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HI content in galaxies in loose groups
Gas deficiency in cluster spirals is well known and ram-pressurestripping is considered the main gas removal mechanism. In some compactgroups too gas deficiency is reported. However, gas deficiency in loosegroups is not yet well established. Lower dispersion of the membervelocities and the lower density of the intragroup medium in small loosegroups favour tidal stripping as the main gas removal process in them.Recent releases of data from the HI Parkes All-Sky Survey (HIPASS) andcatalogues of nearby loose groups with associated diffuse X-ray emissionhave allowed us to test this notion. In this paper, we address thefollowing questions: (i) do galaxies in groups with diffuse X-rayemission statistically have lower gas content compared to the ones ingroups without diffuse X-ray emission? (ii) does HI deficiency vary withthe X-ray luminosity, LX, of the loose group in a systematicway? We find that (i) galaxies in groups with diffuse X-ray emission, onaverage, are HI deficient, and have lost more gas compared to those ingroups without X-ray emission; the latter are found not to havesignificant HI deficiency; (ii) no systematic dependence of the HIdeficiency with LX is found. Ram-pressure-assisted tidalstripping and evaporation by thermal conduction are the two possiblemechanisms to account for this excess gas loss.
| On the Lack of a Soft X-Ray Excess from Clusters of Galaxies
A soft X-ray excess has been claimed to exist in and around a number ofgalaxy clusters, and this emission has been attributed to the warm-hotintergalactic medium that may constitute most of the baryons in thelocal universe. We have reexamined a study of the XMM-Newtonobservations on this topic by Kaastra and coworkers and find that theX-ray excess (or deficit) depends on Galactic latitude and appears to bemost closely related to the surface brightness of the 1/4 keV emission,which is largely due to emission from the local hot bubble and the haloof the Milky Way. We suggest that the presence of the soft X-ray excessis due to incorrect subtraction of the soft X-ray background. Ananalysis is performed for which we choose a 1/4 keV background that issimilar to the background near the cluster (and a similar H I column).We find that the soft X-ray excess largely disappears using ourbackground subtraction and conclude that these soft X-ray excesses arenot associated with the target clusters. We also show that thedetections of ``redshifted'' O VII lines claimed by Kaastra andcoworkers are correlated with solar system charge exchange emission,suggesting that they are not extragalactic either.
| 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.
| Effervescent heating: constraints from nearby cooling flow clusters observed with XMM-Newton
Aims.We have used deprojected radial density and temperature profiles ofa sample of 16 nearby CF clusters observed with XMM-Newton to testwhether the effervescent heating model can satisfactorily explain thedynamics of CF clusters.Methods.For each cluster we derived therequired extra heating as a function of cluster-centric distance forvarious values of the unknown parameters dot M (mass deposition rate)and fc (conduction efficiency). We fitted the extra heatingcurve using the AGN effervescent heating function and derived the AGNparameters L (the time-averaged luminosity) and r0 (the scaleradius where the bubbles start rising in the ICM).Results.While wedo not find any solution with the effervescent heating model for onlyone object, we do show that AGN and conduction heating are notcooperating effectively for half of the objects in our sample. For mostof the clusters we find that, when a comparison is possible, the derivedAGN scale radius r0 and the observed AGN jet extension havethe same order of magnitude. The AGN luminosities required to balanceradiative losses are substantially lowered if the fact that the AGNdeposits energy within a finite volume is taken into account. For theVirgo cluster, we find that the AGN power derived from the effervescentheating model is in good agreement with the observed jet power.
| Evidence for radio-source heating of groups
We report evidence that the gas properties of X-ray groups containingradio galaxies differ from those of radio-quiet groups. For awell-studied sample of ROSAT-observed groups, we found that more thanhalf of the elliptical-dominated groups can be considered `radio-loud',and that radio-loud groups are likely to be hotter at a given X-rayluminosity than radio-quiet groups. We tested three different models forthe origin of the effect and conclude that radio-source heating is themost likely explanation. We found several examples of groups where thereis strong evidence from Chandra or XMM-Newton images for interactionsbetween the radio source and the group gas. A variety of radio-sourceheating processes are important, including shock-heating by youngsources and gentler heating by larger sources. The heating effects canbe longer-lasting than the radio emission. We show that the sample ofX-ray groups used in our study is not significantly biased in thefraction of radio-loud groups that it contains. This allows us toconclude that the energy per particle that low-power radio galaxies caninject over the group lifetime is comparable to the requirements ofstructure formation models.
