Contents
Images
Upload your image
DSS Images Other Images
Related articles
The Vertical Stellar Kinematics in Face-On Barred Galaxies: Estimating the Ages of Bars
In order to perform a detailed study of the stellar kinematics in thevertical axis of bars, we obtained high signal-to-noise spectra alongthe major and minor axes of the bars in a sample of 14 face-on galaxiesand used them to determine the line-of-sight stellar velocitydistribution, parameterized as a Gauss-Hermite series. With these data,we developed a diagnostic tool that allows one to distinguish betweenrecently formed and evolved bars, as well as to estimate their ages,assuming that bars form in vertically thin disks that are recognizableby low values for the vertical velocity dispersion σz.Through N-body realizations of bar unstable disk galaxies we were alsoable to check the timescales involved in the processes that give bars animportant vertical structure. We show that σz inevolved bars is roughly 100 km s-1, which translates to aheight scale of about 1.4 kpc, giving support to scenarios in whichbulges form through disk material. Furthermore, the bars in ournumerical simulations have values for σz generallysmaller than 50 km s-1, even after evolving for 2 Gyr,suggesting that a slow process is responsible for making bars asvertically thick as we observe. We verify theoretically that theSpitzer-Schwarzschild mechanism is quantitatively able to explain theseobservations if we assume that giant molecular clouds are twice asconcentrated along the bar as in the rest of the disk.
| RX J0152.7-1357: Stellar Populations in an X-Ray Luminous Galaxy Cluster at z = 0.83
We present a study of the stellar populations of galaxies in the clusterRX J0152.7-1357 at a redshift of 0.83. The study is based on new highsignal-to-noise ratio spectroscopy of 29 cluster members covering thewavelength range 5000-10000 Å, as well asr'i'z' photometry of the cluster. Weuse scaling relations between the central velocity dispersions of thegalaxies and their luminosities, Balmer line strengths, and variousmetal line strengths to parameterize the differences between the membersof RX J0152.7-1357 and our low-redshift comparison sample. Theluminosities of the RX J0152.7-1357 galaxies and the strengths of thehigher order Balmer lines Hγ and Hδ (for non-emission-linegalaxies) appear to be in agreement with pure passive evolution of thestellar populations with a formation redshift zform~4.However, the strengths of the D4000 indices and the metal indices do notsupport this interpretation. Compared with our low-redshift comparisonsample, the metal indices (C4668, Fe4383, CN3883, G4300, andCN2) show that at least half of the non-emission-linegalaxies in RX J0152.7-1357 have an α-element abundance ratio[α/Fe] of 0.2 dex higher, and about half of the galaxies havesignificantly lower metal content. X-ray data have previously shown thatRX J0152.7-1357 is in the process of merging from two subclumps. We findthat differences in stellar populations of the galaxies are associatedwith the location of the galaxies relative to the X-ray emission. Thegalaxies with weak C4668 and G4300, as well as galaxies for which weak[O II] emission indicates a very recent star formation episode involvingabout 1% of the mass, are located in areas of low X-ray luminosity, onthe outskirts of the two subclumps. It is possible that these galaxiesare experiencing the effect of the cluster merger as (short) episodes ofstar formation, while the galaxies in the cores of the subclumps areunaffected by the merger. The spectroscopy of the RX J0152.7-1357galaxies shows for the first time galaxies in a rich cluster atintermediate redshift that cannot evolve passively into the present-daygalaxy population in rich clusters. Additional physical processes may beat work, and we speculate that merging with infalling (disk) galaxies inwhich stars have formed over an extended period might produce therequired reduction in [α/Fe]. However, the merging could not beaccompanied by star formation involving a substantial mass fraction. Wenote that our conclusions, in part, rely on stellar population modelsfor which the predictions of the indices in the rest-frame blue have notyet been tested extensively.
| 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).
| Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters
The availability of the Hipparcos Catalogue has triggered many kinematicand dynamical studies of the solar neighbourhood. Nevertheless, thosestudies generally lacked the third component of the space velocities,i.e., the radial velocities. This work presents the kinematic analysisof 5952 K and 739 M giants in the solar neighbourhood which includes forthe first time radial velocity data from a large survey performed withthe CORAVEL spectrovelocimeter. It also uses proper motions from theTycho-2 catalogue, which are expected to be more accurate than theHipparcos ones. An important by-product of this study is the observedfraction of only 5.7% of spectroscopic binaries among M giants ascompared to 13.7% for K giants. After excluding the binaries for whichno center-of-mass velocity could be estimated, 5311 K and 719 M giantsremain in the final sample. The UV-plane constructed from these datafor the stars with precise parallaxes (σπ/π≤20%) reveals a rich small-scale structure, with several clumpscorresponding to the Hercules stream, the Sirius moving group, and theHyades and Pleiades superclusters. A maximum-likelihood method, based ona Bayesian approach, has been applied to the data, in order to make fulluse of all the available stars (not only those with precise parallaxes)and to derive the kinematic properties of these subgroups. Isochrones inthe Hertzsprung-Russell diagram reveal a very wide range of ages forstars belonging to these groups. These groups are most probably relatedto the dynamical perturbation by transient spiral waves (as recentlymodelled by De Simone et al. \cite{Simone2004}) rather than to clusterremnants. A possible explanation for the presence of younggroup/clusters in the same area of the UV-plane is that they have beenput there by the spiral wave associated with their formation, while thekinematics of the older stars of our sample has also been disturbed bythe same wave. The emerging picture is thus one of dynamical streamspervading the solar neighbourhood and travelling in the Galaxy withsimilar space velocities. The term dynamical stream is more appropriatethan the traditional term supercluster since it involves stars ofdifferent ages, not born at the same place nor at the same time. Theposition of those streams in the UV-plane is responsible for the vertexdeviation of 16.2o ± 5.6o for the wholesample. Our study suggests that the vertex deviation for youngerpopulations could have the same dynamical origin. The underlyingvelocity ellipsoid, extracted by the maximum-likelihood method afterremoval of the streams, is not centered on the value commonly acceptedfor the radial antisolar motion: it is centered on < U > =-2.78±1.07 km s-1. However, the full data set(including the various streams) does yield the usual value for theradial solar motion, when properly accounting for the biases inherent tothis kind of analysis (namely, < U > = -10.25±0.15 kms-1). This discrepancy clearly raises the essential questionof how to derive the solar motion in the presence of dynamicalperturbations altering the kinematics of the solar neighbourhood: doesthere exist in the solar neighbourhood a subset of stars having no netradial motion which can be used as a reference against which to measurethe solar motion?Based on observations performed at the Swiss 1m-telescope at OHP,France, and on data from the ESA Hipparcos astrometry satellite.Full Table \ref{taba1} is only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/430/165}
| Structure and Kinematics of NGC 615 and Its Nuclear Star Formation History
The results of a complex photometric and spectral investigation of theregular Sb galaxy NGC 615 are presented. The observations were made withthe 6 m, 1 m, and 0.6 m telescopes of the Special AstrophysicalObservatory RAS (Nizhnij Arkhyz, Russia) and the 1.5 m ESO telescope (LaSilla, Chile). The analysis of the radial brightness profiles revealsthe existence of at least two decoupled exponential components; theparameters of the outer component are typical for the global disks of Sbgalaxies, and the inner component seen in the radius range 9"-30"(1.0-3.5 kpc) is distinguished by compactness and high surfacebrightness. A combination of two-dimensional velocity fields for starsand ionized gas in the central part of the galaxy and of the long-slitvelocity profiles along the major axis up to the optical border of NGC615 provides some interesting findings. In the very center, R<3" (0.3kpc), stars and gas rotate together, and the dynamical and photometricmajor axes are turned with respect to the global line of nodes; weconclude that an inclined circumnuclear disk is detected. In the bulge,R=3"-6" (0.35-0.75 kpc), the stellar velocity dispersion is more than100 km s-1, the stars rotate twice as slowly as the ionizedgas, and a counterrotating gaseous component is observed. In the innerexponential component the stars rotate together with the ionized gas,and the stellar velocity dispersion drops to about 50 km s-1.As the photometric major axis of this component is turned with respectto the line of nodes, we call it ``an oval inner disk.'' The mean age ofthe stellar populations in the nucleus and in the inner disk beyond itsH II regions is 5 Gyr, while the bulge is much older. Both thechemically decoupled nucleus of NGC 615 and the inner disk probablyformed the bulk of their more luminous stars in a secondary burst ofstar formation, perhaps provoked by the close passage of another galaxysome gigayears ago. Based on observations collected with the 6 m, 1 m,and 0.6 m telescopes of the Special Astrophysical Observatory (SAO) ofthe Russian Academy of Sciences (RAS) and with the 1.52 m ESO telescopeat La Silla.
