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Multicolor Surface Photometry of Lenticular Galaxies. I. The Data
We present multicolor surface and aperture photometry in the B, V, R,and K' bands for a sample of 34 lenticular galaxies from the UppsalaGeneral Catalogue. From surface photometric analysis, we obtain radialprofiles of surface brightness, colors, ellipticity, position angle, andthe Fourier coefficients that describe the departure of isophotal shapesfrom a purely elliptical form; we find the presence of dust lanes,patches, and ringlike structure in several galaxies in the sample. Weobtain total integrated magnitudes and colors and find that these are ingood agreement with the values from the Third Reference Catalogue.Isophotal colors are correlated with each other, following the sequenceexpected for early-type galaxies. The color gradients in lenticulargalaxies are more negative than the corresponding gradients inelliptical galaxies. There is a good correlation between B-V and B-Rcolor gradients, and the mean gradients in the B-V, B-R, and V-K' colorsare -0.13+/-0.06, -0.18+/-0.06, and -0.25+/-0.11 mag dex-1 inradius, respectively.
| The Group Evolution Multiwavelength Study (GEMS): bimodal luminosity functions in galaxy groups
We present B- and R-band luminosity functions (LFs) for a sample of 25nearby groups of galaxies. We find that the LFs of the groups with lowX-ray luminosity (LX < 1041.7 ergs-1) are significantly different from those of the X-raybrighter groups, showing a prominent dip around MB=-18. Whileboth categories show lack of late-type galaxies in their centralregions, X-ray dim groups also show a more marked concentration ofoptical luminosity towards the centre. A toy simulation shows that inthe low velocity dispersion environment, as in the X-ray dim group,dynamical friction would facilitate more rapid merging, thus depletingintermediate-luminosity galaxies to form a few giant central galaxies,resulting in the prominent dip seen in our LFs. We suggest that X-raydim (or low velocity dispersion) groups are the present sites of rapiddynamical evolution rather than their X-ray bright counterparts, and maybe the modern precursors of fossil groups. We predict that these groupsof low velocity dispersion would harbour younger stellar populationsthan groups or clusters with higher velocity dispersion.
| The isolated elliptical NGC 4555 observed with Chandra
We present analysis of a Chandra observation of the elliptical galaxyNGC 4555. The galaxy lies in a very low density environment, eitherisolated from all galaxies of similar mass or on the outskirts of agroup. Despite this, NGC 4555 has a large gaseous halo, extending to~60kpc. We find the mean gas temperature to be ~0.95keV and the Feabundance to be ~0.5Zsolar. We model the surface brightness,temperature and abundance distribution of the halo and use these resultsto estimate parameters such as the entropy and cooling time of the gas,and the total gravitational mass of the galaxy. In contrast to recentresults showing that moderate luminosity ellipticals contain relativelysmall quantities of dark matter, our results show that NGC 4555 has amassive dark halo and large mass-to-light ratio(56.8+34.2-35.8Msolar/LBsolarat 50kpc, 42.7+14.6-21.2 at 5re,1σ errors). We discuss this disparity and consider possiblemechanisms by which galaxies might reduce their dark matter content.
| 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.
| 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.
| Scaling relations in early-type galaxies belonging to groups
We present a photometric analysis of a large sample of early-typegalaxies in 16 nearby groups, imaged with the Wide-Field Camera on theIsaac Newton Telescope. Using a two-dimensional surface brightnessdecomposition routine, we fit Sersic (r1/n) and exponentialmodels to their bulge and disc components, respectively. Dividing thegalaxies into three subsamples according to the X-ray luminosities oftheir parent groups, we compare their photometric properties. Galaxiesin X-ray luminous groups tend to be larger and more luminous than thosein groups with undetected or low X-ray luminosities, but no significantdifferences in n are seen. Both normal and dwarf elliptical galaxies inthe central regions of groups are found to have cuspier profiles thantheir counterparts in group outskirts.Structural differences between dwarf and normal elliptical galaxies areapparent in terms of an offset between their `photometric planes' in thespace of n, re and μ0. Dwarf ellipticals arefound to populate a surface, with remarkably low scatter, in this spacewith significant curvature, somewhat similar to the surfaces of constantentropy proposed by Màrquez et al. Normal ellipticals are offsetfrom this distribution in a direction of higher specific entropy. Thismay indicate that the two populations are distinguished by the action ofgalaxy merging on larger galaxies.
