Contents
Images
Upload your image
DSS Images Other Images
Related articles
HI content in galaxies in loose groups
Gas deficiency in cluster spirals is well known and ram-pressurestripping is considered the main gas removal mechanism. In some compactgroups too gas deficiency is reported. However, gas deficiency in loosegroups is not yet well established. Lower dispersion of the membervelocities and the lower density of the intragroup medium in small loosegroups favour tidal stripping as the main gas removal process in them.Recent releases of data from the HI Parkes All-Sky Survey (HIPASS) andcatalogues of nearby loose groups with associated diffuse X-ray emissionhave allowed us to test this notion. In this paper, we address thefollowing questions: (i) do galaxies in groups with diffuse X-rayemission statistically have lower gas content compared to the ones ingroups without diffuse X-ray emission? (ii) does HI deficiency vary withthe X-ray luminosity, LX, of the loose group in a systematicway? We find that (i) galaxies in groups with diffuse X-ray emission, onaverage, are HI deficient, and have lost more gas compared to those ingroups without X-ray emission; the latter are found not to havesignificant HI deficiency; (ii) no systematic dependence of the HIdeficiency with LX is found. Ram-pressure-assisted tidalstripping and evaporation by thermal conduction are the two possiblemechanisms to account for this excess gas loss.
| The hot, warm and cold gas in Arp 227 - an evolving poor group
Arp 227 represents a prototypical example of an interacting mixed pairof galaxies located in a low-density environment. We investigate the gasproperties of the pair in the X-ray, Hα, HI and CO bands. We alsodetect two additional members of the group in HI which indicates thatthe pair constitutes the dominant members of a loose group.The HI distribution shows a tail of gas that connects the spiral member,NGC 470, to the lenticular, NGC 474, showing that the two main membersare currently undergoing interaction. The Hα emission reveals thepresence of secondary components at the centre of NGC 470, superposed onthe main component tracing the rotation of the galaxy. This latter mapsa nearly unperturbed velocity field. The dominant, nearly unperturbedtrend of the kinematics is confirmed by CO observations, althoughrestricted to the centre of the galaxy. The X-ray luminosity of NGC 470is comparable with that of a `normal' spiral galaxy. NGC 474 on theother hand is very gas-poor and has not been detected in Hα. ItsX-ray luminosity is consistent with the low end of the expected emissionfrom discrete sources.Arp 227 as a loose group shows several signatures of galaxy-galaxyinteraction. Our observations suggest the presence of signatures ofinteraction in the overall kinematics of the spiral companion. Theongoing interaction is clearly visible only in the outer HI halo of NGC470. While the large shell system of NGC 474 could be associated with anaccretion event, the secondary components in the Hα profile in thecentre of NGC 470 could be due to the interaction with the companion.The low X-ray luminosity of NGC 470 seems to be a characteristic ofdynamically young systems. All the above evidence suggest that Arp 227is an evolving group in the early phase of its evolution and that itsdrivers are the accretion of faint galaxies and the ongoing large-scaleinteraction between NGC 470 and 474.
| The Ages of Elliptical Galaxies from Infrared Spectral Energy Distributions
The mean ages of early-type galaxies obtained from the analysis ofoptical spectra give a mean age of 8 Gyr at z=0, with 40% being youngerthan 6 Gyr. Independent age determinations are possible by usinginfrared spectra (5-21 μm), which we have obtained with the InfraredSpectrograph on Spitzer. This age indicator is based on the collectivemass-loss rate of stars, in which mass loss from AGB stars produces asilicate emission feature at 9-12 μm. This feature decreases morerapidly than the shorter wavelength continuum as a stellar populationages, providing an age indicator. From observations of 30 nearbyearly-type galaxies, 29 show a spectral energy distribution dominated bystars, and one has significant emission from the ISM and is excluded.The infrared age indicators for the 29 galaxies show them all to be old,with a mean age of about 10 Gyr and a standard deviation of only a fewGyr. This is consistent with the ages inferred from the values ofM/LB, but is inconsistent with the ages derived from theoptical line indices, which can be much younger. All of these ageindicators are luminosity weighted and should be correlated, even ifmultiple-age components are considered. The inconsistency indicates thatthere is a significant problem with either the infrared and theM/LB ages, which agree, or with the ages inferred from theoptical absorption lines.
| The Complex X-Ray Morphology of NGC 7618: A Major Group-Group Merger in the Local Universe?
