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A data-driven Bayesian approach for finding young stellar populations in early-type galaxies from their ultraviolet-optical spectra
Efficient predictive models and data analysis techniques for theanalysis of photometric and spectroscopic observations of galaxies arenot only desirable, but also required, in view of the overwhelmingquantities of data becoming available. We present the results of a novelapplication of Bayesian latent variable modelling techniques, where wehave formulated a data-driven algorithm that allows one to explore thestellar populations of a large sample of galaxies from their spectra,without the application of detailed physical models. Our only assumptionis that the galaxy spectrum can be expressed as a linear superpositionof a small number of independent factors, each a spectrum of a stellarsubpopulation that cannot be individually observed. A probabilisticlatent variable architecture that explicitly encodes this assumption isthen formulated, and a rigorous Bayesian methodology is employed forsolving the inverse modelling problem from the available data. Apowerful aspect of this method is that it formulates a density model ofthe spectra, based on which we can handle observational errors. Further,we can recover missing data both from the original set of spectra whichmight have incomplete spectral coverage of each galaxy, or frompreviously unseen spectra of the same kind.We apply this method to a sample of 21 ultraviolet-optical spectra ofwell-studied early-type galaxies, for which we also derive detailedphysical models of star formation history (i.e. age, metallicity andrelative mass fraction of the component stellar populations). We alsoapply it to synthetic spectra made up of two stellar populations,spanning a large range of parameters. We apply four different datamodels, starting from a formulation of principal component analysis(PCA), which has been widely used. We explore alternative factor models,relaxing the physically unrealistic assumption of Gaussian factors, aswell as constraining the possibility of negative flux values that areallowed in PCA, and show that other models perform equally well orbetter, while yielding more physically acceptable results. Inparticular, the more physically motivated assumptions of our rectifiedfactor analysis enable it to perform better than PCA, and to recoverphysically meaningful results.We find that our data-driven Bayesian modelling allows us to identifythose early-type galaxies that contain a significant stellar populationthat is <~1-Gyr old. This experiment also concludes that our sampleof early-type spectra showed no evidence of more than two major stellarpopulations differing significantly in age and metallicity. This methodwill help us to search for such young populations in a large ensemble ofspectra of early-type galaxies, without fitting detailed models, andthereby to study the underlying physical processes governing theformation and evolution of early-type galaxies, particularly thoseleading to the suppression of star formation in dense environments. Inparticular, this method would be a very useful tool for automaticallydiscovering various interesting subclasses of galaxies, for example,post-starburst or E+A galaxies.
| 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 SAI Catalog of Supernovae and Radial Distributions of Supernovae of Various Types in Galaxies
We describe the Sternberg Astronomical Institute (SAI) catalog ofsupernovae. We show that the radial distributions of type-Ia, type-Ibc,and type-II supernovae differ in the central parts of spiral galaxiesand are similar in their outer regions, while the radial distribution oftype-Ia supernovae in elliptical galaxies differs from that in spiraland lenticular galaxies. We give a list of the supernovae that arefarthest from the galactic centers, estimate their relative explosionrate, and discuss their possible origins.
