Contents
Images
Upload your image
DSS Images Other Images
Related articles
Gemini/GMOS spectra of globular clusters in the Virgo giant elliptical NGC 4649
NGC 4649 (M60) is one of a handful of giant Virgo ellipticals. We haveobtained Gemini/GMOS (Gemini North Multi-Object Spectrograph) spectrafor 38 globular clusters (GCs) associated with this galaxy. Applying themulti-index χ2 minimization technique of Proctor andSansom with the single stellar population models of Thomas, Maraston andKorn, we derive ages, metallicities and α-element abundanceratios. We find several young (2-3 Gyr old) supersolar metallicity GCs,while the majority are old (>10 Gyr), spanning a range ofmetallicities from solar to [Z/H]=-2. At least two of these young GCsare at large projected radii of 17-20 kpc. The galaxy itself shows noobvious signs of a recent starburst, interaction or merger. A trend ofdecreasing α-element ratio with increasing metallicity is found.
| Gemini/GMOS spectra of globular clusters in the Leo group elliptical NGC 3379
The Leo group elliptical NGC 3379 is one of the few normal ellipticalgalaxies close enough to make possible observations of resolved stellarpopulations, deep globular cluster (GC) photometry and highsignal-to-noise ratio GC spectra. We have obtained Gemini/GMOS spectrafor 22 GCs associated with NGC 3379. We derive ages, metallicities andα-element abundance ratios from simple stellar population modelsusing the recent multi-index χ2 minimization method ofProctor & Sansom. All of these GCs are found to be consistent withold ages, i.e. >~10Gyr, with a wide range of metallicities. This iscomparable to the ages and metallicities that Gregg et al. found acouple of years ago for resolved stellar populations in the outerregions of this elliptical. A trend of decreasing α-elementabundance ratio with increasing metallicity is indicated.The projected velocity dispersion of the GC system is consistent withbeing constant with radius. Non-parametric, isotropic models require asignificant increase in the mass-to-light ratio at large radii. Thisresult is in contrast to that of Romanowsky et al., who recently found adecrease in the velocity dispersion profile as determined from planetarynebulae (PN). Our constant dispersion requires a normal-sized dark halo,although without anisotropic models we cannot rigorously determine thedark halo mass.A two-sided χ2 test over all radii gives a 2σdifference between the mass profile derived from our GCs compared to thePN-derived mass model of Romanowsky et al. However, if we restrict ouranalysis to radii beyond one effective radius and test if the GCvelocity dispersion is consistently higher, we determine a > 3σdifference between the mass models, and hence we favour the conclusionthat NGC 3379 does indeed have dark matter at large radii in its halo.
| Nearby early-type galaxies with ionized gas. II. Line-strength indices for 18 additional galaxies
We previously presented a data-set of line-strength indices for 50early-type galaxies in the nearby Universe. The galaxy sample is biasedtoward galaxies showing emission lines, located in environmentscorresponding to a broad range of local galaxy densities, althoughpredominantly in low density environments. The present addendum enlargesthe above data-set of line-strength indices by analyzing 18 additionalearly-type galaxies (three galaxies, NGC 3607, NGC 5077 and NGC 5898were presented in the previous set). We measured 25 line-strengthindices, defined by the Lick IDS "standard" system (Trager et al. 1998,ApJS, 116, 1; Worthey & Ottaviani 1997, ApJS, 111, 377), for 7luminosity weighted apertures and 4 gradients of each galaxy. Thisaddendum presents the line-strength data-set and compares it with theavailable data in the literature.
