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X-ray observations of three young, early-type galaxies
Massive haloes of hot plasma exist around some, but not all ellipticalgalaxies. There is evidence that this is related to the age of thegalaxy. In this paper, new X-ray observations are presented for threeearly-type galaxies that show evidence of youth, in order to investigatetheir X-ray components and properties. NGC 5363 and NGC 2865 were foundto have X-ray emission dominated by purely discrete stellar sources.Limits are set on the mass distribution in one of the galaxies observedwith XMM-Newton, NGC 4382, which contains significant hot gas. We detectthe X-ray emission in NGC 4382 out to 4re. The mass-to-lightratio is consistent with a stellar origin in the inner regions but risessteadily to values indicative of some dark matter by 4re.These results are set in context with other data drawn from theliterature, for galaxies with ages estimated from dynamical orspectroscopic indicators. Ages obtained from optical spectroscopyrepresent central luminosity-weighted stellar ages. We examine the X-rayevolution with age, normalized by B- and K-band luminosities. Low valuesof Log(LX/LB) and Log(LX/LK)are found for all galaxies with ages between 1 and 4 Gyr. Luminous X-rayemission only appears in older galaxies. This suggests that theinterstellar medium is removed and then it takes several gigayears forhot gas haloes to build up, following a merger. A possible mechanism forgas expulsion might be associated with feedback from an active nucleustriggered during a merger.
| Star formation history in early-type galaxies - I. The line absorption indices diagnostics
To unravel the formation mechanism and the evolutionary history ofelliptical galaxies (EGs) is one of the goals of modern astrophysics. Ina simplified picture of the issue, the question to be answered iswhether they have formed by hierarchical merging of pre-existingsubstructures (maybe disc galaxies) made of stars and gas, with eachmerging event probably accompanied by strong star formation, orconversely, whether they originated from the early aggregation of lumpsof gas turned into stars in the remote past via a burst-like episodeever since followed by quiescence so as to mimic a sort of monolithicprocess. Even if the two alternatives seem to oppose each other,actually they may both contribute to shaping the final properties of EGsas seen today. Are there distinct signatures of the underlying dominantprocess in the observational data? To this aim we have examined the lineabsorption indices on the Lick system of the normal, field EGs of Tragerand the interacting EGs (pair- and shell-objects) of Longhetti et al.The data show that both normal, field and interacting galaxies have thesame scattered but smooth distribution in the Hβ versus [MgFe]plane even if the interacting ones show a more pronounced tail towardhigh Hβ values. This may suggest that a common physical cause is atthe origin of their distribution. There are two straightforwardinterpretations of increasing complexity. (i) EGs span true large rangesof ages and metallicities. A young age is the signature of theaggregation mechanism, each event accompanied by metal enrichment. Thissimple scheme cannot, however, explain other spectro-photometricproperties of EGs and has to be discarded. (ii) The bulk population ofstars is old but subsequent episodes of star formation scatter the EGsin the diagnostic planes. However, this scheme would predict anoutstanding clump at low Hβ values, contrary to what is observed.The model can be cured by supposing that the primary star formationactivity lasted for a significant fraction of the Hubble time (5<=T<= 13 Gyr) accompanied by global metal enrichment. The`younger' galaxies are more metal-rich. The later burst of starformation should be small otherwise too many high-Hβ objects wouldbe observed. Therefore, the distribution of normal, pair- andshell-galaxies in the Hβ versus [MgFe] plane is due to global metalenrichment. Even though the above schemes provide a formal explanation,they seem to be too demanding because of the many ad hoc ingredientsthat have to be introduced. Furthermore, they neglect theobservationally grounded hint that the stellar content of EGs is likelyto be enhanced in α-elements with [α/Fe] ranging from 0.1 to0.4 dex. Here we propose a new scheme, in which the bulk dispersion ofgalaxies in the Hβ versus [MgFe] plane is caused by a differentmean degree of enhancement. In this model, neither the large age rangesnor the universal enrichment law for the old component are required andthe observed distribution along Hβ is naturally recovered.Furthermore, later bursts of stellar activity are a rare event,involving only those galaxies with very high Hβ (roughly >2.5).Finally, simulations of the scatter in broad-band colours of EGs seem toconfirm that the bulk stars have formed in the remote past, and thatmergers and companion star formation in a recent past are not likely,unless the intensity of the secondary activity is very small.