We present results from a short Chandra ACIS-S observation of NGC 7618,the dominant central galaxy of a nearby (z=0.017309, d=74.1 Mpc) group.We detect a sharp surface brightness discontinuity 14.4 kpc north of thenucleus subtending an angle of 130° with an X-ray tail extending ~70kpc in the opposite direction. The temperature of the gas inside andoutside the discontinuity is 0.79+/-0.03 and 0.81+/-0.07 keV,respectively. There is marginal evidence for a discontinuous change inthe elemental abundance (Zinner=0.65+/-0.25,Zouter=0.17+/-0.21 at 90% confidence), suggesting that thismay be an ``abundance'' front. Fitting a two-temperature model to theASCA GIS spectrum of the NGC 7618/UGC 12491 pair shows the presence of asecond, much hotter (T=~2.3 keV) component. We consider severalscenarios for the origin of the edge and the tail, including a radiolobe/IGM interaction, nonhydrostatic ``sloshing,'' equal-mass merger andcollision, and ram pressure stripping. In the last case, we consider thepossibility that NGC 7618 is falling into UGC 12491 or that both groupsare falling into a gas-poor cluster potential. There are significantproblems with the first two models, however, and we conclude that thediscontinuity and tail are most likely the result of ram pressurestripping of the NGC 7618 group, as it falls into a larger dark matterpotential.
| A Chandra Survey of Early-Type Galaxies. I. Metal Enrichment in the Interstellar Medium
We present a Chandra study of the emission-weighted metal abundances in28 early-type galaxies, spanning ~3 orders of magnitude in X-rayluminosity (LX). We report constraints for Fe, O, Ne, Mg, Si,S, and Ni. We find no evidence of the very subsolar Fe abundance(ZFe) historically reported, confirming a trend in recentobservations of bright galaxies and groups, nor do we find anycorrelation between ZFe and luminosity. Excepting one case,the ISM is single-phase, indicating that multitemperature fits foundwith ASCA reflected temperature gradients that we resolve with Chandra.We find no evidence that ZFe (ISM) is substantially lowerthan the stellar metallicity estimated from simple stellar populationmodels. In general, these quantities are similar, which is inconsistentwith galactic wind models and recent hierarchical chemical enrichmentsimulations. Our abundance ratio constraints imply that 66%+/-11% of theISM Fe was produced in SNe Ia, similar to the solar neighborhood,indicating similar enrichment histories for elliptical galaxies and theMilky Way. Although these values are sensitive to the considerablesystematic uncertainty in the supernova yields, they are in agreementwith observations of more massive systems. This indicates considerablehomology in the enrichment process operating from cluster scales tolow-to-intermediate-LX galaxies. The data uniformly exhibitlow ZO/ZMg ratios, which have been reported insome clusters, groups, and galaxies. This is inconsistent with standardSN II metal yield calculations and may indicate an additional source ofenrichment, such as Population III hypernovae.
| Scaling Mass Profiles around Elliptical Galaxies Observed with Chandra and XMM-Newton
We investigated the dynamical structure of 53 elliptical galaxies usingthe Chandra archival X-ray data. In X-ray-luminous galaxies, temperatureincreases with radius and gas density is systematically higher at theoptical outskirts, indicating the presence of a significant amount ofthe group-scale hot gas. In contrast, X-ray-dim galaxies show a flat ordeclining temperature profile against radius and the gas density isrelatively lower at the optical outskirts. Thus, it is found thatX-ray-bright and faint elliptical galaxies are clearly distinguished bythe temperature and gas density profile. The mass profile is well scaledby a virial radius r200 rather than an optical half-radiusre, is quite similar at (0.001-0.03)r200 betweenX-ray-luminous and dim galaxies, and smoothly connects to those profilesof clusters of galaxies. At the inner region of(0.001-0.01)r200 or (0.1-1)re, the mass profilewell traces a stellar mass with a constant mass-to-light ratio ofM/LB=3-10 Msolar/Lsolar. TheM/LB ratio of X-ray-bright galaxies rises up steeply beyond0.01r200 and thus requires a presence of massive dark matterhalo. From the deprojection analysis combined with the XMM-Newton data,we found that X-ray-dim galaxies NGC 3923, NGC 720, and IC 1459 alsohave a high M/LB ratio of 20-30 at 20 kpc, comparable to thatof X-ray-luminous galaxies. Therefore, dark matter is indicated to becommon in elliptical galaxies; their dark matter distribution, as wellas that of galaxy clusters, almost follows the NFW profile.