| On the Relation between Circular Velocity and Central Velocity Dispersion in High and Low Surface Brightness Galaxies
In order to investigate the correlation between the circular velocityVc and the central velocity dispersion of the spheroidalcomponent σc, we analyzed these quantities for a sampleof 40 high surface brightness (HSB) disk galaxies, eight giant lowsurface brightness (LSB) spiral galaxies, and 24 elliptical galaxiescharacterized by flat rotation curves. Galaxies have been selected tohave a velocity gradient <=2 km s-1 kpc-1 forR>=0.35R25. We used these data to better define theprevious Vc-σc correlation for spiralgalaxies (which turned out to be HSB) and elliptical galaxies,especially at the lower end of the σc values. We findthat the Vc-σc relation is described by alinear law out to velocity dispersions as low as σc~50km s-1, while in previous works a power law was adopted forgalaxies with σc>80 km s-1. Ellipticalgalaxies with Vc based on dynamical models or directlyderived from the H I rotation curves follow the same relation as the HSBgalaxies in the Vc-σc plane. On the otherhand, the LSB galaxies follow a different relation, since most of themshow either higher Vc or lower σc withrespect to the HSB galaxies. This argues against the relevance of baryoncollapse to the radial density profile of the dark matter halos of LSBgalaxies. Moreover, if the Vc-σc relation isequivalent to one between the mass of the dark matter halo and that ofthe supermassive black hole, then these results suggest that the LSBgalaxies host a supermassive black hole (SMBH) with a smaller masscompared to HSB galaxies with an equal dark matter halo. On the otherhand, if the fundamental correlation of SMBH mass is with the halocircular velocity, then LSB galaxies should have larger black holemasses for a given bulge dispersion. Elliptical galaxies withVc derived from H I data and LSB galaxies were not consideredin previous studies.Based on observations made with European Southern Observatory telescopesat the Paranal Observatory under programs 67.B-0283, 69.B-0573, and70.B-0171.
| Globular clusters in NGC 4365: new K-band imaging and a reassessment of the case for intermediate-age clusters
We study the globular cluster (GC) system of the Virgo giant ellipticalgalaxy NGC 4365, using new wide-field K-band imagingfrom the ESO 3.5 m New Technology Telescope, archive V and I imagingfrom FORS1 on the ESO VLT and HST/WFPC2+ACS data. As in most other largeellipticals, the GC colour distribution has (at least) two peaks, butthe colours of the red GCs appear more strongly weighted towardsintermediate colours compared to most other large ellipticals and theintegrated galaxy light. The intermediate-color/red peak may itself becomposed of two sub-populations, with clusters of intermediate coloursmore concentrated towards the centre of the galaxy than both the blueand red GCs. Nearly all GCs in our sample fall along a well-definednarrow sequence in the (V-K, V-I) two-colour diagram, with an offsettowards red V-K and/or blue V-I colours compared to simple stellarpopulation models for old ages. This has in the past been interpreted asevidence for an intermediate-age population of GCs. The offset ishowever seen for nearly all metal-rich clusters within the 5arcmin×5 arcmin SOFI field, not just those of intermediatecolours. We combine our VIK data with previously published spectroscopyresulting in a sample of 25 GCs with both spectroscopy and photometry.The differences between observed and model colour-metallicity relationsare consistent with the offsets observed in the two-colour diagram, withthe metal-rich GCs being too red (by ≈0.2 mag) in V-K and too blue(by ≈0.05 mag) in V-I compared to the models at a given metallicity.These offsets cannot easily be explained as an effect of younger ages.We further compare the colour-metallicity relation for GCs in NGC 4365with previously published data for NGC 3115 and theSombrero galaxy, both of which are believed from spectroscopic studiesto host exclusively old GC populations, and find the colour-metallicityrelations for all three galaxies to be very similar. We review theavailable evidence for intermediate-age GCs in NGC 4365 and concludethat, while this cannot be definitively ruled out, an alternativescenario is more likely whereby all the GCs are old but the relativenumber of intermediate-metallicity GCs is greater than typical for giantellipticals. The main obstacle to reaching a definitive conclusion isthe lack of robust calibrations of integrated spectral and photometricproperties for stellar populations with near-solar metallicity. In anycase, it is puzzling that the significant intermediate-colour GCpopulation in NGC 4365 is not accompanied by a corresponding shift ofthe integrated galaxy light towards bluer colours.
