Contents
Images
Upload your image
DSS Images Other Images
Related articles
Correlations of near-infrared, optical and X-ray luminosity for early-type galaxies
The relation between X-ray luminosity and near-infrared (NIR) luminosityfor early-type galaxies has been examined. NIR luminosities shouldprovide a superior measure of stellar mass compared to opticalluminosities used in previous studies, especially if there issignificant star formation or dust present in the galaxies. However, weshow that the X-ray-NIR relations are remarkably consistent with theX-ray-optical relations. This indicates that the large scatter of therelations is dominated by scatter in the X-ray properties of early-typegalaxies, and is consistent with early-types consisting of old,quiescent stellar populations.We have investigated scatter in terms of environment, surface brightnessprofile, Mg2, Hβ, Hγ line strength indices,spectroscopic age and nuclear Hα emission. We found that galaxieswith high Mg2 index, low Hβ and Hγ indices or a`core' profile have a large scatter in LX, whereas galaxieswith low Mg2, high Hβ and Hγ indices or`power-law' profiles generally have LX < 1041erg s-1. There is no clear trend in the scatter withenvironment or nuclear Hα emission.
| Dry Mergers in GEMS: The Dynamical Evolution of Massive Early-Type Galaxies
We have used the 28'×28' Hubble SpaceTelescope image mosaic from the GEMS (Galaxy Evolution from Morphologyand SEDs) survey in conjunction with the COMBO-17 photometric redshiftsurvey to constrain the incidence of major mergers betweenspheroid-dominated galaxies with little cold gas (dry mergers) sincez=0.7. A set of N-body merger simulations was used to explore themorphological signatures of such interactions: they are recognizableeither as <5 kpc separation close pairs or because of broad, lowsurface brightness tidal features and asymmetries. Data with the depthand resolution of GEMS are sensitive to dry mergers between galaxieswith MV<~-20.5 for z<~0.7 dry mergers at higherredshifts are not easily recovered in single-orbit HST imaging. Six drymergers (12 galaxies) with luminosity ratios between 1:1 and 4:1 werefound from a sample of 379 red early-type galaxies withMV<-20.5 and 0.1
| Small-Scale Systems of Galaxies. II. Properties of the NGC 4756 Group of Galaxies
This paper is part of a series that focuses on investigating galaxyformation and evolution in small-scale systems of galaxies inlow-density environments. We present results from a study of the NGC4756 group, which is dominated by the elliptical galaxy NGC 4756. Thecharacteristics of the group are investigated through (1) the detailedinvestigation of the morphological, photometric, and spectroscopicproperties of nine galaxies among the dominant members of the group; (2)the determination of the photometric parameters of the faint galaxypopulation in an area of 34'×34' centered onNGC 4756 and (3) an analysis of the X-ray emission in the area based onarchival data.The nine member galaxies are located in the core part of the NGC 4756group (a strip ~300 kpc in diameter, H0=70 km s-1Mpc-1), which has a very loose configuration. The centralpart of the NGC 4756 group contains a significant fraction of early-typegalaxies. Three new group members with previously unknown systemicvelocities are identified, one of which is type dE. At about 7.5 arcminsouthwest of NGC 4756 a substructure of the group is detected, includingIC 829, MCG -2-33-35, MCG -2-33-36, and MCG -2-33-38, that meets theHickson criteria for being a compact group. Most of the galaxies in thissubstructure show interaction signatures. We do not detect apparent finestructure and signatures of recent interaction events in the early-typegalaxy population, with the exception of a strong dust lane in theelliptical galaxy MCG -2-33-38. However, this galaxy displays signaturesof nuclear activity. Strong [O III], [N II], and [S II] line emission,combined with comparatively weak but broad Hα emission, suggestsan intermediate Seyfert type classification. Although the area isheavily contaminated by the background cluster A1631, X-ray data suggestthe presence of a hot intergalactic medium related to the detected X-rayemission of the group. The present results are discussed in the contextof group evolution.Based on observations obtained at the European Southern Observatory, LaSilla, Chile (program 65.P-252).
| 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.
| 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.
| 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.