| 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.
| 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.
| Nature and environment of Very Luminous Galaxies
The most luminous galaxies in the blue passband have a largercorrelation amplitude than L* galaxies. They do not appear tobe preferentially located in rich clusters or groups, but a significantfraction of them seem to be in systems which include fainter members. Wepresent an analysis of fields centered on 18 Very Luminous Galaxies(MB <=-21) selected from the Southern Sky Redshift Survey2, based on new observations and public data of the 2dF Galaxy RedshiftSurvey; we present also additional data on a CfA VLG and on Arp 127. Wefind that all the selected VLGs are physically associated with faintercompanions. Moreover, there is a relation between the VLG morphology(early or late) and the dynamical properties of the system, whichreflects the morphology-density relation. 6 out of the 18 SSRS2 VLGs areearly type galaxies: 2 are in the center of rich Abell clusters withvelocity dispersion sigma ~ 600 km s-1, and the other 4are in poor clusters or groups with sigma ~ 300. The VLG extractedfrom the CfA catalog is also an elliptical in a Zwicky cluster. Theremaining 2/3 of the sample are late-type VLGs, generally found inpoorer systems with a larger spread in velocity dispersion, from ~ 100up to ~ 750 km s-1. The low velocity dispersion, late-typeVLG dominated systems appear to be analogous to our own Local Group. Thepossibile association of VLG systems with dark matter halos with masscomparable to rich groups or clusters, as suggested by the comparablecorrelation amplitude, would imply significant differences in the galaxyformation process. This work also shows that observing fields aroundVLGs represents an effective way of identifying galaxy systems which arenot selected through other traditional techniques.Figures 1, 2 and Appendix B are only available in electronic form athttp://www.edpsciences.org
| 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.
| Redshift-Distance Survey of Early-Type Galaxies. I. The ENEARc Cluster Sample
This paper presents data on the ENEARc subsample of the larger ENEARsurvey of nearby early-type galaxies. The ENEARc galaxies belong toclusters and were specifically chosen to be used for the construction ofa Dn-σ template. The ENEARc sample includes newmeasurements of spectroscopic and photometric parameters (redshift,velocity dispersion, line index Mg2, and the angular diameterdn), as well as data from the literature. New spectroscopicdata are given for 229 cluster early-type galaxies, and new photometryis presented for 348 objects. Repeat and overlap observations withexternal data sets are used to construct a final merged catalogconsisting of 640 early-type galaxies in 28 clusters. Objectivecriteria, based on catalogs of groups of galaxies derived from completeredshift surveys of the nearby universe, are used to assign galaxies toclusters. In a companion paper, these data are used to construct thetemplate Dn-σ distance relation for early-typegalaxies, which has been used to estimate galaxy distances and derivepeculiar velocities for the ENEAR all-sky sample. Based on observationsat Complejo Astronomico El Leoncito, operated under agreement betweenthe Consejo Nacional de Investigaciones Científicas de laRepública Argentina and the National Universities of La Plata,Córdoba, and San Juan; Cerro Tololo Inter-American Observatory,National Optical Astronomical Observatory, which is operated by theAssociation of Universities for Research in Astronomy, Inc., undercooperative agreement with the National Science Foundation; the EuropeanSouthern Observatory (ESO), partially under the ESO-ON agreement; theFred Lawrence Whipple Observatory; the Observatório do Pico dosDias, operated by the Laboratório Nacional de Astrofísicaand the MDM Observatory at Kitt Peak.
