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The AMIGA sample of isolated galaxies. II. Morphological refinement
We present a refinement of the optical morphologies for galaxies in theCatalog of Isolated Galaxies that forms the basis of the AMIGA (Analysisof the interstellar Medium of Isolated GAlaxies) project. Uniformreclassification using the digitized POSS II data benefited from thehigh resolution and dynamic range of that sky survey. Comparison withindependent classifications made for an SDSS overlap sample of more than200 galaxies confirms the reliability of the early vs. late-typediscrimination and the accuracy of spiral subtypes within Δ T =1-2. CCD images taken at the Observatorio de Sierra Nevada were alsoused to solve ambiguities in early versus late-type classifications. Aconsiderable number of galaxies in the catalog (n = 193) are flagged forthe presence of nearby companions or signs of distortion likely due tointeraction. This most isolated sample of galaxies in the local Universeis dominated by two populations: 1) 82% are spirals (Sa-Sd) with thebulk being luminous systems with small bulges (63% between types Sb-Sc)and 2) a significant population of early-type E-S0 galaxies (14%). Mostof the types later than Sd are low luminosity galaxies concentrated inthe local supercluster where isolation is difficult to evaluate. Thelate-type spiral majority of the sample spans a luminosity rangeMB-corr = -18 to -22 mag. Few of the E/S0 population are moreluminous than -21.0 marking the absence of the often-sought superL* merger (e.g. fossil elliptical) population. The rarity ofhigh luminosity systems results in a fainter derived M* forthis population compared to the spiral optical luminosity function(OLF). The E-S0 population is from 0.2 to 0.6 mag fainter depending onhow the sample is defined. This marks the AMIGA sample as unique amongsamples that compare early and late-type OLFs separately. In othersamples, which always involve galaxies in higher density environments,M^*_E/S0 is almost always 0.3-0.5 mag brighter than M^*_S, presumablyreflecting a stronger correlation between M* andenvironmental density for early-type galaxies.
| The Epochs of Early-Type Galaxy Formation as a Function of Environment
The aim of this paper is to set constraints on the epochs of early-typegalaxy formation through the ``archaeology'' of the stellar populationsin local galaxies. Using our models of absorption-line indices thataccount for variable abundance ratios, we derive ages, totalmetallicities, and element ratios of 124 early-type galaxies in high-and low-density environments. The data are analyzed by comparison withmock galaxy samples created through Monte Carlo simulations taking thetypical average observational errors into account, in order to eliminateartifacts caused by correlated errors. We find that all threeparameters, age, metallicity, and α/Fe ratio, are correlated withvelocity dispersion. We show that these results are robust againstrecent revisions of the local abundance pattern at high metallicities.To recover the observed scatter we need to assume an intrinsic scatterof about 20% in age, 0.08 dex in [Z/H], and 0.05 dex in [α/Fe].All low-mass objects withM*<~1010Msolar (σ<~130kms-1) show evidence for the presence of intermediate-agestellar populations with low α/Fe ratios. About 20% of theintermediate-mass objects with1010<~M*/Msolar<~1011[110<~σ/(kms-1)<~230 both elliptical andlenticular galaxies] must have either a young subpopulation or a bluehorizontal branch. On the basis of the above relationships, valid forthe bulk of the sample, we show that the Mg-σ relation is mainlydriven by metallicity, with similar contributions from the α/Feratio (23%) and age (17%). We further find evidence for an influence ofthe environment on the stellar population properties. Massive early-typegalaxies in low-density environments seem on average ~2 Gyr younger andslightly (~0.05-0.1 dex) more metal-rich than their counterparts inhigh-density environments. No offsets in the α/Fe ratios areinstead detected. With the aid of a simple chemical evolution model, wetranslate the derived ages and α/Fe ratios into star formationhistories. We show that most star formation activity in early-typegalaxies is expected to have happened between redshifts ~3 and 5 inhigh-density environments and between redshifts 1 and 2 in low-densityenvironments. We conclude that at least 50% of the total stellar massdensity must have already formed at z~1, in good agreement withobservational estimates of the total stellar mass density as a functionof redshift. Our results suggest that significant mass growth in theearly-type galaxy population below z~1 must be restricted to lessmassive objects, and a significant increase of the stellar mass densitybetween redshifts 1 and 2 should be present, caused mainly by the fieldgalaxy population. The results of this paper further imply the presenceof vigorous star formation episodes in massive objects at z~2-5 andevolved elliptical galaxies around z~1, both observationally identifiedas SCUBA galaxies and extremely red objects, respectively.