| K-band Properties of Galaxy Clusters and Groups: Brightest Cluster Galaxies and Intracluster Light
We investigate the near-infrared K-band properties of the brightestcluster galaxies (BCGs) in a sample of 93 X-ray galaxy clusters andgroups, using data from the Two Micron All Sky Survey. Our clustersample spans a factor of 70 in mass, making it sensitive to any clustermass-related trends. We derive the cumulative radial distribution forthe BCGs in the ensemble and find that 70% of the BCGs are centered inthe cluster to within 5% of the virial radius r200; thisquantifies earlier findings that BCG position coincides with the clustercenter as defined by the X-ray emission peak. We study the correlationsbetween the luminosity of the BCGs (Lb) and the mass and theluminosity of the host clusters, finding that BCGs in more massiveclusters are more luminous than their counterparts in less massivesystems and that the BCGs become less important in the overall clusterlight (L200) as cluster mass increases. By examining a largesample of optically selected groups, we find that these correlationshold for galactic systems less massive than our clusters(<3×1013 Msolar). From the differencesbetween luminosity functions in high- and low-mass clusters, we arguethat BCGs grow in luminosity mainly by merging with other luminousgalaxies as the host clusters grow hierarchically; the decreasing BCGluminosity fraction (Lb/L200) with cluster massindicates that the rate of luminosity growth in BCGs is slow compared tothe rate at which clusters acquire galaxy light from the field or othermerging clusters. Utilizing the observed correlation between the clusterluminosity and mass and a merger tree model for cluster formation, weestimate that the amount of intracluster light (ICL) increases withcluster mass; our calculations suggest that in 1015Msolar clusters more than 50% of total stellar mass is inICL, making the role of ICL very important in the evolution andthermodynamic history of clusters. The cluster baryon fractionaccounting for the ICL is in good agreement with the value derived fromcosmic microwave background observations. The inclusion of ICL reducesthe discrepancy between the observed cluster cold baryon fraction andthat found in hydrodynamical simulations. Based on the observed ironabundance in the intracluster medium, we find that the ICL predicted byour model, together with the observed galaxy light, match the ironmass-to-light ratio expected from simple stellar population models,provided that the Salpeter initial mass function is adopted. The ICLalso makes it easier to produce the ``iron excess'' found in the centralregions of cool-core clusters.
| K-Band Properties of Galaxy Clusters and Groups: Luminosity Function, Radial Distribution, and Halo Occupation Number
We explore the near-infrared (NIR) K-band properties of galaxies within93 galaxy clusters and groups using data from the Two Micron All SkySurvey. We use X-ray properties of these clusters to pinpoint clustercenters and estimate cluster masses. By stacking all these systems, westudy the shape of the cluster luminosity function and the galaxydistribution within the clusters. We find that the galaxy profile iswell described by the Navarro, Frenk, & White (NFW) profile with aconcentration parameter c~3, with no evidence for cluster massdependence of the concentration. Using this sample, whose masses spanthe range from 3×1013 to2×1015Msolar, we confirm the existence of atight correlation between total galaxy NIR luminosity and clusterbinding mass, which indicates that NIR light can serve as a cluster massindicator. From the observed galaxy profile, together with cluster massprofile measurements from the literature, we find that the mass-to-lightratio is a weakly decreasing function of cluster radius and that itincreases with cluster mass. We also derive the mean number of galaxieswithin halos of a given mass, the halo occupation number. We find thatthe mean number scales as N~M0.84+/-0.04 for galaxiesbrighter than MK=-21, indicating that high-mass clusters havefewer galaxies per unit mass than low-mass clusters. Using publishedobservations at high redshift, we show that higher redshift clustershave higher mean occupation numbers than nearby systems of the samemass. By comparing the luminosity function and radial distribution ofgalaxies in low-mass and high-mass clusters, we show that there is amarked decrease in the number density of galaxies fainter thanM* as one moves to higher mass clusters; in addition,extremely luminous galaxies are more probable in high-mass clusters. Weexplore several processes, including tidal interactions and merging, asa way of explaining the variation in galaxy population with clustermass.