| Cold Dust in Early-Type Galaxies. I. Observations
We describe far-infrared observations of early-type galaxies selectedfrom the Infrared Space Observatory (ISO) archive. This ratherinhomogeneous sample includes 39 giant elliptical galaxies and 14 S0 (orlater) galaxies. These galaxies were observed with the array photometerPHOT on-board the ISO satellite using a variety of different observingmodes-sparse maps, mini-maps, oversampled maps, and singlepointings-each of which requires different and often rather elaboratephotometric reduction procedures. The ISO background data agree wellwith the COBE-DIRBE results to which we have renormalized ourcalibrations. As a further check, the ISO fluxes from galaxies at 60 and100 μm agree very well with those previously observed with IRAS atthese wavelengths. The spatial resolution of ISO is several timesgreater than that of IRAS, and the ISO observations extend out to 200μm, which views a significantly greater mass of colder dust notassessable to IRAS. Most of the galaxies are essentially point sourcesat ISO resolution, but a few are clearly extended at FIR wavelengthswith image sizes that increase with FIR wavelength. The integratedfar-infrared luminosities do not correlate with optical luminosities,suggesting that the dust may have an external, merger-related origin. Ingeneral, the far-infrared spectral energy distributions can be modeledwith dust at two temperatures, ~43 and ~20 K, which probably representlimits of a continuous range of temperatures. The colder dust componentdominates the total mass of dust, 106-107Msolar, which is typically more than 10 times larger than thedust masses previously estimated for the same galaxies using IRASobservations. For S0 galaxies we find that the optically normalizedfar-infrared luminosity LFIR/LB correlatesstrongly with the mid-infrared luminosityL15μm/LB, but that correlation is weaker forelliptical galaxies.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries: France, Germany, theNetherlands, and United Kingdom) and with the participation of ISAS andNASA.
| 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.
| 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
| FLASH redshift survey - I. Observations and catalogue
The FLAIR Shapley-Hydra (FLASH) redshift survey catalogue consists of4613 galaxies brighter than bJ= 16.7 (corrected for Galacticextinction) over a 700-deg2 region of sky in the generaldirection of the Local Group motion. The survey region is a70°× 10° strip spanning the sky from the ShapleySupercluster to the Hydra cluster, and contains 3141 galaxies withmeasured redshifts. Designed to explore the effect of the galaxyconcentrations in this direction (in particular the Supergalactic planeand the Shapley Supercluster) upon the Local Group motion, the 68 percent completeness allows us to sample the large-scale structure betterthan similar sparsely-sampled surveys. The survey region does notoverlap with the areas covered by ongoing wide-angle (Sloan or 2dF)complete redshift surveys. In this paper, the first in a series, wedescribe the observation and data reduction procedures, the analysis forthe redshift errors and survey completeness, and present the surveydata.
| 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
| Supernovae in isolated galaxies, in pairs and in groups of galaxies
In order to investigate the influence of environment on supernova (SN)production, we have performed a statistical investigation of the SNediscovered in isolated galaxies, in pairs and in groups of galaxies. 22SNe in 18 isolated galaxies, 48 SNe in 40 galaxy members of 37 pairs and211 SNe in 170 galaxy members of 116 groups have been selected andstudied. We found that the radial distributions of core-collapse SNe ingalaxies located in different environments are similar, and consistentwith those reported by Bartunov, Makarova & Tsvetkov. SNe discoveredin pairs do not favour a particular direction with respect to thecompanion galaxy. Also, the azimuthal distributions inside the hostmembers of galaxy groups are consistent with being isotropics. The factthat SNe are more frequent in the brighter components of the pairs andgroups is expected from the dependence of the SN rates on the galaxyluminosity. There is an indication that the SN rate is higher in galaxypairs compared with that in groups. This can be related to the enhancedstar formation rate in strongly interacting systems. It is concludedthat, with the possible exception of strongly interacting systems, theparent galaxy environment has no direct influence on SN production.
| 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.
| The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and Distances
We report data for I-band surface brightness fluctuation (SBF)magnitudes, (V-I) colors, and distance moduli for 300 galaxies. Thesurvey contains E, S0, and early-type spiral galaxies in the proportionsof 49:42:9 and is essentially complete for E galaxies to Hubblevelocities of 2000 km s-1, with a substantial sampling of Egalaxies out to 4000 km s-1. The median error in distancemodulus is 0.22 mag. We also present two new results from the survey.(1) We compare the mean peculiar flow velocity (bulk flow) implied byour distances with predictions of typical cold dark matter transferfunctions as a function of scale, and we find very good agreement withcold, dark matter cosmologies if the transfer function scale parameterΓ and the power spectrum normalization σ8 arerelated by σ8Γ-0.5~2+/-0.5. Deriveddirectly from velocities, this result is independent of the distributionof galaxies or models for biasing. This modest bulk flow contradictsreports of large-scale, large-amplitude flows in the ~200 Mpc diametervolume surrounding our survey volume. (2) We present adistance-independent measure of absolute galaxy luminosity, N and showhow it correlates with galaxy properties such as color and velocitydispersion, demonstrating its utility for measuring galaxy distancesthrough large and unknown extinction. Observations in part from theMichigan-Dartmouth-MIT (MDM) Observatory.
