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|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.
|Bar Galaxies and Their Environments|
The prints of the Palomar Sky Survey, luminosity classifications, andradial velocities were used to assign all northern Shapley-Ames galaxiesto either (1) field, (2) group, or (3) cluster environments. Thisinformation for 930 galaxies shows no evidence for a dependence of barfrequency on galaxy environment. This suggests that the formation of abar in a disk galaxy is mainly determined by the properties of theparent galaxy, rather than by the characteristics of its environment.
|The UZC-SSRS2 Group Catalog|
We apply a friends-of-friends algorithm to the combined Updated ZwickyCatalog and Southern Sky Redshift Survey to construct a catalog of 1168groups of galaxies; 411 of these groups have five or more members withinthe redshift survey. The group catalog covers 4.69 sr, and all groupsexceed the number density contrast threshold, δρ/ρ=80. Wedemonstrate that the groups catalog is homogeneous across the twounderlying redshift surveys; the catalog of groups and their membersthus provides a basis for other statistical studies of the large-scaledistribution of groups and their physical properties. The medianphysical properties of the groups are similar to those for groupsderived from independent surveys, including the ESO Key Programme andthe Las Campanas Redshift Survey. We include tables of groups and theirmembers.
|Nearby Optical Galaxies: Selection of the Sample and Identification of Groups|
In this paper we describe the Nearby Optical Galaxy (NOG) sample, whichis a complete, distance-limited (cz<=6000 km s-1) andmagnitude-limited (B<=14) sample of ~7000 optical galaxies. Thesample covers 2/3 (8.27 sr) of the sky (|b|>20deg) andappears to have a good completeness in redshift (97%). We select thesample on the basis of homogenized corrected total blue magnitudes inorder to minimize systematic effects in galaxy sampling. We identify thegroups in this sample by means of both the hierarchical and thepercolation ``friends-of-friends'' methods. The resulting catalogs ofloose groups appear to be similar and are among the largest catalogs ofgroups currently available. Most of the NOG galaxies (~60%) are found tobe members of galaxy pairs (~580 pairs for a total of ~15% of objects)or groups with at least three members (~500 groups for a total of ~45%of objects). About 40% of galaxies are left ungrouped (field galaxies).We illustrate the main features of the NOG galaxy distribution. Comparedto previous optical and IRAS galaxy samples, the NOG provides a densersampling of the galaxy distribution in the nearby universe. Given itslarge sky coverage, the identification of groups, and its high-densitysampling, the NOG is suited to the analysis of the galaxy density fieldof the nearby universe, especially on small scales.
|A Test for Large-Scale Systematic Errors in Maps of Galactic Reddening|
Accurate maps of Galactic reddening are important for a number ofapplications, such as mapping the peculiar velocity field in the nearbyuniverse. Of particular concern are systematic errors which vary slowlyas a function of position on the sky, as these would induce spuriousbulk flow. We have compared the reddenings of Burstein & Heiles (BH)and those of Schlegel, Finkbeiner, & Davis (SFD) to independentestimates of the reddening, for Galactic latitudes |b|>10^deg. Ourprimary source of Galactic reddening estimates comes from comparing thedifference between the observed B-V colors of early-type galaxies, andthe predicted B-V color determined from the B-V-Mg_2 relation. We havefitted a dipole to the residuals in order to look for large-scalesystematic deviations. There is marginal evidence for a dipolar residualin the comparison between the SFD maps and the observed early-typegalaxy reddenings. If this is due to an error in the SFD maps, then itcan be corrected with a small (13%) multiplicative dipole term. Weargue, however, that this difference is more likely to be due to a small(0.01 mag) systematic error in the measured B-V colors of the early-typegalaxies. This interpretation is supported by a smaller, independentdata set (globular cluster and RR Lyrae stars), which yields a resultinconsistent with the early-type galaxy residual dipole. BH reddeningsare found to have no significant systematic residuals, apart from theknown problem in the region 230^deg
|Arcsecond Positions of UGC Galaxies|
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.