| The scaling relation of early-type galaxies in clusters. II. Spectroscopic data for galaxies in eight nearby clusters
Aims.We present low and intermediate resolution spectroscopic datacollected for 152 early type galaxies in 8 nearby clusters with z ≤0.10. Methods: .We use low resolution data to produce the redshiftand the K-correction for each galaxy, as well as to give their overallspectral energy distribution and some spectral indicators, including the4000 Å break, the Mg2 strength and the NaD equivalent width. Wehave also obtained higher resolution data for early type galaxies inthree of the clusters, to determine their central velocity dispersion. Results: .The effect of the resolution on the measured parametersis discussed. Conclusions: .A new accurate systemic redshift andvelocity dispersion is presented for four of the surveyed clusters, A98,A3125, A3330, and DC2103-39. We have found that the K-correction valuesfor E/S0 bright galaxies in the given nearby clusters are very similar.We also find that the distribution of the line indicators significantlydiffers from cluster to cluster.
| 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.
| Group, field and isolated early-type galaxies - II. Global trends from nuclear data
We have derived ages, metallicities and enhanced-element ratios[α/Fe] for a sample of 83 early-type galaxies essentially ingroups, the field or isolated objects. The stellar-population propertiesderived for each galaxy correspond to the nuclear re/8aperture extraction. The median age found for Es is 5.8+/-0.6 Gyr andthe average metallicity is +0.37+/-0.03 dex. For S0s, the median age is3.0+/-0.6 Gyr and [Z/H]= 0.53+/-0.04 dex. We compare the distribution ofour galaxies in the Hβ-[MgFe] diagram with Fornax galaxies. Ourelliptical galaxies are 3-4 Gyr younger than Es in the Fornax cluster.We find that the galaxies lie in a plane defined by [Z/H]= 0.99logσ0- 0.46 log(age) - 1.60, or in linear terms Z~σ0× (age) -0.5. More massive (largerσ0) and older galaxies present, on average, large[α/Fe] values, and therefore must have undergone shorterstar-formation time-scales. Comparing group against field/isolatedgalaxies, it is not clear that environment plays an important role indetermining their stellar-population history. In particular, ourisolated galaxies show ages differing by more than 8 Gyr. Finally weexplore our large spectral coverage to derive log(O/H) metallicity fromthe Hα and NIIλ6584 and compare it with model-dependent[Z/H]. We find that the O/H abundances are similar for all galaxies, andwe can interpret it as if most chemical evolution has already finishedin these galaxies.
| Group, field and isolated early-type galaxies - I. Observations and nuclear data
This is the first paper of a series on the investigation of stellarpopulation properties and galaxy evolution of an observationallyhomogeneous sample of early-type galaxies in groups, field and isolatedgalaxies.Here we present high signal-to-noise ratio (S/N) long-slit spectroscopyof 86 nearby elliptical and S0 galaxies. Eight of them are isolated,selected according to a rigorous criterion, which guarantees a genuinelow-density subsample. The present survey has the advantage of coveringa larger wavelength range than normally found in the literature, whichincludes [OIII]λ5007 and Hα, both lines important foremission correction. Among the 86 galaxies with S/N >= 15 (perresolution element, for re/8 central aperture), 57 have theirHβ-index corrected for emission (the average correction is 0.190Åin Hβ) and 42 galaxies reveal [OIII]λ5007 emission,of which 16 also show obvious Hα emission. Most of the galaxies inthe sample do not show obvious signs of disturbances nor tidal featuresin the morphologies, although 11 belong to the Arp catalogue of peculiargalaxies; only three of them (NGC 750, 751 and 3226) seem to be stronglyinteracting. We present the measurement of 25 central line-strengthindices calibrated to the Lick/IDS system. Kinematic information isobtained for the sample. We analyse the line-strength index versusvelocity dispersion relations for our sample of mainly low-densityenvironment galaxies, and compare the slope of the relations withcluster galaxies from the literature. Our main findings are that theindex-σ0 relations presented for low-density regionsare not significantly different from those of cluster E/S0s. The slopeof the index-σ0 relations does not seem to change forearly-type galaxies of different environmental densities, but thescatter of the relations seems larger for group, field and isolatedgalaxies than for cluster galaxies.
| Why Are Radio Galaxies Prolific Producers of Type Ia Supernovae?