| ROSAT-HRI observations of six southern galaxy pairs
We present the detailed analysis of the X-ray data for 6 pairs, isolatedor in poor groups, observed at high resolution with the ROSAT HRI . Inall cases, the stronger X-ray source is associated with the brighterearly-type member and is extended. The extent varies from galactic togroup scale, from 3 (RR 210b) to 182 kpc( RR 22a). The fainter membersare detected only in two pairs, RR 210 and RR 259. Except for one case,no significant substructures have been detected in the X-ray maps,possibly also as a consequence of the poor statistics. The core radii ofthe X-ray surface brightness profiles are in the range 1-3 kpc. Thedistribution of the luminosities of galaxies in pairs encompasses a verywide range of both luminosities and LX / LBratios, in spite of the very small number of objects studied so far. Ourdata provide no evidence that pair membership affects the X-rayproperties of galaxies. Observation are discussed in the context of thepair/group evolution.
| SUPERBOX - an efficient code for collisionless galactic dynamics
We present Superbox, a particle-mesh code with high resolution sub-gridsand an NGP (nearest grid point) force-calculation scheme based on thesecond derivatives of the potential. Superbox implements a fastlow-storage FFT-algorithm, giving the possibility to work with millionsof particles on desk-top computers. Test calculations show energy andangular momentum conservation to one part in 10^5 per crossing-time. Theeffects of grid and numerical relaxation remain negligible, even whenthese calculations cover a Hubble-time of evolution. As the sub-gridsfollow the trajectories of individual galaxies, the code allows a highlyresolved treatment of interactions in clusters of galaxies, such ashigh-velocity encounters between elliptical galaxies and the tidaldisruption of dwarf galaxies. Excellent agreement is obtained in acomparison with a direct-summation N-body code running onspecial-purpose Grape 3 hardware. The orbital decay of satellitegalaxies due to dynamical friction obtained with Superbox agrees withChandrasekhar's treatment when the Coulomb logarithm lnLambda ~= 1.5.
| 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.
| Interstellar Gas in the NGC 4410 Galaxy Group
We present new radio continuum, 21 cm H I, and 2.6 mm CO data for thepeculiar radio galaxy NGC 4410A and its companion NGC 4410B and comparewith available optical and X-ray maps. Our radio continuum maps show anasymmetric double-lobed structure, with a high surface brightness lobeextending 3.6′ (~100 kpc) to the southeast and a 6.2′(~180 kpc) low surface brightness feature in the northwest. Moleculargas is abundant in NGC 4410A, withMH2~4×109 Msolar(using the standard Galactic conversion factor) but is undetected in NGC4410B. H I is less abundant, with MHI~109Msolar for the pair. Our H I map shows a3×108 Msolar H I tail extending 1.7′(50 kpc) to the southeast of the pair, coincident with a faint opticaltail and partially overlapping with the southeastern radio lobe. The H Itail is anticoincident with a 2' (56 kpc) long X-ray structure alignedwith a stellar bridge that connects the pair to a third galaxy. If thisX-ray emission is associated with the group, we infer(3-8)×108 Msolar of hot gas in this feature.This may be either intracluster gas or shocked gas associated with thebridge. Our detection of abundant interstellar gas in this pair,including an H I-rich tidal tail near the southeastern radio lobe,suggests that the observed distortions in this lobe may have been causedby the interstellar medium in this system. The gravitational interactionof the two galaxies and the subsequent motion of the interstellar mediumin the system relative to the jet may have produced sufficient rampressure to bend and distort the radio jet. An alternative hypothesis isthat the jet was distorted by ram pressure due to an intraclustermedium, although the small radial velocity of NGC 4410A relative to thegroup and the lack of diffuse X-ray emission in the group makes thisless likely unless the group is not virialized or is in the process ofmerging with another group. Using our VLA data, we also searched for H Icounterparts to the other 10 known members of the NGC 4410 group and COfrom three other galaxies in the inner group. In our velocity range of6690-7850 km s-1, we detected six other galaxies above our HI sensitivity limits of 2×108 Msolar for theinner group and 4×108 Msolar for the outergroup. The total H I in the group is 1.4×1010Msolar, 80% of which arises from four galaxies in the outergroup. Three of these galaxies (VCC 822, VCC 831, and VCC 847) arespirals with MHI/LB ratios typical of fieldgalaxies, while FGC 170A appears to be a gas-rich dwarf galaxy(MB~-18, MHI~3×109Msolar). In the inner group, the SBa galaxy NGC 4410D (VCC934) was detected in H I and CO (MHI~5×108Msolar and MH2~8×108Msolar) and has a 1' (28 kpc) long H I tail that pointstoward the nearby disk galaxy NGC 4410F. NGC 4410F was also detected inH I (MHI~4×108 Msolar). Thegalaxies in the inner group appear to be somewhat deficient in H Icompared to their blue luminosities, suggesting phase changes driven bygalaxy-galaxy or galaxy-intracluster medium encounters.