| Line-strength indices and velocity dispersions for 148 early-type galaxies in different environments
We have derived high quality line-strength indices and velocitydispersions for a sample of 148 early-type galaxies in differentenvironments. The wavelength region covered by the observations (lambda=~ 4600 to 6600 Å) includes the Lick/IDS indices Hβ,Mg1, Mg2, Mgb, Fe5015, Fe5270, Fe5335, Fe5406,Fe5709, Fe5782, NaD, TiO1 and TiO2. The data areintended to address possible differences of the stellar populations ofearly-type galaxies in low- and high-density environments. This paperdescribes the sample properties, explains the data reduction andpresents the complete list of all the measurements. Most galaxies of thesample (85%) had no previous measurements of any Lick/IDS indices andfor 30% of the galaxies we present first-time determinations of theirvelocity dispersions. Special care is taken to identify galaxies withemission lines. We found that 62 per cent of the galaxies in the samplehave emission lines, as measured by the equivalent width of the [OIII]5007Å line, EW[OIII] > 0.3 Å. Tables 5 and 6 are onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/ A+A/395/431. They are also available via ftp atftp.mpe.mpg.de in the directory people/dthomas/Beuing02 or via WWW atftp://ftp.mpe.mpg.de/people/dthomas/Beuing02.
| 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.
| 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.
| 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.
| Four Extreme Relic Radio Sources in Clusters of Galaxies
We describe the results of the highest-resolution radio observations yetmade of four relic radio sources in the Abell clusters A13, A85, A133,and A4038. Our Very Large Array images at 1.4 GHz with 4" resolution anda noise level of 1 σ~20 μJy beam-1 (1.1 K) show aremarkable variety of fine structure in the form of spectacular arcs,wisps, plumes, and loops. Their integrated radio flux densities fallvery rapidly with frequency, with power-law slopes, α, between 2.1and 4.4 near 1.4 GHz [where Sν~(ν/ν0)-α]. The relics possess linear polarizationlevels ranging between 2.3% (A133) and 35% (A85) the higher polarizationfractions imply a highly ordered magnetic field in the fine structureand low differential Faraday rotation in the intervening cluster gas.The optical identification of a host galaxy formerly associated with arelic remains problematic. In A85, A133, and A4038 the travel times forthe brightest cluster galaxies are significantly longer than the modeledages of the relics; there is always at least one nearby relativelybright elliptical galaxy that provides a better match. Excess X-rayemission in the 0.5 to 2 keV band was found near the relics in A85 andA133. The surface brightness was too high to be attributed to theinverse Compton mechanism alone. We found excellent fits to thebroadband radio spectra using the anisotropic model of spectral aging,and we have extended the model to include diffusion of particles betweenregions of different field strength. The steep radio spectra imply agesfor the relics of ~108 yr, at the start of which period theirradio luminosities would have been ~1025 W Hz-1 at1.4 GHz, and so their progenitors were on the boundary between FR I andFR II radio galaxies and hence among the most luminous 7% of radiogalaxies. We find that the relics are in approximate pressureequilibrium with the surrounding intracluster gas, which has probablylimited their free expansion and prevented them from fading by adiabaticcooling.
| Star formation history of early-type galaxies in low density environments. IV. What do we learn from nuclear line-strength indices?
In this paper we analyze the line-strength indices in the Lick-systemmeasured by Longhetti et al. (1998a, b) for a sample of 51 early-typegalaxies located in low density environments (LDE) and showingsignatures of fine structures and/or interactions. The sample contains21 shell-galaxies and 30 members of interacting pairs. Firstly weperform a preliminary comparison between three different sources ofcalibrations of the line strength indices, namely Buzzoni et al. (1992,1994), Worthey (1992), Worthey et al. (1994) and Idiart et al. (1995),derived from stars with different effective temperature, gravity, andmetallicity. Looking at the three indices in common, i.e. Mg2, Fe5270,and Hβ , the calibrations by Buzzoni et al. (1992, 1994), Worthey(1992) and Worthey et al. (1994) lead to mutually consistent results.The calibration of Hβ by Idiart et al. (1995) can be compared withthe previous ones only for a limited range of ages, in which goodagreement is found. Mg2 and Mgb indices predicted by the Idiart's et al.