An analysis of SN Ia events in early-type galaxies from the database ofCappellaro and coworkers provides conclusive evidence that the rate ofSNe Ia in radio-loud galaxies is about 4 times higher than the ratemeasured in radio-quiet galaxies, i.e., SN Ia rate(radio-loudgalaxies)=0.43+0.19-0.14h275 SNu as compared to SN Ia rate(radio-quietgalaxies)=0.11+0.06-0.03h275 SNu. The actual value of the enhancement islikely to be in the range ~2-7 (P~10-4). This finding puts onrobust empirical grounds the results obtained by Della Valle &Panagia on the basis of a smaller sample of SNe. We analyze the possiblecauses of this result and conclude that the enhancement of the SN Iaexplosion rate in radio-loud galaxies has the same origin as their beingstrong radio sources, but there is no causal link between the twophenomena. We argue that repeated episodes of interaction and/or mergersof early-type galaxies with dwarf companions, on timescales of about 1Gyr, are responsible for both inducing strong radio activity observed in~14% of early-type galaxies and supplying an adequate number of SN Iaprogenitors to the stellar population of elliptical galaxies.
| The Ages of Elliptical Galaxies from Mid-Infrared Emission
The mid-infrared (10-20 μm) luminosity of elliptical galaxies isdominated by the integrated emission from circumstellar dust in redgiant stars. As a single stellar population evolves, the rate of dustymass loss from red giant stars decreases with time, so the mid-infraredluminosity should also decline with stellar age. To seek such acorrelation, we have used archival Infrared Space Observatory (ISO)observations to determine surface brightness profiles and central fluxesat 15 μm in 17 early-type galaxies for which stellar ages have beendetermined from optical spectral indices. The radial surface brightnessdistributions at 15 μm generally follow the stellar de Vaucouleursprofile, as expected. We find that the surface brightness ratioμ15μm/μIband is systematically higher inelliptical galaxies with ages <~5 Gyr and in galaxies that exhibitevidence of recent mergers. Within the accuracy of our observations,μ15μm/μIband shows no age dependence forages >~5 Gyr. The corresponding flux ratiosF15μm/FIband within apertures scaled to theeffective radius (Re/8) are proportional to theμ15μm/μIband ratios at larger galacticradii, indicating that no 15 μm emission is detected from centraldust clouds visible in optical images in some of our sample galaxies.Emission at 15 μm is observed in noncentral massive clouds of dustand cold gas in NGC 1316, an elliptical galaxy that is thought to havehad a recent merger. Recent Spitzer Space Telescope data also indicatethe presence of polycyclic aromatic hydrocarbon (PAH) emission at 8μm. Several ellipticals have extended regions of 15 μm emissionthat have no obvious counterparts at other frequencies.
| 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.
| Peculiarities and populations in elliptical galaxies. II. Visual-near IR colours as population indices
As a complement to the data collected and discussed in Paper I of thisseries, 2MASS near-IR images have been used, in connection withavailable V light aperture photometry, to derive the colours V-J, V-K,J-H and J-K within the effective aperture A_e: nearly the same completesample of 110 E-type galaxies is treated. In Paper I these wereclassified, based on morphological criteria, into the ``peculiar'' (orPec) and ``normal'' (or Nop) subsamples. For the Nop subsample, thederived colour indices are tightly related to the galaxy masses, asmeasured by the central velocity dispersion σ0,although with rather small slopes as regards J-H and J-K. For the Pecsubsample, the V-J and V-K colours behave as UBV and line-indices: partof the objects show blue residuals from the appropriatecolour-σ0 regression, which is evidence of a youngerpopulation mixed with the ``normal'' one traced by the Nop regressions;the other shows no deviations from the Nop subsample. The distinctionamong Pec objects between the YP family (NGC 2865 type), and the NP one(NGC 3923 type), is statistically supported, and generally confirmed inspecific cases.Based in part on observations collected at the Observatoire deHaute-Provence.Table 4 is only available in electonic form at the CDS via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/429/819
| Nuclear activity and the dynamics of elliptical galaxies
This Letter looks for any correlation between the internal dynamics ofelliptical galaxies and the relatively mild nuclear activity found inmany such systems. We show that there is such a relation in the sensethat the active ellipticals tend to be significantly less rotationallysupported than their inactive cousins. The correlation can partly berelated to the galaxies' luminosities: the brightest galaxies tend to bemore active and less rotationally supported. However, even at lowerluminosities the active and inactive galaxies seem to havesystematically different dynamics. This variation suggests that thereare significant large-scale structural differences between active andinactive elliptical galaxies, and hence that the existence of both typesof system cannot just be the result of random sporadic nuclear activity.