| 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
| An X-Ray Survey of Galaxies in Pairs
Results are reported from the first survey of X-ray emission fromgalaxies in pairs. The sample consists of 52 pairs of galaxies from theCatalog of Paired Galaxies whose coordinates overlap the ROSAT PositionSensitive Proportional Counter pointed observations. The mean observedlogl_X for early-type pairs is 41.35+/-0.21, while the mean logl_Xpredicted using the l_X-l_b relationship for isolated early-typegalaxies is 42.10+/-0.19. With 95% confidence, the galaxies in pairs areunderluminous in the X-ray, compared with isolated galaxies, for thesame l_b. A significant fraction of the mixed pair sample also appearssimilarly underluminous. A spatial analysis shows that the X-rayemission from pairs of both types typically has an extent of ~10-50 kpc,much smaller than the group intergalactic medium, and thus likelyoriginates from the galaxies. CPG 564, the most X-ray luminousearly-type pair, 4.7x10^42 ergs s^-1, is an exception. The extent of itsX-ray emission, greater than 169 kpc, and HWHM, ~80 kpc, is comparableto that expected from an intergalactic medium. The sample shows only aweak correlation, ~81% confidence, between l_X and l_b, presumably dueto variations in gas content within the galaxies. No correlation betweenl_X and the pair velocity difference (Deltav), separation (Deltar), orfar-infrared luminosity (l_fir) is found, although the detection rate islow, 22%.
| X-ray wakes as probes of galaxy cluster dynamics
If a galaxy resides in a cluster, then its passage through the pervasiveintracluster medium will produce a detectable signature in the X-rayemission from the cluster. The simplest kinematic information that canbe extracted from this signature is the galaxy's direction of motion onthe plane of the sky. This paper explores the constraints on clusterdynamics that could be derived from such information. In particular, weshow that it is possible to define a projected anisotropy parameter,B(r), which is directly analogous to the usual orbital anisotropyparameter. We describe an estimator for this quantity which can bederived in a robust and straightforward manner. We present a simpledynamical model for a cluster consisting of a Michie distributionfunction of galaxies orbiting in a truncated singular isothermal spherepotential. Using this model, we demonstrate the ambiguity between thedistribution of mass and the distribution of galaxy orbits wheninterpreting the traditional measures of cluster kinematics. As anexample, we show how two very different dynamical models can fit thekinematic properties of the Coma cluster. We demonstrate that themeasurement of the estimator using a relatively small sample of wakedirections would provide an effective mechanism for lifting thisdegeneracy. Thus, by combining X-ray measurements of wake directionswith number counts and line-of-sight velocities derived from opticaldata, it will prove possible to measure both the orbit distribution andthe form of the gravitational potential in clusters of galaxies. Therequisite X-ray observations lie within reach of the soon-to-be-launchedAXAF satellite.
| Far-Infrared Emission from E and E/S0 Galaxies
Early-type galaxies are filled with hot X-ray-emitting gas, but thestudy of the less plentiful cold gaseous component has been morechallenging. Studies of cold material through IRAS 60 and 100 mu mobservations indicated that half of ordinary E and E/S0 galaxies weredetected above the 3 sigma level, indicating that cold gas is common,although no correlation was found between the optical and far-infraredfluxes. Most detections were near the instrumental threshold, and givenan improved understanding of detection confidence, we reconsider the 60and 100 mu m detection rate. After excluding active galactic nuclei,peculiar systems, and background contamination, only 15 nonpeculiar Eand E/S0 galaxies from the RSA catalog are detected above the 98%confidence level, about 12% of the sample. An unusually high percentageof these 15 galaxies possess cold gas (H I CO) and optical emissionlines (H alpha ), supporting the presence of gas cooler than 104 K. The60-100 mu m flux ratios imply a median dust temperature for the sampleof 30 K, with a range of 23-28 K. These detections define the upperenvelope of the optical to far-infrared relationship,F_{{fir}}~F^{0.24+/-0.08}B , showing that optically brightobjects are also brighter in the infrared, although with considerabledispersion. A luminosity correlation is present wthL_{{fir}}~L^{1.65+/-0.28}B , but the dust temperature isuncorrelated with luminosity. The dust masses inferred from thefar-infrared measurements are 1 order of magnitude greater than thosefrom extinction observations, except for the recent merger candidate NGC4125, where they are equal. We suggest that the ratio of thefar-infrared dust mass to the extinction dust mass may be an indicatorof the time since the last spiral-spiral merger. These results arecompared to the model in which most of the dust comes from stellar massloss and the heating is primarily by stellar photons. Models thatcontain large dust grains composed of amorphous carbon plus silicatescome close to reproducing the typical 60-100 mu m flux ratios, thefar-infrared luminosity, and the Lfir-LB relationship.
