Contingut
Imatges
Carregar la teva Imatge
DSS Images Other Images
Articles Relacionats
Stellar populations in a complete sample of local radio galaxies
We investigate the nature of the continuum emission and stellarpopulations in the inner 1-3 kpc of a complete sample of 24 southernradio galaxies, and we compare the results with a control sample of 18non-active early-type galaxies. 12 of the radio galaxies are classifiedas Fanaroff-Riley type I (FR I), eight as FR II and four as intermediateor undefined type (FR x). Optical long-slit spectra are used to performspectral synthesis as a function of distance from the nucleus at anaverage sampling of 0.5-1.0 kpc and to quantify the relativecontributions of a blue featureless continuum and stellar populationcomponents of different ages. Our main finding is a systematicdifference between the stellar populations of the radio and controlsample galaxies: the former have a larger contribution from anintermediate-age (1 Gyr) component, suggesting a connection between thepresent radio activity and a starburst which occurred ~1 Gyr ago. Inaddition, we find a correlation between the contribution of the 1-Gyrcomponent and the radio power, suggesting that more massive starburstshave led to more powerful radio emission. A similar relation is foundbetween the radio power and the mean age of the stellar population, inthe sense that stronger nuclear activity is found in younger galaxies.We also find that the stellar populations of FR I galaxies are, onaverage, older and more homogeneous than those of FR IIs. Significantpopulation gradients were found in only four radio galaxies, which arealso those with more than 10 per cent of their total flux at 4020Åcontributed by age components younger than 100 Myr and/or afeatureless continuum (indistinguishable from a 3-Myr-old stellarpopulation).
| The X-ray emission properties and the dichotomy in the central stellar cusp shapes of early-type galaxies
The Hubble Space Telescope has revealed a dichotomy in the centralsurface brightness profiles of early-type galaxies, which havesubsequently been grouped into two families: core, boxy, anisotropicsystems; and cuspy (`power-law'), discy, rotating ones. Here weinvestigate whether a dichotomy is also present in the X-ray propertiesof the two families. We consider both their total soft emission(LSX,tot), which is a measure of the galactic hot gascontent, and their nuclear hard emission (LHX,nuc), mostlycoming from Chandra observations, which is a measure of the nuclearactivity. At any optical luminosity, the highest LSX,totvalues are reached by core galaxies; this is explained by their beingthe central dominant galaxies of groups, subclusters or clusters, inmany of the logLSX,tot (ergs-1) >~ 41.5 cases.The highest LHX,nuc values, similar to those of classicalactive galactic nuclei (AGNs), in this sample are hosted only by core orintermediate galaxies; at low luminosity AGN levels, LHX,nucis independent of the central stellar profile shape. The presence ofoptical nuclei (also found by HST) is unrelated to the level ofLHX,nuc, even though the highest LHX,nuc are allassociated with optical nuclei. The implications of these findings forgalaxy evolution and accretion modalities at the present epoch arediscussed.
| Dark matter in early-type galaxies: dynamical modelling of IC 1459, IC 3370, NGC 3379 and NGC 4105
We analyse long-slit spectra of four early-type galaxies which extendfrom ~1 to 3 effective radii: IC 1459; IC 3370; NGC 3379 and NGC 4105.We have extracted the full line-of-sight velocity distribution (in thecase of NGC 3379 we also used data from the literature), which we modelusing the two-integral approach. Using two-integral modelling, we findno strong evidence for dark haloes, but the fits suggest thatthree-integral modelling is necessary. We also find that the inferredconstant mass-to-light ratio in all the four cases is typical forearly-type galaxies. Finally, we also discuss the constraints on themass-to-light ratio, which can be obtained using X-ray haloes in thecase of IC 1459, NGC 3379 and NGC 4105, and compare the estimated valueswith the predictions from the dynamical modelling.
| Do Observed Metallicity Gradients of Early-Type Galaxies Support a Hybrid Formation Scenario?