(1995) fitting functions result to be systematically lower than thoseobtained from using Worthey (1992) calibrations. Secondly, we discussthe properties of the galaxies in our sample by comparing them both withtheoretical Single Stellar Populations (SSPs) and the normal galaxies ofthe González (1993: G93) sample. The analysis is performed bymeans of several diagnostic planes. In the sigma , Mg2, Fe5270 andFe5335 space, normal, shell- and pair-galaxies have a differentbehavior. First of all, normal and pair-galaxies follow the universalsigma vs. Mg2 relation, whereas shell-galaxies lie above it; secondlythe Fe versus Mg2 relation of normal, shell- and pair-galaxies isflatter than the theoretical expectation. This fact hints forenhancement of alpha -elements with respect to solar partition ingalaxies with strong Fe indices and/or high velocity dispersion, massand luminosity in turn. In the sigma vs. Hβ plane normal galaxiesseem to follow a nice relation suggesting that objects with shallowgravitational potential have strong Hβ values (youth signature?),whereas shell- and pair-galaxies scatter all over the plane. A group ofgalaxies with deep gravitational potential and strong Hβ is found.Is this a signature of recent star formation? In the Hβ vs. [MgFe]plane, which is perhaps best suited to infer the age of the stellarpopulations, the peculiar galaxies in our sample show nearly the samedistribution of the normal galaxies in the G93 sample. There is howevera number of peculiar galaxies with much stronger Hβ . Does thismean that the scatter in the Hβ vs. [MgFe] plane, of normal, shell-and pair-galaxies has a common origin, perhaps a secondary episode ofstar formation? We suggest that, owing to their apparent youth, shell-and pair-galaxies should have experienced at least one interaction eventafter their formation. The explanation comes natural for shell- andpair-galaxies where the signatures of interactions are evident. It ismore intrigued in normal galaxies (perhaps other causes may concur).Noteworthy, the distribution in the Hβ vs. [MgFe] plane of normal,shell- and pair-galaxies is confined within a narrow strip that runssignificantly steeper than the path followed by aging SSPs. This featureis explained as due to metal enrichment always accompanying starformation. Shell-galaxies encompass the whole range of ages inferredfrom the Hβ vs. [MgFe] plane, indicating that among them recent andold interaction/acquisition events are equally probable. If shells areformed at the same time at which the rejuvenating event took place,shells ought to be long lasting phenomena. [MgFe] = sqrt { xMgb}, = (Fe5270 + Fe5335)/2 }
| X-ray luminosities for a magnitude-limited sample of early-type galaxies from the ROSAT All-Sky Survey
For a magnitude-limited optical sample (B_T <= 13.5 mag) ofearly-type galaxies, we have derived X-ray luminosities from the ROSATAll-Sky Survey. The results are 101 detections and 192 useful upperlimits in the range from 10^36 to 10^44 erg s^-1. For most of thegalaxies no X-ray data have been available until now. On the basis ofthis sample with its full sky coverage, we find no galaxy with anunusually low flux from discrete emitters. Below log (L_B) ~ 9.2L_⊗ the X-ray emission is compatible with being entirely due todiscrete sources. Above log (L_B) ~ 11.2 L_osolar no galaxy with onlydiscrete emission is found. We further confirm earlier findings that L_xis strongly correlated with L_B. Over the entire data range the slope isfound to be 2.23 (+/- 0.12). We also find a luminosity dependence ofthis correlation. Below log L_x = 40.5 erg s^-1 it is consistent with aslope of 1, as expected from discrete emission. Above this value theslope is close to 2, as expected from gaseous emission. Comparing thedistribution of X-ray luminosities with the models of Ciotti et al.leads to the conclusion that the vast majority of early-type galaxiesare in the wind or outflow phase. Some of the galaxies may have alreadyexperienced the transition to the inflow phase. They show X-rayluminosities in excess of the value predicted by cooling flow modelswith the largest plausible standard supernova rates. A possibleexplanation for these super X-ray-luminous galaxies is suggested by thesmooth transition in the L_x--L_B plane from galaxies to clusters ofgalaxies. Gas connected to the group environment might cause the X-rayoverluminosity.
