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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).
| 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.
| The Birmingham-CfA cluster scaling project - II. Mass composition and distribution
We investigate the spatial distribution of the baryonic and non-baryonicmass components in a sample of 66 virialized systems. We have used X-raymeasurements to determine the deprojected temperature and densitystructure of the intergalactic medium and have employed these to map theunderlying gravitational potential. In addition, we have measured thedeprojected spatial distribution of galaxy luminosity for a subset ofthis sample, spanning over two decades in mass. With this combinedX-ray/optical study, we examine the scaling properties of the baryonsand address the issue of mass-to-light (M/L) ratio in groups andclusters of galaxies.We measure a median mass-to-light ratio of 249h70(M/L)solar in the rest frame BJband, in good agreement with other measurements based on X-raydetermined masses. There is no trend in M/L with X-ray temperature andno significant trend for mass to increase faster than luminosity:M~L1.08 +/- 0.12BJ. This implied lackof significant variation in star formation efficiency suggests that gascooling cannot be greatly enhanced in groups, unless it drops out toform baryonic dark matter. Correspondingly, our results indicate thatnon-gravitational heating must have played a significant role inestablishing the observed departure from self-similarity in low-masssystems. The median baryon fraction for our sample is 0.162h-3/270, which allows us to place an upper limiton the cosmological matter density, Ωm<= 0.27h-170, in good agreement with the latest resultsfrom WMAP.We find evidence of a systematic trend towards higher central densityconcentration in the coolest haloes, indicative of an early formationepoch and consistent with hierarchical formation models.
| The Birmingham-CfA cluster scaling project - I. Gas fraction and the M-TX relation
We have assembled a large sample of virialized systems, comprising 66galaxy clusters, groups and elliptical galaxies with high-quality X-raydata. To each system we have fitted analytical profiles describing thegas density and temperature variation with radius, corrected for theeffects of central gas cooling. We present an analysis of the scalingproperties of these systems and focus in this paper on the gasdistribution and M-TX relation. In addition to clusters andgroups, our sample includes two early-type galaxies, carefully selectedto avoid contamination from group or cluster X-ray emission. We comparethe properties of these objects with those of more massive systems andfind evidence for a systematic difference between galaxy-sized haloesand groups of a similar temperature.We derive a mean logarithmic slope of the M-TX relationwithin R200 of 1.84 +/- 0.06, although there is some evidenceof a gradual steepening in the M-TX relation, with decreasingmass. We recover a similar slope using two additional methods ofcalculating the mean temperature. Repeating the analysis with theassumption of isothermality, we find the slope changes only slightly, to1.89 +/- 0.04, but the normalization is increased by 30 per cent.Correspondingly, the mean gas fraction within R200 changesfrom (0.13 +/- 0.01) h-3/270 to (0.11+/- 0.01) h-3/270, for the isothermalcase, with the smaller fractional change reflecting different behaviourbetween hot and cool systems. There is a strong correlation between thegas fraction within 0.3R200 and temperature. This reflectsthe strong (5.8σ) trend between the gas density slope parameter,β, and temperature, which has been found in previous work.These findings are interpreted as evidence for self-similarity breakingfrom galaxy feedback processes, active galactic nuclei heating orpossibly gas cooling. We discuss the implications of our results in thecontext of a hierarchical structure formation scenario.
| Infrared Observations of Galaxies in the Local Universe. II. 391 Calibrated Images with Photometric and Structural Measurements
This paper presents empirical results from a deep imaging survey ofgalaxies in the local universe at the J and Ks wavelengths.Three hundred ninety-one images have been obtained and calibrated usingthe same camera and filter set with the Steward Observatory 1.6 m KuiperTelescope on Mount Bigelow and the 2.3 m Bok Telescope on Kitt Peak. Thelimiting magnitude is typically 22 mag arcsec-1 at J and 21mag arcsec-1 at Ks. The central surfacebrightness, apparent magnitudes, sizes, scale lengths, and inclinationsare tabulated from measurements made using these data. The purpose ofthis paper is to provide basic near-infrared data on a variety of galaxytypes.
| 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.
| 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
| ASCA Observations of Groups at Radii of Low Overdensity: Implications for the Cosmic Preheating
Through a three-dimensional modeling of ASCA observations, we performeda spatially resolved X-ray spectroscopic study, extending to radiiexceeding 150 kpc, for a sample of nine groups of galaxies. Combinedwith published ROSAT results, we conclude that these systems generallyexhibit a strong temperature decline at outer radii. In our best case,NGC 3268, this corresponds to a flattening of the entropy profile at alevel of ~400 keV cm2. This value is high compared both tothe observed entropy floor of ~100 keV cm2 and to theexpected value from gravitational heating. We suggest that the observedentropy profile in most groups at densities exceeding 500 times thecritical is driven purely by nongravitational heating processes. Aftercomparison with a larger sample of groups and clusters, we conclude thatthere is a variation in the level of nongravitational heating between~100 and ~400 keV cm2 within every system. Using models ofcluster formation as a reference frame, we established that the accretedgas reaches an entropy level of 400 keV cm2 by redshift2.0-2.5, while such high entropies where not present at redshifts higherthan 2.8-3.5, favoring nearly instantaneous preheating. Adoptinggalactic winds as a source of preheating and scaling the released energyby the observed metal abundance, the variation in the preheating couldbe ascribed mostly to variation in the typical overdensity of the energyinjection, from ~30 for an entropy floor of 100 keV cm2 to ~5for an entropy of 400 keV cm2.