| 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.
| A dichotomy in the orientation of dust and radio jets in nearby low-power radio galaxies
We examine the properties of central dust in nearby quiescent and activeearly-type galaxies. The active galaxies are low-power radio galaxieswith Fanaroff & Riley type I or I/II radio jets. We focus on (a) thecomparison of the dust distributions in the active and quiescent galaxysamples; and (b) the relation between the radio jet and dustorientations. Our main observational conclusions are: (i) in line withprevious studies, the dust detection rate is higher in radio-jetgalaxies than in non radio-jet galaxies; (ii) radio galaxies contain ahigher fraction of regular dust “ellipses” compared toquiescent galaxies which contain more often irregular dustdistributions; (iii) the morphology, size and orientation of dustellipses and lanes in quiescent early-types and active early-types withkpc-scale radio jets is very similar; (iv) dust ellipses are alignedwith the major axis of the galaxy, dust lanes do not show a preferredalignment except for large (>kpc) dust lanes which are aligned withthe minor axis of the galaxy; and (v) as projected on the sky, jets donot show a preferred orientation relative to the galaxy major axis (andhence dust ellipses), but jets are preferentially perpendicular to dustlanes. We show that the dust ellipses are consistent with being nearlycircular thin disks viewed at random viewing angles. The lanes arelikely warped dust structures, which may be in the process of settlingdown to become regular disks or are being perturbed by anon-gravitational force. We use the observed dust-jet orientations toconstrain the three-dimensional angle θDJ between jetand dust. For dust-lane galaxies, the jet is approximately perpendicularto the dust structure, while for dust-ellipse galaxies there is a muchwider distribution of θDJ. We discuss two scenariosthat could explain the dust/jet/galaxy orientation dichotomy. If lanesare indeed settling, then the jet orientation apparently is roughlyaligned with the angular momentum of the dust before it settles. Iflanes are perturbed by a jet-related force, it appears that it causesthe dust to move out of its equilibrium plane in the galaxy into a planewhich is perpendicular to the jet.
| A Sample of Field Ellipticals
Using well-defined selection criteria derived from Zaritsky et al.applied to the LEDA galaxy catalog, we have constructed a sample ofelliptical galaxies that can be taken to lie in the field. Such criteriacan easily be applied to theoretical simulations for direct comparisonwith observations. The variation of the number of ``isolated''ellipticals with selection criteria is also investigated. A preliminarystudy of the environment of the field ellipticals shows that, in themean, they are surrounded by a population of dwarf galaxies, out toprojected radii of at least 500 kpc, with a radial density profile ofr-0.6+/-0.2 and a luminosity function slope of α~-1.8.The results are compared and contrasted to the satellite populationaround isolated spiral galaxies.