We measure radial gradients of the Mg2 index in 15 E-E/S0 and14 S0 galaxies. Our homogeneous data set covers a large range ofinternal stellar velocity dispersions (2.0
| The Nuclear Disk in the Dwarf Elliptical Galaxy NGC 4486A
Many ellipticals contain nuclear disks of dust and gas. Some ellipticalscontain nuclear disks of stars that are distinct from the rest of thegalaxy. We show that the dwarf E2 galaxy NGC 4486A contains both-it is a``Rosetta stone'' object that tells us how nuclear disks evolve. Itsproperties suggest that, as accreted gas dissipates and settles towardthe center, it forms stars and builds a stellar disk. Secular growth mayexplain not only the most distinct nuclear disks such as the one in NGC4486A but also some of the disky distortions that are commonly seen inelliptical galaxies. That is, density distributions may grow secularlycuspier. This would result in chaotic mixing of stellar orbits in phasespace and would tend to make an elliptical galaxy evolve toward a morenearly axisymmetric shape.Based on observations with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Science Institute, which is operated by AURA,Inc., under NASA contract NAS5-26555.
| 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.
| The host galaxy/AGN connection in nearby early-type galaxies. Sample selection and hosts brightness profiles
This is the first of a series of three papers exploring the connectionbetween the multiwavelength properties of AGNs in nearby early-typegalaxies and the characteristics of their hosts. We selected twosamples, both with high resolution 5 GHz VLA observations available andproviding measurements down to 1 mJy level, reaching radio-luminositiesas low as 1019 W Hz-1. We focus on the 116radio-detected galaxies as to boost the fraction of AGN with respect toa purely optically selected sample. Here we present the analysis of theoptical brightness profiles based on archival HST images, available for65 objects. We separate early-type galaxies on the basis of the slope oftheir nuclear brightness profiles, into core and power-law galaxiesfollowing the Nuker's scheme, rather than on the traditionalmorphological classification (i.e. into E and S0 galaxies). Our sampleof AGN candidates is indistinguishable, when their brightness profilesare concerned, from galaxies of similar optical luminosity but hostingweaker (or no) radio-sources. We confirm previous findings thatrelatively bright radio-sources (Lr > 1021.5 WHz-1) are uniquely associated to core galaxies. However,below this threshold in radio-luminosity core and power-law galaxiescoexist and they do not show any apparent difference in theirradio-properties. Not surprisingly, since our sample is deliberatelybiased to favour the inclusion of active galaxies, we found a higherfraction of optically nucleated galaxies. Addressing the multiwavelengthproperties of these nuclei will be the aim of the two forthcomingpapers.
| 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.
| Self-Gravitating Eccentric Disk Models for the Double Nucleus of M31
We present new dynamical models of weakly self-gravitating, finitedispersion eccentric stellar disks around central black holes for thedouble nucleus of M31. The disk is fixed in a frame rotating at constantprecession speed and is populated by stars on quasi-periodic orbitswhose parents are numerically integrated periodic orbits in the totalpotential. A distribution of quasi-periodic orbits about a given parentis approximated by a distribution of Kepler orbits dispersed ineccentricity and orientation, using an approximate phase-spacedistribution function written in terms of the integrals of motion in theKepler problem. We use these models, along with an optimization routine,to fit available published kinematics and photometry in the inner 2" ofthe nucleus. A grid of 24 best-fit models is computed to accuratelyconstrain the mass of the central black hole and nuclear diskparameters. We find that the supermassive black hole in M31 has massMBH=5.62+/-0.66×107 Msolar, whichis consistent with the observed correlation between the central blackhole mass and the velocity dispersion of its host spheroid. Our modelsprecess rapidly, at Ω=36.5+/-4.2 km s-1pc-1, and possess a characteristic radial eccentricitydistribution, which gives rise to multimodal line-of-sight velocitydistributions along lines of sight near the black hole. These featurescan be used as sensitive discriminants of disk structure.