| Nearby Optical Galaxies: Selection of the Sample and Identification of Groups
In this paper we describe the Nearby Optical Galaxy (NOG) sample, whichis a complete, distance-limited (cz<=6000 km s-1) andmagnitude-limited (B<=14) sample of ~7000 optical galaxies. Thesample covers 2/3 (8.27 sr) of the sky (|b|>20deg) andappears to have a good completeness in redshift (97%). We select thesample on the basis of homogenized corrected total blue magnitudes inorder to minimize systematic effects in galaxy sampling. We identify thegroups in this sample by means of both the hierarchical and thepercolation ``friends-of-friends'' methods. The resulting catalogs ofloose groups appear to be similar and are among the largest catalogs ofgroups currently available. Most of the NOG galaxies (~60%) are found tobe members of galaxy pairs (~580 pairs for a total of ~15% of objects)or groups with at least three members (~500 groups for a total of ~45%of objects). About 40% of galaxies are left ungrouped (field galaxies).We illustrate the main features of the NOG galaxy distribution. Comparedto previous optical and IRAS galaxy samples, the NOG provides a densersampling of the galaxy distribution in the nearby universe. Given itslarge sky coverage, the identification of groups, and its high-densitysampling, the NOG is suited to the analysis of the galaxy density fieldof the nearby universe, especially on small scales.
| The Ratio of α-Elements to Iron in Early-Type Galaxies from TIO and MG2
In order to derive the ratio of α-elements to iron in galaxies, wehave observed the strongest TiO band heads of the γ and γ'systems at 7000-7500 Å in a sample of a dozen early-type galaxies.The equivalent widths of the TiO bands are compared with syntheticspectra for single-aged stellar populations and composite galaxy models,all computed with [α/Fe]=0.0 and +0.3. The same method is alsoapplied to the and Mg2 Lick indices for the samplegalaxies. The results obtained are [Ti/Fe]~[Mg/Fe]~+0.3, indicating aclear enhancement of the α-elements-to-iron ratio for our sampleof early-type galaxies. Based on observations in the Observatóriodo Pico dos Dias, operated by the Laboratório Nacional deAstrofísica/CNPq/MCT, Brazil.
| Line-of-sight velocity distributions of 53 early-type galaxies
55 long-slit spectra of 53 early-type galaxies were observed at LaSilla/ESO and reduced using standard methods. The line-of-sight velocitydistributions (LOSVDs) were measured using the fourier quotient methodand the fourier fitting method as described by van der Marel et al.(\cite{vdmarel93}). 32% of the examined galaxies contain kinematicallydecoupled stellar omponents, the size of these cores was 0.40 +/- 0.28kpc, in each case the core was smaller than 1 kpc. Analysis of thekinematics reveals in 49% of the sample galaxies the signature of astellar disk component, in 15% this is uncertain. There is evidence thatthe phenomenon of kinematically decoupled components is present in thewhole class of early-type galaxies. Several correlations betweenphotometric and kinematic parameters like the (v/sigma )* vs.epsilon diagram, the anisotropy - luminosity correlation or kappa -spacewere as well examined using measurement results for spectroscopic dataand photometric data out of literature. It is also shown that thosesample galaxies with kinematically decoupled components are more likelyto be found in groups of high density, strengthening the assumption thatsuch components are remnants of merging events. Full Fig. 6 is onlyavailable at http://www.edpsciences.org