| Very Isolated Early-Type Galaxies
We use the Karachentseva Catalogue of Very Isolated Galaxies toinvestigate a candidate list of more than 100 very isolated early-typegalaxies. Broadband imaging and low-resolution spectroscopy areavailable for a large fraction of these candidates and result in asample of 102 very isolated early-type galaxies, including 65 elliptical(E) and 37 S0 galaxies. Many of these systems are quite luminous, andthe resulting optical luminosity functions of the E and early-type(E+S0) galaxies show no statistical differences when compared toluminosity functions dominated by group and cluster galaxies. However,whereas S0 galaxies outnumber E galaxies 4:1 in the CfA survey, isolatedE outnumber S0 galaxies by nearly 2:1. We conclude that very isolatedelliptical galaxies show no evidence of a different formation and/orevolution process compared to those formed in groups or clusters, butthat most S0 galaxies are formed by a mechanism (e.g., gas stripping)that occurs only in groups and rich clusters. Our luminosity functionresults for elliptical galaxies are consistent with very isolatedelliptical galaxies being formed by merger events, in which nocompanions remain. Chandra observations were proposed specifically totest the merger hypothesis for isolated elliptical galaxies. However,this program has resulted in the observation of only one isolatedearly-type galaxy, the S0 KIG 284, which was not detected at a limitwell below that expected for a remnant group of galaxies. Therefore, thehypothesis remains untested that very isolated elliptical galaxies arethe remains of a compact group of galaxies that have completely merged.
| 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
| Redshift-Distance Survey of Early-Type Galaxies: Spectroscopic Data
We present central velocity dispersions and Mg2 line indicesfor an all-sky sample of ~1178 elliptical and S0 galaxies, of which 984had no previous measures. This sample contains the largest set ofhomogeneous spectroscopic data for a uniform sample of ellipticalgalaxies in the nearby universe. These galaxies were observed as part ofthe ENEAR project, designed to study the peculiar motions and internalproperties of the local early-type galaxies. Using 523 repeatedobservations of 317 galaxies obtained during different runs, the dataare brought to a common zero point. These multiple observations, takenduring the many runs and different instrumental setups employed for thisproject, are used to derive statistical corrections to the data and arefound to be relatively small, typically <~5% of the velocitydispersion and 0.01 mag in the Mg2 line strength. Typicalerrors are about 8% in velocity dispersion and 0.01 mag inMg2, in good agreement with values published elsewhere.
| 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.
| Revised positions for CIG galaxies
We present revised positions for the 1051 galaxies belonging to theKarachentseva Catalog of Isolated Galaxies (CIG). New positions werecalculated by applying SExtractor to the Digitized Sky Survey CIG fieldswith a spatial resolution of 1 arcsper 2. We visually checked theresults and for 118 galaxies had to recompute the assigned positions dueto complex morphologies (e.g. distorted isophotes, undefined nuclei,knotty galaxies) or the presence of bright stars. We found differencesbetween older and newer positions of up to 38 arcsec with a mean valueof 2 arcsper 96 relative to SIMBAD and up to 38 arcsec and 2 arcsper 42respectively relative to UZC. Based on star positions from the APMcatalog we determined that the DSS astrometry of five CIG fields has amean offset in (alpha , delta ) of (-0 arcsper 90, 0 arcsper 93) with adispersion of 0 arcsper 4. These results have been confirmed using the2MASS All-Sky Catalog of Point Sources. The intrinsic errors of ourmethod combined with the astrometric ones are of the order of 0 arcsper5.Full Table 1 is 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/411/391
| 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.
| An elliptical galaxy luminosity function and velocity dispersion sample of relevance for gravitational lensing statistics
We have selected 42 elliptical galaxies from the literature andestimated their velocity dispersions at the effective radius(σRe) and at 0.54 effective radii(σ0.54Re). We find by a dynamical analysisthat the normalized velocity dispersion of the dark halo of anelliptical galaxy σDM is roughlyσRe multiplied by a constant, which isalmost independent of the core radius or the anisotropy parameter ofeach galaxy. Our sample analysis suggests that σDM*lies in the range 178-198 km s-1. The power law relation wefind between the luminosity and the dark matter velocity dispersionmeasured in this way is(L/L*)=(σDM/σDM*)γ,where /γ is between 2 and 3. These results are of interest forstrong gravitational lensing statistics studies. In order to determinethe value of σDM*, we calculateMBT* in the same BT band in whichσDM* has been estimated. We select 131 ellipticalgalaxies as a complete sample set with apparent magnitudes BTbetween 9.26 and 12.19. We find that the luminosity function is wellfitted to the Schechter form, with parametersMBT*=-19.66+5.log10h+/-0.30,/α=0.15+/-0.55, and the normalization constantφ*=(1.34+/-0.30)×10-3h3Mpc-3, with the Hubble constant Ho=100 /h kms-1 Mpc-1. This normalization implies thatmorphology type E galaxies make up (10.8 /+/- 1.2) per cent of allgalaxies.