|Molecular Gas in Strongly Interacting Galaxies. I. CO (1-0) Observations|
We present observations of the CO (1-0) line in 80 interacting galaxiesas part of a program to study the role of interactions and mergers intriggering starbursts. The sample, which only includes obviouslyinteracting pairs of galaxies, is the largest such sample observed inCO. The observations were carried out at the NRAO 12 m and IRAM 30 mtelescopes. CO emission was detected in 56 galaxies (of which 32 are newdetections), corresponding to a detection rate of 70%. Because mostgalaxies are slightly larger than the telescope beam, correction factorswere applied to include CO emission outside the beam. The correctionfactors were derived by fitting a Gaussian function or an exponential CObrightness distribution to galaxies with multiple pointings and byassuming an exponential model for galaxies with single pointing. Wecompared the global CO fluxes of 10 galaxies observed by us at bothtelescopes. We also compared the measured fluxes for another 10 galaxiesobserved by us with those by other authors using the NRAO 12 m and FCRAO14 m telescopes. These comparisons provide an estimate of the accuracyof our derived global fluxes, which is ~40%. Mapping observations of twoclose pairs of galaxies, UGC 594 (NGC 317) and UGC 11175 (NGC 6621), arealso presented. In subsequent papers we will report the statisticalanalyses of the molecular properties in our sample galaxies and makecomparisons between isolated spirals and interacting galaxies.
|A catalogue of Mg_2 indices of galaxies and globular clusters|
We present a catalogue of published absorption-line Mg_2 indices ofgalaxies and globular clusters. The catalogue is maintained up-to-datein the HYPERCAT database. The measurements are listed together with thereferences to the articles where the data were published. A codeddescription of the observations is provided. The catalogue gathers 3541measurements for 1491 objects (galaxies or globular clusters) from 55datasets. Compiled raw data for 1060 galaxies are zero-point correctedand transformed to a homogeneous system. Tables 1, 3, and 4 areavailable in electronic form only at the CDS, Strasbourg, via anonymousftp 184.108.40.206. Table 2 is available both in text and electronic form.
|Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies|
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
|A catalogue of spatially resolved kinematics of galaxies: Bibliography|
We present a catalogue of galaxies for which spatially resolved data ontheir internal kinematics have been published; there is no a priorirestriction regarding their morphological type. The catalogue lists thereferences to the articles where the data are published, as well as acoded description of these data: observed emission or absorption lines,velocity or velocity dispersion, radial profile or 2D field, positionangle. Tables 1, 2, and 3 are proposed in electronic form only, and areavailable from the CDS, via anonymous ftp to cdsarc.u-strasbg.fr (to220.127.116.11) or via http://cdsweb.u-strasbg.fr/Abstract.html
|The fundamental plane of early-type galaxies: stellar populations and mass-to-light ratio.|
We analyse the residuals to the fundamental plane (FP) of ellipticalgalaxies as a function of stellar-population indicators; these are basedon the line-strength parameter Mg_2_ and on UBVRI broad-band colors, andare partly derived from new observations. The effect of the stellarpopulations accounts for approximately half the observed variation ofthe mass-to-light ratio responsible for the FP tilt. The residual tiltcan be explained by the contribution of two additional effects: thedependence of the rotational support, and possibly that of the spatialstructure, on the luminosity. We conclude to a constancy of thedynamical-to-stellar mass ratio. This probably extends to globularclusters as well, but the dominant factor would be here the luminositydependence of the structure rather than that of the stellar population.This result also implies a constancy of the fraction of dark matter overall the scalelength covered by stellar systems. Our compilation ofinternal stellar kinematics of galaxies is appended.
|A Spectrophotometric Survey of Merging Galaxies|
We present long-slit spectrophotometry of 40 merging or stronglyinteracting galaxy systems in the wavelength range 3650-7100 A. Alongwith optically selected objects, the sample includes 10 ultraluminousIRAS galaxies with evidence of ongoing merger activity. The data show awide variety of phenomena, with spectra resembling those of isolatedelliptical galaxies, early and late-type spiral galaxies, activegalactic nuclei starbursts, and poststarburst systems.