| Eccentric-Disk Models for the Nucleus of M31
We construct dynamical models of the ``double'' nucleus of M31 in whichthe nucleus consists of an eccentric disk of stars orbiting a centralblack hole. The principal approximation in these models is that the diskstars travel in a Keplerian potential; i.e., we neglect the mass of thedisk relative to the black hole. We consider both ``aligned'' models, inwhich the eccentric disk lies in the plane of the large-scale M31 disk,and ``nonaligned'' models, in which the orientation of the eccentricdisk is fitted to the data. Both types of model can reproduce the doublestructure and overall morphology seen in Hubble Space Telescopephotometry. In comparison with the best available ground-basedspectroscopy, the models reproduce the asymmetric rotation curve, thepeak height of the dispersion profile, and the qualitative behavior ofthe Gauss-Hermite coefficients h3 and h4. Alignedmodels fail to reproduce the observation that the surface brightness atP1 is higher than at P2 and yield significantly poorer fits to thekinematics; thus, we favor nonaligned models. Eccentric-disk modelsfitted to ground-based spectroscopy are used to predict the kinematicsobserved at much higher resolution by the Space Telescope ImagingSpectrograph on the Hubble Space Telescope, and we find generallysatisfactory agreement.
| Supermassive Black Hole Binaries as Galactic Blenders
This paper focuses on the dynamical implications of close supermassiveblack hole binaries both as an example of resonant phase mixing and as apotential explanation of inversions and other anomalous featuresobserved in the luminosity profiles of some elliptical galaxies. Thepresence of a binary comprised of black holes executing nearly periodicorbits leads to the possibility of a broad resonant coupling between theblack holes and various stars in the galaxy. This can result inefficient chaotic phase mixing and, in many cases, systematic increasesin the energies of stars and their consequent transport toward largerradii. Allowing for a supermassive black hole binary with plausibleparameter values near the center of a spherical, or nearly spherical,galaxy characterized initially by a Nuker density profile enables one toreproduce in considerable detail the central surface brightnessdistributions of such galaxies as NGC 3706.
| On the calibration of the COBE/IRAS dust emission reddening maps
In this work we study the spectral properties (3600-6800 Å) of thenuclear region of early-type galaxies at low (|b|<25deg),intermediate (including surroundings of the Magellanic Clouds) and high(South Polar Cap) Galactic latitudes. We determine the E(B-V) reddeningvalues of the galaxies by matching their continuum distribution withrespect to those of reddening-free spectral galaxy templates withsimilar stellar populations. We also compare the spectroscopic reddeningvalue of each galaxy with that derived from 100 mu m dust emission(E(B-V)FIR) in its line of sight, and we find that there isagreement up to E(B-V)=0.25. Beyond this limit E(B-V)FIRvalues are higher. Taking into account the data up to E(B-V) ~ 0.7, wederive a calibration factor of 0.016 between the spectroscopic E(B-V)values and Schlegel et al.'s (\cite{Schlegel1998}) opacities. Bycombining this result with an AK extinction map built withinten degrees of the Galactic centre using Bulge giants as probes (Dutraet al. \cite{Dutra2003}), we extended the calibration of dust emissionreddening maps to low Galactic latitudes down to |b|=4deg andE(B-V)= 1.6 (AV ~ 5). According to this new calibration, amultiplicative factor of ~0.75 must be applied to the COBE/IRAS dustemission reddening maps.Based on observations made at Complejo Astronómico El Leoncito,which is operated under agreement between the Consejo Nacional deInvestigaciones Científicas y Técnicas de laRepública Argentina and the National Universities of La Pata,Córdoba and San Juan, Argentina.