| A catalogue of Mg_2 indices of galaxies and globular clusters
We present a catalogue of published absorption-line Mg_2 indices ofgalaxies and globular clusters. The catalogue is maintained up-to-datein the HYPERCAT database. The measurements are listed together with thereferences to the articles where the data were published. A codeddescription of the observations is provided. The catalogue gathers 3541measurements for 1491 objects (galaxies or globular clusters) from 55datasets. Compiled raw data for 1060 galaxies are zero-point correctedand transformed to a homogeneous system. Tables 1, 3, and 4 areavailable in electronic form only at the CDS, Strasbourg, via anonymousftp 130.79.128.5. Table 2 is available both in text and electronic form.
| Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
| A catalogue of spatially resolved kinematics of galaxies: Bibliography
We present a catalogue of galaxies for which spatially resolved data ontheir internal kinematics have been published; there is no a priorirestriction regarding their morphological type. The catalogue lists thereferences to the articles where the data are published, as well as acoded description of these data: observed emission or absorption lines,velocity or velocity dispersion, radial profile or 2D field, positionangle. Tables 1, 2, and 3 are proposed in electronic form only, and areavailable from the CDS, via anonymous ftp to cdsarc.u-strasbg.fr (to130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| An Einstein X-Ray Survey of Optically Selected Galaxies. I. Data
We present the results of a complete Einstein imaging proportionalcounter X-ray survey of optically selected galaxies from theShapley-Ames Catalog, the Uppsala General Catalogue, and the EuropeanSouthern Observatory Catalog. Well-defined optical criteria are used toselect the galaxies, and X-ray fluxes are measured at the opticallydefined positions. The result is a comprehensive list of X-ray detectionand upper limit measurements for 1018 galaxies. Of these, 827 haveeither independent distance estimates or radial velocities. Associatedoptical, redshift, and distance data have been assembled for thesegalaxies, and their distances come from a combination of directlypredicted distances and those predicted from the Faber-Burstein GreatAttractor/Virgocentric infall model. The accuracy of the X-ray fluxeshas been checked in three different ways; all are consistent with thederived X-ray fluxes being of <=0.1 dex accuracy. In particular,there is agreement with previously published X-ray fluxes for galaxiesin common with a 1991 study by Roberts et al. and a 1992 study byFabbiano et al. The data presented here will be used in further studiesto characterize the X-ray output of galaxies of various morphologicaltypes and thus to enable the determination of the major sourcescontributing to the X-ray emission from galaxies.
| Classification of colliding galaxies
Not Available
| Spectroscopy of the NGC 4782/3 Dumbbell Dominated Group of Galaxies: Dark Haloes and Merger of Subgroups
A nearly complete sample of new velocities for 96 galaxies covering anarea 1^deg^ x 1.25^deg^ centered on NGC 4782/3 are presented. Includingdata from the literature a total of 125 velocities are compiled. Wededuce that 40 galaxies are likely members of the group centered on NGC4782/3, more than doubling the original confirmed 13 members. Based onthis extended velocity sample we analyze the velocity structure of thisunusual group. A bi-modal velocity structure centered on each of thedumbbell components provides evidence for an ongoing collision of twosubgroups associated to these components. In velocity space the richersubgroup is centered on the more massive NGC 4782. From the subgroupdynamics we derive approximate dynamical masses of 5 x 10^13^ M_sun_ and1 x 10^13^ M_sun_ for the NGC 4782 and NGC 4783 subgroups, respectively.This leads to a group M/L ~ 300 (M/L)_sun_, implying that -90% of thegroup mass is in dark form, within subsystems associated to eachsubgroup. The colliding elliptical galaxies have massive haloes whichshould be important in shaping the outcome of the collision and mergerprocess. In particular, haloes could change the interpretation of thetidal distortions and play a role in the shaping of the radio doublebent jet structure of 3C 278.
| A survey of the ISM in early-type galaxies. I. The ionized gas.
