, complete up to thelimiting apparent magnitude B0 = 14.0. Moreover, in order to considersolely the galaxies of the local universe, all the selected galaxieshave a known recession velocity smaller than 5500 km/s. Two methods wereused in group construction: a Huchra-Geller (1982) derived percolationmethod and a Tully (1980) derived hierarchical method. Each method gaveus one catalog. These were then compared and synthesized to obtain asingle catalog containing the most reliable groups. There are 485 groupsof a least three members in the final catalog.
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