| VLT spectroscopy of globular cluster systems. II. Spectroscopic ages, metallicities, and [ α/Fe] ratios of globular clusters in early-type galaxies
An analysis of ages, metallicities, and [ α/Fe] ratios of globularcluster systems in early-type galaxies is presented, based on Lick indexmeasurements summarized in Puzia et al. (2004, A&A, 415, 123, PaperI of this series). In the light of calibration and measurementuncertainties, age-metallicity degeneracy, and the relative dynamicrange of Lick indices, as well as systematics introduced by abundanceratio variations (in particular variations of [ α/Fe] ratios), wefind that the most reliable age indicator for our dataset is acombination of the Lick Balmer-line indices Hγ_A, Hβ, andHδ_A. [MgFe]´ is used as a spectroscopic metallicityindicator which is least affected by [ α/Fe] variations. Weintroduce an interpolation routine to simultaneously derive ages,metallicities, and [ α/Fe] ratios from diagnostic gridsconstructed from Lick indices. From a comparison of high-quality datawith SSP model predictions, we find that 2/3 of the globular clustersin early-type galaxies are older than 10 Gyr, up to 1/3 have ages in therange 5{-}10 Gyr, and only a few cluster are younger than 5 Gyr. Oursample of globular clusters covers metallicities from [Z/H] ≈ -1.3 upto 0.5 dex. We find that metal-rich globular clusters show on average asmaller mean age and a larger age scatter than their metal-poorcounterparts. [ α/Fe] diagnostic plots show that globular clustersystems in early-type galaxies have super-solar α/Fe abundanceratios with a mean [ α/Fe] = 0.47 ± 0.06 dex and adispersion of 0.3 dex. We find evidence for a correlation between [α/Fe] and metallicity, in the sense that more metal-rich clustersexhibit lower α-element enhancements. A discussion of systematicsrelated to the Lick index system shows that the method suffers to someextent from uncertainties due to unknown horizontal branch morphologiesat high metallicities. However, these systematics still allow us to makegood qualitative statements. A detailed investigation of indices as afunction of data quality reveals that the scatter in Balmer index valuesdecreases for higher-quality data. In particular, extremely low Balmerindex values that are lower than any SSP model prediction tend todisappear. Furthermore, we find that observed photometric colors are ingood agreement with computed SSP colors using ages and metallicities asderived from the spectroscopic line indices.
| Nearby early-type galaxies with ionized gas. I. Line-strength indices of the underlying stellar population
With the aim of building a data-set of spectral properties of wellstudied early-type galaxies showing emission lines, we presentintermediate resolution spectra of 50 galaxies in the nearby Universe.The sample, which covers several of the E and S0 morphologicalsub-classes, is biased toward objects that might be expected to haveongoing and recent star formation, at least in small amounts, because ofthe presence of the emission lines. The emission is expected to comefrom the combination of active galactic nuclei and star formationregions within the galaxies. Sample galaxies are located in environmentscorresponding to a broad range of local galaxy densities, althoughpredominantly in low density environments. Our long-slit spectra coverthe 3700-7250 Å wavelength range with a spectral resolution of≈7.6 Å at 5550 Å. The specific aim of this paper, and ourfirst step in the investigation, is to map the underlying galaxy stellarpopulation by measuring, along the slit positioned along the galaxymajor axis, line-strength indices at several, homogeneousgalacto-centric distances. For each object we extracted 7luminosity-weighted apertures (with radii 1.5´´,2.5´´, 10´´, r_e/10, r_e/8, r_e/4 and r_e/2)corrected for the galaxy ellipticity and 4 gradients (0 ≤ r ≤r_e/16, r_e/16 ≤ r ≤ r_e/8, r_e/8 ≤ r ≤ r_e/4 and r_e/4≤ r ≤ r_e/2). For each aperture and gradient we measured 25line-strength indices: 21 of the set defined by the Lick-IDS“standard” system (Trager et al. [CITE], ApJS, 116, 1) and 4introduced by Worthey & Ottaviani ([CITE], ApJS, 111, 377).Line-strength indices have been transformed to the Lick-IDS system.Indices derived then include Hβ, Mg1, Mg2, Mgb, MgFe, Fe5270,Fe5335 commonly used in classic index-index diagrams. The paperintroduces the sample, presents the observations, describes the datareduction procedures, the extraction of apertures and gradients, thedetermination and correction of the line-strength indices, the procedureadopted to transform them into the Lick-IDS System and the proceduresadopted for the emission correction. We finally discuss the comparisonsbetween our dataset and line-strength indices available in theliterature. A significant fraction, about 60%, of galaxies in thepresent sample has one previous measurement in the Lick-IDS system butbasically restricted within the r_e/8 region. Line-strength measuresobtained both from apertures and gradients outside this area and withinthe r_e/8 region, with the present radial mapping, are completely new.Full appendix and Figs. 8 to 13 are only available in electronic form athttp://www.edpsciences.org Full Tables 6, 7, 9 and 10 are only availableat the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/433/497 Based onobservations obtained at the European Southern Observatory, La Silla,Chile (Programs Nr. 60.A-0647 and 61.A-0406).
| 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.