| Star formation history of early-type galaxies in low density environments. V. Blue line-strength indices for the nuclear region
We analyze the star formation properties of a sample of 21 shellgalaxies and 30 early-type galaxies members of interacting pairs,located in low density environments (Longhetti et al. 1998a, 1998b). Thestudy is based on new models developed to interpret the informationcoming from `blue' Hdelta /FeI, H+K(CaII) and Delta 4000 line-strengthindices proposed by Rose (1984; 1985) and Hamilton (1985). We find thatthe last star forming event that occurred in the nuclear region of shellgalaxies is statistically old (from 0.1 up to several Gyr) with respectto the corresponding one in the sub-sample of pair galaxies (<0.1 Gyror even ongoing star formation). If the stellar activity is somehowrelated to the formation of shells, as predicted by several dynamicalmodels of galaxy interaction, shells have to be considered long lastingstructures. Since pair members show evidence of very recent starformation, we suggest that either large reservoirs of gas have to bepresent to maintain active star formation, if these galaxies are onperiodic orbits, or most of the pair members in the present sample areexperiencing unbound encounters. Table~2 is available in electronic formonly, at CDS: via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/Abstract.html
| The Southern Sky Redshift Survey
We report redshifts, magnitudes, and morphological classifications for5369 galaxies with m_B <= 15.5 and for 57 galaxies fainter than thislimit, in two regions covering a total of 1.70 sr in the southerncelestial hemisphere. The galaxy catalog is drawn primarily from thelist of nonstellar objects identified in the Hubble Space TelescopeGuide Star Catalog (GSC). The galaxies have positions accurate to ~1"and magnitudes with an rms scatter of ~0.3 mag. We compute magnitudes(m_SSRS2) from the relation between instrumental GSC magnitudes and thephotometry by Lauberts & Valentijn. From a comparison with CCDphotometry, we find that our system is homogeneous across the sky andcorresponds to magnitudes measured at the isophotal level ~26 magarcsec^-2. The precision of the radial velocities is ~40 km s^-1, andthe redshift survey is more than 99% complete to the m_SSRS2 = 15.5 maglimit. This sample is in the direction opposite that of the CfA2; incombination the two surveys provide an important database for studies ofthe properties of galaxies and their large-scale distribution in thenearby universe. Based on observations obtained at Cerro TololoInter-American Observatory, National Optical Astronomy Observatories,operated by the Association of Universities for Research in Astronomy,Inc., under cooperative agreement with the National Science Foundation;Complejo Astronomico El Leoncito, operated under agreement between theConsejo Nacional de Investigaciones Científicas de laRepública Argentina and the National Universities of La Plata,Córdoba, and San Juan; the European Southern Observatory, LaSilla, Chile, partially under the bilateral ESO-ObservatórioNacional agreement; Fred Lawrence Whipple Observatory;Laboratório Nacional de Astrofísica, Brazil; and the SouthAfrican Astronomical Observatory.
| Properties of Very Luminous Galaxies
Recent analysis of the data from the Southern Sky Redshift Surveyextension (SSRS2) based on cell counts and the two-point correlationfunction has shown that very luminous galaxies are much more stronglyclustered than fainter galaxies. In fact, the amplitude of thecorrelation function of very luminous galaxies (L > L^*)asymptotically approaches that of R >= 0 clusters. In this paper weinvestigate the properties of the most luminous galaxies, with blueabsolute magnitudes M_B <= -21. We find that (1) the population mixis comparable to that in other ranges of absolute magnitude; (2) only asmall fraction are located in bona fide clusters; (3) the brightgalaxy-cluster cross-correlation function is significantly higher onlarge scales than that measured for fainter galaxies; (4) thecorrelation length of galaxies brighter than M_B ~ -20.0, expressed as afunction of the mean interparticle distance, appears to follow theuniversal dimensionless correlation function found for clusters andradio galaxies; (5) a large fraction of the bright galaxies are ininteracting pairs, while others show evidence for tidal distortions andsome appear to be surrounded by faint satellite galaxies. We concludethat very luminous optical galaxies differ from the normal population ofgalaxies in both clustering and other respects. We speculate that thispopulation is a highly biased tracer of mass, being associated with darkhalos with masses more comparable to clusters than to typical loosegroups.
| A catalogue of Mg_2 indices of galaxies and globular clusters
We present a catalogue of published absorption-line Mg_2 indices ofgalaxies and globular clusters. The catalogue is maintained up-to-datein the HYPERCAT database. The measurements are listed together with thereferences to the articles where the data were published. A codeddescription of the observations is provided. The catalogue gathers 3541measurements for 1491 objects (galaxies or globular clusters) from 55datasets. Compiled raw data for 1060 galaxies are zero-point correctedand transformed to a homogeneous system. Tables 1, 3, and 4 areavailable in electronic form only at the CDS, Strasbourg, via anonymousftp 130.79.128.5. Table 2 is available both in text and electronic form.