| BUDDA: A New Two-dimensional Bulge/Disk Decomposition Code for Detailed Structural Analysis of Galaxies
We present BUDDA (Bulge/Disk Decomposition Analysis), a new code devotedto perform a two-dimensional bulge/disk decomposition directly from theimages of galaxies. The bulge component is fitted with a generalizedSérsic profile, whereas disks have an exponential profile. Noother components are included. Bars and other substructures, likelenses, rings, inner bars, and inner disks, are studied with theresidual images obtained through the subtraction of bulges and disksfrom the original images. This means that a detailed structural analysisof galaxies may be performed with a small number of parameters, andsubstructures may be directly studied with no a priori assumptions. Ashas been already shown by several studies, two-dimensional fitting ismuch more reliable than one-dimensional profile fitting. Moreover, ourcode has been thoroughly tested with artificial data, and we demonstrateit to be an accurate tool for determining structural parameters ofgalaxies. We also show that our code is useful in various kinds ofstudies, including galaxies of, e.g., different morphological types, andinclinations, which also may be observed at different spatialresolutions. Thus, the code has a broader range of potentialapplications than most of the previous codes, which are developed totackle specific problems. To illustrate its usefulness, we present theresults obtained with a sample of 51 mostly early-type galaxies (butcovering the whole Hubble sequence). These results show some of theapplications in which the code may be used: the determination ofparameters for fundamental plane and structural studies, quantitativemorphological classification of galaxies, and the identification andstudy of hidden substructures. We have determined the structuralparameters of the galaxies in our sample and found many examples ofhidden inner disks in ellipticals, secondary bars, nuclear rings anddust lanes in lenticulars and spirals, and also wrong morphologicalclassification cases. We now make BUDDA generally available to theastronomical community.Based on observations made at the Pico dos Dias Observatory(PDO/LNA-CNPq), Brazil.
| Hot Gas Structure in the Elliptical Galaxy NGC 4472
We present X-ray spectroscopic and morphological analyses using ChandraACIS and ROSAT observations of the giant elliptical galaxy NGC 4472 inthe Virgo Cluster. We discuss previously unobserved X-ray structureswithin the extended galactic corona. In the inner 2' of the galaxy, wefind X-ray holes or cavities with radii of ~2 kpc, corresponding to theposition of radio lobes. These holes were produced during a period ofnuclear activity that began 1.2×107 yr ago and may beongoing. We also find an asymmetrical edge in the galaxy X-ray emission3' (14 kpc) northeast of the core and an ~8' tail (36 kpc) extendingsouthwest of the galaxy. These two features probably result from theinteraction of NGC 4472 gas with the Virgo gas, which producescompression in the direction of NGC 4472's infall and an extended tailfrom ram pressure stripping. Assuming that the tail is in pressureequilibrium with the surrounding gas, we compute its angle to our lineof sight and estimate that its true extent exceeds 100 kpc. Finally, inaddition to emission from the nucleus (first detected by Soldatenkov,Vikhlinin, and Pavlinsky), we detect two small extended sources within10" of the nucleus of the galaxy, both of which have luminosities of~7×1038 ergs s-1.
| An Unusual Discontinuity in the X-Ray Surface Brightness Profile of NGC 507: Evidence of an Abundance Gradient?