| A Test for Large-Scale Systematic Errors in Maps of Galactic Reddening
Accurate maps of Galactic reddening are important for a number ofapplications, such as mapping the peculiar velocity field in the nearbyuniverse. Of particular concern are systematic errors which vary slowlyas a function of position on the sky, as these would induce spuriousbulk flow. We have compared the reddenings of Burstein & Heiles (BH)and those of Schlegel, Finkbeiner, & Davis (SFD) to independentestimates of the reddening, for Galactic latitudes |b|>10^deg. Ourprimary source of Galactic reddening estimates comes from comparing thedifference between the observed B-V colors of early-type galaxies, andthe predicted B-V color determined from the B-V-Mg_2 relation. We havefitted a dipole to the residuals in order to look for large-scalesystematic deviations. There is marginal evidence for a dipolar residualin the comparison between the SFD maps and the observed early-typegalaxy reddenings. If this is due to an error in the SFD maps, then itcan be corrected with a small (13%) multiplicative dipole term. Weargue, however, that this difference is more likely to be due to a small(0.01 mag) systematic error in the measured B-V colors of the early-typegalaxies. This interpretation is supported by a smaller, independentdata set (globular cluster and RR Lyrae stars), which yields a resultinconsistent with the early-type galaxy residual dipole. BH reddeningsare found to have no significant systematic residuals, apart from theknown problem in the region 230^deg
| X-ray luminosities for a magnitude-limited sample of early-type galaxies from the ROSAT All-Sky Survey
For a magnitude-limited optical sample (B_T <= 13.5 mag) ofearly-type galaxies, we have derived X-ray luminosities from the ROSATAll-Sky Survey. The results are 101 detections and 192 useful upperlimits in the range from 10^36 to 10^44 erg s^-1. For most of thegalaxies no X-ray data have been available until now. On the basis ofthis sample with its full sky coverage, we find no galaxy with anunusually low flux from discrete emitters. Below log (L_B) ~ 9.2L_⊗ the X-ray emission is compatible with being entirely due todiscrete sources. Above log (L_B) ~ 11.2 L_osolar no galaxy with onlydiscrete emission is found. We further confirm earlier findings that L_xis strongly correlated with L_B. Over the entire data range the slope isfound to be 2.23 (+/- 0.12). We also find a luminosity dependence ofthis correlation. Below log L_x = 40.5 erg s^-1 it is consistent with aslope of 1, as expected from discrete emission. Above this value theslope is close to 2, as expected from gaseous emission. Comparing thedistribution of X-ray luminosities with the models of Ciotti et al.leads to the conclusion that the vast majority of early-type galaxiesare in the wind or outflow phase. Some of the galaxies may have alreadyexperienced the transition to the inflow phase. They show X-rayluminosities in excess of the value predicted by cooling flow modelswith the largest plausible standard supernova rates. A possibleexplanation for these super X-ray-luminous galaxies is suggested by thesmooth transition in the L_x--L_B plane from galaxies to clusters ofgalaxies. Gas connected to the group environment might cause the X-rayoverluminosity.