| Extragalactic globular clusters in the near infrared. IV. Quantifying the age structure using Monte-Carlo simulations
In previous papers of the series, we used a combination of optical andnear-infrared colours to derive constrains on the relative age structurein globular cluster systems. Here, we present the details, strength andlimitations of our method based on Monte-Carlo simulations ofcolour-colour diagrams and cumulative age distributions. The simulationsare based on general informations about the globular cluster systems(e.g. colour-ranges, the number ratios between sub-populations) and thedifferent single stellar population models (SSP's) which are used toderive relative ages. For both the modeled systems and the observedglobular cluster systems we derive the cumulative age distribution andintroduce two parameters to define it, the so-called 50% age and theresult of the reduced χ2 test of the comparison betweenmodels and observations. The method was tested successfully on severalsystems and allowed to reveal significant intermediate age populationsin two of them.
| VLT spectroscopy of globular cluster systems. I. The photometric and spectroscopic data set
We present Lick line-index measurements of extragalactic globularclusters in seven early-type galaxies (NGC 1380, 2434, 3115, 3379, 3585,5846, and 7192) with different morphological types (E-S0) located infield and group/cluster environments. High-quality spectra were takenwith the FORS2 instrument at ESO's Very Large Telescope. 50% of ourdata allows an age resolution Δ t/t≈0.3 and a metallicityresolution 0.25-0.4 dex, depending on the absolute metallicity.Globular cluster candidates are selected from deep B, V, R, I, KFORS2/ISAAC photometry with 80-100% success rate inside one effectiveradius. Using combined optical/near-infrared colour-colour diagrams wepresent a method to efficiently reduce fore-/background contaminationdown to 10%. We find clear signs for bi-modality in the globularcluster colour distributions of NGC 1380, 3115, and 3585. The colourdistributions of globular clusters in NGC 2434, 3379, 5846, and 7192 areconsistent with a broad single-peak distribution. For the analysedglobular cluster systems the slopes of projected radial surface densityprofiles, of the form Σ(R) R -Γ, varybetween 0.8 and 2.6. Blue and red globular cluster sub-populationsshow similar slopes in the clearly bi-modal systems. For galaxies withsingle-peak globular cluster colour distributions, there is a hint thatthe blue cluster system seems to have a more extended radialdistribution than the red one. Using globular clusters as a tracerpopulation we determine total dynamical masses of host galaxies out tolarge radii (1.6-4.8 R_eff). For the sample we find masses in therange 8.8×1010 M_ȯ up to1.2×1012 M_ȯ. The line index data presentedhere will be used in accompanying papers of this series to derive ages,metallicities and abundance ratios. A compilation of currently availablehigh-quality Lick index measurements for globular clusters inelliptical, lenticular, and late-type galaxies is provided and willserve to augment the current data set.Based on observations collected at the European Southern Observatory,Cerro Paranal, Chile under programme ID P65.N-0281, P66.B-0068, andP67.B-0034.Appendix A is only available in electronic form athttp://www.edpsciences.orgAppendices B and C are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/415/123
| 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.
| Line-of-Sight Reddening Predictions: Zero Points, Accuracies, the Interstellar Medium, and the Stellar Populations of Elliptical Galaxies
Revised (B-V)0-Mg2 data, which are used to testreddening predictions, are presented for 402 elliptical galaxies. Thesereddening predictions can tell us both what the intrinsic errors are inthis relationship among gE galaxy stellar populations as well as detailsof nearby structure in the interstellar medium (ISM) of our Galaxy, andof the intrinsic errors in reddening predictions. Using least-squaresfits, the explicit 1 σ errors in reddenings predicted by theBurstein-Heiles (BH) method and the Schlegel and coworkers (IR) methodare calculated, as well as the 1 σ observational error in the(B-V)0-Mg2 for gE galaxies. It is found that indirections with E(B-V)<0.100 mag (where most of these galaxies lie),1 σ errors in the IR reddening predictions are 0.006-0.009 mag inE(B-V), those for BH reddening predictions are 0.011 mag, and the 1σ agreement between the two reddening predictions is 0.007 mag.The IR predictions have an accuracy of 0.010-0.011 mag in directionswith E(B-V)>=0.100 mag, significantly better than those of the BHpredictions (0.024-0.025). Both methods yield good evidence thatgas-to-dust variations that vary by a factor of 3, both high and low,exist along many lines of sight in our Galaxy. Both methods also predictmany directions with E(B-V)<0.015 mag, despite the difference in zeropoint that each has assumed. The ~0.02 higher reddening zero point inE(B-V) previously determined by Schlegel and coworkers is confirmed,primarily at the Galactic poles. Independent evidence of reddening atthe north Galactic pole (NGP) is reviewed, with the conclusion thatdirections still exist at the NGP that have E(B-V)<<0.01. Twolines of evidence suggest that IR reddenings are overpredicted indirections with high gas-to-dust ratios. As high gas-to-dust directionsin the ISM also include the Galactic poles, this overprediction is thelikely cause of the E(B-V)~0.02 mag larger IR reddening zero pointrelative to that of BH.
