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The hot, warm and cold gas in Arp 227 - an evolving poor group
Arp 227 represents a prototypical example of an interacting mixed pairof galaxies located in a low-density environment. We investigate the gasproperties of the pair in the X-ray, Hα, HI and CO bands. We alsodetect two additional members of the group in HI which indicates thatthe pair constitutes the dominant members of a loose group.The HI distribution shows a tail of gas that connects the spiral member,NGC 470, to the lenticular, NGC 474, showing that the two main membersare currently undergoing interaction. The Hα emission reveals thepresence of secondary components at the centre of NGC 470, superposed onthe main component tracing the rotation of the galaxy. This latter mapsa nearly unperturbed velocity field. The dominant, nearly unperturbedtrend of the kinematics is confirmed by CO observations, althoughrestricted to the centre of the galaxy. The X-ray luminosity of NGC 470is comparable with that of a `normal' spiral galaxy. NGC 474 on theother hand is very gas-poor and has not been detected in Hα. ItsX-ray luminosity is consistent with the low end of the expected emissionfrom discrete sources.Arp 227 as a loose group shows several signatures of galaxy-galaxyinteraction. Our observations suggest the presence of signatures ofinteraction in the overall kinematics of the spiral companion. Theongoing interaction is clearly visible only in the outer HI halo of NGC470. While the large shell system of NGC 474 could be associated with anaccretion event, the secondary components in the Hα profile in thecentre of NGC 470 could be due to the interaction with the companion.The low X-ray luminosity of NGC 470 seems to be a characteristic ofdynamically young systems. All the above evidence suggest that Arp 227is an evolving group in the early phase of its evolution and that itsdrivers are the accretion of faint galaxies and the ongoing large-scaleinteraction between NGC 470 and 474.
| Gemini/GMOS spectra of globular clusters in the Virgo giant elliptical NGC 4649
NGC 4649 (M60) is one of a handful of giant Virgo ellipticals. We haveobtained Gemini/GMOS (Gemini North Multi-Object Spectrograph) spectrafor 38 globular clusters (GCs) associated with this galaxy. Applying themulti-index χ2 minimization technique of Proctor andSansom with the single stellar population models of Thomas, Maraston andKorn, we derive ages, metallicities and α-element abundanceratios. We find several young (2-3 Gyr old) supersolar metallicity GCs,while the majority are old (>10 Gyr), spanning a range ofmetallicities from solar to [Z/H]=-2. At least two of these young GCsare at large projected radii of 17-20 kpc. The galaxy itself shows noobvious signs of a recent starburst, interaction or merger. A trend ofdecreasing α-element ratio with increasing metallicity is found.
| Gemini/GMOS spectra of globular clusters in the Leo group elliptical NGC 3379
The Leo group elliptical NGC 3379 is one of the few normal ellipticalgalaxies close enough to make possible observations of resolved stellarpopulations, deep globular cluster (GC) photometry and highsignal-to-noise ratio GC spectra. We have obtained Gemini/GMOS spectrafor 22 GCs associated with NGC 3379. We derive ages, metallicities andα-element abundance ratios from simple stellar population modelsusing the recent multi-index χ2 minimization method ofProctor & Sansom. All of these GCs are found to be consistent withold ages, i.e. >~10Gyr, with a wide range of metallicities. This iscomparable to the ages and metallicities that Gregg et al. found acouple of years ago for resolved stellar populations in the outerregions of this elliptical. A trend of decreasing α-elementabundance ratio with increasing metallicity is indicated.The projected velocity dispersion of the GC system is consistent withbeing constant with radius. Non-parametric, isotropic models require asignificant increase in the mass-to-light ratio at large radii. Thisresult is in contrast to that of Romanowsky et al., who recently found adecrease in the velocity dispersion profile as determined from planetarynebulae (PN). Our constant dispersion requires a normal-sized dark halo,although without anisotropic models we cannot rigorously determine thedark halo mass.A two-sided χ2 test over all radii gives a 2σdifference between the mass profile derived from our GCs compared to thePN-derived mass model of Romanowsky et al. However, if we restrict ouranalysis to radii beyond one effective radius and test if the GCvelocity dispersion is consistently higher, we determine a > 3σdifference between the mass models, and hence we favour the conclusionthat NGC 3379 does indeed have dark matter at large radii in its halo.
| A Chandra Survey of Early-Type Galaxies. I. Metal Enrichment in the Interstellar Medium
We present a Chandra study of the emission-weighted metal abundances in28 early-type galaxies, spanning ~3 orders of magnitude in X-rayluminosity (LX). We report constraints for Fe, O, Ne, Mg, Si,S, and Ni. We find no evidence of the very subsolar Fe abundance(ZFe) historically reported, confirming a trend in recentobservations of bright galaxies and groups, nor do we find anycorrelation between ZFe and luminosity. Excepting one case,the ISM is single-phase, indicating that multitemperature fits foundwith ASCA reflected temperature gradients that we resolve with Chandra.We find no evidence that ZFe (ISM) is substantially lowerthan the stellar metallicity estimated from simple stellar populationmodels. In general, these quantities are similar, which is inconsistentwith galactic wind models and recent hierarchical chemical enrichmentsimulations. Our abundance ratio constraints imply that 66%+/-11% of theISM Fe was produced in SNe Ia, similar to the solar neighborhood,indicating similar enrichment histories for elliptical galaxies and theMilky Way. Although these values are sensitive to the considerablesystematic uncertainty in the supernova yields, they are in agreementwith observations of more massive systems. This indicates considerablehomology in the enrichment process operating from cluster scales tolow-to-intermediate-LX galaxies. The data uniformly exhibitlow ZO/ZMg ratios, which have been reported insome clusters, groups, and galaxies. This is inconsistent with standardSN II metal yield calculations and may indicate an additional source ofenrichment, such as Population III hypernovae.