| A Fundamental Plane Relation for the X-Ray Gas in Normal Elliptical Galaxies
We report on the discovery of a new correlation between globalparameters of the hot interstellar gas in elliptical galaxies. Wereanalyze archival Chandra data for 30 normal early-type systems,removing the contributions of resolved and unresolved point sources toreveal the X-ray morphology of the hot gas. We determine the half-lightradius, RX, and the mean surface brightness, IX,from the gas surface brightness profiles. A spectral analysis determinesthe temperature, TX, of the gas within 3 optical effectiveradii. We find that the galaxies lie on an X-ray gas fundamental plane(XGFP) of the formTX~R0.28XI0.22X.This is close to, but distinct from, a simple luminosity-temperaturerelation. The intrinsic width of the XGFP is only 0.07 dex, nearlyidentical to that of the stellar (optical) fundamental plane (SFP). Thisis surprising since X-ray gas masses are typically ~10-2 ofthe stellar masses. We show that the XGFP is not a simple consequence ofthe virial theorem or hydrostatic equilibrium and that it is essentiallyindependent of the SFP. The XGFP thus represents a genuinely newconstraint on the hydrodynamical evolution of elliptical galaxies.
| Temperature and entropy profiles of nearby cooling flow clusters observed with XMM-Newton
We investigate temperature and entropy profiles of 13 nearby coolingflow clusters observed with the EPIC cameras of XMM-Newton. Whennormalized and scaled by the virial radius the temperature profiles turnout to be remarkably similar. At large radii the temperature profilesshow a clear decline starting from a break radius at ~0.1rvir. The temperature decreases by ~30 % between 0.1rvir and 0.5 rvir. As expected for systems wherenon-gravitational processes are of great importance, the scale lengthcharacterizing the central temperature drop is not found to beproportional to the virial radius of the system. The entropy of theplasma increases monotonically moving outwards almost proportional tothe radius and the central entropy level is tightly correlated with thecore radius of the X-ray emission. The dispersion in the entropyprofiles is smaller if the empirical relation S ∝ T0.65is used instead of the standard self-similar relation S ∝ T and, asexpected for cooling flow clusters, no entropy cores are observed.
| The GEMS project: X-ray analysis and statistical properties of the group sample
The Group Evolution Multiwavelength Study (GEMS) involves amultiwavelength study of a sample of 60 galaxy groups, chosen to span awide range of group properties. Substantial ROSAT Position SensitiveProportional Counter (PSPC) observations, available for all of thesegroups, are used to characterize the state of the intergalactic mediumin each. We present the results of a uniform analysis of these ROSATdata and a statistical investigation of the relationship between X-rayand optical properties across the sample. Our analysis improves inseveral respects on previous work: (i) we distinguish between systems inwhich the hot gas is a group-scale medium and those in which it appearsto be just a hot halo associated with a central galaxy; (ii) weextrapolate X-ray luminosities to a fixed overdensity radius(r500) using fitted surface brightness models, in order toavoid biases arising from the fact that cooler systems are detectable tosmaller radii, and (iii) optical properties have been rederived in auniform manner from the NASA Extragalactic Database, rather than relyingon the data in the disparate collection of group catalogues from whichour systems are drawn.The steepening of the LX-TX relation in the groupregime reported previously is not seen in our sample, which fits well onto the cluster trend, albeit with large non-statistical scatter. Anumber of biases affect the fitting of regression lines under thesecircumstances, and until the impact of these has been thoroughlyinvestigated it seems best to regard the slope of the groupLX-TX relation as being poorly determined. Asignificant problem in comparing the properties of groups and clustersis the derivation of system radii, to allow different systems to becompared within regions having the same overdensity. We find evidencethat group velocity dispersion (σv) provides a veryunreliable measure of system mass (and hence radius), with a number ofgroups having remarkably low values of σv, given thatthey appear from their X-ray properties to be collapsed systems. Weconfirm that the surface brightness profiles of groups are significantlyflatter than those of clusters - the maximum value of theβfit parameter for our sample is 0.58, lower than thetypical value of 0.67 seen in clusters - however, we find no significanttendency within our sample for cooler groups to show flatter profiles.This result is inconsistent with simple universal pre-heating models.The morphology of the galaxies in the GEMS groups is correlated to theirX-ray properties in a number of ways: we confirm the very strongrelationship between X-ray emission and a dominant early-type centralgalaxy, which has been noted since the early X-ray studies of groups,and also find that spiral fraction is correlated with the temperature ofthe hot gas and hence the depth of the gravitational potential. A classof spiral-rich groups with little or no X-ray emission probablycorresponds to groups that have not yet fully collapsed.