| Extragalactic globular clusters in the near infrared III. NGC 5846 and NGC 7192. Quantifying the age distribution of sub-populations
In this third paper of our series on near-IR and optical photometry ofglobular cluster systems in early-type galaxies we concentrate on thephotometric results for NGC 5846 and NGC 7192, two group ellipticals,and on a first comparison between the globular cluster systemsinvestigated so far. In NGC 5846 the colour-colour diagram shows clearbi-modality in (V-K), which is confirmed by a KMM test. The mean colourof both peaks were estimated to be (V-K)blue=2.57+/-0.06 and(V-K)red=3.18+/-0.06. The situation in NGC 7192 is different,in that the colour-colour diagram gives no evidence for a distinctsecond population of globular clusters. Using simulated colourdistributions of globular cluster systems, we make a first step inquantifying the cumulative age distribution in globular cluster systems.Also here the result for NGC 5846 leads us to the conclusion that itsmetal-rich globular cluster population contains two globular clusterpopulations which differ in age by several Gyr. The age structure forNGC 7192 shows instead strong similarity with a single-age population.Based on observations at the Very Large Telescope of the EuropeanSouthern Observatory, Chile (Program 63.N-0287).Based on observations made with the NASA/ESA Hubble Space Telescope,obtained from the data archive at the Space Telescope Science Institute.STScI is operated by the association of Universities for Research inAstronomy, Inc. under the NASA contract NAS 5-26555.
| 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
| Core Radio and Optical Emission in the Nuclei of nearby FR I Radio Galaxies
In this paper we analyze the relation between radio, optical continuumand Hα+[N II] emission from the cores of a sample of 21 nearbyFanaroff and Riley type I galaxies as observed with the VLBA and HST.The emission arises inside the inner tens of parsecs of the galaxies.Core radio emission is observed in 19/20 galaxies, optical corecontinuum emission is detected in 12/21 galaxies and Hα+[N II]core emission is detected in 20/21 galaxies. We confirm the recentlydetected linear correlation between radio and optical core emission inFR I galaxies and show that both core emissions also correlate withcentral Hα+[N II] emission. The tight correlations between radio,optical, and Hα+[N II] core emission constrain the bulk Lorentzfactor to γ~2-5 and γ<~2 for a continuous jet and a jetconsisting of discrete blobs, respectively, assuming jet-viewing anglesin the range 30°-90°. Radio and optical core emissions arelikely to be synchrotron radiation from the inner jet, possibly with asignificant contribution from emission by an accretion disk and/or flow.Elliptical galaxies with LINER nuclei without large-scale radio jetsseem to follow the core emission correlations found in FR I galaxies.This suggests that the central engines could be very similar for the twoclasses of active galactic nuclei. Based on observations with theNASA/ESA Hubble Space Telescope obtained at the Space Telescope ScienceInstitute, which is operated by the Association of Universities forResearch in Astronomy, Inc., under NASA contract NAS 5-26555.
| Line-strength indices and velocity dispersions for 148 early-type galaxies in different environments
We have derived high quality line-strength indices and velocitydispersions for a sample of 148 early-type galaxies in differentenvironments. The wavelength region covered by the observations (lambda=~ 4600 to 6600 Å) includes the Lick/IDS indices Hβ,Mg1, Mg2, Mgb, Fe5015, Fe5270, Fe5335, Fe5406,Fe5709, Fe5782, NaD, TiO1 and TiO2. The data areintended to address possible differences of the stellar populations ofearly-type galaxies in low- and high-density environments. This paperdescribes the sample properties, explains the data reduction andpresents the complete list of all the measurements. Most galaxies of thesample (85%) had no previous measurements of any Lick/IDS indices andfor 30% of the galaxies we present first-time determinations of theirvelocity dispersions. Special care is taken to identify galaxies withemission lines. We found that 62 per cent of the galaxies in the samplehave emission lines, as measured by the equivalent width of the [OIII]5007Å line, EW[OIII] > 0.3 Å. Tables 5 and 6 are onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/ A+A/395/431. They are also available via ftp atftp.mpe.mpg.de in the directory people/dthomas/Beuing02 or via WWW atftp://ftp.mpe.mpg.de/people/dthomas/Beuing02.