| 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
| Galaxies with a Central Minimum in Stellar Luminosity Density
We used Hubble Space Telescope WFPC2 images to identify six early-typegalaxies with surface brightness profiles that decrease inward over alimited range of radii near their centers. The inferred luminositydensity profiles of these galaxies have local minima interior to theircore break radii. NGC 3706 harbors a high surface brightness ring ofstarlight with radius ~20 pc. Its central structure may be related tothat in the double-nucleus galaxies M31 and NGC 4486B. NGC 4406 and NGC6876 have nearly flat cores that, on close inspection, are centrallydepressed. Colors for both galaxies imply that this is not due to dustabsorption. The surface brightness distributions of both galaxies areconsistent with stellar tori that are more diffuse than the sharplydefined system in NGC 3706. The remaining three galaxies are thebrightest cluster galaxies in A260, A347, and A3574. Color informationis not available for these objects, but they strongly resemble NGC 4406and NGC 6876 in their cores. The thin ring in NGC 3706 may have formeddissipatively. The five other galaxies resemble the endpoints of somesimulations of the merging of two gas-free stellar systems, eachharboring a massive nuclear black hole. In one version of this scenario,diffuse stellar tori are produced when stars initially bound to oneblack hole are tidally stripped away by the second black hole.Alternatively, some inward-decreasing surface brightness profiles mayreflect the ejection of stars from a core during the hardening of thebinary black hole created during the merger. Based on observations madewith the NASA/ESA Hubble Space Telescope, obtained at the SpaceTelescope Science Institute, which is operated by the Association ofUniversities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations are associated with GO proposals 5454, 5512,6099, 6587, and 8683.
| 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.
| 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.
| Ages, Metallicities and Abundances in Elliptical Galaxies
In this paper we present a recent attempt to infer the age, metallicityand abundance ratios for a selected sample of elliptical galaxies,adopting the line-strength indices H_β, Mg_2 and , whichrespond in different ways to different parameters such as age(H_β), metallicity and abundance ratios ( and Mg_2).
| 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.
| 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.
| The Mass-to-Light Ratio of Binary Galaxies
We report on the mass-to-light ratio determination based on a newlyselected binary galaxy sample, which includes a large number of pairswhose separations exceed a few hundred kpc. The probabilitydistributions of the projected separation and the velocity differencehave been calculated considering the contamination of optical pairs, andthe mass-to-light (M/L) ratio has been determined based on the maximumlikelihood method. The best estimate of the M/L in the B band for 57pairs is found to be 28-36 depending on the orbital parameters and thedistribution of optical pairs (solar unit: H_0=50 km s^-1 Mpc^-1). Thebest estimate of the M/L for 30 pure spiral pairs is found to be 12-16.These results are relatively smaller than those obtained in previousstudies but are consistent with each other within the errors. Althoughthe number of pairs with large separation is significantly increasedcompared with previous samples, the M/L does not show any tendency ofincrease but is found to be almost independent of the separation ofpairs beyond 100 kpc. The constancy of the M/L beyond 100 kpc mayindicate that the typical halo size of spiral galaxies is less than ~100kpc.
| 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.
| Stellar disks and embedded bars in early-type galaxies. I. 2-D photometric decomposition of 28 southern early-type galaxies
We present photometric disk-bulge decompositions of 28 southernearly-type galaxies with types T<-3 in either the RC3 or ESO-Lauberts& Valentijn catalogues. The decomposition method applied here isbased on that developed by \cite[Scorza & Bender (1995)]{scor95} butthe improved version allows for arbitrary surface brightness profiles ofthe disk models. We find three types of objects in this sample:bulge-dominated systems, with fully embedded close to edge-on disks;disk-dominated close to edge-on objects and objects with barred disksbeing modestly inclined down to face-on. Like in \cite[Scorza &Bender (1995)]{scor95}, the analysis made here indicates that thesuperposition of a thin disk and an elliptical bulge can give goodaccount for the morphology of most of the galaxies. We find the disks tohave a diversity of surface brightness profiles, the most frequent casebeing that of a disk with an exponential profile, which becomes steeperat small radii. After disk subtraction, the bulges follow more closelythe r(1/4) law. Five of the galaxies show signatures of embedded barcomponents. These have flat surface brightness profiles at small radiiand rectangular shape, which are typical features of barred early-typegalaxies. We find that the properties of the galaxies, most notably thedisk-to-total ratio, correlates only modestly with the originalclassification of the galaxies.