| 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.
| Peculiarities and populations in elliptical galaxies. III. Dating the last star formation event
Using 6 colours and 4 Lick line-indices we derive two-component modelsof the populations of ellipticals, involving a "primary" and a"juvenile" population. The first component is defined by the regressionsof indices against the central velocity dispersion found in Papers I andII for the {Nop} sample of non-peculiar objects. The second one isapproximated by an SSP, and the modeling derives its age A, metallicityZ and fractional V-luminosity q_V, the fractional mass qMbeing found therefrom. The model is designed for "blueish" peculiargalaxies, i.e. the {Pec} sample and NGC 2865 family in the terminologyof Paper I. The morphological peculiarities and the population anomalyare then believed to involve the same event, i.e. a merger plusstarburst. It is possible to improve the models in a few cases byintroducing diffuse dust (as suggested by far IR data), and/or by takinginto account the fact that Lick- and colour indices do not relate toidentical galaxy volumes. In most of the cases, the mass ratio of youngstars qM seems too small for the product of a recent majormerger: the events under consideration might be minor mergers bringing"the final touch" to the build-up of the structure of the E-type object.The same modeling has been successfully applied to blueish galaxies ofthe {Nop} sample, without morphological peculiarities however, tosupport the occurence of a distinct perturbing event. A few reddishobjects of the {Pec} sample (NGC 3923 family) and of the {Nop} sampleare also modeled, in terms of an excess of high metallicity stars, ordiffuse dust, or both, but the results are inconclusive.
| Stellar populations in a complete sample of local radio galaxies
We investigate the nature of the continuum emission and stellarpopulations in the inner 1-3 kpc of a complete sample of 24 southernradio galaxies, and we compare the results with a control sample of 18non-active early-type galaxies. 12 of the radio galaxies are classifiedas Fanaroff-Riley type I (FR I), eight as FR II and four as intermediateor undefined type (FR x). Optical long-slit spectra are used to performspectral synthesis as a function of distance from the nucleus at anaverage sampling of 0.5-1.0 kpc and to quantify the relativecontributions of a blue featureless continuum and stellar populationcomponents of different ages. Our main finding is a systematicdifference between the stellar populations of the radio and controlsample galaxies: the former have a larger contribution from anintermediate-age (1 Gyr) component, suggesting a connection between thepresent radio activity and a starburst which occurred ~1 Gyr ago. Inaddition, we find a correlation between the contribution of the 1-Gyrcomponent and the radio power, suggesting that more massive starburstshave led to more powerful radio emission. A similar relation is foundbetween the radio power and the mean age of the stellar population, inthe sense that stronger nuclear activity is found in younger galaxies.We also find that the stellar populations of FR I galaxies are, onaverage, older and more homogeneous than those of FR IIs. Significantpopulation gradients were found in only four radio galaxies, which arealso those with more than 10 per cent of their total flux at 4020Åcontributed by age components younger than 100 Myr and/or afeatureless continuum (indistinguishable from a 3-Myr-old stellarpopulation).
| The X-ray emission properties and the dichotomy in the central stellar cusp shapes of early-type galaxies
The Hubble Space Telescope has revealed a dichotomy in the centralsurface brightness profiles of early-type galaxies, which havesubsequently been grouped into two families: core, boxy, anisotropicsystems; and cuspy (`power-law'), discy, rotating ones. Here weinvestigate whether a dichotomy is also present in the X-ray propertiesof the two families. We consider both their total soft emission(LSX,tot), which is a measure of the galactic hot gascontent, and their nuclear hard emission (LHX,nuc), mostlycoming from Chandra observations, which is a measure of the nuclearactivity. At any optical luminosity, the highest LSX,totvalues are reached by core galaxies; this is explained by their beingthe central dominant galaxies of groups, subclusters or clusters, inmany of the logLSX,tot (ergs-1) >~ 41.5 cases.The highest LHX,nuc values, similar to those of classicalactive galactic nuclei (AGNs), in this sample are hosted only by core orintermediate galaxies; at low luminosity AGN levels, LHX,nucis independent of the central stellar profile shape. The presence ofoptical nuclei (also found by HST) is unrelated to the level ofLHX,nuc, even though the highest LHX,nuc are allassociated with optical nuclei. The implications of these findings forgalaxy evolution and accretion modalities at the present epoch arediscussed.
| O VI in Elliptical Galaxies: Indicators of Cooling Flows
Early-type galaxies often contain a hot X-ray-emitting interstellarmedium [(3-8)×106 K] with an apparent radiative coolingtime much less than a Hubble time. If unopposed by a heating mechanism,the gas will radiatively cool to temperatures <~104 K at arate proportional to LX/TX, typically 0.03-1Msolar yr-1. We can test whether gas is coolingthrough the 3×105 K range by observing the O VIdoublet, whose luminosity is proportional to the cooling rate. Here wereport on a study of an unbiased sample of 24 galaxies, obtaining FarUltraviolet Spectroscopic Explorer spectra to complement the X-ray dataof ROSAT and Chandra. The O VI line emission was detected in about 40%of the galaxies and at a luminosity level similar to the prediction fromthe cooling flow model. There is a correlation betweenM˙OVI and M˙X, although there issignificant dispersion about the relationship, where the O VI isbrighter or dimmer than expected by a factor of 3 or more. If thecooling flow picture is to be retained, then this dispersion requiresthat cooling flows be time-dependent, as might occur by the activity ofan AGN. However, of detected objects, those with the highest or lowestvalues of M˙OVI/M˙X are not systematicallyhot or cool, as one might predict from AGN heating.