| BeppoSAX observation of NGC 3923, and the problem of the X-ray emission in E/S0 galaxies of low and medium L_X/L_B
We present the results of the analysis of the BeppoSAX LECS and MECSpointed observation of the E4 galaxy NGC 3923, for which previous X-raymeasurements had given a medium X-ray to optical ratio L_X/L_B. Thespectral analysis over (0.5-10) keV reveals that the best representationof the data is the superposition of two thermal components attemperatures of 0.4 keV and 6-8 keV. The total emission is roughlyequally divided between the two components, over (0.5-4.5) keV.Abundances are very subsolar at the best fit, but not constrained by thedata. The harder component is consistent with an origin from stellarsources; the softer component likely comes from hot gas. L_X of this hotgas is not as large as expected for a global inflow, in a galaxy of anoptical luminosity as high as that of NGC 3923. So, it is suggested thata substantial amount of hot gas was removed by internal agents, and thatthis process was helped by the flat mass distribution of the galaxy.Another possibility is that gas was lost as a consequence of the episodof interaction or merger that produced the system of shells visible inthe optical band. Finally, the possible origins of the large scatter inthe X-ray emission shown by galaxies of similar L_B are also reviewed.Like NGC 3923, many other low and medium L_X/L_B galaxies reside insmall groups, in which the ambient medium (if present) cannot strip themof their hot gas; so, if only environmental factors are invoked to lowerL_X/L_B, the most effective mechanism must be galaxy interactions. Thelower L_X/L_B galaxies, though, are seen to occur across the whole rangeof galaxy densities. Another possibility, to remove some or all of thehot gas, appeals to mechanisms internal to the galaxies, such as heatingof the gas by supernovae explosions or accretion onto central massiveblack holes. This has been shown to work in general, for a large rangeof L_B, but it is not clear yet whether the hot gas abundances estimatedfrom recent observations can be accomodated in it.
| The M/L vs M Relation and the Tilt of the Fundamental Plane
With extended kinematical data, we explore the tilt of the Fundamental Plane - commonly interpreted as a relation between mass and mass-to-light ratio for the elliptical galaxies. We show that dynamical non-homology is largely responsible for the tilt of the Fundamental Plane, and that when the non-homology is accounted for, no correlation is found between mass and mass-to-light ratio.
| Far-Infrared Emission from E and E/S0 Galaxies
Early-type galaxies are filled with hot X-ray-emitting gas, but thestudy of the less plentiful cold gaseous component has been morechallenging. Studies of cold material through IRAS 60 and 100 mu mobservations indicated that half of ordinary E and E/S0 galaxies weredetected above the 3 sigma level, indicating that cold gas is common,although no correlation was found between the optical and far-infraredfluxes. Most detections were near the instrumental threshold, and givenan improved understanding of detection confidence, we reconsider the 60and 100 mu m detection rate. After excluding active galactic nuclei,peculiar systems, and background contamination, only 15 nonpeculiar Eand E/S0 galaxies from the RSA catalog are detected above the 98%confidence level, about 12% of the sample. An unusually high percentageof these 15 galaxies possess cold gas (H I CO) and optical emissionlines (H alpha ), supporting the presence of gas cooler than 104 K. The60-100 mu m flux ratios imply a median dust temperature for the sampleof 30 K, with a range of 23-28 K. These detections define the upperenvelope of the optical to far-infrared relationship,F_{{fir}}~F^{0.24+/-0.08}B , showing that optically brightobjects are also brighter in the infrared, although with considerabledispersion. A luminosity correlation is present wthL_{{fir}}~L^{1.65+/-0.28}B , but the dust temperature isuncorrelated with luminosity. The dust masses inferred from thefar-infrared measurements are 1 order of magnitude greater than thosefrom extinction observations, except for the recent merger candidate NGC4125, where they are equal. We suggest that the ratio of thefar-infrared dust mass to the extinction dust mass may be an indicatorof the time since the last spiral-spiral merger. These results arecompared to the model in which most of the dust comes from stellar massloss and the heating is primarily by stellar photons. Models thatcontain large dust grains composed of amorphous carbon plus silicatescome close to reproducing the typical 60-100 mu m flux ratios, thefar-infrared luminosity, and the Lfir-LB relationship.
| 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.