| Near-infrared surface photometry of early-type galaxies
CCD infrared (JHKs) photometry was performed on a sample of10 elliptical and 2 lenticular galaxies. Isophotal parameters,brightness profiles, integrated colors and color gradients arepresented. Color gradients found are very weak, showing bluer colorstowards the outer regions. The colors of the sample galaxies arecompatible with stellar populations like those found in metal-richclusters of the Galaxy; objects NGC 7192, NGC 7562 and NGC 7619 arecompatible with less metal-rich populations. The brightness profile ofmost galaxies is well described by the r1/4 law. The profilesof NGC 1600 and NGC 720 are described by Sérsic's law with n ~1.5 and n ~ 1.8 respectively. The infrared effective radius of theobjects studied is typically one half of its counterpart in the B band,which can be an indication that the stellar population that dominatesthe infrared emission is more concentrated in the central regions. Weshow that the sample satisfies the Fundamental Plane relation ofelliptical galaxies in the infrared, with an rms scatter of 0.20 for Jand H and 0.23 for Ks.
| The Colors of Globular Clusters
A compilation has been made of available data on the ratio of the numberof metal-rich ([Fe/H]>-1.0) to metal-poor ([Fe/H]<-1.0) clustersin various globular cluster systems. Among early-type galaxies of typesE, E/S0, and S0, the ratio of blue to red globular clusters is found tovary by almost 2 orders of magnitude. The data suggest that cD galaxieshave the widest range of evolutionary histories. The fraction ofmetal-rich red clusters is largest among early-type galaxies and appearsto decrease toward later Hubble types.
| A catalogue and analysis of X-ray luminosities of early-type galaxies
We present a catalogue of X-ray luminosities for 401 early-typegalaxies, of which 136 are based on newly analysed ROSAT PSPC pointedobservations. The remaining luminosities are taken from the literatureand converted to a common energy band, spectral model and distancescale. Using this sample we fit the LX:LB relationfor early-type galaxies and find a best-fit slope for the catalogue of~2.2. We demonstrate the influence of group-dominant galaxies on the fitand present evidence that the relation is not well modelled by a singlepower-law fit. We also derive estimates of the contribution to galaxyX-ray luminosities from discrete-sources and conclude that they provideLdscr/LB~=29.5ergs-1LBsolar-1. Wecompare this result with luminosities from our catalogue. Lastly, weexamine the influence of environment on galaxy X-ray luminosity and onthe form of the LX:LB relation. We conclude thatalthough environment undoubtedly affects the X-ray properties ofindividual galaxies, particularly those in the centres of groups andclusters, it does not change the nature of whole populations.
| A synthesis of data from fundamental plane and surface brightness fluctuation surveys
We perform a series of comparisons between distance-independentphotometric and spectroscopic properties used in the surface brightnessfluctuation (SBF) and fundamental plane (FP) methods of early-typegalaxy distance estimation. The data are taken from two recent surveys:the SBF Survey of Galaxy Distances and the Streaming Motions of AbellClusters (SMAC) FP survey. We derive a relation between(V-I)0 colour and Mg2 index using nearly 200galaxies and discuss implications for Galactic extinction estimates andearly-type galaxy stellar populations. We find that the reddenings fromSchlegel et al. for galaxies with E(B-V)>~0.2mag appear to beoverestimated by 5-10 per cent, but we do not find significant evidencefor large-scale dipole errors in the extinction map. In comparison withstellar population models having solar elemental abundance ratios, thegalaxies in our sample are generally too blue at a given Mg2;we ascribe this to the well-known enhancement of the α-elements inluminous early-type galaxies. We confirm a tight relation betweenstellar velocity dispersion σ and the SBF `fluctuation count'parameter N, which is a luminosity-weighted measure of the total numberof stars in a galaxy. The correlation between N and σ is eventighter than that between Mg2 and σ. Finally, we deriveFP photometric parameters for 280 galaxies from the SBF survey data set.Comparisons with external sources allow us to estimate the errors onthese parameters and derive the correction necessary to bring them on tothe SMAC system. The data are used in a forthcoming paper, whichcompares the distances derived from the FP and SBF methods.