| The Centers of Early-Type Galaxies with Hubble Space Telescope. V. New WFPC2 Photometry
We present observations of 77 early-type galaxies imaged with the PC1CCD of the Hubble Space Telescope (HST) WFPC2. ``Nuker-law'' parametricfits to the surface brightness profiles are used to classify the centralstructure into ``core'' or ``power-law'' forms. Core galaxies aretypically rounder than power-law galaxies. Nearly all power-law galaxieswith central ellipticities ɛ>=0.3 have stellar disks,implying that disks are present in power-law galaxies withɛ<0.3 but are not visible because of unfavorable geometry. Afew low-luminosity flattened core galaxies also have disks; these may betransition forms from power-law galaxies to more luminous core galaxies,which lack disks. Several core galaxies have strong isophote twistsinterior to their break radii, although power-law galaxies have interiortwists of similar physical significance when the photometricperturbations implied by the twists are evaluated. Central colorgradients are typically consistent with the envelope gradients; coregalaxies have somewhat weaker color gradients than power-law galaxies.Nuclei are found in 29% of the core galaxies and 60% of the power-lawgalaxies. Nuclei are typically bluer than the surrounding galaxy. Whilesome nuclei are associated with active galactic nuclei (AGNs), just asmany are not; conversely, not all galaxies known to have a low-level AGNexhibit detectable nuclei in the broadband filters. NGC 4073 and 4382are found to have central minima in their intrinsic starlightdistributions; NGC 4382 resembles the double nucleus of M31. In general,the peak brightness location is coincident with the photocenter of thecore to a typical physical scale of <1 pc. Five galaxies, however,have centers significantly displaced from their surrounding cores; thesemay be unresolved asymmetric double nuclei. Finally, as noted byprevious authors, central dust is visible in about half of the galaxies.The presence and strength of dust correlates with nuclear emission;thus, dust may outline gas that is falling into the central black hole.The prevalence of dust and its morphology suggest that dust clouds form,settle to the center, and disappear repeatedly on ~108 yrtimescales. We discuss the hypothesis that cores are created by thedecay of a massive black hole binary formed in a merger. Apart fromtheir brightness profiles, there are no strong differences between coregalaxies and power-law galaxies that demand this scenario; however, therounder shapes of core, their lack of disks, and their reduced colorgradients may be consistent with it.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy (AURA), Inc.,under NASA contract NAS 5-26555. These observations are associated withGO and GTO proposals 5236, 5446, 5454, 5512, 5943, 5990, 5999, 6099,6386, 6554, 6587, 6633, 7468, 8683, and 9107.
| Near infra-red and optical colour gradients in E-type galaxies. Inferences on dust content
Colour gradients are considered for a sample of circa 50 E-type galaxiesin the Local Supercluster. The new data includes isophotal colourprofiles in J-H, J-K, V-J and V-K, measured using 2MASS frames mostlyfrom the Large Galaxies Atlas, V frames from previous work and Vprofiles from the literature. This is supplemented by U-B, B-V, B-R, V-Icolour gradients obtained anew from published photometric data. Colourgradients in E galaxies show remarkably large variations from object toobject and do not correlate with other properties. Metallicity gradientsare the primary cause as shown before. Age gradients with oppositeeffects are possibly needed to explain objects with small colourgradients. Some empirical evidence of such age effects has been foundfor a subset of objects with morphological peculiarities and youngerstars mixed. Dust has only modest effects on colour gradients, as shownby the fact that objects with zero IRAS 100 μ flux have the sameaverage values of the gradients, except in V-J and V-K, as those withnon zero flux (cf. Table 7). This last subsample however exhibits poorbut definite correlations between IRAS flux and gradients, which mightbe caused by the presence of a few relatively dusty galaxies in thesample. Given the absence of a correlation between any gradients andgalaxy velocity dispersion (and hence mass), the observations do notagree with the predictions of the monolithic scenario for the formationof E galaxies. Simulated datasets of “dummy” objectsmimicking the hierarchical scenario have been obtained, and used to testa technique for estimating the dust content of E-galaxies from thecomparison of the V-K (or V-J) colour gradients with the U-B (or B-V)ones: the contents of diffuse dust, gauged in terms of published models,are obtained for a dozen objects.