| 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.
| 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 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.
| Details of the mass-temperature relation for clusters of galaxies
We present results on the total mass and temperature determination usingtwo samples of clusters of galaxies. One sample is constructed withemphasis on the completeness of the sample, while the advantage of theother is the use of the temperature profiles, derived with ASCA. Weobtain remarkably similar fits to the M-T relation for both samples,with the normalization and the slope significantly different from bothprediction of self-similar collapse and hydrodynamical simulations. Wediscuss the origin of these discrepancies and also combine the X-raymass with velocity dispersion measurements to provide a comparison withhigh-resolution dark matter simulations. Finally, we discuss theimportance of a cluster formation epoch in the observed M-T relation.
| The intragroup medium in loose groups of galaxies
We have used the ROSAT PSPC to study the properties of a sample of 24X-ray-bright galaxy groups, representing the largest sample examined indetail to date. Hot plasma models are fitted to the spectral data toderive temperatures, and modified King models are used to characterizethe surface brightness profiles. In agreement with previous work, wefind evidence for the presence of two components in the surfacebrightness profiles. The extended component is generally found to bemuch flatter than that observed in galaxy clusters, and there isevidence that the profiles follow a trend with system mass. We deriverelationships between X-ray luminosity, temperature and optical velocitydispersion. The relation between X-ray luminosity and temperature isfound to be LX~T4.9, which is significantlysteeper than the same relation in galaxy clusters. These results are ingood agreement with pre-heating models, in which galaxy winds raise theinternal energy of the gas, inhibiting its collapse into the shallowpotential wells of poor systems.
| X-ray evidence for multiphase hot gas with nearly solar Fe abundances in the brightest groups of galaxies
We analyse the ASCA spectra accumulated within ~100kpc radii of 12 ofthe brightest groups of galaxies. Upon fitting isothermal models (1T)jointly to the ASCA SIS and GIS spectra we obtain fits for most groupsthat are of poor or at best marginal quality and give very subsolarmetallicities similar to previous studies,=0.29+/-0.12Zsolar. Two-temperature models (2T)provide significantly better fits for 11 out of the 12 groups, and inevery case have metallicities that are substantially larger thanobtained for the 1T models, =0.75+/-0.24Zsolar.Though not very well constrained, for most of the groups absorption inexcess of the Galactic value is indicated for the cooler temperaturecomponent of the 2T models. A simple multiphase cooling flow model givesresults analogous to the 2T models including large metallicities,=0.65+/-0.17Zsolar. The nearly solar Fe abundancesand also solar α/Fe ratios indicated by the 2T and cooling flowmodels are consistent with models of the chemical enrichment ofellipticals, groups, and clusters which assume ratios of Type Ia to TypeII supernovae and an initial mass function (IMF) similar to those of theMilky Way. Thus we have shown that the very subsolar Fe abundances andSi/Fe enhancements obtained from most previous studies within r~100kpcof galaxy groups are an artefact of fitting isothermal models to theX-ray spectra, which also has been recently demonstrated for thebrightest elliptical galaxies. Owing to the importance of these resultsfor interpreting X-ray spectra, in an appendix we use simulated ASCAobservations to examine in detail the `Fe bias' and `Si bias' associatedwith the spectral fitting of ellipticals, groups and clusters ofgalaxies.
| The Properties of Poor Groups of Galaxies. III. The Galaxy Luminosity Function
The form of the galaxy luminosity function (GLF) in poor groups-regionsof intermediate galaxy density that are common environments forgalaxies-is not well understood. Multiobject spectroscopy and wide-fieldCCD imaging now allow us to measure the GLF of bound group membersdirectly (i.e., without statistical background subtraction) and tocompare the group GLF with the GLFs of the field and of rich clusters.We use R-band images in 1.5×1.5 degree2 mosaics toobtain photometry for galaxies in the fields of six nearby(2800=MR>-19+5logh) to giants(MR<=-19+5logh) is significantly larger for the fivegroups with luminous X-ray halos than for the one marginallyX-ray-detected group; (2) the composite GLF for the luminous X-raygroups is consistent in shape with two measures of the composite R-bandGLF for rich clusters (Trentham; Driver et al.) and flatter at the faintend than another (α~-1.5 Smith et al.); (3) the composite groupGLF rises more steeply at the faint end than the R-band GLF of the LasCampanas Redshift Survey (LCRS; α=-0.7 from Lin et al.), a largevolume survey dominated by galaxies in environments more rarefied thanluminous X-ray groups; (4) the shape difference between the LCRS fieldand composite group GLFs results mostly from the population ofnon-emission line galaxies (EW [O II]<5 Å), whosedwarf-to-giant ratio is larger in the denser group environment than inthe field (cf. Ferguson & Sandage; Bromley et al.); and (5) thenon-emission line dwarfs are more concentrated about the group centerthan the non-emission line giants, except for the central, brightest(MR
| 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.