| Star formation history of early-type galaxies in low density environments. II. Kinematics
The present paper is a companion of two others dedicated one to themeasurement of the line-strength indices \cite[(Longhetti et al.1997a)]{Lo7a} and the second to trace back the star formation history ofa sample of early-type galaxies by comparing observed indices to thepredictions of new spectro-photometric models \cite[(Longhetti et al.1997b).]{Lo7b} The sample of 51 early-type galaxies in low densityenvironments is composed of two sub-sets of galaxies: 21 shell galaxiesfrom the \cite[Malin & Carter (1983)]{Ma3} catalogue (one of whichshows double nucleous and has been considered as two separate objects)and 30 members of isolated interacting pairs from the \cite[Reduzzi& Rampazzo (1995)]{Re5} catalogue. Most of the objects show finestructures. The paper collects nuclear kinematic data together with thevelocity and velocity dispersion curves of the stellar and gaseouscomponents as a function of the distance from the galaxies centres. Thegalaxies heliocentric systemic velocity compares within -1+/- 32 kms(-1) with RC3 data, while their central velocity dispersion compareswithin 9+/- 9 km s(-1) , 10+/- 27 km s(-1) and 2+/- 33 km s(-1) with\cite[Gonzalez (1993),]{Go3} \cite[Davies et al. (1987)]{Da7} and\cite[Carter et al. (1988)]{Ca8} respectively. The detailed comparisonbetween our velocity and velocity dispersion curves and those fromseveral authors is discussed. 9 out of 22 shell galaxies nuclei showemission lines, 4 of which, using data in the literature, have lineratios characteristic of LINERs. 10 members of pairs out of 30 showemission lines. RR 331a has a Seyfert like nucleus, while for theremaining galaxies the ([O III] lambda 5007)/Hβ ratio ischaracteristic of low ionization regions. In a small fraction of theobjects the emission component is detectable outside the central value.None of the objects in the sample shows counter-rotation of the gaseousversus the stellar component. The two components appear associated,although, in two cases there is evidence that gas and stars lie ondifferent planes. This latter phenomenon could be associated toaccretion events. Emission lines in the central part of the RR 331a showa secondary component in the emission lines profile. E 2400100 has twonuclei embedded in the main body of the galaxy. The U-shape profile ofthe stellar velocity profile shows the ongoing interaction of the twonuclei. V/sigma profile of shell galaxies is, finally, discussed inrelation to the hypothesis of the accretion/merging origin of thesegalaxies. Based on observations obtained at ESO, La Silla, Chile. Dataand and kinematical profiles are available at CDS.
| Star formation history of early-type galaxies in low density environments. I. Nuclear line-strength indices
This paper is the first of a series \cite[(Longhetti et al.1997a,b)]{lon97} dedicated to the study of the star formation history inearly-type galaxies which show fine structures and/or signatures ofinteraction. It presents nuclear line-strength indices for a samplecomposed of 21 shell galaxies, from the \cite[Malin & Carter(1983)]{mal83} southern survey, and 30 members of isolated interactingpairs, from the \cite[Reduzzi & Rampazzo (1995)]{red95} catalogue,located in low density environments. The spectral range covers 3700Angstroms < lambda < 5700 Angstroms at 2.1 Angstroms FWHMresolution. We measure 16 red (lambda > 4200 Angstroms) indicesdefined by the Lick Group. Measures have been transformed into theLick-IDS ``standard'' system. The procedure has been tested on a set of5 elliptical galaxies selected from the \cite[Gonzalez (1993)]{gon93}sample. We derive also three blue (lambda < 4200) indices, namelyDelta (4000 Angstroms) defined by \cite[Hamilton (1985)]{ham85},H+K(CaII) and Hdelta /FeI defined by \cite[Rose (1984, 1985)]{ros84}.Blue indices are correlated to the age of the last starburst occurred ina galaxy \cite[(Leonardi & Rose 1996)]{leo96}. The determination ofthese indices, the estimate of the measurement errors and the correctionfor the galaxies velocity dispersions are discussed in detail. In theAppendix A we present the indices for a set of hot stars (T> 10000 K)which may be used for extending W92 fitting functions toward hightemperatures. Based on observations obtained at ESO, La Silla, Chile.Tables 1-8 are also available in electronic form at CDS and Tables 9-15are only available in electronic form at CDS: via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
| A VLA survey of rich clusters of galaxies. III. The weaker sources: maps and identifications.