| Spatially resolved spectroscopy of Coma cluster early-type galaxies. I. The database
We present long slit spectra for a magnitude limited sample of 35 E andS0 galaxies of the Coma cluster. The high quality of the data allowed usto derive spatially resolved spectra for a substantial sample of Comagalaxies for the first time. From these spectra we obtained rotationcurves, the velocity dispersion profiles and the H_3 and H_4coefficients of the Hermite decomposition of the line of sight velocitydistribution. Moreover, we derive the radial line index profiles of Mg,Fe and Hβ line indices out to R~ 1 r_e - 3 r_e with highsignal-to-noise ratio. We describe the galaxy sample, the observationsand data reduction, and present the spectroscopic database. Ground-basedphotometry for a subsample of 8 galaxies is also presented. The Comacluster is one of the richest known clusters of galaxies, spanning about4 decades in density. Hence it is the ideal place to study the structureof galaxies as a function of environmental density in order to constrainthe theories of galaxy formation and evolution. Based on thespectroscopic database presented, we will discuss these issues in aseries of future papers. Tables 1 and 4 are also available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http://cdsweb.u-strasbg.fr/Abstract.html Tables 5 to 82 are onlyavailable in electronic form at CDS.
| Fundamental plane distances to early-type field galaxies in the South Equatorial Strip. I. The spectroscopic data
Radial velocities and central velocity dispersions are derived for 238E/S0 galaxies from medium-resolution spectroscopy. New spectroscopicdata have been obtained as part of a study of the Fundamental Planedistances and peculiar motions of early-type galaxies in three selecteddirections of the South Equatorial Strip, undertaken in order toinvestigate the reality of large-scale streaming motion; results of thisstudy have been reported in Müller et al. (1998). The new APM SouthEquatorial Strip Catalog (-17fdg 5 < delta < +2fdg 5) was used toselect the sample of field galaxies in three directions: (1) 15h10 -16h10; (2) 20h30 - 21h50; (3) 00h10 - 01h30. The spectra obtained have amedian S/N per Å of 23, an instrumental resolution (FWHM) of ~ 4Å, and the spectrograph resolution (dispersion) is ~ 100 kms-1. The Fourier cross-correlation method was used to derivethe radial velocities and velocity dispersions. The velocity dispersionshave been corrected for the size of the aperture and for the galaxyeffective radius. Comparisons of the derived radial velocities with datafrom the literature show that our values are accurate to 40 kms-1. A comparison with results from Jo rgensen et al. (1995)shows that the derived central velocity dispersion have an rms scatterof 0.036 in log sigma . There is no offset relative to the velocitydispersions of Davies et al. (1987).
| H gamma and H delta Absorption Features in Stars and Stellar Populations
The H gamma and H delta absorption features are measured in a sample of455 (out of an original 460) Lick/IDS stars with pseudo--equivalentwidth indices. For each Balmer feature, two definitions, involving anarrow (~20 Angstroms) and a wide (~40 Angstroms) central bandpass, aremeasured. These four new Balmer indices augment 21 indices previouslydetermined by Worthey et al., and polynomial fitting functions that giveindex strengths as a function of stellar temperature, gravity, and[Fe/H] are provided. The new indices are folded into models for theintegrated light of stellar populations, and predictions are given forsingle-burst stellar populations of a variety of ages and metallicities.Contrary to our initial hopes, the indices cannot break a degeneracybetween burst age and burst strength in post-starburst objects, but theyare successful mean-age indicators when used with sensitive metallicityindicators. An appendix gives data, advice, and examples of how totransform new spectra to the 25-index Lick/IDS system.
| An Estimate of H 0 from Keck Spectroscopy of the Gravitational Lens System 0957+561
We present long-slit LRIS/Keck spectroscopic observations of thegravitational lens system 0957+561. Averaged over all of our data, therest-frame velocity dispersion sigma v of the central lens galaxy G1 issigma v = 279 +/- 12 km s-1. However, there appears to be a significantdecrease in sigma v as a function of distance from the center of G1 thatis not typical of the brightest cluster galaxies. Within 0."2 of thecenter of G1, we find the average sigma v = 316 +/- 14 km s-1, whereasfor positions greater than 0."2 from the center of G1, we find theaverage sigma v = 266 +/- 12 km s-1. A plausible explanation is that G1contains a central massive dark object of mass MMDO ~ 4 x 109h^{-1}100 Mȯ (h100 = H0/100 km s-1 Mpc-1), whichcontributes to the central velocity dispersion, and that the outer valueof sigma v is the appropriate measure of the depth of the potential wellof G1. The determination of a luminosity-weighted estimate of sigma v isessential for a determination of H0 from Q0957+561; our accuratemeasurements remove one of the chief uncertainties in the assumed formof the mass distribution of the lens. Thus, with the recent apparentreduction in the uncertainty in the measurement of the time delay forthe images A and B of Q0957+561, Delta tau BA = 417 +/- 3 days (Kundicet al.), we obtain an estimate for the Hubble constant: H0 = 62 +/- 7 kms-1 Mpc-1. If for some reason the trend of sigma v with slit position isspurious and we should use the dispersion averaged along the slit, thenthe estimate of H0 increases to 67 +/- 8 km s-1 Mpc-1. These standarderrors, however, do not include any contribution from any errors in theassumed form of the mass distribution of the lens. In particular, weused the mass model described by Falco, Gorenstein, & Shapiro, asupdated by Grogin & Narayan. The reduced chi 2 of model fits to theavailable position and magnification data for this system is relativelyhigh (~4), indicating that the estimate of H0 may have a significantcontribution from model errors. Further observations, discussed herein,should allow such errors to be estimated reliably.