| The Dynamics of Poor Systems of Galaxies
We assemble and observe a sample of poor galaxy systems that is suitablefor testing N-body simulations of hierarchical clustering and otherdynamical halo models. We (1) determine the parameters of the densityprofile rho(r) and the velocity dispersion profile sigma_p(R), (2)separate emission-line galaxies from absorption-line galaxies, examiningthe model parameters and as a function of spectroscopic type, and (3)for the best-behaved subsample, constrain the velocity anisotropyparameter, beta, which determines the shapes of the galaxy orbits. Oursample consists of 20 systems, 12 of which have extended X-ray emissionin the ROSAT All-Sky Survey. We measure the 877 optical spectra ofgalaxies brighter than m_R~15.4 within 1.5 h^-1 Mpc of the systemcenters (we take H_0=100 h km s^-1 Mpc^-1). Thus, we sample the systemmembership to a radius typically three times larger than other recentoptical group surveys. The average system population is 30 galaxies, andthe average line-of-sight velocity dispersion is ~300 km s^-1. TheNavarro, Frenk, & White universal profile and the Hernquist modelboth provide good descriptions of the spatial data. In most cases anisothermal sphere is ruled out. Systems with declining sigma_p(R) arewell-matched by theoretical profiles in which the star-forming galaxieshave predominantly radial orbits (beta>0) many of these galaxies areprobably falling in for the first time. There is significant evidencefor spatial segregation of the spectroscopic classes regardless ofsigma_p(R).
| The Isolated Elliptical NGC 1132: Evidence for a Merged Group of Galaxies?
Numerical simulations predict that some poor groups of galaxies havemerged by the present epoch into giant ellipticals. To identify thepossible remnants of such mergers, we have compiled a sample of nearbyisolated ellipticals. ASCA observations of the first galaxy studied, NGC1132, reveal an X-ray halo that extends out to at least ~250 kpch^-1_100. The temperature (~1 keV), metallicity (~0.25 solar), andluminosity (~2.5x10^42 h^-2_100 ergs s^-1) of NGC 1132's X-ray halo arecomparable with those of poor group halos. The total mass inferred fromthe X-ray emission, ~1.9^+0.8_-0.6x10^13 h^-1_100 M_solar, is also likethat of an X-ray detected group. Optical imaging uncovers a dwarf galaxypopulation clustered about NGC 1132 that is consistent in number densityand projected radial distribution with that of an X-ray group. Thesimilarities of NGC 1132 to poor groups in both the X-ray band and atthe faint end of the galaxy luminosity function, combined with thedeficit of luminous galaxies in the NGC 1132 field, are compatible withthe merged group picture. Another possibility is that the NGC 1132system is a ``failed'' group (i.e., a local overdensity in which otherbright galaxies never formed).
| 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.
| Infrared Observations of Galaxies in the Local Universe. I. The Survey and Some Representative Results
This paper introduces a continuing survey of galaxies in the localuniverse. Consistent deep images are being acquired for a representativesample of 321 galaxies in the Uppsala General Catalogue down to 21.7 magarcsec-2 at Ks (2.16 mu m) and 22.4 mag arcsec-2 at J (1.25 mu m) usinga NICMOS camera with a 3.'8 x 3.'8 field of view attached to the 61 inch(1.5 m) telescope on Mount Bigelow. We provide some examples of theresults being obtained by employing 64 deep images of a subset of 44galaxies. Bulge-to-disk ratios are tabulated for 30 galaxies. Thebrightness of the central region of 44 galaxies declines approximately 5mag from Hubble type S0 to Sm. An exponential vertical scale height atKs is found to be 500 pc for the disk of UGC 5173. Arm amplitudes offour nearly face-on spiral galaxies are found to range between 11% and88% compared to the interarm region. There is some evidence that the armamplitude is larger at Ks than it is at J. Color gradients are measuredfor 15 galaxies with only one showing a significant nonzero result. Ameasurement of galactic symmetry applied to 64 deep images reveals anaverage asymmetry of 7.6% ( sigma = 4.6%) for these galaxies.
| Groups of galaxies. III. Some empirical characteristics.
Not Available
| 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.
| Kinematical data on early-type galaxies. IV.
We present kinematical data for a sample of 25 galaxies. Rotation curvesand velocity-dispersion profiles are determined for 16 objects, whilethe central velocity dispersions are given for the whole sample. This isour fourth paper in a series devoted to the presentation of kinematicaldata on elliptical and S0 galaxies, derived from long-slit absorptionspectroscopy. Based on observations collected at the Observatoire deHaute-Provence.
| 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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