| VLT spectroscopy of globular cluster systems. II. Spectroscopic ages, metallicities, and [ α/Fe] ratios of globular clusters in early-type galaxies
An analysis of ages, metallicities, and [ α/Fe] ratios of globularcluster systems in early-type galaxies is presented, based on Lick indexmeasurements summarized in Puzia et al. (2004, A&A, 415, 123, PaperI of this series). In the light of calibration and measurementuncertainties, age-metallicity degeneracy, and the relative dynamicrange of Lick indices, as well as systematics introduced by abundanceratio variations (in particular variations of [ α/Fe] ratios), wefind that the most reliable age indicator for our dataset is acombination of the Lick Balmer-line indices Hγ_A, Hβ, andHδ_A. [MgFe]´ is used as a spectroscopic metallicityindicator which is least affected by [ α/Fe] variations. Weintroduce an interpolation routine to simultaneously derive ages,metallicities, and [ α/Fe] ratios from diagnostic gridsconstructed from Lick indices. From a comparison of high-quality datawith SSP model predictions, we find that 2/3 of the globular clustersin early-type galaxies are older than 10 Gyr, up to 1/3 have ages in therange 5{-}10 Gyr, and only a few cluster are younger than 5 Gyr. Oursample of globular clusters covers metallicities from [Z/H] ≈ -1.3 upto 0.5 dex. We find that metal-rich globular clusters show on average asmaller mean age and a larger age scatter than their metal-poorcounterparts. [ α/Fe] diagnostic plots show that globular clustersystems in early-type galaxies have super-solar α/Fe abundanceratios with a mean [ α/Fe] = 0.47 ± 0.06 dex and adispersion of 0.3 dex. We find evidence for a correlation between [α/Fe] and metallicity, in the sense that more metal-rich clustersexhibit lower α-element enhancements. A discussion of systematicsrelated to the Lick index system shows that the method suffers to someextent from uncertainties due to unknown horizontal branch morphologiesat high metallicities. However, these systematics still allow us to makegood qualitative statements. A detailed investigation of indices as afunction of data quality reveals that the scatter in Balmer index valuesdecreases for higher-quality data. In particular, extremely low Balmerindex values that are lower than any SSP model prediction tend todisappear. Furthermore, we find that observed photometric colors are ingood agreement with computed SSP colors using ages and metallicities asderived from the spectroscopic line indices.
| Peculiarities and populations in elliptical galaxies. II. Visual-near IR colours as population indices
As a complement to the data collected and discussed in Paper I of thisseries, 2MASS near-IR images have been used, in connection withavailable V light aperture photometry, to derive the colours V-J, V-K,J-H and J-K within the effective aperture A_e: nearly the same completesample of 110 E-type galaxies is treated. In Paper I these wereclassified, based on morphological criteria, into the ``peculiar'' (orPec) and ``normal'' (or Nop) subsamples. For the Nop subsample, thederived colour indices are tightly related to the galaxy masses, asmeasured by the central velocity dispersion σ0,although with rather small slopes as regards J-H and J-K. For the Pecsubsample, the V-J and V-K colours behave as UBV and line-indices: partof the objects show blue residuals from the appropriatecolour-σ0 regression, which is evidence of a youngerpopulation mixed with the ``normal'' one traced by the Nop regressions;the other shows no deviations from the Nop subsample. The distinctionamong Pec objects between the YP family (NGC 2865 type), and the NP one(NGC 3923 type), is statistically supported, and generally confirmed inspecific cases.Based in part on observations collected at the Observatoire deHaute-Provence.Table 4 is only available in electonic form at the CDS via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/429/819
| XMM-Newton and Chandra observations of three X-ray-faint early-type galaxies
We present XMM-Newton observations of three X-ray-underluminouselliptical galaxies, NGC 3585, 4494 and 5322. All three galaxies haverelatively large optical luminosities (logLB= 10.35-10.67Lsolar) but have X-ray luminosities consistent with emissionfrom discrete sources only. In conjunction with a Chandra observation ofNGC 3585, we analyse the XMM-Newton data and show that the threegalaxies are dominated by discrete source emission, but do possess someX-ray-emitting gas. The gas is at relatively low temperatures, kT~=0.25-0.44 keV. All three galaxies show evidence of recent dynamicaldisturbance and formation through mergers, including kinematicallydistinct cores, young stellar ages and embedded stellar discs. Thisleads us to conclude that the galaxies formed relatively recently andhave yet to build up large X-ray haloes. They are likely to be in adevelopmental phase where the X-ray gas has a very low density, makingit undetectable outside the galaxy core. However, if the gas is aproduct of stellar mass loss, as seems most probable, we would expect toobserve supersolar metal abundances. While abundance is not wellconstrained by the data, we find best-fitting abundances <0.1Zsolar for single-temperature models, and it seems unlikelythat we could underestimate the metallicity by such a large factor.
| The Ultraluminous X-Ray Source Population from the Chandra Archive of Galaxies
One hundred fifty-four discrete non-nuclear ultraluminous X-ray (ULX)sources, with spectroscopically determined intrinsic X-ray luminositiesgreater than 1039 ergs s-1, are identified in 82galaxies observed with Chandra's Advanced CCD Imaging Spectrometer.Source positions, X-ray luminosities, and spectral and timingcharacteristics are tabulated. Statistical comparisons between theseX-ray properties and those of the weaker discrete sources in the samefields (mainly neutron star and stellar-mass black hole binaries) aremade. Sources above ~1038 ergs s-1 display similarspatial, spectral, color, and variability distributions. In particular,there is no compelling evidence in the sample for a new and distinctclass of X-ray object such as the intermediate-mass black holes.Eighty-three percent of ULX candidates have spectra that can bedescribed as absorbed power laws with index <Γ>=1.74 andcolumn density =2.24×1021cm-2, or ~5 times the average Galactic column. About 20% ofthe ULXs have much steeper indices indicative of a soft, and likelythermal, spectrum. The locations of ULXs in their host galaxies arestrongly peaked toward their galaxy centers. The deprojected radialdistribution of the ULX candidates is somewhat steeper than anexponential disk, indistinguishable from that of the weaker sources.About 5%-15% of ULX candidates are variable during the Chandraobservations (which average 39.5 ks). Comparison of the cumulative X-rayluminosity functions of the ULXs to Chandra Deep Field results suggests~25% of the sources may be background objects, including 14% of the ULXcandidates in the sample of spiral galaxies and 44% of those inelliptical galaxies, implying the elliptical galaxy ULX population isseverely compromised by background active galactic nuclei. Correlationswith host galaxy properties confirm the number and total X-rayluminosity of the ULXs are associated with recent star formation andwith galaxy merging and interactions. The preponderance of ULXs instar-forming galaxies as well as their similarities to less-luminoussources suggest they originate in a young but short-lived populationsuch as the high-mass X-ray binaries with a smaller contribution (basedon spectral slope) from recent supernovae. The number of ULXs inelliptical galaxies scales with host galaxy mass and can be explainedmost simply as the high-luminosity end of the low-mass X-ray binarypopulation.