| 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 Stellar Population Histories of Early-Type Galaxies. II. Controlling Parameters of the Stellar Populations
This paper analyzes single stellar population (SSP)-equivalentparameters for 50 local elliptical galaxies as a function of theirstructural parameters. The galaxy sample is drawn from the high-qualityspectroscopic surveys of González (1993) and Kuntschner (1998).The basic data are central values of SSP-equivalent ages, t,metallicities, [Z/H], and ``enhancement'' ratios, [E/Fe], derived inPaper I, together with global structural parameters including velocitydispersions, radii, surface brightnesses, masses, and luminosities. Thegalaxies fill a two-dimensional plane in the four-dimensional space of[Z/H], logt, logσ, and [E/Fe]. SSP age, t, and velocitydispersion, σ, can be taken as the two independent parameters thatspecify a galaxy's location in this ``hyperplane.'' The hyperplane canbe decomposed into two subrelations: (1) a ``Z-plane,'' in which [Z/H]is a linear function of logσ and logt and (2) a relation between[E/Fe] and σ in which [E/Fe] is larger in high-σ galaxies.Velocity dispersion is the only structural parameter that is found tomodulate the stellar populations; adding other structural variables suchas Ie or re does not predict [Z/H] or [E/Fe] moreaccurately. Cluster and field ellipticals follow the same hyperplane,but their (σ,t) distributions within it differ. Most Fornax andVirgo cluster galaxies are old, with a only a small sprinkling ofgalaxies to younger ages. The field ellipticals span a larger range inSSP age, with a tendency for lower σ galaxies to be younger. Thepresent sample thus suggests that the distribution of local ellipticalsin the (σ,t) plane may depend on environment. Since the(σ,t) distribution affects all two-dimensional projectionsinvolving SSP parameters, many of the familiar scaling laws attributedto ellipticals may also depend on environment. Some evidence for this isseen in the current sample. For example, only Fornax ellipticals showthe classic mass-metallicity relation, whereas other subsamples do not.The tight Mg-σ relations of these ellipticals can be understood astwo-dimensional projections of the metallicity hyperplane showing itedge-on. At fixed σ, young age tends to be offset by high [Z/H],preserving Mg nearly constant. The tightness of the Mg-σ relationsdoes not necessarily imply a narrow range of ages at fixed σ.Although SSP parameters are heavily weighted by young stars, modelingthem still places tight constraints on the total star formation historyof elliptical galaxies. The relation between [E/Fe] and σ isconsistent with a higher effective yield of Type II SNe elements athigher σ. This might occur if the IMF is enhanced in massive starsat high σ, or if more SNe II-enriched gas is retained by deepergalactic potential wells. Either way, modulating Type II yields versusσ seems to fit the data better than modulating Type Ia yields. TheZ-plane is harder to explain and may be a powerful clue to starformation in elliptical galaxies if it proves to be general. Presentdata favor a ``frosting'' model in which low apparent SSP ages areproduced by adding a small frosting of younger stars to an older``base'' population (assuming no change in σ). If the frostingabundances are close to or slightly greater than the base population,simple two-component models run along lines of constant σ in theZ-plane, as required. This favors star formation from well-mixedpre-enriched gas rather than unmixed low-metallicity gas from anaccreted object.