We present results from a 45 ks Chandra ACIS-I observation of the nearby(z=0.01646) NGC 507 group. The X-ray surface brightness profile of theouter region of the group is well described by an isothermalβ-profile consistent with earlier ROSAT observations. We find asharp edge or discontinuity in the radial surface brightness profile 55kpc east and southeast of NGC 507 covering an ~125° arc. At thesharpest part of the discontinuity, the surface brightness declines by afactor of ~2 over a distance of 6.9 kpc (~15"). The inner and outer gastemperatures across the discontinuity differ by only about 0.2 keV(interior and exterior gas temperatures are 1.2 and 1.4 keV,respectively). Spectral analysis indicates that there is a gradient inthe elemental abundance across the discontinuity, and comparison withthe low-resolution NRAO VLA Sky Survey radio maps suggests that thediscontinuity is aligned with a low surface brightness radio lobe. Weconclude that the appearance of this discontinuity may be the result oftwo phenomena: the transonic (M~0.75-1) expansion/inflation of the radiolobe close to our line of sight and the transport of high-abundancematerial from the center of the galaxy due to this expansion.
| 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
| X-ray scaling properties of early-type galaxies
We present an analysis of 39 X-ray luminous early-type galaxies observedwith the ROSAT PSPC. Using multicomponent spectral and spatial fits tothese data, we have measured halo abundance, temperature, luminosity andsurface brightness profile. We compare these measurements to similarresults from galaxy groups and clusters, fitting a number of relationscommonly used in the study of these larger objects. In particular, wefind that the σ-TX relation for our sample is similarto that reported for clusters, consistent with βspec= 1,and that the LX-TX relation has a steep slope(gradient 4.8 +/- 0.7) comparable with that found for galaxy groups.Assuming isothermality, we construct three-dimensional models of ourgalaxies, allowing us to measure gas entropy. We find no correlationbetween gas entropy and system mass, but do find a trend forlow-temperature systems to have reduced gas fractions. We conclude thatthe galaxies in our sample are likely to have developed their haloesthrough galaxy winds, influenced by their surrounding environment.
| Infrared Observations of Galaxies in the Local Universe. II. 391 Calibrated Images with Photometric and Structural Measurements
This paper presents empirical results from a deep imaging survey ofgalaxies in the local universe at the J and Ks wavelengths.Three hundred ninety-one images have been obtained and calibrated usingthe same camera and filter set with the Steward Observatory 1.6 m KuiperTelescope on Mount Bigelow and the 2.3 m Bok Telescope on Kitt Peak. Thelimiting magnitude is typically 22 mag arcsec-1 at J and 21mag arcsec-1 at Ks. The central surfacebrightness, apparent magnitudes, sizes, scale lengths, and inclinationsare tabulated from measurements made using these data. The purpose ofthis paper is to provide basic near-infrared data on a variety of galaxytypes.
| An X-Ray Atlas of Groups of Galaxies
A search was conducted for a hot intragroup medium in 109 low-redshiftgalaxy groups observed with the ROSAT PSPC. Evidence for diffuse,extended X-ray emission is found in at least 61 groups. Approximatelyone-third of these detections have not been previously reported in theliterature. Most of the groups are detected out to less than half of thevirial radius with ROSAT. Although some spiral-rich groups do contain anintragroup medium, diffuse emission is restricted to groups that containat least one early-type galaxy.
| Metallicity distributions of globular cluster systems in galaxies
We collected a sample of 100 galaxies for which different observers havedetermined colour indices of globular cluster candidates. The sampleincludes representatives of galaxies of various morphological types anddifferent luminosities. Colour indices (in most cases (V-I), but also(B-I) and (C-T_1)) were transformed into metallicities [Fe/H] accordingto a relation by Kissler-Patig (1998). These data were analysed with theKMM software in order to estimate similarity of the distribution withuni- or bimodal Gaussian distribution. We found that 45 of 100 systemshave bimodal metallicity distributions. Mean metallicity of themetal-poor component for these galaxies is < [Fe/H]> = -1.40 +/-0.02, of the metal-rich component < [Fe/H]> = -0.69 +/- 0.03.Dispersions of the distributions are 0.15 and 0.18, respectively.Distribution of unimodal metallicities is rather wide. These data willbe analysed in a subsequent paper in order to find correlations withparameters of galaxies and galactic environment.
| 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.