| A Chandra View of the Normal S0 Galaxy NGC 1332. II. Solar Abundances in the Hot Gas and Implications for Supernova Enrichment
Using a new Chandra ACIS-S3 observation of the normal, isolated,moderate-LX lenticular galaxy NGC 1332, we resolve theemission into ~75 point sources and a significant diffuse component. Wepresent a detailed analysis of the spectral properties of the diffuseemission, constraining both the temperature profile and the metalabundances in the hot gas. The characteristics of the point-sourcepopulation and the spatial properties of the diffuse emission arediscussed in two companion papers. The diffuse component comprises hotgas with an ~isothermal temperature profile (~0.5 keV) and emission fromunresolved point sources. In contrast with the cool cores of many groupsand clusters, we find a small central temperature peak. We obtainemission-weighted abundance constraints within 20 kpc for several keyelements: Fe, O, Ne, Mg, and Si. The measured iron abundance(ZFe=1.1 in solar units; >0.53 at 99% confidence) stronglyexcludes the very subsolar values often historically reported forearly-type galaxies. This continues, in a lower LX system, atrend in recent observations of bright galaxies and groups. Theabundance ratios, with respect to Fe, of the other elements were alsofound to be ~solar, with the exception of ZO/ZFe,which was significantly lower (<0.4), as seen in several brightgalaxies, groups, and clusters. Such a low O abundance is not predictedby simple models of ISM enrichment by Type Ia and Type II supernovae(SNe) and may indicate a significant contribution from primordialhypernovae. Revisiting Chandra observations of themoderate-LX, isolated elliptical galaxy NGC 720, we obtainsimilar abundance constraints(ZFe=0.71+0.40-0.21, 90% confidence;ZO/ZFe=0.23+/-0.21). Adopting standard SNe Ia andSNe II metal yield models, our abundance ratio constraints imply that73%+/-5% and 85%+/-6% of the Fe enrichment in NGC 1332 and NGC 720,respectively, arises from SNe Ia. Although these results are sensitiveto the considerable systematic uncertainty in the SNe yields, they arein good agreement with observations of more massive systems. These twocases of moderate-LX early-type galaxies reveal a consistentpattern of metal enrichment from cluster scales to moderateLX/LB galaxies.
| Companions to Isolated Elliptical Galaxies: Revisiting the Bothun-Sullivan Sample
We investigate the number of physical companion galaxies for a sample ofrelatively isolated elliptical galaxies. The NASA/IPAC ExtragalacticDatabase (NED) has been used to reinvestigate the incidence of satellitegalaxies for a sample of 34 elliptical galaxies, first investigated byBothun & Sullivan using a visual inspection of Palomar Sky Surveyprints out to a projected search radius of 75 kpc. We have repeatedtheir original investigation using data cataloged in NED. Nine of theseelliptical galaxies appear to be members of galaxy clusters; theremaining sample of 25 galaxies reveals an average of +1.0+/-0.5apparent companions per galaxy within a projected search radius of 75kpc, in excess of two equal-area comparison regions displaced by 150-300kpc. This is significantly larger than the +0.12+/-0.42companions/galaxy found by Bothun & Sullivan for the identicalsample. Making use of published radial velocities, mostly availablesince the completion of the Bothun-Sullivan study, identifies thephysical companions and gives a somewhat lower estimate of +0.4companions per elliptical galaxy. This is still 3 times larger than theoriginal statistical study, but given the incomplete and heterogeneousnature of the survey redshifts in NED, it still yields a firm lowerlimit on the number (and identity) of physical companions. An expansionof the search radius out to 300 kpc, again restricted to sampling onlythose objects with known redshifts in NED, gives another lower limit of4.5 physical companions per galaxy. (Excluding five elliptical galaxiesin the Fornax Cluster, this average drops to 3.5 companions perelliptical.) These physical companions are individually identified andlisted, and the ensemble-averaged radial density distribution of theseassociated galaxies is presented. For the ensemble, the radial densitydistribution is found to have a falloff consistent withρ~R-0.5 out to approximately 150 kpc. For non-FornaxCluster companions the falloff continues out to the 300 kpc limit of thesurvey. The velocity dispersion of these companions is found to reach amaximum of 350 km s-1 at around 120 kpc, after which theyfall at a rate consistent with Keplerian falloff. This falloff may thenindicate the detection of a cut-off in the mass-density distribution inthe elliptical galaxies' dark matter halo at ~100 kpc.