| The Stellar Population Histories of Local Early-Type Galaxies. I. Population Parameters
This paper commences a series of investigations into the stellarpopulations of local elliptical galaxies as determined from theirintegrated spectra. The goal of the series is to determine the starformation and chemical evolution histories of present-day ellipticalgalaxies. The primary galaxy sample analyzed is that of González,which consists of 39 elliptical galaxies drawn primarily from the localfield and nearby groups, plus the bulge of Messier 31. Single-burststellar population (SSP)-equivalent ages, metallicities, and abundanceratios are derived from Hβ, Mg b, and line strengthsusing an extension of the Worthey models that incorporates nonsolarline-strength ``response functions'' by Tripicco & Bell. Thesefunctions account for changes in the Lick/IDS indices caused by nonsolarabundance ratios, allowing us to correct the Worthey models for theenhancements of Mg and other α-like elements relative to theFe-peak elements. SSP-equivalent ages of the González ellipticalgalaxies are found to vary widely, 1.5 Gyr<~t<~18 Gyr, whilemetallicities [Z/H] and enhancement ratios [E/Fe] are strongly peakedaround <[Z/H]>=+0.26 and <[E/Fe]>=+0.20 (in an aperture ofradius re/8). The enhancement ratios [E/Fe] are milder thanprevious estimates because of the application of nonsolar abundancecorrections to both Mg b and for the first time. While [E/Fe]is usually greater than zero, it is not the ``E'' elements that areactually enhanced but rather the Fe-peak elements that are depressed;this serves not only to weaken but also to strengthen Mg b,accounting for the overall generally mild enhancements. Based on indexstrengths from the Lick/IDS galaxy library (Trager et al.), C is notdepressed with Fe but rather seems to be on a par with other elementssuch as Mg in the E group. Gradients in stellar populations withingalaxies are found to be mild, with SSP-equivalent age increasing by25%, metallicity decreasing by <[Z/H]>=0.20 dex, and [E/Fe]remaining nearly constant out to an aperture of radius re/2for nearly all systems. Our ages have an overall zero-point uncertaintyof at least ~25% because of uncertainties in the stellar evolutionprescription, the oxygen abundance, the effect of [E/Fe]≠0 on theisochrones, and other unknowns. However, the relative age rankings ofstellar populations should be largely unaffected by these errors. Inparticular, the large spread in ages appears to be real and cannot beexplained by contamination of Hβ by blue stragglers orhot horizontal-branch stars, or by fill-in of Hβ byemission. Correlations between these derived SSP-equivalent parametersand other galaxy observables will be discussed in future papers.
| 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 }
| 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
| On the relationship between age and dynamics in elliptical galaxies
Galaxy age estimates (mostly from spectroscopy of the central regions)are now available for many early-type galaxies. In a previous paper weshowed that the offset of galaxies from the fundamental plane depends ongalaxy age. Here, using the same sample of 88 galaxies, we examine thescatter about the Faber-Jackson (FJ) relation, and find that theposition of a galaxy relative to this relation depends on its age. Inparticular, younger ellipticals are systematically brighter inMB and/or have a lower central velocitydispersion (σ0). The mean relation corresponds togalaxies that are ~10Gyr old. We attempt to reproduce the observed trendof the FJ residuals with age using two simple models. The first assumesthat galaxy age is tracing the last major star formation event in anelliptical galaxy. We assume that this starburst was instantaneous,centrally located and involved 10per cent of the galaxy by mass. Thefading of this burst changes the MBcomponent of the FJ residuals, with time. Such a model was verysuccessful at reproducing the B-V and Mg2 evolution reportedin our previous paper, but is unable to reproduce the strength of the FJtrend. A second model is required to describe age-correlated changes ingalaxy dynamics. Following expectations from cosmological simulations,we assume that σ0, for a galaxy of a given mass, scaleswith the epoch of galaxy formation, i.e. with the mean density of theUniverse. Hence recently formed ellipticals have systematically lowervelocity dispersions than do old ellipticals. We find that a combinationof these two models provides a good match to the change in FJ residualswith galaxy age. This suggests that young ellipticals will have subtlydifferent dynamical properties from old ellipticals. We also find thatthere is not a strong relationship between the age of a galaxy and itsluminosity for our sample. This suggests that the tilt of thefundamental plane is not totally driven by age.