We present radio and optical parameters for 737 weak sources in 60 Abellcluster fields observed with the Very Large Array (VLA) using scaledarrays at 1.5 and 4.9 GHz. The measurements extend to a lower 1.5 GHzlimit of 1.0 mJy and comprise a complete sample with 1.5-GHz fluxdensity 2.5 < S_1.5 < 20 mJy. The combined sky area within thehalf-power circle on the maps is 3.5 x 10^-3 sr, and the cluster fieldsare distributed over 24 h of right ascension and between declinations+35deg and -30deg. Contour maps of the extended sources at 1.5 GHz arepresented and source parameters such as position, angular size andspectral index are tabulated. We also derive the emitted power andlinear size for those sources with published redshifts. We try toidentify the radio sources with optical images on the Palomar and SERCsurvey plates and give their accurate optical positions, morphologiesand apparent magnitudes.
| Structure and kinematics of galaxy clusters. I. The redshift catalogue.
An extensive redshift survey has been conducted on a sample of 15 nearby(0.01<~z<~0.05) clusters of galaxies. A total number of 860redshifts were determined by fitting of emission-lines and/orcross-correlation techniques. Of this sample, 735 galaxies are within0.2-0.8Mpc (H_0_=50km/s/Mpc) of the center of clusters. Approximatemorphological types are available for most of the galaxies. A comparisonof the present redshifts with published data allows an extensive erroranalysis. The agreement is excellent with the most modern data, showinga zero point error of 5km/s and an overall consistency of themeasurements and their uncertainties. We estimate our redshifts to havemean random errors around 30km/s. A population analysis of the clusterswill be given in a forthcoming paper.
| The fundamental plane of early-type galaxies: stellar populations and mass-to-light ratio.
We analyse the residuals to the fundamental plane (FP) of ellipticalgalaxies as a function of stellar-population indicators; these are basedon the line-strength parameter Mg_2_ and on UBVRI broad-band colors, andare partly derived from new observations. The effect of the stellarpopulations accounts for approximately half the observed variation ofthe mass-to-light ratio responsible for the FP tilt. The residual tiltcan be explained by the contribution of two additional effects: thedependence of the rotational support, and possibly that of the spatialstructure, on the luminosity. We conclude to a constancy of thedynamical-to-stellar mass ratio. This probably extends to globularclusters as well, but the dominant factor would be here the luminositydependence of the structure rather than that of the stellar population.This result also implies a constancy of the fraction of dark matter overall the scalelength covered by stellar systems. Our compilation ofinternal stellar kinematics of galaxies is appended.