| The Lack of Very Ultraluminous X-Ray Sources in Early-Type Galaxies
We have searched for ultraluminous X-ray sources (ULXs) in a sample of28 elliptical and S0 galaxies observed with Chandra. We find that thenumber of X-ray sources detected at a flux level that would correspondto a 0.3-10 keV X-ray luminosity of ~2×1039 ergss-1 or greater (for which we have used the designation veryultraluminous X-ray sources [VULXs]) at the distance of each galaxy isequal to the number of expected foreground/background objects. Inaddition, the VULXs are uniformly distributed over the Chandra field ofview rather than distributed like the optical light of the galaxies,strengthening the argument that the high-flux sources are unassociatedwith the galaxies. We have also taken the VULX candidate list of Colbertand Ptak and determined the spatial distribution of VULXs in early-typegalaxies and late-type galaxies separately. While the spiral galaxyVULXs are clearly concentrated toward the centers of the galaxies, theearly-type galaxy VULXs are distributed randomly over the ROSAT HRIfield of view, again indicating that they are not associated with thegalaxies themselves. We conclude that with the exception of two rarehigh-luminosity objects within globular clusters of the ellipticalgalaxy NGC 1399, VULXs are generally not found within old stellarsystems. However, we do find a significant population of sources withluminosities of (1-2)×1039 ergs s-1 thatreside within the sample galaxies that can be explained by accretiononto 10-20 Msolar black holes. Given our results, we proposethat ULXs be defined as X-ray sources with LX(0.3-10keV)>2×1039 ergs s-1.
| Peculiarities and populations in elliptical galaxies. I. An old question revisited
Morphological peculiarities, as defined from isophote asymmetries andnumber of detected shells, jets or similar features, have been estimatedin a sample of 117 E classified galaxies, and qualified by an ad hocΣ2 index. The overall frequency of ``peculiar'' objects(Pec subsample) is 32.5%. It decreases with the cosmic density of theenvironment, being minimal for the Virgo cluster, the densestenvironment in the sampled volume. This environmental effect is strongerfor galaxies with relatively large Σ2.The Pec subsample objects are compared with ``normal'' objects (Nopsubsample) as regards their basic properties. Firstly, theysystematically deviate from the Fundamental Plane and the Faber-Jacksonrelation derived for the Nop subsample, being too bright for their mass.Secondly, the dust content of galaxies, as estimated from IRAS fluxes,are similar in both subsamples. Third, the same is true of the frequencyof Kinematically Distinct cores (KDC), suggesting that KDC andmorphological peculiarities do not result from the same events in thehistory of E-galaxies.Using the Nop sample alone, we obtain very tight reference relationsbetween stellar population indicators (U-B, B-V, B-R, V-I,Mg2, Hβ, , Mgb) and the central velocitydispersion σ0. The discussion of the residuals of theserelations allows us to classify the Pec galaxies in two families i.e.the YP or NGC 2865 family, and the NP or NGC 3923 one. Galaxies in thefirst group show consistent evidence for a younger stellar populationmixed with the old one, in agreement with classical results (Schweizeret al. \cite{Schweizer1990}; Schweizer & Seitzer\cite{Schweizer1992}). The second group, however, has ``normal``, orreddish, populations. It is remarkable that a fraction (circa 40%) ofmorphologically perturbed objects do not display any signature of ayoung population, either because the event responsible for thepecularity is too ancient, or because it did not produce significantstar formation (or eventually that the young sub-population has highmetallicity).A preliminary attempt is made to interpret the populations of Pecobjects by combining a young Single Stellar Population with a Nopgalaxy, with only limited success, perhaps largely due to uncertaintiesin the SSP indices used.Based in part on observations collected at the Observatoire deHaute-Provence.Figures \ref{fig1}-\ref{fig3} are only available in electronic form athttp://www.edpsciences.orgTable 10 is only 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/423/833
| VLT spectroscopy of globular cluster systems. I. The photometric and spectroscopic data set
We present Lick line-index measurements of extragalactic globularclusters in seven early-type galaxies (NGC 1380, 2434, 3115, 3379, 3585,5846, and 7192) with different morphological types (E-S0) located infield and group/cluster environments. High-quality spectra were takenwith the FORS2 instrument at ESO's Very Large Telescope. 