| 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
| Spectro-photometric evolution of elliptical galaxies. III. Infall models with gradients in mass density and star formation
In this study we present a simple model of elliptical galaxies aimed atinterpreting the gradients in colours and narrow band indices observedacross these systems. Salient features of the model are the gradients inmass density and star formation and infall of primordial gas aimed atsimulating the collapse of a galaxy into the potential well of darkmatter. Adopting a multi-zone model we follow in detail the history ofstar formation, gas consumption, and chemical enrichment of the galaxyand also allow for the occurrence of galactic winds according to theclassical supernova (and stellar winds) energy deposit. The outline ofthe model, the time scale of gas accretion and rate of star formation asa function of the galacto-centric distance in particular, seek toclosely mimic the results from Tree-SPH dynamical models. Although somespecific ingredients of the model can be questioned from many points ofview (of which we are well aware), the model has to be considered as agross tool for exploring the consequences of different recipes of gasaccretion and star formation in which the simple one-zone scheme isabandoned. With the aid of this model we discuss the observational dataon the gradients in metallicity, colours, and narrow band indices acrosselliptical galaxies. Tables~4 and 6 are only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http:// cdsweb.u-strasbg.fr/Abstract.html
| Color distributions in E-S0 galaxies. I. Frequency and importance of dust patterns for various brands of E classified galaxies
>From the consideration of a sample of color distributions in 67 Eclassified objects of the Local Supercluster, it is found that localdust features are much more frequent and important in disky E's thanboxy E's. The subclass of undeterminate objects, those which cannot beassigned to the diE or boE groups, is intermediate. Subsets of objectsof common properties are considered from the point of view of local dustfeatures occurrence: giant boxy E's; minor boxy E's with rotationalsupport; compact dwarfs; SB0-like E's. It is noted that the detection ofdust features is more than twice less frequent in Virgo clusterellipticals than in the full sample, but the significance of this resultis not clear. Based on observations collected at theCanada-France-Hawaii Telescope and at the Observatoire du Pic du Midi
| Ages and metallicities in elliptical galaxies from the H_beta, , and Mg_2 diagnostics
Systematic variations in the line strength indices H_β, \Mg2, and< Fe > are observed across elliptical galaxies and limited to thecentral regions passing from one object to another. Furthermore, sincethe gradients in \Mg2\ and < Fe > have often different slopesarguments are given for an enhancement of Mg (alpha -elements ingeneral) with respect to Fe toward the center of these galaxies.Finally, the inferred degree of enhancement seems to increase passingfrom dwarfs to massive ellipticals. In this study we have investigatedthe ability of the H_β, \Mg2\ and < Fe > diagnostics toassess the metallicity, [Mg/Fe] ratios, and ages of elliptical galaxies.To this aim, first we derive basic calibrations for the variations deltaH_β, delta Mg_2 and delta < Fe > as a function of variationin age Delta log (t), metallicity Delta log (Z/Zsun), andDelta [Mg/Fe]. Second, examining the gradients observed in a smallsample of galaxies, we analyze how the difference delta H_β, deltaMg2, and delta < Fe > between the external and centralvalues of each index translates into Delta [Mg/Fe], Delta log(Z/Zsun), and Delta log (t). We find that out of six galaxiesunder examination, four have the nuclear region more metal-rich, moreenhanced in alpha -elements, and younger (i.e. containing a significantfraction of stars of relatively young age) than the external regions. Incontrast the remaining two galaxies have the nuclear region moremetal-rich, more enhanced in alpha -elements but marginally older thanthe external zones. Third, we explore the variation from galaxy togalaxy of the nuclear values of H_β, \Mg2, and < Fe > limitedto a sub-sample