We present results of a CCD optical imaging survey of the ionized gas in73 luminous elliptical and lenticular galaxies, selected from the RC3catalog to represent a broad variety of X-ray, radio, infrared andkinematical properties. For each galaxy we have used broad-band R imagesand narrow-band images centered at the Hα and [NII] emission linesto derive the luminosity and distribution of the ionized gas. We foundthat a large fraction of E (72%) and S0 (85%) galaxies in our samplecontain ionized gas. The gas morphology appears to be rather smooth formost galaxies; however ~12% of the sample galaxies show a very extendedfilamentary structure. According to the morphology and size of the gasdistribution, the galaxies have been classified into three broad groups,named small disk (SD), regular extended (RE) and filamentary structure(F). The mean diameter of the emitting region ranges between 1 and10kpc; the derived mass of the ionized gas ranges between 10^3^ and10^5^ solar masses. A significant correlation between Hα+[NII] andX-ray luminosities is found for those galaxies (27% of the sample) forwhich we have detected ionized gas and are also listed as X-ray sources.However, there are relatively strong X-ray emitting galaxies for whichwe have not detected Hα+[NII] emission and objects which showemission-lines but are not listed either in the EINSTEIN or in the ROSATdatabases. The distribution of datapoint and upper limits in thisdiagram suggests that galaxies with warm gas are also X-ray emitters,while there are X-ray emitters without measurable Hα+[NII]emission. Similar characteristics are present in the correlation betweenthe infrared luminosity in the 12 μm band and L_Hα+[NII]_;correlations with other infrared wavelengths are weaker. A strongcorrelation was also found between the Hα+[NII] luminosity and theluminosity in the B band inside the region occupied by the line-emittinggas. We use these correlations to discuss the possible mechanismsresponsible for the gas ionization and excitation, analyzing inparticular the role of the post-AGB stars and the thermal conductionfrom the X-ray halo in providing the necessary source of ionization.
| An image database. II. Catalogue between δ=-30deg and δ=70deg.
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
| 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 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.
| A multiparametric analysis of the Einstein sample of early-type galaxies. 1: Luminosity and ISM parameters
We have conducted bivariate and multivariate statistical analysis ofdata measuring the luminosity and interstellar medium of the Einsteinsample of early-type galaxies (presented by Fabbiano, Kim, &Trinchieri 1992). We find a strong nonlinear correlation betweenLB and LX, with a power-law slope of 1.8 +/- 0.1,steepening to 2.0 +/- if we do not consider the Local Group dwarfgalaxies M32 and NGC 205. Considering only galaxies with logLX less than or equal to 40.5, we instead find a slope of 1.0+/- 0.2 (with or without the Local Group dwarfs). Although E and S0galaxies have consistent slopes for their LB-LXrelationships, the mean values of the distribution functions of bothLX and LX/LB for the S0 galaxies arelower than those for the E galaxies at the 2.8 sigma and 3.5 sigmalevels, respectively. We find clear evidence for a correlation betweenLX and the X-ray color C21, defined by Kim,Fabbiano, & Trinchieri (1992b), which indicates that X-rayluminosity is correlated with the spectral shape below 1 keV in thesense that low-LX systems have relatively large contributionsfrom a soft component compared with high-LX systems. We findevidence from our analysis of the 12 micron IRAS data for our samplethat our S0 sample has excess 12 micron emission compared with the Esample, scaled by their optical luminosities. This may be due toemission from dust heated in star-forming regions in S0 disks. Thisinterpretation is reinforced by the existence of a strongL12-L100 correlation for our S0 sample that is notfound for the E galaxies, and by an analysis of optical-IR colors. Wefind steep slopes for power-law relationships between radio luminosityand optical, X-ray, and far-IR (FIR) properties. This last point arguesthat the presence of an FIR-emitting interstellar medium (ISM) inearly-type galaxies is coupled to their ability to generate nonthermalradio continuum, as previously argued by, e.g., Walsh et al. (1989). Wealso find that, for a given L100, galaxies with largerLX/LB tend to be stronger nonthermal radiosources, as originally suggested by Kim & Fabbiano (1990). We notethat, while LB is most strongly correlated withL6, the total radio luminosity, both LX andLX/LB are more strongly correlated with L6CO, the core radio luminosity. These points support the argument(proposed by Fabbiano, Gioia, & Trinchieri 1989) that radio cores inearly-type galaxies are fueled by the hot ISM.