50% of ourdata allows an age resolution Δ t/t≈0.3 and a metallicityresolution 0.25-0.4 dex, depending on the absolute metallicity.Globular cluster candidates are selected from deep B, V, R, I, KFORS2/ISAAC photometry with 80-100% success rate inside one effectiveradius. Using combined optical/near-infrared colour-colour diagrams wepresent a method to efficiently reduce fore-/background contaminationdown to 10%. We find clear signs for bi-modality in the globularcluster colour distributions of NGC 1380, 3115, and 3585. The colourdistributions of globular clusters in NGC 2434, 3379, 5846, and 7192 areconsistent with a broad single-peak distribution. For the analysedglobular cluster systems the slopes of projected radial surface densityprofiles, of the form Σ(R) R -Γ, varybetween 0.8 and 2.6. Blue and red globular cluster sub-populationsshow similar slopes in the clearly bi-modal systems. For galaxies withsingle-peak globular cluster colour distributions, there is a hint thatthe blue cluster system seems to have a more extended radialdistribution than the red one. Using globular clusters as a tracerpopulation we determine total dynamical masses of host galaxies out tolarge radii (1.6-4.8 R_eff). For the sample we find masses in therange 8.8×1010 M_ȯ up to1.2×1012 M_ȯ. The line index data presentedhere will be used in accompanying papers of this series to derive ages,metallicities and abundance ratios. A compilation of currently availablehigh-quality Lick index measurements for globular clusters inelliptical, lenticular, and late-type galaxies is provided and willserve to augment the current data set.Based on observations collected at the European Southern Observatory,Cerro Paranal, Chile under programme ID P65.N-0281, P66.B-0068, andP67.B-0034.Appendix A is only available in electronic form athttp://www.edpsciences.orgAppendices B and C are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/415/123
| X-Ray Spectral Properties of Low-Mass X-Ray Binaries in Nearby Galaxies
We have investigated the X-ray spectral properties of a collection oflow-mass X-ray binaries (LMXBs) within a sample of 15 nearby early-typegalaxies using proprietary and archival data from the Chandra X-RayObservatory. We find that the spectrum of the sum of the sources in agiven galaxy is remarkably similar from galaxy to galaxy when onlysources with X-ray luminosities less than 1039 ergss-1 (0.3-10 keV) are considered. Fitting these lowerluminosity sources in all galaxies simultaneously with a power-law modelled to a best-fit power-law exponent of Γ=1.56+/-0.02 (90%confidence), and using a thermal bremsstrahlung model yieldedkTbrem=7.3+/-0.3 keV. This is the tightest constraint to dateon the spectral properties of LMXBs in external galaxies. The spectralproperties of the LMXBs do not vary with galactic radius out to threeeffective radii. There is also no apparent difference between thespectral properties of LMXBs that reside within globular clusters andthose that do not. We demonstrate how the uniformity of the spectralproperties of LMXBs can lead to more accurate determinations of thetemperature and metallicity of the hot gas in galaxies that havecomparable amounts of X-ray emission from hot gas and LMXBs. Althoughfew in number in any given galaxy, sources with luminosities of(1-2)×1039 ergs s-1 are present in 10 of thegalaxies. The spectra of these luminous sources are softer than thespectra of the rest of the sources and are consistent with the spectraof Galactic black hole X-ray binary candidates when they are in theirvery high state. The spatial distribution of these sources is muchflatter than the optical light distribution, suggesting that asignificant portion of them must reside within globular clusters. Thesimplest explanation of these sources is that they are ~10-15Msolar black holes accreting near their Eddington limit. Thespectra of these sources are very different from those of ultraluminousX-ray sources (ULXs) that have been found within spiral galaxies,suggesting that the two populations of X-ray-luminous objects havedifferent formation mechanisms. The number of sources with apparentluminosities above 2×1039 ergs s-1 whendetermined using the distance of the galaxy is equal to the number ofexpected background active galactic nuclei and thus appears not to beassociated with the galaxy, indicating that very luminous sources areabsent or very rare in early-type galaxies. The lack of ULXs withinelliptical galaxies strengthens the argument that ULXs are associatedwith recent star formation.
| Redshift-Distance Survey of Early-Type Galaxies: Circular-Aperture Photometry
We present R-band CCD photometry for 1332 early-type galaxies, observedas part of the ENEAR survey of peculiar motions using early-typegalaxies in the nearby universe. Circular apertures are used to tracethe surface brightness profiles, which are then fitted by atwo-component bulge-disk model. From the fits, we obtain the structuralparameters required to estimate galaxy distances using theDn-σ and fundamental plane relations. We find thatabout 12% of the galaxies are well represented by a pure r1/4law, while 87% are best fitted by a two-component model. There are 356repeated observations of 257 galaxies obtained during different runsthat are used to derive statistical corrections and bring the data to acommon system. We also use these repeated observations to estimate ourinternal errors. The accuracy of our measurements are tested by thecomparison of 354 galaxies in common with other authors. Typical errorsin our measurements are 0.011 dex for logDn, 0.064 dex forlogre, 0.086 mag arcsec-2 for<μe>, and 0.09 for mRC,comparable to those estimated by other authors. The photometric datareported here represent one of the largest high-quality and uniformall-sky samples currently available for early-type galaxies in thenearby universe, especially suitable for peculiar motion studies.Based on observations at Cerro Tololo Inter-American Observatory (CTIO),National Optical Astronomy Observatory, which is operated by theAssociation of Universities for Research in Astronomy, Inc., undercooperative agreement with the National Science Foundation (NSF);European Southern Observatory (ESO); Fred Lawrence Whipple Observatory(FLWO); and the MDM Observatory on Kitt Peak.