| K-Band Properties of Well-Sampled Groups of Galaxies
We use a sample of 55 groups and six clusters of galaxies ranging inmass from 7×1011 to 1.5×1015Msolar to examine the correlation of the Ks-bandluminosity with mass discovered by Lin and coauthors in 2003. We use theTwo-Micron All-Sky Survey catalog and published redshifts to constructcomplete magnitude-limited redshift surveys of the groups. From thesesurveys we explore the IR photometric properties of groups members,including their IR color distribution and luminosity function. Althoughwe find no significant difference between the group Ksluminosity function and the general field, there is a difference betweenthe color distribution of luminous group members and their counterparts(generally background) in the field. There is a significant populationof luminous galaxies with H-Ks>~0.35, which are rarely, ifever, members of the groups in our sample. The most luminous galaxiesthat populate the groups have a very narrow range of IR color. Over theentire mass range covered by our sample, the Ks luminosityincreases with mass asLKs~M0.64+/-0.06, implying that themass-to-light ratio in the Ks band increases with mass. Theagreement between this result and earlier investigations of essentiallynonoverlapping sets of systems shows that this window in galaxyformation and evolution is insensitive to the selection of the systemsand to the details of the mass and luminosity computations.
| The Chandra Large Area Synoptic X-Ray Survey (CLASXS) of the Lockman Hole-Northwest: The X-Ray Catalog
We present the X-ray catalog and basic results from our Chandra LargeArea Synoptic X-ray Survey (CLASXS) of the Lockman Hole-Northwest field.Our nine ACIS-I fields cover a contiguous solid angle of ~0.4deg2 and reach fluxes of 5×10-16 ergscm-2 s-1 (0.4-2 keV) and 3×10-15ergs cm-2 s-1 (2-8 keV). Our survey bridges thegap between ultradeep pencil-beam surveys, such as the Chandra DeepFields (CDFs), and shallower, large-area surveys, allowing a betterprobe of the X-ray sources that contribute most of the 2-10 keV cosmicX-ray background (CXB). We find a total of 525 X-ray point sources andfour extended sources. At ~10-14 ergs cm-2s-1 (2-8 keV), our number counts are significantly higherthan those of several noncontiguous, large-area surveys. Such a largedifference is an indication of clustering in the X-ray sources. On theother hand, the integrated flux from the CLASXS field, combined withASCA and Chandra ultradeep surveys, is consistent with results fromother large-area surveys, within the variance of the CXB. We seespectral evolution in the hardening of the sources at fluxes below10-14 ergs cm-2 s-1, which agrees withprevious observations from Chandra and XMM-Newton. About one third ofthe sources in the CLASXS field have multiple observations, which allowvariability tests. Above 4×10-14 ergs cm-2s-1 (0.4-8 keV), ~60% of the sources are variable. We alsoinvestigated the spectral variability of the variable sources. Whilemost show spectral softening with increasing flux, or no significantspectral change, there are a few sources that show a different trend. Weobserved four extended sources in CLASXS, which is consistent with thepreviously measured logN-logS relation for galaxy clusters. Using X-rayspectra and optical colors, we argue that three of the four extendedsources are galaxy clusters or galaxy groups. We report the discovery ofa gravitational lensing arc associated with one of these sources. Usingred-sequence and brightest cluster galaxy methods, we find that theredshifts of the extended sources are in the range z~0.5-1. The inferredmasses within the Einstein radii are consistent with the mass profilesof local groups scaled to the same virial radii.
| Spectrophotometry of galaxies in the Virgo cluster. II. The data
Drift-scan mode (3600-6800 Å) spectra with 500
| 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.
| 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.
| 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.
| Entropy scaling in galaxy clusters: Insights from an XMM-Newton observation of the poor cluster A1983
An XMM-Newton observation of the cool (kT =2.1 keV ) cluster A1983, atz=0.044, is presented. Gas density and temperature profiles arecalculated over the radial range up to 500 h50-1kpc, corresponding to ~ 0.35 rv . The outer regions of the surfacebrightness profile are well described with a beta -model with beta=0.74, but the central regions require the introduction of a secondcomponent. The temperature profile is flat at the exterior with a slightdip towards the centre. The total mass profile, calculated from thetemperature and density information assuming hydrostatic equilibrium, isconsistent with an NFW profile, but with a low concentration parameterc=3.75 +/- 0.74, which may be due to the cluster not being totallyrelaxed. Published optical data are used to calculate the mlb ratioprofile and the overall iron mass over luminosity ratio. The mlb ratioprofile shows that, at large scale, light traces mass to a reasonableextent, and the mlb ratio at 0.35 r200 (M/LB= 135+/- 45 h50 Msun/Lsun) is consistentwith the trends with mass observed in the optical. The iron mass overluminosity ratio is about two times less than that observed for acluster at 5 keV. The gas mass fraction rises rapidly in the centralregions to level off quickly at ~ 200 h50-1 kpc;the value at 0.35 rv is ~ 8%. The scaling properties of the emissionmeasure profile are consistent with the empirical relationMgas, ~ Tx 1.94; use of the standard self-similarrelation Mgas, ~ Tx 1.5 results in a scaledprofile that is a factor of about two too low as compared to thereference mean profile for hot clusters. Comparison of the entropyprofile of this cool cluster with that of the hot cluster A1413 showsthat the two profiles are extremely well scaled using the empiricallydetermined relation S ~ Tx 0.65, suggesting that the slope ofthe S-Tx relation is shallower than expected in the standardself-similar model. The form of the two entropy profiles is remarkablysimilar, and there is no sign of a larger isentropic core in the coolercluster. These data provide powerful agruments against preheatingmodels. In turn, there is now increasing observational support for atrend of fgas with system mass, which may go some way towardsexplaining the observed scaling behaviour.