| The Unusal X-Ray Collision Morphology of NGC 4782/4783 (3C 278)
Deep ROSAT HRI (High-Resolution Imager) imaging of the X-ray--emittinggas associated with the colliding elliptical galaxy pair NGC 4782/4783reveals for the first time the complexity of the hot gas distribution ina pair of close interacting galaxies. The HRI image of NGC 4782/4783shows hot gas around each galaxy, a high surface brightness X-ray bridgeconnecting the galaxy pair, tidal-like tails emerging from the twogalaxies, and a sheet of gas at the interaction interface between thetwo galaxies. The hot gas distributions do not peak at the opticalcenters of the galaxies but are displaced in the same sense as the tidaldistensions seen in the optical luminosity distributions. All of theseremarkable features show the complexity of structure that develops inthe hot gas distribution when both hydrodynamical and tidal forces comeinto play during collisions between ellipticals with hot gas components.Models by Borne and Colina of the bent two-sided radio jet 3C 278(associated with NGC 4782) indicated that there must be a stronginteraction between the hot gas components of NGC 4782/4783 and that thedeflection of the radio jets is likely caused by the ram pressureexerted on the jet plasma by the hot gas associated with the passingcompanion NGC 4783. These conclusions are qualitatively confirmed by theHRI image and substantiate the major role played by the hot interstellarmedium, and its asymmetries, in the propagation and entrainment of radiojets in colliding radio host ellipticals.
| Collisions of Ellipticals and the Onset of Fanaroff-Riley Type I Radio Sources
This paper presents the first detailed quantitative study on themorphological characterization of Fanaroff-Riley type I radio source (FRI) host galaxies. The study is based on a two-dimensional isophoteanalysis of the largest sample (44) available so far of FR I hostgalaxies. FR I host galaxies are luminous ellipticals following the sameμ_e_ - r_e_ relation as nonradio ellipticals. However, a largefraction (60%) of FR I host galaxies in the sample show at least two ofthe following morphological peculiarities: (1) isophote twists which arelarger than 15^deg^, (2) isophote displacements which are larger than3.5%, (3) excesses over a de Vaucouleurs law which exceeds 0.10 magarcsec^-2^ at radii beyond r_e_, and (4) one companion galaxy at adistance of less than 50 kpc. These morphological peculiarities are thesignature of a recent strong gravitational collision. The collision,involving a pair of ellipticals, is characterized by (1) a median massratio (companion to FR I host galaxy) of ~0.2, (2) a median projecteddistance of ~23 kpc, (3) a median relative velocity of ~492 km s^-1^,(4) a median age of ~4.0 x 10^7^ years, and (5) a median interactionstrength parameter of 0.19. Collisions between ellipticals which sharethe above mentioned mean properties appear. to be very efficient ingenerating a FR I radio source. Therefore, the scenario of the onset ofan active nucleus by galaxy collisions, well established for veryluminous starbursts and radio galaxies, can also be extended to FR Iradio sources. In a broader scenario, the conclusions of this paper alsoreinforce the idea that collisions between different type of galaxiesgive rise to different type of activity in their nuclei: collisionsinvolving two spirals produce luminous circumnuclear starbursts,collisions involving one elliptical and one spiral generate powerfulFanaroff-Riley type II sources (FR II), which collisions between twoellipticals ignite FR I radio sources.