| Mass profiles and anisotropies of early-type galaxies
We discuss the problem of using stellar kinematics of early-typegalaxies to constrain the orbital anisotropies and radial mass profilesof galaxies. We demonstrate that compressing the light distribution of agalaxy along the line of sight produces approximately the same signaturein the line-of-sight velocity profiles as radial anisotropy. Inparticular, fitting spherically symmetric dynamical models to apparentlyround, isotropic face-on flattened galaxies leads to a spurious biastowards radial orbits in the models, especially if the galaxy has a weakface-on stellar disc. Such face-on stellar discs could plausibly be thecause of the radial anisotropy found in spherical models of intermediateluminosity ellipticals such as NGC 2434, 3379 and 6703. In the light ofthis result, we use simple dynamical models to constrain the outer massprofiles of a sample of 18 round, early-type galaxies. The galaxiesfollow a Tully-Fisher relation parallel to that for spiral galaxies, butfainter by at least 0.8mag (I-band) for a given mass. The most luminousgalaxies show clear evidence for the presence of a massive dark halo,but the case for dark haloes in fainter galaxies is more ambiguous. Wediscuss the observations that would be required to resolve thisambiguity.
| The LX-σ Relation for Galaxies and Clusters of Galaxies
We demonstrate that individual elliptical galaxies and clusters ofgalaxies form a continuous X-ray luminosity-velocity dispersion(LX-σ) relation. Our samples of 280 clusters and 57galaxies have LX~σ4.4 andLX~σ10, respectively. This unifiedLX-σ relation spans 8 orders of magnitude inLX and is fully consistent with the observed and theoreticalluminosity-temperature scaling laws. Our results support the notion thatgalaxies and clusters of galaxies are the luminous tracers of similardark matter halos.
| The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and Distances
We report data for I-band surface brightness fluctuation (SBF)magnitudes, (V-I) colors, and distance moduli for 300 galaxies. Thesurvey contains E, S0, and early-type spiral galaxies in the proportionsof 49:42:9 and is essentially complete for E galaxies to Hubblevelocities of 2000 km s-1, with a substantial sampling of Egalaxies out to 4000 km s-1. The median error in distancemodulus is 0.22 mag. We also present two new results from the survey.(1) We compare the mean peculiar flow velocity (bulk flow) implied byour distances with predictions of typical cold dark matter transferfunctions as a function of scale, and we find very good agreement withcold, dark matter cosmologies if the transfer function scale parameterΓ and the power spectrum normalization σ8 arerelated by σ8Γ-0.5~2+/-0.5. Deriveddirectly from velocities, this result is independent of the distributionof galaxies or models for biasing. This modest bulk flow contradictsreports of large-scale, large-amplitude flows in the ~200 Mpc diametervolume surrounding our survey volume. (2) We present adistance-independent measure of absolute galaxy luminosity, N and showhow it correlates with galaxy properties such as color and velocitydispersion, demonstrating its utility for measuring galaxy distancesthrough large and unknown extinction. Observations in part from theMichigan-Dartmouth-MIT (MDM) Observatory.
| Dynamical Family Properties and Dark Halo Scaling Relations of Giant Elliptical Galaxies
Based on a uniform dynamical analysis of the line-profile shapes of 21mostly luminous, slowly rotating, and nearly round elliptical galaxies,we have investigated the dynamical family relations and dark haloproperties of ellipticals. Our results include: (i) The circularvelocity curves (CVCs) of elliptical galaxies are flat to within ~=10%for R>~0.2Re. (ii) Most ellipticals are moderatelyradially anisotropic; their dynamical structure is surprisingly uniform.(iii) Elliptical galaxies follow a Tully-Fisher (TF) relation withmarginally shallower slope than spiral galaxies, andvmaxc~=300 km s-1 for anL*B galaxy. At given circular velocity, they are~1 mag fainter in B and ~0.6 mag in R and appear to have slightly lowerbaryonic mass than spirals, even for the maximum M/LB allowedby the kinematics. (iv) The luminosity dependence of M/LBindicated by the tilt of the fundamental plane (FP) is confirmed. Thetilt of the FP is not caused by dynamical or photometric nonhomology,although the latter might influence the slope of M/L versus L. It canalso not be due only to an increasing dark matter fraction with L forthe range of IMF currently discussed. It is, however, consistent withstellar population models based on published metallicities and ages. Themain driver is therefore probably metallicity, and a secondarypopulation effect is needed to explain the K-band tilt. (v) Theseresults make it likely that elliptical galaxies have nearly maximalM/LB (minimal halos). (vi) Despite the uniformly flat CVCs,there is a spread in the luminous to dark matter ratio and in cumulativeM/LB(r). Some galaxies have no indication for dark matterwithin 2Re, whereas for others we obtain localM/LB-values of 20-30 at 2Re. (vii) In models withmaximum stellar mass, the dark matter contributes ~10%-40% of the masswithin Re. Equal interior mass of dark and luminous matter ispredicted at ~2-4Re. (viii) Even in these maximum stellarmass models, the halo core densities and phase-space densities are atleast ~25 times larger and the halo core radii ~4 times smaller than inspiral galaxies of the same circular velocity. The increase in M/L setsin at ~10 times larger acceleration than in spirals. This could implythat elliptical galaxy halos collapsed at high redshifts or that some ofthe dark matter in ellipticals might be baryonic.