|A Catalog of Stellar Velocity Dispersions. II. 1994 Update|
A catalog of central velocity dispersion measurements is presented,current through 1993 September. The catalog includes 2474 measurementsof 1563 galaxies. A standard set of 86 galaxies is defined, consistingof galaxies with at least three reliable, concordant measurements. It issuggested that future studies observe some of these standard galaxies sothat different studies can be normalized to a consistent system. Allmeasurements are reduced to a normalized system using these standards.
|Spectrophotometric Properties of Merging Galaxies|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...450..547L&db_key=AST
|The surface distortion caused by the tides in galactic binary system.|
|Stellar dynamics in E+E pairs of galaxies. 2: Simulations and interpretation|
We have presented in a companion article a kinematic study of three E+Egalaxy pairs, NGC741/742, 1587/1588 (CPG 99) and 2672/2673 (CPG 175). Wefind some evidence for perturbed velocity dispersion profiles. Theseperturbation features are now reported for 14 galaxies in theliterature. They occur, or require observations for detection, at largeradii where the S/N in the data is low. While observations of individualgalaxies are sometimes uncertain, the large number of objects where suchfeatures are suspected gives confidence that they are real. Theseperturbations can be attributed to projection effects contaminationalong the line of sight, or directly to the tidal interaction. We reportthe results of several self-gravitating simulations of unbound pairs inan effort to better understand these perturbations another genericfeatures of close E+E pairs reported in the literature. The modelsfrequently show off-center envelopes created by the asymmetry of tidalforces during interpenetrating encounters. The envelopes last for a few108 yrs, which explains the frequency of such features inobserved pairs. This phenomenon is stronger in the self-gravitatingsimulations than in the MTBA runs. U-shaped (and an equal number ofinverse U shaped velocity profiles are seen in the simulations, a resultof ablation in the outer envelopes. Simulations including inner galaxyrotation also preserve this feature, irrespective of the spin vectordirection in each galaxy. U-shape velocity structure is found to be arobust indicator of the ongoing interaction. All simulations showevidence for enhanced velocity dispersion between the galaxies even inthe case of simple superposition of two non interacting objects. Wetherefore conclude that this cannot be considered an unambiguousindicator of the interaction.
|Interacting binary galaxies. 7: Kinematic data for 12 disturbed ellipticals|
We have analyzed long-slit spectroscopic data for a sample of 12 tidallydisturbed elliptical galaxies. The spectra were obtained with the KittPeak National Observatory (KPNO) 4 m RC spectrograph. Rotation curvesand velocity dispersion profiles have been measured at a variety ofposition angles in these galaxies and have been used to analyze thedynamical response and internal kinematics of stellar systems involvedin strong gravitational encounters. We have confirmed with these dataour previous observation that such galaxies often reveal U-shaped'rotation' profiles, indicative of a strong resonant tidal effect amongthose stars that are moving prograde with respect to the galacticencounter. Additional kinematic peculiarities, including U-shaped andW-shaped velocity dispersion profiles, are also revealed in these data.The observed morphologies of the tidal features seen in some of thesample galaxies are consistent with the idea that elliptical galaxiesoften contain an embedded disk component. Our velocity profiles alongnew position angles confirm the validity of tidal interaction modelsthat we previously derived for specific pairs in our sample using only asingle slit position angle per galaxy. Additional insight into possiblerefinements of those collision models has also resulted from this study.