| 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
| 1.65-μm (H -band) surface photometry of galaxies - VIII. The near-IR κ space at z =0
We present the distribution of a statistical sample of nearby galaxiesin the κ -space (κ 1 ~logM , κ 2~logI e 3 M /L , κ 3 ~logM /L ).Our study is based on near-IR (H -band: λ =1.65μm)observations, for the first time comprising early- and late-typesystems. Our data confirm that the mean effective dynamicalmass-to-light ratio M /L of the E+S0+S0a galaxies increases withincreasing effective dynamical mass M , as expected from the existenceof the Fundamental Plane relation. Conversely, spiral and Im/BCDgalaxies show a broad distribution in M /L with no detected trend of M/L with M , the former galaxies having M /L values about twice largerthan the latter, on average. For all the late-type galaxies, the M /Lincreases with decreasing effective surface intensity I e ,consistent with the existence of the Tully-Fisher relation. Theseresults are discussed on the basis of the assumptions behind theconstruction of the κ -space and their limitations. Our study iscomplementary to a previous investigation in the optical (B -band:λ =0.44μm) and allows us to study wavelength dependences ofthe galaxy distribution in the κ -space. As a first result, wefind that the galaxy distribution in the κ 1 -κ2 plane reproduces the transition from bulgeless tobulge-dominated systems in galaxies of increasing dynamical mass.Conversely, it appears that the M /L of late-types is higher (lower)than that of early-types with the same M in the near-IR (optical). Theorigins of this behaviour are discussed in terms of dust attenuation andstar formation history.
| 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.
| 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.
| The far-ultraviolet emission of early-type galaxies
We have assembled a UV-flux selected sample of 82 early-type galaxiesand collected additional information at other wavelengths. These dataconfirm a large spread of the UV-V color in the range 2 to 5. The spreadin UV-V is accompanied by a spread in B-V that is mainly attributed tothe range of morphological types and luminosities. A large fraction ofthe objects have red colors, UV-V = 4 +/- 0.4, corresponding to a weakUV-upturn as observed with IUE. If the current interpretation for the UVemission from early-type galaxies is applicable to our sample, the PAGB(Post-Asymptotic Giant Branch) tracks are the most common evolution pathfor the low-mass stars responsible for the UV emission. A small numberof very blue (UV-V < 1.4) objects have been found that can bereasonably interpreted as harbouring some low level of star formation.In contrast to a previous sample based on IUE observations, nocorrelation is found between the UV-V color and the Mg2spectral line index; possible explanations are reviewed. The potentialof a more extended UV survey like GALEX is briefly presented.
| 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.