| A new catalogue of ISM content of normal galaxies
We have compiled a catalogue of the gas content for a sample of 1916galaxies, considered to be a fair representation of ``normality''. Thedefinition of a ``normal'' galaxy adopted in this work implies that wehave purposely excluded from the catalogue galaxies having distortedmorphology (such as interaction bridges, tails or lopsidedness) and/orany signature of peculiar kinematics (such as polar rings,counterrotating disks or other decoupled components). In contrast, wehave included systems hosting active galactic nuclei (AGN) in thecatalogue. This catalogue revises previous compendia on the ISM contentof galaxies published by \citet{bregman} and \citet{casoli}, andcompiles data available in the literature from several small samples ofgalaxies. Masses for warm dust, atomic and molecular gas, as well asX-ray luminosities have been converted to a uniform distance scale takenfrom the Catalogue of Principal Galaxies (PGC). We have used twodifferent normalization factors to explore the variation of the gascontent along the Hubble sequence: the blue luminosity (LB)and the square of linear diameter (D225). Ourcatalogue significantly improves the statistics of previous referencecatalogues and can be used in future studies to define a template ISMcontent for ``normal'' galaxies along the Hubble sequence. The cataloguecan be accessed on-line and is also available at the Centre desDonnées Stellaires (CDS).The catalogue is available in electronic form athttp://dipastro.pd.astro.it/galletta/ismcat and at the CDS via anonymousftp to\ cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/405/5
| A catalogue and analysis of local galaxy ages and metallicities
We have assembled a catalogue of relative ages, metallicities andabundance ratios for about 150 local galaxies in field, group andcluster environments. The galaxies span morphological types from cD andellipticals, to late-type spirals. Ages and metallicities were estimatedfrom high-quality published spectral line indices using Worthey &Ottaviani (1997) single stellar population evolutionary models. Theidentification of galaxy age as a fourth parameter in the fundamentalplane (Forbes, Ponman & Brown 1998) is confirmed by our largersample of ages. We investigate trends between age and metallicity, andwith other physical parameters of the galaxies, such as ellipticity,luminosity and kinematic anisotropy. We demonstrate the existence of agalaxy age-metallicity relation similar to that seen for local galacticdisc stars, whereby young galaxies have high metallicity, while oldgalaxies span a large range in metallicities. We also investigate theinfluence of environment and morphology on the galaxy age andmetallicity, especially the predictions made by semi-analytichierarchical clustering models (HCM). We confirm that non-clusterellipticals are indeed younger on average than cluster ellipticals aspredicted by the HCM models. However we also find a trend for the moreluminous galaxies to have a higher [Mg/Fe] ratio than the lowerluminosity galaxies, which is opposite to the expectation from HCMmodels.
| 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.
| The Colors of Globular Clusters
A compilation has been made of available data on the ratio of the numberof metal-rich ([Fe/H]>-1.0) to metal-poor ([Fe/H]<-1.0) clustersin various globular cluster systems. Among early-type galaxies of typesE, E/S0, and S0, the ratio of blue to red globular clusters is found tovary by almost 2 orders of magnitude. The data suggest that cD galaxieshave the widest range of evolutionary histories. The fraction ofmetal-rich red clusters is largest among early-type galaxies and appearsto decrease toward later Hubble types.
| 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.
| A synthesis of data from fundamental plane and surface brightness fluctuation surveys
We perform a series of comparisons between distance-independentphotometric and spectroscopic properties used in the surface brightnessfluctuation (SBF) and fundamental plane (FP) methods of early-typegalaxy distance estimation. The data are taken from two recent surveys:the SBF Survey of Galaxy Distances and the Streaming Motions of AbellClusters (SMAC) FP survey. We derive a relation between(V-I)0 colour and Mg2 index using nearly 200galaxies and discuss implications for Galactic extinction estimates andearly-type galaxy stellar populations. We find that the reddenings fromSchlegel et al. for galaxies with E(B-V)>~0.2mag appear to beoverestimated by 5-10 per cent, but we do not find significant evidencefor large-scale dipole errors in the extinction map. In comparison withstellar population models having solar elemental abundance ratios, thegalaxies in our sample are generally too blue at a given Mg2;we ascribe this to the well-known enhancement of the α-elements inluminous early-type galaxies. We confirm a tight relation betweenstellar velocity dispersion σ and the SBF `fluctuation count'parameter N, which is a luminosity-weighted measure of the total numberof stars in a galaxy. The correlation between N and σ is eventighter than that between Mg2 and σ. Finally, we deriveFP photometric parameters for 280 galaxies from the SBF survey data set.Comparisons with external sources allow us to estimate the errors onthese parameters and derive the correction necessary to bring them on tothe SMAC system. The data are used in a forthcoming paper, whichcompares the distances derived from the FP and SBF methods.
| Cold gas in elliptical galaxies
We explore the evolution of the cold gas (molecular and neutralhydrogen) of elliptical galaxies and merger remnants ordered into a timesequence on the basis of spectroscopic age estimates. We find that thefraction of cold gas in early merger remnants decreases significantlyfor ~1-2Gyr, but subsequent evolution toward evolved elliptical systemssees very little change. This trend can be attributed to an initial gasdepletion by strong star formation, which subsequently declines toquiescent rates. This explanation is consistent with the merger picturefor the formation of elliptical galaxies. We also explore the relationbetween the HI-to-H2 mass ratio and spectroscopic galaxy age,but find no evidence for a statistically significant trend. Thissuggests little net HI-to-H2 conversion for the systems inthe present sample.
| Structural evolution in elliptical galaxies: the age-shape relation
We test the hypothesis that the apparent axial ratio of an ellipticalgalaxy is correlated with the age of its stellar population. We findthat old ellipticals (with estimated ages t>7.5Gyr) are rounder onaverage than younger ellipticals. The statistical significance of thisshape difference is greatest at small radii; a Kolmogorov-Smirnov testcomparing the axial ratios of the two populations at R=Re/16yields a statistical significance greater than 99.96 per cent. Therelation between age and apparent shape is linked to the core/power-lawsurface brightness profile dichotomy. Core ellipticals have olderstellar populations, on average, than power-law ellipticals and arerounder in their inner regions. Our findings are consistent with ascenario in which power-law ellipticals are formed in gas-rich mergers,while core ellipticals form in dissipationless mergers, with coresformed and maintained by the influence of a binary black hole.
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