|A search for secondary nuclei in shell galaxies|
We present the results of our search for secondary nuclei in shellgalaxies. The most recent accretion model simulations of shell galaxyformation, by Salmon, Quinn, & Warren, have included the effects ofdynamical friction and tidal stripping on a captured secondary for thefirst time. In their simulation, the secondary galaxy is disruptedslowly throughout the shell forming process, and should therefore bevisible as a secondary nucleus for a significant fraction of the shelllifetime. We have obtained Charge Couple Device (CCD) images of 29 shellgalaxies, often in two colors, in order to search for secondary nuclei.Identification of possible secondary nuclei was carried out bysubtracting a smooth model of the primary elliptical and carefullyexamining the residual image. We found six galaxies with possiblesecondary nuclei that could be responsible for the shells within theframework of the Salmon, Quinn, & Warren (sinking satellite)accretion model. Foreground contamination by stars or galaxies impliesthat this detection is an upper limit. Based on our resutls, we estimatean upper limit of 200 Myr for the typical lifetime for a secondarynucleus and discuss the frequency of secondary nuclei expected from theweak interaction model and the major merger model.
|Neutral hydrogen observations of elliptical galaxies|
Detection of HI emission from a number of E galaxies is reported. 33galaxies were searched for HI the first time. Seven of the detected Egalaxies are isolated, 9 have nearby companions, and 11 are in compactgroups and/or strongly interacting systems. Nearby confusing sources maybe responsible for some of the detections. The large number ofelliptical galaxies in groups (in this sample) suggests thatgravitational interaction and mergers might be an important source ofsupply of interstellar matter for elliptical galaxies.
|General study of group membership. II - Determination of nearby groups|
We present a whole sky catalog of nearby groups of galaxies taken fromthe Lyon-Meudon Extragalactic Database. From the 78,000 objects in thedatabase, we extracted a sample of 6392 galaxies, complete up to thelimiting apparent magnitude B0 = 14.0. Moreover, in order to considersolely the galaxies of the local universe, all the selected galaxieshave a known recession velocity smaller than 5500 km/s. Two methods wereused in group construction: a Huchra-Geller (1982) derived percolationmethod and a Tully (1980) derived hierarchical method. Each method gaveus one catalog. These were then compared and synthesized to obtain asingle catalog containing the most reliable groups. There are 485 groupsof a least three members in the final catalog.
|Interstellar matter in early-type galaxies. I - The catalog|
A catalog is given of the currently available measurements ofinterstellar matter in the 467 early-type galaxies listed in the secondedition of the Revised Shapley-Ames Catalog of Bright Galaxies. Themorphological type range is E, SO, and Sa. The ISM tracers are emissionin the following bands: IRAS 100 micron, X-ray, radio, neutral hydrogen,and carbon monoxide. Nearly two-thirds of the Es and SOs have beendetected in one or more of these tracers. Additional observed quantitiesthat are tabulated include: magnitude, colors, radial velocity, centralvelocity dispersion, maximum of the rotation curve, angular size, 60micron flux, and supernovae. Qualitative statements as to the presenceof dust or emission lines, when available in the literature, are given.Quantities derivative from the observed values are also listed andinclude masses of H I, CO, X-ray gas, and dust as well as an estimate ofthe total mass and mass-to-luminosity ratio of the individual galaxies.
|Morphology and kinematics of the interacting elliptical galaxies NGC750 and NGC751 = ARP 166 - Velocity fields of tidally distorted elliptical galaxies|
The interacting galaxies NGC750 and 751 are investigated by means ofphotometric and spectroscopic observations and compared to the galaxypair NGC4782 and 4783. The morphological and kinematical properties ofthe pair are discussed, and the examination of the dynamical propertiesof both pairs is used to develop a scenario to describe the encounter of750 and 751. The luminosity profiles of both galaxies deviate from the rexp 1/4 law at all radii, and the shapes of near-central isophotessuggest the slow evolution of their time-varying potentials. NGC750exhibits radial velocity curves that are almost flat while those of 751have large variations; both galaxies have asymmetric and radiallyincreasing velocity-dispersion curves. Both galaxies, therefore, arecharacterized by strong tidal perturbations, and a scenario is developedto describe the galactic encounter as deeply penetrating andlow-velocity. Violent tidal interaction is related to tidal couplingbetween stars on prograde orbits and the bulk orbital motion.