of the Gonzales (1993) list. The differences deltaH_β, delta Mg2, and delta < Fe > are convertedinto the differences Delta log (t), Delta log (Z/Zsun), andDelta [Mg/Fe]. Various correlations among the age, metallicity, andenhancement variations are explored. In particular we thoroughly examinethe relationships Delta log (t)-M_V, Delta log (Z/Zsun)-M_V,and Delta [Mg/Fe]-M_V. It is found that a sort of age limit is likely toexist in the Delta log (t)-M_V plane, traced by galaxies with mild or nosign of rejuvenation. In these objects, the duration of the star formingactivity is likely to have increased at decreasing galactic mass.Limited to these galaxies, the mass-metallicity sequence implied by thecolor-magnitude relation is recovered, likewise for the alpha-enhancement-luminosity relation suggested by the gradients in \Mg2\ and< Fe >. For the remaining galaxies the situation is moreintrigued: sporadic episodes of star formations are likely to haveoccurred scattering the galaxies in the space of age (H_β),metallicity, and [Mg/Fe]. The results are discussed in regard topredictions from the merger and isolation models of galaxy formation andevolution highlighting points of difficulty with each scheme. Finally,the suggestion is advanced that models with an IMF that at the earlyepochs favors higher mass stars in massive ellipticals galaxies, andlower mass stars in low-mass ellipticals, might be able to alleviatesome of the difficulties encountered by the standard SN-driven galacticwind model and lead to a coherent interpretation of the data.
| 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.
| Scale-free dynamical models for galaxies: flattened densities in spherical potentials
This paper presents two families of phase-space distribution functionsthat generate scale-free spheroidal mass densities in scale-freespherical potentials. The assumption of a spherical potential has theadvantage that all integrals of motion are known explicitly. The `caseI' distribution functions are anisotropic generalizations of theflattened f(E,<E1>L_z</E1> model, which theyinclude as a special case. The `case II' distribution functions generateflattened constant-anisotropy models. Free parameters control the radialpower-law slopes of the mass density and potential, the flattening ofthe mass distribution, and the velocity dispersion anisotropy. Themodels can describe the outer parts of galaxies and the density cuspstructure near a central black hole, but also provide general insightinto the dynamical properties of flattened systems. Because of theirsimplicity they provide a useful complementary approach to theconstruction of flattened self-consistent three-integral models forelliptical galaxies. &emspThe dependence of the intrinsic andprojected properties on the model parameters and the inclination isdescribed. The case I models have a larger ratio of rms tangential toradial motion in the equatorial plane than on the symmetry axis, themore so for smaller axial ratios. The case II models have a constantratio of rms tangential to radial motion throughout the system, ascharacterized by Binney's parameter beta. The maximum possible ratio_p/sigma_p of the mean projected line-of-sight velocity and velocitydispersion on the projected major axis always decreases with increasingradial anisotropy. The observed ratio of the rms projected line-of-sightvelocities on the projected major and minor axes of elliptical galaxiesis best fitted by the case II models with beta0. These models alsopredict non-Gaussian velocity profile shapes consistent with existingobservations. &emspThe distribution functions are used to model thegalaxies NGC 2434 (E1) and NGC 3706 (E4), for which stellar kinematicalmeasurements out to two effective radii indicate the presence of darkhaloes. The velocity profile shapes of both galaxies can be well fittedby radially anisotropic case II models with a spherical logarithmicpotential. This contrasts with the f(E,L_z) models studied previously,which require flattened dark haloes to fit the data.
|
Enviar un nou article
Enllaços Relacionats
- - No s'ha trobat enllaços -
Enviar un nou enllaç
Membre dels grups següents:
|
Dades d'Observació i Astrometria
Catàlegs i designacions:
|