| 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 catalogue of spatially resolved kinematics of galaxies: Bibliography
We present a catalogue of galaxies for which spatially resolved data ontheir internal kinematics have been published; there is no a priorirestriction regarding their morphological type. The catalogue lists thereferences to the articles where the data are published, as well as acoded description of these data: observed emission or absorption lines,velocity or velocity dispersion, radial profile or 2D field, positionangle. Tables 1, 2, and 3 are proposed in electronic form only, and areavailable from the CDS, via anonymous ftp to cdsarc.u-strasbg.fr (to130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| Dust in elliptical galaxies: a new dust mass evaluation
In order to investigate the nature and origin of dust in ellipticalgalaxies, a method for the dust mass evaluation, which accounts for thedust temperature distribution, is here presented and discussed. Thederived dust masses turn out to be a factor 2-6 larger than thoseobtained with the single temperature approximation. A correlationbetween the far-infrared and the blue luminosity has been also found.The results are discussed in terms of dust ``mass discrepancy'' and ofthe possible evolution scenarios: evaporation flow and/or cooling flow.While the present data cannot discriminate between these two scenarios,it is conceivable that the dust in elliptical galaxies can be accretedby the contribution of different mechanisms, according to the history ofthe individual objects.
| The Iron Discrepancy in Elliptical Galaxies after ASCA
We present estimates for the iron content of the stellar and diffusedcomponents of elliptical galaxies, as derived respectively fromintegrated optical spectra and from ASCA X-ray observations. Amacroscopic discrepancy emerges between the expected iron abundances inthe hot interstellar medium (ISM) and what is indicated by the X-rayobservations, especially when allowance is made for the current ironenrichment by Type Ia supernovae. This strong discrepancy, that in someextreme instances may be as large as a factor of ~20, calls intoquestion our current understanding of supernova enrichment and chemicalevolution of galaxies. We discuss several astrophysical implications ofthe inferred low iron abundances in the ISM, including the chemicalevolution of galaxies and clusters of galaxies, the evolution of gasflows in elliptical galaxies, and the heating of the intraclustermedium. Some of the consequences appear hard to accept, and in theattempt to avoid some of the difficulties we explore ways of hiding ordiluting iron in the ISM of ellipticals. None of these possibilitiesappears astrophysically plausible, and we alternatively raise thequestion of the reliability of iron L line diagnostic tools that arecurrently used to infer abundances from X-ray spectra. Variousthin-plasma emission models are shown to give iron abundances that maydiffer significantly, especially at low temperatures (kT <~ 1 keV),when the iron L complex is dominated by iron ions with still many boundelectrons. From a collection of ASCA and other X-ray observatory data,it is shown that current thin-plasma codes tend to give very low ironabundances when the temperature of the objects is below ~1 keV. Suchobjects include various types of binary stars, supernova remnants,starburst galaxies, and AGNs, with the case of galaxy groups beingespecially well documented. We conclude that, besides rethinking thechemical evolution of galaxies, one should also consider the possibilitythat existing thin-plasma models may incorporate inaccurate atomicphysics for the ions responsible for the iron L complex.
| Global Relationships Among the Physical Properties of Stellar Systems.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.1365B&db_key=AST
| 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.
| A Catalog of Stellar Velocity Dispersions. II. 1994 Update
A catalog of central velocity dispersion measurements is presented,current through 1993 September. The catalog includes 2474 measurementsof 1563 galaxies. A standard set of 86 galaxies is defined, consistingof galaxies with at least three reliable, concordant measurements. It issuggested that future studies observe some of these standard galaxies sothat different studies can be normalized to a consistent system. Allmeasurements are reduced to a normalized system using these standards.
| Total and effective colors of 501 galaxies in the Cousins VRI photometric system
Total color indices (V-R)T, (V-I)T and effectivecolor indices (V-R)e, (V-I)e in the Cousins VRIphotometric system are presented for 501 mostly normal galaxies. Thecolors are computed using a procedure outlined in the Third ReferenceCatalogue of Bright Galaxies (RC3) whereby standard color curvesapproximated by Laplace-Gauss integrals are fitted to observedphotoelectric multiaperture photometry. 11 sources of such photometrywere used for our analysis, each source being assigned an appropriateweight according to a rigorous analysis of residuals of the data fromthe best-fitting standard color curves. Together with the integrated B-Vand U-B colors provided in RC3, our analysis widens the range ofwavelength of homogeneously defined colors of normal galaxies of allHubble types. We present color-color and color-type relations that canbe modeled to understand the star formation history of galaxies.
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