| Spatial distribution of galaxies in the Puppis region
We determine the spatial distribution of the galaxies located behind thepart of the zone of avoidance of the Milky Way defined by 220°
| XMM-Newton Observations of NGC 507: Supersolar Metal Abundances in the Hot Interstellar Medium
We present the results of the X-ray XMM-Newton observations of NGC 507,a dominant elliptical galaxy in a small group of galaxies, and reportsupersolar metal abundances of both Fe and α-elements in the hotinterstellar medium (ISM) of this galaxy. These results are robust inthat we considered all possible systematic effects in our analysis. Wefind ZFe=2-3 times solar inside the D25 ellipse ofNGC 507. This is the highest ZFe reported so far for the hothalo of an elliptical galaxy; this high iron abundance is fullyconsistent with the predictions of stellar evolution models, whichinclude the yield of both Type II and Type Ia supernovae (SNe). Ouranalysis shows that abundance measurements are critically dependent onthe selection of the proper emission model. The spatially resolved,high-quality XMM-Newton spectra provide enough statistics to formallyrequire at least three emission components in each of four circumnuclearconcentric shells (within 5' or 100 kpc): two soft thermal componentsindicating a range of temperatures in the hot ISM plus a hardercomponent, consistent with the integrated output of low-mass X-raybinaries (LMXBs) in NGC 507. The two-component (thermal+LMXB) modelcustomarily used in past studies yields a much lower ZFe,consistent with previous reports of subsolar metal abundances. Thismodel, however, gives a significantly worse fit to the data (F-testprobability<0.0001). The abundance of α-elements (mostaccurately determined by Si) is also found to be supersolar. Theα-element-to-Fe abundance ratio is close to the solar ratio,suggesting that ~70% of the iron mass in the hot ISM originated fromType Ia SNe. The α-element-to-Fe abundance ratio remains constantout to at least 100 kpc, indicating that Types II and Ia SN ejecta arewell mixed on a scale much larger than the extent of the stellar body.
| Elemental abundances in the intracluster medium as observed with XMM-Newton
XMM-Newton observations of 19 galaxy clusters are used to measure theelemental abundances and their spatial distributions in the intraclustermedium. The sample mainly consists of X-ray bright and relaxed clusterswith a cD galaxy. Along with detailed Si, S and Fe radial abundancedistributions within 300-700 kpc in radius, the O abundances areaccurately derived in the central region of the clusters. The Feabundance maxima towards the cluster center, possibly due to the metalsfrom the cD galaxy, are spatially resolved. The Si and S abundances alsoexhibit central increases in general, resulting in uniform Fe-Si-Sratios within the cluster. In contrast, the O abundances are in generaluniform over the cluster. The mean O to Fe ratio within the cluster coreis sub-solar, while that of the cluster scale is larger than the solarratio. These measurements indicate that most of the Fe-Si-S and O in theintracluster medium have different origins, presumably in supernovae Iaand II, respectively. The obtained Fe and O mass are also used todiscuss the past star formation history in clusters.Table 4 is also available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/420/135
| Spatially resolved X-ray spectroscopy of cooling clusters of galaxies
We present spatially resolved X-ray spectra taken with the EPIC camerasof XMM-Newton of a sample of 17 cooling clusters and three non-coolingclusters for comparison. The deprojected spectra are analyzed with amulti-temperature model, independent of any a priori assumptions aboutthe physics behind the cooling and heating mechanisms. All coolingclusters show a central decrement of the average temperature, most ofthem of a factor of 2. Three clusters (Sérsic 159-3, MKW 3sand Hydra A) only show a weak temperature decrement, while two others (A399 and A 2052) have a very strong temperature decrement. All coolingclusters show a weak pressure gradient in the core. More important, ateach radius within the cooling region the gas is not isothermal. Thedifferential emission measure distribution shows a strong peak near themaximum (ambient) temperature, with a steep decline towards lowertemperatures, approximately proportional to T3, oralternatively a cut-off at about a quarter to half of the maximumtemperature. In general, we find a poor correlation between radio fluxof the central galaxy and the temperature decrement of the cooling flow.This is interpreted as evidence that except for a few cases (like theHydra A cluster) heating by a central AGN is not the most common causeof weak cooling flows. We investigate the role of heat conduction byelectrons and find that the theoretically predicted conductivity ratesare not high enough to balance radiation losses. The differentialemission measure distribution has remarkable similarities with thepredictions from coronal magnetic loop models. Also the physicalprocesses involved (radiative cooling, thermal conduction along theloops, gravity) are similar for clusters loops and coronal loops. Ifcoronal loop models apply to clusters, we find that a few hundred loopsper scale height should be present. The typical loop sizes deduced fromthe observed emission measure distribution are consistent with thecharacteristic magnetic field sizes deduced from Faraday rotationmeasurements.