| Spectroscopy for E and S0 galaxies in nine clusters
Central velocity dispersions, Mg_2 line indices and radial velocitiesfor 220 E and S0 galaxies are derived on the basis of intermediateresolution spectroscopy. Galaxies in the following clusters have beenobserved: Abell 194, Abell 539, Abell 3381, Abell 3574, S639, S753,Doradus, HydraI (Abell 1060) and Grm 15. For 151 of the galaxies, thevelocity dispersion has not previously been measured. 134 of the Mg_2determinations are for galaxies with no previous measurement. Thespectra cover either 500 or 1000A, centred on the magnesium triplet at5177A. The observations were obtained with the Boller & Chivensspectrograph at the ESO 1.5-m telescope and with the OPTOPUS, amulti-object fibre-fed B&C spectrograph, at the ESO 3.6-m telescope.The data are part of our ongoing study of the large-scale motions in theUniverse and the physical background for the Fundamental Plane. TheFourier fitting method was used to derive the velocity dispersions andradial velocities. The velocity dispersions have been corrected for theeffect of the size of the aperture. The correction was established onthe basis of velocity dispersion profiles available in the literature. Acomparison with results from Davies et al. shows that the derivedcentral velocity dispersions have an rms error of 0.036 in logsigma.There is no offset relative to the velocity dispersions from Davies etal. The offset relative to data from Lucey & Carter is-0.017+/-0.011 in logsigma, with our velocity dispersions being thesmallest. The velocity dispersions derived from the B&C and theOPTOPUS observations, as well as the velocity dispersions published byDavies et al., Dressler, Lucey & Carter and Lucey et al., can bebrought on a system consistent within 3 per cent. The Mg_2 line indiceshave been corrected for the size of the apertures, transformed to theLick system, and corrected for the effect of the velocity dispersion.From comparison with data from Davies et al. and from Faber, we findthat the rms error of Mg_2 is 0.013. Comparisons of the radialvelocities with data from the literature show that our determinationsare accurate to within ~=35 km s^-1. The accuracies reached for theseobservations are adequate for the study of the large-scale motions inthe Universe and for investigations of the Fundamental Plane.
| Old stellar populations. 5: Absorption feature indices for the complete LICK/IDS sample of stars
Twenty-one optical absorption features, 11 of which have been previouslydefined, are automatically measured in a sample of 460 stars. FollowingGorgas et al., the indices are summarized in fitting functions that giveindex strengths as functions of stellar temperature, gravity, and(Fe/H). This project was carried out with the purpose of predictingindex strengths in the integrated light of stellar populations ofdifferent ages and metallicities, but the data should be valuable forstellar studies in the Galaxy as well. Several of the new indices appearto be promising indicators of metallicity for old stellar populations. Acomplete list of index data and atmospheric parameters is available incomputer-readable form.
| The central velocity dispersion of the lensing galaxy in the quadruple lens system Q2237 + 0305
A measurement of the projected central velocity dispersion for thelensing galaxy in the quadruple gravitational lens system Q2237 + 0305is reported. Observations of the galaxy nucleus taken in superb seeingconditions with the 4.2-m William Herschel Telescope produce a value forthe central velocity dispersion of 215 +/-30 km/s. The value isconsistent with the predictions of theoretical models of the lensinggalaxy's mass distribution, but the measurement suggests there isevidence for some degree of anisotropy in the velocity dispersion of thegalaxy bulge.
| Polarization measurements of 313 nearby stars
The linear polarization of 313 low galactic latitude stars has beenmeasured. With few exceptions all program stars have a spectral typelater than B9 and are within 600 parsec of the sun. 181 stars aresituated at the southern sky and 132 at the northern sky.
| The Binary System X Ophiuchi.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1959ApJ...130..611F&db_key=AST
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Ophiucus |
| Right ascension: | 18h39m39.68s |
| Declination: | +08°43'58.1" |
| Apparent magnitude: | 6.995 |
| Distance: | 232.558 parsecs |
| Proper motion RA: | -6.7 |
| Proper motion Dec: | -9.3 |
| B-T magnitude: | 8.382 |
| V-T magnitude: | 7.11 |
Catalogs and designations:
|