| A multiparametric analysis of the Einstein sample of early-type galaxies. 2: Galaxy formation history and properties of the interstellar medium
We have conducted bivariate and multivariate statistical analysis ofdata measuring the integrated luminosity, shape, and potential depth ofthe Einstein sample of early-type galaxies (presented by Fabbiano et al.1992). We find significant correlations between the X-ray properties andthe axial ratios (a/b) of our sample, such that the roundest systemstend to have the highest Lx and Lx/LB.The most radio-loud objects are also the roundest. We confirm theassertion of Bender et al. (1989) that galaxies with high Lxare boxy (have negative a4). Both a/b and a4 arecorrelated with LB, but not with IRAS 12 um and 100 umluminosities. There are strong correlations between Lx,Mg2, and sigmanu in the sense that those systemswith the deepest potential wells have the highest Lx andMg2. Thus the depth of the potential well appears to governboth the ability to retain an ISM at the present epoch and to retain theenriched ejecta of early star formation bursts. BothLx/LB and L6 (the 6 cm radioluminosity) show threshold effects with sigmanu exhibitingsharp increases at log sigmanu approximately = 2.2. Finally,there is clearly an interrelationship between the various stellar andstructural parameters: The scatter in the bivariate relationshipsbetween the shape parameters (a/b and a4) and the depthparameter sigmanu is a function of abundance in the sensethat, for a given a4 or a/b, the systems with the highestsigmanu also have the highest Mg2. Furthermore,for a constant sigma(sun nu), disky galaxies tend to have higherMg2 than boxy ones. Alternatively, for a given abundance,boxy ellipticals tend to be more massive than disky ellipticals. Onepossibility is that early-type galaxies of a given mass, originatingfrom mergers (boxy ellipticals), have lower abundances than 'primordial'(disky) early-type galaxies. Another is that disky inner isophotes aredue not to primordial dissipation collapse, but to either theself-gravitating inner disks of captured spirals or the dissipationalcollapse of new disk structures from the premerger ISM. The highmeasured nuclear Mg2 values would thus be due to enrichmentfrom secondary bursts of star formation triggered by the merging event.
| Dynamics of Binary Galaxies. III. Details of the Close Pairs
In a previous paper [Chengalur et al. ApJ, 107, 1984(1994)] H Isynthesis data and CCD images were presented for an objectively chosensample of six close spiral-spiral galaxy pairs. In this paper we presenta detailed analysis of the data. Although the presence of tidal featureswas not an explicit selection criterion, five of our six pairs showtidal tails and bridges. The remaining pair also shows signs ofinteraction: both galaxies in the pair have disturbed velocity fieldsand one of the two galaxies has a central concentration of molecular gasand is undergoing a starburst. The morphology of three of the six pairsimplies that the galaxies are on high eccentricity, low total energyorbits, and for one of these pairs there is some evidence that theimpact parameter is as small as ~1 disk radius. For the remaining threepairs the tidal features are not as pronounced, and the observations donot yield as much information on the orbit. However, even for thesepairs, the observed morphology is consistent with the galaxies being onslow, small impact parameter orbits, provided the galaxies are at arelatively early phase of the orbit, i.e., prior to the first closeencounter. We also find weak evidence for preferential alignment in thepairs (with the lack of preferential alignment being ruled out at the97% level), in the sense that the major axis of a galaxy tends to pointtoward the companion galaxy. This sample of close pairs is complementedby a larger sample of wide pairs (Chengalur et al. 1993). The medianvelocity difference {DELTA}V of the sample of close pairs in low-densityregions is not much different from that for the wide pairs sample, inparticular, there is no evidence for positive energy impacts. The effectof dynamical friction on infall velocities is controversial and will bediscussed in the following paper [Chengalur et al., in preparation(1995)] which combines the data on close and wide pairs.
| Kinematic profiles of dumbbell galaxies with twisted radio jets.
We study the orbital properties of dumbbell galaxies which harbortwisted radio jets. Velocity and velocity dispersion profiles for fourdumbbell pairs (3C66B, 3C75, 3C449, 0326+39) are presented. We analyzeoptical CCD images in search of isophote off-centering and largeisophote twists. Combining the kinematic and isophotal information, wediscuss whether each system is an interacting pair, and deriveconstraints on the relative orbit. The types of isophotal distortions,combined with the prograde/retrograde nature of the relative orbit,suggest that three of the objects (3C66B, 3C75 and 0326+39) are unlikelyto be in circular orbits. Only 3C449 may be in a close,moderate-ellipticity orbit. We find that the distribution of relativevelocity with separation for dumbbells with distorted radio morphologyfrom the catalogue of Parma et al. (1991) also suggests a prevalence ofeccentric orbits. We discuss that dumbbells with distorted radiomorphology may deviate significantly from the circular orbit modelproposed by Valentijn & Casertano (1988). The genesis of radiodistortions could be related to such distinct orbital behaviour. Theamplitude and wavelength of jet oscillations in these objects correlateswith the projected separation of the pairs, pointing at a dynamicalorigin for the jet oscillations. However, for three of the four systemsstudied in detail here, the jet oscillations cannot be easily traced toorbital displacements of the parent galaxies. Either interactionstrigger radio beam precession, or the intracluster medium plays a rolein setting the radio beam oscillations.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
Catalogs and designations:
|