| Color Gradients in Early-Type Galaxies in Abell 2199
We performed B- and R-band surface photometry for E/S0 galaxies in thenearby rich cluster Abell 2199 to investigate their B-R color gradients[d(B-R)/dlogr]. Our aims are to study statistical properties of thecolor gradients and, by comparing them with those in less denseenvironments, to examine environmental dependence of color gradients inelliptical galaxies. We studied the distribution of the B-R colorgradients in the cluster elliptical galaxies and found that the meanvalue of the color gradients is -0.09+/-0.04 mag dex-1, whichcan be converted to a metallicity gradient (dlogZ/dlogr) of -0.3+/-0.1.The gradient seems to be comparable to that expected by a recentmonolithic collapse model. We further studied the relations between theB-R color gradients and global properties of the galaxies. Our datasuggest that for the galaxies brighter than an R-band magnitude of ~15mag, which is roughly equivalent to L* at the distance of the cluster,brighter galaxies tend to have steeper color gradients. In addition, forthe galaxies with effective radii larger than ~3", which nearlycorresponds to L* considering the correlation between galaxy luminosityand effective radius for elliptical galaxies, the galaxies with largereffective radii seem to have steeper color gradients. These trends couldappear if elliptical galaxies formed through the monolithic collapsescenario. On the contrary, it is found based on the published data thatsuch trends are not clearly seen for elliptical galaxies in less denseenvironments, suggesting that elliptical galaxies in sparse environmentsformed by galaxy mergers, although the distribution of the colorgradients is quite similar to that in the rich cluster. In other words,our data and those in the literature suggest that there is anenvironmental dependence in the relationship between color gradient andglobal properties of elliptical galaxies, while the distribution of thevalues of color gradients is nearly independent of galaxy environment.These results do not fully support the view that elliptical galaxies inrich clusters formed through monolithic collapse, while those in sparseenvironments formed through galaxy mergers, because the latterelliptical galaxies are expected to have color gradients shallower onaverage than the former. This apparent conflict may be reconciled bytaking into account star formation and subsequent chemical enrichmentinduced by a galaxy merger, which may allow a merger remnant to acquirea metallicity gradient and thus compensate the dilution of the existingmetallicity gradients in the progenitors by mixture of stars during thegalaxy merger.
| Dust and the Infrared Kinematic Properties of Early-Type Galaxies
We have obtained spectra and measured the stellar kinematics in a sampleof 25 nearby early-type galaxies (with velocity dispersions from lessthan 100 km s-1 to over 300 km s-1) using thenear-infrared CO absorption band head at 2.29 μm. Our medianuncertainty for the dispersions is ~10%. We examine the effects of duston existing optical kinematic measurements. We find that thenear-infrared velocity dispersions are, in general, smaller than opticalvelocity dispersions, with differences as large as 30%. The mediandifference is 11% smaller, and the effect is of greater magnitude forhigher dispersion galaxies. The lenticular galaxies (18 out of 25)appear to be causing the shift to lower dispersions, while the classicalelliptical galaxies (7 out of 25) are consistent between the twowavelength regimes. If uniformly distributed dust causes thesedifferences, we would expect to find a correlation between the relativeamount of dust in a galaxy and the fractional change in dispersion, butwe do not find such a correlation. We do see correlations between bothvelocity dispersion and CO band head equivalent width, and velocitydispersion and Mg2 index. The differences in dispersion arenot well explained by current models of dust absorption. The lack ofcorrelation between the relative amount of dust and shift in dispersionpossibly suggests that dust does not have a similar distribution fromgalaxy to galaxy. The CO equivalent widths of these galaxies are quitehigh (>~10 Å for almost all), requiring the light at thesewavelengths to be dominated by very cool stars.
| 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
| H0 measurement from VLT deep I-band surface brightness fluctuations in NGC 564 and NGC 7619
We have measured the Hubble constant H0 in NGC 564 at cz ~5800 km s-1 and in NGC 7619 at cz ~ 3700 km s-1with deep I-band Surface Brightness Fluctuation distance measurements atthe ESO Very Large Telescope (VLT). We obtain H0 = 70 +/- 7+/- 6 km s-1/Mpc for NGC 564 and H0 = 68 +/- 6 +/-6 for NGC 7619. The actual SBF sample used for the measurement ofH0 in the Hubble Space Telescope Key Project on theExtragalactic Distance Scale (Freedman et al. 2001) amounts to sixgalaxies. When we combine the measurements from this work with ourprevious VLT I-band SBF distance measurement in IC 4296 (Mei et al.2000), we obtain: H0 = 68 +/- 5 +/- 6 km s-1/Mpc.When we add the Freedman et al. (2001) SBF sample, we obtainH0 = 71 +/- 4 +/- 6 km s-1/Mpc.Based on observations performed at the European Southern Observatory,Paranal, Chile ESO program No 66.A-0361.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
Catalogs and designations:
|