| Entropy Evolution in Galaxy Groups and Clusters: a Comparison of External and Internal Heating
The entropy in hot, X-ray-emitting gas in galaxy groups and clusters isa measure of past heating events, except for the entropy lost byradiation from denser regions. Observations of galaxy groups indicatehigher entropies than can be achieved in the accretion shock experiencedby gas when it fell into the dark halos. These observations generallyrefer to the dense, most luminous inner regions where the gas that firstentered the halo may still reside. It has been proposed that thisnongravitational entropy excess results from some heating process in theearly universe that is external to the group and cluster halos and thatit occurred before most of the gas had entered the dark halos. Thisuniversal heating of cosmic gas could be due to active galactic nuclei(AGNs), Population III stars, or some as yet unidentified source.Alternatively, the heating of the hot gas in groups may be producedinternally by Type II supernovae when the galactic stars in thesesystems formed. We investigate here the consequences of various amountsof external, high-redshift heating with a suite of gasdynamicalcalculations. We consider the influence of radiation losses anddistributed mass dropout on the X-ray luminosity and emission-weightedtemperature of the hot gas as well as its central entropy. In general,we find that externally heated flows are unsatisfactory; when theheating is high enough to bring the X-ray luminosities into agreementwith observations, the gas entropy is too high. We compare thesesolutions with flows that are internally heated by Type II supernovae;this type of heating depends on the initial mass function (IMF) and theefficiency that the supernova energy is conveyed to the hot gas. Theseinternally heated flows give much better agreement with X-rayobservations of galaxy groups and are insensitive to the levels ofsupernova heating that we consider as well as to the epoch and spatialdistribution of the supernova heating process. However, to fit X-rayobservations, a large fraction of the energy produced by high-redshiftType II supernovae must heat the hot gas if the number of supernovae isbased on a Salpeter IMF. Alternatively, only about 20% of the Type IIsupernova energy would be required to heat the gas if the IMF has aflatter slope than Salpeter, as suggested by stellar mass-to-lightratios.
| 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.
| 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.
| The IRAS PSCz dipole
We use the PSCz IRAS galaxy redshift survey to analyse the cosmologicalgalaxy dipole out to a distance of 300h-1Mpc. The masked areais filled in three different ways, first by sampling the whole sky atrandom, secondly by using neighbouring areas to fill a masked region,and thirdly using a spherical harmonic analysis. The method of treatmentof the mask is found to have a significant effect on the finalcalculated dipole. The conversion from redshift space to real space isaccomplished by using an analytical model of the cluster and voiddistribution, based on 88 nearby groups, 854 clusters and 163 voids,with some of the clusters and all of the voids found from the PSCz database. The dipole for the whole PSCz sample appears to have convergedwithin a distance of 200h-1Mpc and yields a value forβΩ0.6b0.750.11-0.08, consistent with earlier determinations from IRAS samples bya variety of methods. For b=1, the 2σ range forΩ0 is 0.43-1.02. The direction of the dipole is within13° of the cosmic microwave background (CMB) dipole, the mainuncertainty in direction being associated with the masked area behindthe Galactic plane. The improbability of further major contributions tothe dipole amplitude coming from volumes larger than those surveyed heremeans that the question of the origin of the CMB dipole is essentiallyresolved.
| 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.
| ROSAT Evidence for Intrinsic Oxygen Absorption in Cooling Flow Galaxies and Groups
The existence of large quantities of gas that have cooled and droppedout of the hot phase in massive elliptical galaxies, groups, andclusters is the key prediction of the inhomogeneous cooling flowscenario. Using spatially resolved, deprojected ROSAT Position SensitiveProportional Counter (PSPC) spectra of 10 of the brightest cooling flowgalaxies and groups with low Galactic column densities, we have detectedintrinsic absorption over energies ~0.4-0.8 keV at the 2 σ/3σ level in half of the sample. Since no intrinsic absorption isindicated for energies below ~0.4 keV, the most reasonable model for theabsorber is collisionally ionized gas at temperatures T=105-6K with most of the absorption arising from ionized states of oxygen butwith a significant contribution from carbon and nitrogen. The soft X-rayemission of this warm gas can also explain the sub-Galactic columndensities of cold gas inferred within the central regions of most of thesystems. (This could not be explained by an absorber composed only ofdust.) Attributing the absorption to ionized gas reconciles the largecolumns of cold H and He inferred from Einstein and ASCA with the lackof such columns inferred from ROSAT. Within the central ~10-20 kpc,where the constraints are most secure, the mass of the ionized absorberis consistent with most (perhaps all) of the matter deposited by acooling flow over the lifetime of the flow. Since the warm absorberproduces no significant H or He absorption, the large absorber massesare consistent with the negligible atomic and molecular H inferred fromH I and CO observations of cooling flows. It is also found that ifT>~2×105 K, then the optical and far-ultravioletemission implied by the warm gas does not violate published constraints.An important theoretical challenge is to understand how the warmtemperature is maintained and how the gas is supported gravitationally,and we discuss possible solutions to these problems that would requirefundamental modification of the standard cooling flow scenario. Finally,we discuss how the prediction of warm ionized gas as the product of massdropout in these and other cooling flows can be verified with newChandra and XMM observations.
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