| 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.
| X-ray bright groups and their galaxies
Combining X-ray data from the ROSAT PSPC and optical data drawn from theliterature, we examine in detail the relationship between the X-ray andoptical properties of X-ray bright galaxy groups. We find a relationshipbetween optical luminosity and X-ray temperature consistent with thatexpected from self-similar scaling of galaxy systems,LB~T1.6+/-0.2. The self-similar form andcontinuity of the LB : T relation from clusters to groups andthe limited scatter seen in this relation, implies that the starformation efficiency is rather similar in all of these systems. We findthat the bright extended X-ray components associated with many centralgalaxies in groups appear to be more closely related to the group thanthe galaxy itself, and we suggest that these are group cooling flowsrather than galaxy haloes. In addition we find that the optical light inthese groups appears to be more centrally concentrated than the light inclusters.We also use the optical and X-ray data to investigate whether early- orlate-type galaxies are primarily responsible for pre-heating in groups.Using three different methods, we conclude that spiral galaxies appearto play a comparable role to early types in the pre-heating of theintragroup medium. This tends to favour models in which the pre-heatingarises primarily from galaxy winds rather than active galactic nucleiand implies that spirals have played a significant role in the metalenrichment of the intragroup medium.
| An X-Ray Atlas of Groups of Galaxies
A search was conducted for a hot intragroup medium in 109 low-redshiftgalaxy groups observed with the ROSAT PSPC. Evidence for diffuse,extended X-ray emission is found in at least 61 groups. Approximatelyone-third of these detections have not been previously reported in theliterature. Most of the groups are detected out to less than half of thevirial radius with ROSAT. Although some spiral-rich groups do contain anintragroup medium, diffuse emission is restricted to groups that containat least one early-type galaxy.
| XMM-Newton and Chandra Observations of the Galaxy Group NGC 5044. II. Metal Abundances and Supernova Fraction
Using new XMM and Chandra observations, we present an analysis of themetal abundances of the hot gas within a radius of 100 kpc of the brightnearby galaxy group NGC 5044. Motivated by the inconsistent abundanceand temperature determinations obtained by different observers for X-raygroups, we provide a detailed investigation of the systematic errors onthe derived abundances considering the effects of the temperaturedistribution, calibration, plasma codes, bandwidth, GalacticNH, and background rate. The iron abundance (ZFe)drops from ZFe~1 Zsolar within R~50 kpc toZFe~0.4 Zsolar near R=100 kpc. This radial declinein ZFe is highly significant:ZFe=1.09+/-0.04(statistical)+/-0.05+0.18(systematic) in solarunits within R=48 kpc (5') compared toZFe=0.44+/-0.02(statistical)+/-0.10+0.13(systematic) in solarunits over R=48-96 kpc (5'-10'). There is no evidence that the radialprofile of ZFe flattens at large radius. The data rule outwith high confidence a very subsolar value for ZFe withinR=48 kpc, confirming that previous claims of very subsolar centralZFe values in NGC 5044 were primarily the result of the Febias, i.e., the incorrect assumption of spatially isothermal andsingle-phase gas when in fact temperature variations exist. Next to ironthe data provide the best constraints on the silicon and sulfurabundances. Within R=48 kpc we obtainZSi/ZFe=0.83+/-0.02(statistical)+/-0.02+0.07(systematic)andZS/ZFe=0.54+/-0.02(statistical)+/-0.01+0.01(systematic)in solar units. These ratios (1) are consistent with their values atlarger radii, (2) strongly favor convective deflagration models overdelayed detonation models of Type Ia supernovae (SNe Ia), and (3) implythat SNe Ia have contributed 70%-80% of the iron mass within a 100 kpcradius of NGC 5044. This SN Ia fraction is also similar to that inferredfor the Sun and therefore suggests a stellar initial mass functionsimilar to that of the Milky Way. We mention that at the very center(R~2 kpc) the XMM and Chandra CCDs and the XMM Reflection GratingSpectrometer (RGS) show that the Fe and Si abundances drop to ~50% oftheir values at immediately larger radius analogously to that seen insome galaxy clusters observed with Chandra. We find the magnitude ofthis dip to be sensitive to assumptions in the spectral model, but ifreal it is difficult to reconcile with the expectation that metalenrichment from the stars in the central galaxy should result in acentrally peaked metal abundance profile in the hot gas.