| Stellar population of ellipticals in different environments: near-infrared spectroscopic observations
Near-infrared spectra of 50 elliptical galaxies in the Pisces, Abell2199 and 2634 clusters, and in the general field, have been obtained.The strength of the CO (2.3-mu m) absorption feature in these galaxiesis used to explore the presence of an intermediate-age population (e.g.asymptotic giant branch stars) in ellipticals in different environments.We find that the strongest evidence for such a population comes fromellipticals in groups of a few members, which we interpret as the resultof recent minor merging of these galaxies with later-type galaxies.Field galaxies from very isolated environments, on the other hand, showno evidence for young or intermediate-age stars as revealed by Hβand CO absorptions, and appear to form a very uniform, old populationwith very little scatter in metallicity and star formation history.
| Arcsecond Positions of UGC Galaxies
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.
| Gradients of Absorption-Line Strengths in Elliptical Galaxies
We have restudied line-strength gradients of 80 elliptical galaxies.Typical metallicity gradients of elliptical galaxies areΔ[Fe/H]/Δlogr~=-0.3, which is flatter than the gradientspredicted by monolithic collapse simulations. The metallicity gradientsdo not correlate with any physical properties of galaxies, includingcentral and mean metallicities, central velocity dispersionsσ0, absolute B magnitudes MB, absoluteeffective radii Re, and dynamical masses of galaxies. Byusing the metallicity gradients, we have calculated mean stellarmetallicities for individual ellipticals. Typical mean stellarmetallicities are <[Fe/H]>~=-0.3 and range from<[Fe/H]>~=-0.8 to +0.3, which is contrary to what Gonzalez &Gorgas claimed; the mean metallicities of ellipticals are not universal.The mean metallicities correlate well with σ0 anddynamical masses, though relations for MB and Reinclude significant scatters. We find fundamental planes defined bysurface brightnesses SBe, <[Fe/H]>, and Re(or MB), the scatters of which are much smaller than those ofthe <[Fe/H]>-Re (or <[Fe/H]>-MB)relations. The <[Fe/H]>-logσ0 relation is nearlyparallel to the [Fe/H]0-logσ0 relation butsystematically lower by 0.3 dex; thus the mean metallicities are aboutone-half of the central values. The metallicity-mass relation or,equivalently, the color-magnitude relation of ellipticals holds not onlyfor the central parts of galaxies but also for entire galaxies. Assumingthat Mg2 and Fe1 give [Mg/H] and [Fe/H],respectively, we find <[Mg/Fe]>~=+0.2 in most of ellipticalgalaxies. <[Mg/Fe]> shows no correlation with galaxy mass tracerssuch as σ0, in contrast to what was claimed for thecentral [Mg/Fe]. This can be most naturally explained if the starformation had stopped in elliptical galaxies before the bulk of Type Iasupernovae began to occur. Elliptical galaxies can have significantlydifferent metallicity gradients and <[Fe/H]>, even if they havethe same galaxy mass. This may result from galaxy mergers, but noevidence is found from presently available data to support the sameorigin for metallicity gradients, the scatters around themetallicity-mass relation, and dynamical disturbances. This may suggestthat the scatters have their origin at the formation epoch of galaxies.
| Central Mg_2 indices for early-type galaxies
We present 210 new measurements of the central absorption line-strength{Mg_2} index for 87 early-type galaxies drawn from the \cite[Prugniel& Simien (1996)]{PS96} sample. 28 galaxies were not observed before.The results are compared to measurements published previously asavailable in HYPERCAT, and rescaled to the Lick system. The meanindividual internal error on these measurements is 0.009m+/-0.003m andthe mean external error is 0.012m+/-0.002m for this series ofmeasurements. Based on observations collected at the Observatoire deHaute-Provence. Tables 1, 3 and 4 are available in electronic form fromthe CDS, Strasbourg (via anonymous ftp to 130.79.128.5). Tables 1 and 3are available from CDS only.
| 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.
| 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 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
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