| Spectroscopy for E and S0 galaxies in nine clusters
Central velocity dispersions, Mg_2 line indices and radial velocitiesfor 220 E and S0 galaxies are derived on the basis of intermediateresolution spectroscopy. Galaxies in the following clusters have beenobserved: Abell 194, Abell 539, Abell 3381, Abell 3574, S639, S753,Doradus, HydraI (Abell 1060) and Grm 15. For 151 of the galaxies, thevelocity dispersion has not previously been measured. 134 of the Mg_2determinations are for galaxies with no previous measurement. Thespectra cover either 500 or 1000A, centred on the magnesium triplet at5177A. The observations were obtained with the Boller & Chivensspectrograph at the ESO 1.5-m telescope and with the OPTOPUS, amulti-object fibre-fed B&C spectrograph, at the ESO 3.6-m telescope.The data are part of our ongoing study of the large-scale motions in theUniverse and the physical background for the Fundamental Plane. TheFourier fitting method was used to derive the velocity dispersions andradial velocities. The velocity dispersions have been corrected for theeffect of the size of the aperture. The correction was established onthe basis of velocity dispersion profiles available in the literature. Acomparison with results from Davies et al. shows that the derivedcentral velocity dispersions have an rms error of 0.036 in logsigma.There is no offset relative to the velocity dispersions from Davies etal. The offset relative to data from Lucey & Carter is-0.017+/-0.011 in logsigma, with our velocity dispersions being thesmallest. The velocity dispersions derived from the B&C and theOPTOPUS observations, as well as the velocity dispersions published byDavies et al., Dressler, Lucey & Carter and Lucey et al., can bebrought on a system consistent within 3 per cent. The Mg_2 line indiceshave been corrected for the size of the apertures, transformed to theLick system, and corrected for the effect of the velocity dispersion.From comparison with data from Davies et al. and from Faber, we findthat the rms error of Mg_2 is 0.013. Comparisons of the radialvelocities with data from the literature show that our determinationsare accurate to within ~=35 km s^-1. The accuracies reached for theseobservations are adequate for the study of the large-scale motions inthe Universe and for investigations of the Fundamental Plane.
| A study of the large-scale distribution of galaxies in the South Galactic Pole region - I. The data*
We present the data from an extensive, moderately deep (b_J~19.5)spectroscopic survey of ~600 galaxies within four regions of sky locatednear the South Galactic Pole. About 75 per cent of the measured galaxiesare in approximately 3 degx1.5 deg region dominated by the rich clusterof galaxies Klemola 44 (Abell 4038). The other three smaller areas coverabout 1deg^2 each. Here, we discuss in detail the observing and datareduction strategies, and the completeness of and errors in the measuredredshifts. The data collected are being used for: (i) a study of thelarge-scale redshift distribution of the galaxies in each field, and(ii) a thorough dynamical investigation of Klemola 44. Results fromthese analyses will be presented in forthcoming papers.
| Multicolour CCD surface photometry for E and S0 galaxies in 10 clusters
CCD surface photometry for 232 E and S0 galaxies is presented. Thegalaxies are observed in Gunn r and Johnson B, or Gunn r and g. For 48of the galaxies surface photometry in Johnson U is also presented.Aperture magnitudes in Gunn nu are derived for half of the galaxies.Galaxies in the following clusters have been observed: Abell 194, Abell539, Abell 3381, Abell 3574, Abell S639, Abell S753, HydraI (Abell1060), DC2345-28, Doradus and Grm15. The data are part of our ongoingstudy of the large-scale motions in the Universe and the physicalbackground for the fundamental plane. We use a full model fittingtechnique for analysing the CCD images. This gives radial profiles oflocal surface brightness, colour, ellipticity and position angle. Theresiduals relative to the elliptical isophotes are describedquantitatively by Fourier expansions. Effective radius, mean surfacebrightness and total magnitude are derived by fitting a de Vaucouleursr^¼ growth curve. We have derived a characteristic radius r_nsimilar to the diameter D_n introduced by Dressler et al. The derivationof the effective parameters and of r_n takes the seeing into account. Weconfirm the results by Saglia et al. that the effects of the seeing canbe substantial. Seeing-corrected values of the effective parameters andr_n are also presented for 147 E and S0 galaxies in the Coma cluster.Colours, colour gradients and geometrical parameters are derived. Thephotometry is internally consistent within 0.016 mag. Comparison withthe photoelectric aperture photometry from Burstein et al. shows a meanoffset of 0.010 mag with an rms scatter of 0.034 mag. The globalphotometric parameters are compared with data from Faber et al., Luceyet al. and Lucey & Carter. These comparisons imply that the typicalrms errors are as follows - log r_n:+/-0.015 log r_e:+/-0.045m_T:+/-0.09 mag; _e:+/-0.16 mag. The rms error on thecombination log r_e-0.35_e which enters the fundamental planeis +/-0.020. Also, comparisons with data from Saglia et al. arepresented. The accuracy of the absolute photometry, as well as thederived parameters, makes the data suitable for our investigations ofthe fundamental plane and of the large-scale motions in the Universe.
| Candidates for a southern extension of the Karachentsev catalogue of isolated pairs of galaxies.
Not Available
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