| High-Resolution X-Ray Spectroscopic Constraints on Cooling-Flow Models for Clusters of Galaxies
We present high-resolution X-ray spectra of 14 putative cooling-flowclusters of galaxies obtained with the Reflection Grating Spectrometeron XMM-Newton. The clusters in the sample span a large range oftemperatures and mass deposition rates. Various of these spectra exhibitline emission from O VIII, Ne X, Mg XII and XI, Al XIII and XII, Si XIVand XIII, N VII, and C VI as well as all Fe L ions. The spectra exhibitstrong emission from cool plasma at just below the ambient temperature,T0, down to T0/2, but also exhibit a severedeficit of emission relative to the predictions of the isobariccooling-flow model at lower temperatures (
| 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.
| 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
| XMM-Newton confirmation of soft X-ray excess emission in clusters of galaxies - The discovery of O VII emission from an extended warm baryonic component
We investigate a sample of 14 clusters of galaxies observed withXMM-Newton in a search for soft X-ray excess emission. In five of theseclusters a significant soft excess is evident. This soft X-ray excess iscompared with the thermal emission from both the hot intracluster gasand any cooling (flow) gas that may be present. A warm (kT=0.2 keV),extended (several Mpc), plasma component is particularly clear in theouter parts of the cluster, where the normal cluster X-ray emission isweak. This warm component causes both a thermal soft X-ray excess at lowenergies (below 0.4-0.5 keV), as well as O Vii line emission with aredshift consistent with a cluster origin, and not easily interpreted asGalactic foreground emission. The intensity of this component iscommensurate with what has been measured before with the ROSAT PSPC inthe 1/4 keV band. We attribute this component to emission fromintercluster filaments of the Warm-Hot Intergalactic Medium in thevicinity of these clusters. For the central regions of clusters thedetection of lines in the soft X-ray spectrum is more difficult, due tothe predominance of the X-ray emitting hot plasma there, hence we cannotdiscriminate between the thermal and nonthermal origin of the softexcess, leaving several options open. These include thermal emissionfrom warm filaments seen in projection in front of or behind the clustercenter, thermal or nonthermal emission in the cluster core itselfrelated to magnetic reconnection, or Inverse Compton emission from thecosmic microwave background on relativistic electrons.
| The ROSAT All-Sky Survey: a Catalog of Clusters of Galaxies in a Region of 1 steradian around the South Galactic Pole
A field of 1.013 sr in the ROSAT All-Sky Survey (RASS), centered on thesouth Galactic pole (SGP), has been searched in a systematic, objectivemanner for clusters of galaxies. The procedure relied on a correlationof the X-ray positions and properties of ROSAT sources in the field withthe distribution of galaxies in the COSMOS digitized database, which wasobtained from scanning the plates of the UK Schmidt IIIa-J opticalsurvey of the southern sky. The study used the second ROSAT surveydatabase (RASS-2) and included several optical observing campaigns tomeasure cluster redshifts. The search, which is a precursor to thelarger REFLEX survey encompassing the whole southern sky, reached thedetection limits of both the RASS and the COSMOS data and yielded acatalog of 186 clusters in which the lowest flux is1.5×10-12 ergs cm-2 s-1 in the0.1-2.4 keV band. Of these 157 have measured redshifts. Using a fluxlimit of 3.0×10-12 ergs cm-2 s-1a complete subset of 112 clusters was obtained, of which 110 havemeasured redshifts. The spatial distribution of the X-ray clusters outto a redshift of 0.15 shows an extension of the Local Supercluster tothe Pisces-Cetus supercluster (z<~0.07), and an orthogonal structureat higher redshift (0.07
| Observational Mass-to-Light Ratio of Galaxy Systems from Poor Groups to Rich Clusters
We study the mass-to-light ratio of galaxy systems from poor groups torich clusters and present for the first time a large database for usefulcomparisons with theoretical predictions. We extend a previous work,where Bj band luminosities and optical virial masses wereanalyzed for a sample of 89 clusters. Here we also consider a sample of52 more clusters, 36 poor clusters, seven rich groups, and two catalogs,of ~500 groups each, recently identified in the Nearby Optical Galaxysample by using two different algorithms. We obtain the blue luminosityand virial mass for all systems considered. We devote a large effort toestablishing the homogeneity of the resulting values, as well as toconsidering comparable physical regions, i.e., those included within thevirial radius. By analyzing a fiducial, combined sample of 294 systemswe find that the mass increases faster than the luminosity: the linearfit gives M~L1.34+/-0.03B, with a tendency for asteeper increase in the low-mass range. In agreement with the previouswork, our present results are superior owing to the much higherstatistical significance and the wider dynamical range covered(~1012-1015 Msolar). We present acomparison between our results and the theoretical predictions on therelation between M/LB and halo mass, obtained by combiningcosmological numerical simulations and semianalytic modeling of galaxyformation.