| 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.
| Orbital structure and mass distribution in elliptical galaxies
We report on a homogeneous dynamical analysis of a sample of 21 round(17 E0/E1, 4 E2) elliptical galaxies. We present new kinematic data foreight of these galaxies and new photometry for one object. The remainingkinematic and photometric data and the required distance information aretaken from the literature. The analysis uses non-parametric sphericalmodels and takes into account line profile information as well asvelocity dispersions. We present model fits to the kinematic data andthe derived radial profiles of orbital anisotropy and B-bandmass-to-light ratio, including confidence intervals. The circularvelocity curves resulting from our model fits are all consistent withbeing flat outside R~ 0.3 R_e. Generally, the M/L ratio profiles show anoutward increase, although models based on luminous matter are ruled outat 95% confidence only for three galaxies (NGC 2434, NGC 7507, NGC7626). For NGC 1399, NGC 4472, NGC 4486, and NGC 4636, where X-rayobservations are available, the mass profiles of the best fit modelsmatch the ones derived from the X-ray analysis. The best models for mostgalaxies are isotropic to slightly radially anisotropic, with typicalbeta <~0.3, in a few cases beta <~0 .5 at R_e/2. We discuss thegenerally small effects of flattening along the line-of-sight (theexpected = 0.79 for this sample of luminous ellipticals)and of small embedded disks. Our results suggest that ellipticalgalaxies have surprisingly uniform dynamical properties.
| 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.
| Gradients of Absorption-Line Strengths in Elliptical Galaxies
We have restudied line-strength gradients of 80 elliptical galaxies.Typical metallicity gradients of elliptical galaxies areΔ[Fe/H]/Δlogr~=-0.3, which is flatter than the gradientspredicted by monolithic collapse simulations. The metallicity gradientsdo not correlate with any physical properties of galaxies, includingcentral and mean metallicities, central velocity dispersionsσ0, absolute B magnitudes MB, absoluteeffective radii Re, and dynamical masses of galaxies. Byusing the metallicity gradients, we have calculated mean stellarmetallicities for individual ellipticals. Typical mean stellarmetallicities are <[Fe/H]>~=-0.3 and range from<[Fe/H]>~=-0.8 to +0.3, which is contrary to what Gonzalez &Gorgas claimed; the mean metallicities of ellipticals are not universal.The mean metallicities correlate well with σ0 anddynamical masses, though relations for MB and Reinclude significant scatters. We find fundamental planes defined bysurface brightnesses SBe, <[Fe/H]>, and Re(or MB), the scatters of which are much smaller than those ofthe <[Fe/H]>-Re (or <[Fe/H]>-MB)relations. The <[Fe/H]>-logσ0 relation is nearlyparallel to the [Fe/H]0-logσ0 relation butsystematically lower by 0.3 dex; thus the mean metallicities are aboutone-half of the central values. The metallicity-mass relation or,equivalently, the color-magnitude relation of ellipticals holds not onlyfor the central parts of galaxies but also for entire galaxies. Assumingthat Mg2 and Fe1 give [Mg/H] and [Fe/H],respectively, we find <[Mg/Fe]>~=+0.2 in most of ellipticalgalaxies. <[Mg/Fe]> shows no correlation with galaxy mass tracerssuch as σ0, in contrast to what was claimed for thecentral [Mg/Fe]. This can be most naturally explained if the starformation had stopped in elliptical galaxies before the bulk of Type Iasupernovae began to occur. Elliptical galaxies can have significantlydifferent metallicity gradients and <[Fe/H]>, even if they havethe same galaxy mass. This may result from galaxy mergers, but noevidence is found from presently available data to support the sameorigin for metallicity gradients, the scatters around themetallicity-mass relation, and dynamical disturbances. This may suggestthat the scatters have their origin at the formation epoch of galaxies.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
Catalogs and designations:
|
INHABITED SKY