|The surface brightness test for the expansion of the universe. II - Radii, surface brightness, and absolute magnitude correlations for nearby E galaxies|
Data for elliptical galaxies in the Virgo, Fornax, and Coma clusters andin the general field are analyzed in order to determine the dispersionin average surface brightness. The data are discussed using measures ofboth the effective radius and the Petrosian r(eta) radii. The dispersionis found to be about 0.5 mag after reducing the data to absolutemagnitude M(B) = -22. This value is smaller than the 1.8 mag Tolman (1 +z) exp 4 factor, even at the modest redshift of z = 0.5, showing thatthe Tolman test is feasible in practice as well as in principle.
|The dumb-bell galaxy NGC 750/751|
A quantitative analysis of this system from BVR CCD photometry and longslit spectroscopy is presented. The results indicate that theyconstitute a physically interacting system. The presence of a duststructure along the line joining the nuclei and the members showisophotal distortion is detected, indicating a nonelliptical component,which is also seen in the surface brightness profiles.
|Galaxies possibly resembling M82-type galaxies|
A list of 298 galaxies with possible features of M82 galaxies ispresented. This list contains those Irr II candidates whose images onPalomar photographs shown no trace of dust although the objects are redand suspected to be peculiar.
|Can E and S0 Galaxies Be Distinguished Photometrically?|
Modern CCD photometry of early type galaxies does not allow one todifferentiate unambiguously between E and SO galaxies. A de Vaucouleurslaw fits the major axis profiles of SO galaxies as frequently as it doesthose of ellipticals. The data do, however, indicate that exponentialdisks occur more often in SOs than they do in elliptical galaxies.Furthermore, ellipticals exhibit their maximum flattening atintermediate radii more frequently than do SO galaxies.
|The dynamics of dumb-bell galaxies|
This paper presents theoretical models for a particular class of closebinary galaxies, the 'dumb-bell galaxies'. In these models twocomponents of equal size orbit each other on bound, circular orbitswithin a common envelope of adjustable extent. A series ofself-consistent equilibria is constructed for such dumb-bell systems.These equilibria are based on distribution functions that depend on theJacobian energy E(j) only, and as a result they all rotate as solidbodies. N-body experiments indicate that the presence of a commonenvelope per se does not cause violent dynamical instabilities, and thattherefore binary systems with a common envelope of limited extent do notnecessarily coalesce within a few orbital periods. However, mass andangular momentum loss through the Lagrangian point L3 can lead to arapid merging of the two subsystems. An application of these results tobinary stars suggests that the initial merging of a double white dwarfwill not produce a massive enough remnant to ignite a supernova. Apreliminary investigation of the orbital structure within the presentdumb-bell potential reveals the presence of two additional integrals ofmotion for particles that remain within one half of the dumb-bell.
|Morphology of interacting elliptical galaxy pairs|
The effect of galaxy interaction on the morphology of a galaxy pair wasinvestigated using the results of CCD-photometry of 20 elliptical galaxypairs. Deviations from undisturbed brightness profiles were interpretedin terms of ongoing tidal interaction. It was found that the morphologyof the interacting galaxy pairs deviates obviously from the morphologyof isolated elliptical galaxies, indicating a stage of efficientinteraction, with nonconcentric isophotes providing strong evidence ofongoing interaction. Brightness profiles of the brighter components ingalaxy pairs were usually extended in comparison with brightnessprofiles of isolated galaxies. Truncated brightness profiles, prevalentin most of the smaller components of galaxy pairs, are interpreted as aconsequence of a tidally limited galaxy radius imposed by the moremassive component.
|The components of mid- and far-infrared emission from S0 and early-type shell galaxies|
The IRAS database has been used to study detections of about 150early-type elliptical and S0 galaxies exhibiting a shell structure. Nostrong evidence for the expected enhancement of either star formationrates or heating of the interstellar medium is found. It is suggestedthat for some of the sample galaxies either a contribution from warmdust surrounding evolved stars or emission from an active nucleus may besignificant.
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