| Bar Galaxies and Their Environments
The prints of the Palomar Sky Survey, luminosity classifications, andradial velocities were used to assign all northern Shapley-Ames galaxiesto either (1) field, (2) group, or (3) cluster environments. Thisinformation for 930 galaxies shows no evidence for a dependence of barfrequency on galaxy environment. This suggests that the formation of abar in a disk galaxy is mainly determined by the properties of theparent galaxy, rather than by the characteristics of its environment.
| 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.
| High resolution soft X-ray spectroscopy of M 87 with the reflection grating spectrometers on XMM-Newton
We present high-resolution X-ray spectroscopic observations of M 87 withthe Reflection Grating Spectrometers on XMM-Newton. We detect strongK-shell line emission from N, O, Ne, Mg, some emission from He-like Si,a fully resolved set of Fe L-shell emission spectra, and some emissionfrom C. The angular intensity distributions of the strong emission linesare detectably resolved on scales (15-160) arcsec. The gas in the innerarcmin of M 87 has a multi-phase structure, as indicated by thesimilarity of the emission line profiles of Fe L shell ions with widelyseparated ionization potentials. The global Fe L spectrum isapproximately consistent with an isothermal plasma at kTe ~1.8 keV, in addition to a component with a temperature distributionappropriate to an isobaric cooling flow, but with a minimum temperaturecutoff of kTmin ≈ 600 eV. The behaviour of thiscooling-flow component is qualitatively similar to what is seen in othercooling flow clusters. Finally, we do not find any strong evidence for aspatial variation in abundances due to resonance scatteringredistribution in the inner arcminute of the core.
| 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.
| X-ray luminosities of galaxies in groups
We have derived the X-ray luminosities of a sample of galaxies ingroups, making careful allowance for contaminating intragroup emission.The LX:LB and LX:LFIRrelations of spiral galaxies in groups appear to be indistinguishablefrom those in other environments, however the elliptical galaxies fallinto two distinct classes. The first class is central-dominant groupgalaxies, which are very X-ray luminous and may be the focus of groupcooling flows. All other early-type galaxies in groups belong to thesecond class, which populates an almost constant band ofLX/LB over the range9.8
| 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.
| The Optical and Near-Infrared Morphologies of Isolated Early-Type Galaxies
To study early-type galaxies in their simplest environments, we haveconstructed a well-defined sample of 30 isolated galaxies. The samplecontains all early-type galaxies listed in the Third Reference Catalogueof Bright Galaxies (RC3) with no other cataloged galaxy with a knownredshift lying within a projected radius of 1h-1100 Mpc and +/-1000 km s-1 (where weuse the recession velocities in the RC3). We have obtained optical andnear-infrared images of 23 of the galaxies and of a comparison sample of13 early-type galaxies in X-ray-detected poor groups of galaxies. Wehave applied the techniques of unsharp-masking, galaxy model division,and color maps to search for morphological features that might provideclues to the evolution of these galaxies. Evidence for dust features isfound in approximately 75% of both the isolated and group galaxies (17of 22 and 9 of 12, respectively). However, shells or tidal features aremuch more prevalent in our isolated sample than in our group sample (9of 22=41% vs. 1 of 12=8%, respectively). The isolation and colors ofthese shell galaxies make it unlikely that tidal interactions orasymmetric star formation are the causes of such features. One modelthat is not ruled out is that mergers produce the shells. If shells anddust are both merger signatures, the absence of shells in groupelliptical galaxies implies that shells (1) form more easily, (2) areyounger, and/or (3) are longer lived in isolated environments.
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