Contenuti
Immagini
Carica la tua immagine
DSS Images Other Images
Articoli relazionati
Jet speeds in wide-angle tailed radio galaxies
We present a sample of 30 wide-angle tailed radio galaxies (WATs) thatwe use to constrain the jet speeds in these sources. We measure thedistribution of the jet-sidedness ratios for the sample, and assumingthat the jets are beamed, the jet speeds in the range (0.3-0.7)c areobtained. Whilst the core prominence of the sample, which ought to be areliable indicator of beaming, shows little correlation with the jetsidedness, we argue that due to the peculiar nature of the WATs, coreprominence is unlikely to be a good indicator of beaming in thesesources. We further show that if the jets are fast and light, then thegalaxy speeds required to bend the jets into C-shapes such as those seenin 0647+693 are reasonable for a galaxy in a merging or recently mergedcluster.
| TeV Gamma-Ray Observations of the Perseus and Abell 2029 Galaxy Clusters
Galaxy clusters might be sources of TeV gamma rays emitted byhigh-energy protons and electrons accelerated by large-scale structureformation shocks, galactic winds, or active galactic nuclei.Furthermore, gamma rays may be produced in dark matter particleannihilation processes at the cluster cores. We report on observationsof the galaxy clusters Perseus and A2029 using the 10 m Whipple Cerenkovtelescope during the 2003-2004 and 2004-2005 observing seasons. We applya two-dimensional analysis technique to scrutinize the clusters for TeVemission. In this paper we first determine flux upper limits on TeVgamma-ray emission from point sources within the clusters. Second, wederive upper limits on the extended cluster emission. We subsequentlycompare the flux upper limits with EGRET upper limits at 100 MeV andtheoretical models. Assuming that the gamma-ray surface brightnessprofile mimics that of the thermal X-ray emission and that the spectrumof cluster cosmic rays extends all the way from thermal energies tomulti-TeV energies with a differential spectral index of -2.1, ourresults imply that the cosmic-ray proton energy density is less than7.9% of the thermal energy density for the Perseus Cluster.
| K-band Properties of Galaxy Clusters and Groups: Brightest Cluster Galaxies and Intracluster Light
We investigate the near-infrared K-band properties of the brightestcluster galaxies (BCGs) in a sample of 93 X-ray galaxy clusters andgroups, using data from the Two Micron All Sky Survey. Our clustersample spans a factor of 70 in mass, making it sensitive to any clustermass-related trends. We derive the cumulative radial distribution forthe BCGs in the ensemble and find that 70% of the BCGs are centered inthe cluster to within 5% of the virial radius r200; thisquantifies earlier findings that BCG position coincides with the clustercenter as defined by the X-ray emission peak. We study the correlationsbetween the luminosity of the BCGs (Lb) and the mass and theluminosity of the host clusters, finding that BCGs in more massiveclusters are more luminous than their counterparts in less massivesystems and that the BCGs become less important in the overall clusterlight (L200) as cluster mass increases. By examining a largesample of optically selected groups, we find that these correlationshold for galactic systems less massive than our clusters(<3×1013 Msolar). From the differencesbetween luminosity functions in high- and low-mass clusters, we arguethat BCGs grow in luminosity mainly by merging with other luminousgalaxies as the host clusters grow hierarchically; the decreasing BCGluminosity fraction (Lb/L200) with cluster massindicates that the rate of luminosity growth in BCGs is slow compared tothe rate at which clusters acquire galaxy light from the field or othermerging clusters. Utilizing the observed correlation between the clusterluminosity and mass and a merger tree model for cluster formation, weestimate that the amount of intracluster light (ICL) increases withcluster mass; our calculations suggest that in 1015Msolar clusters more than 50% of total stellar mass is inICL, making the role of ICL very important in the evolution andthermodynamic history of clusters. The cluster baryon fractionaccounting for the ICL is in good agreement with the value derived fromcosmic microwave background observations. The inclusion of ICL reducesthe discrepancy between the observed cluster cold baryon fraction andthat found in hydrodynamical simulations. Based on the observed ironabundance in the intracluster medium, we find that the ICL predicted byour model, together with the observed galaxy light, match the ironmass-to-light ratio expected from simple stellar population models,provided that the Salpeter initial mass function is adopted. The ICLalso makes it easier to produce the ``iron excess'' found in the centralregions of cool-core clusters.
| The Complex Cooling Core of A2029: Radio and X-Ray Interactions
We present an analysis of Chandra observations of the central regions ofthe cooling flow cluster A2029. We find a number of X-ray filaments inthe central 40 kpc, some of which appear to be associated with thecurrently active central radio galaxy. The outer southern lobe of thesteep-spectrum radio source appears to be surrounded by a region of coolgas and is at least partially surrounded by a bright X-ray rim similarto that seen around radio sources in the cores of other cooling flowclusters. Spectroscopic fits show that the overall cluster emission isbest fitted by either a two-temperature gas (kThigh=7.47 keVand kTlow=0.11 keV) or a cooling flow model with gas coolingover the same temperature range. This large range of temperatures (overa factor of 50) is relatively unique to A2029 and may suggest that thissystem is a very young cooling flow in which the gas has only recentlystarted cooling to low temperatures. The cooling flow model gives a massdeposition rate of M=56+16-21 Msolaryr-1. In general, the cluster emission is elongated along aposition angle of 22° with an ellipticity of 0.26. The distributionof the X-ray emission in the central region of the cluster isasymmetric, however, with excess emission to the northeast and southeastcompared with that to the southwest and northwest, respectively. Fittingand subtracting a smooth elliptical model from the X-ray data reveals adipolar spiral excess extending in a clockwise direction from thecluster core to radii of ~150 kpc. We estimate a total mass ofMspr~6×1012 Msolar in the spiralexcess. The most likely origin of the excess is either stripping of gasfrom a galaxy group or from bare dark matter potential that has falleninto the cluster or sloshing motions in the cluster core induced by apast merger.
| Chandra Observations of A2029: The Dark Matter Profile Down to below 0.01rvir in an Unusually Relaxed Cluster
We have used a high spatial resolution Chandra observation to examinethe core mass distribution of the unusually regular cD cluster A2029.This bright, nearby system is especially well suited for analysis of itsmass distribution under the assumption of hydrostatic equilibrium; itexhibits an undisturbed, symmetric X-ray morphology and a single-phaseintracluster medium (ICM). From the deprojected temperature and densityprofiles, we estimate the total mass and the contributions of the gasand dark matter (DM) components from less than 3" to ~3'(<4.4-260h-170kpc, 0.001-0.1rvir).The gas density profile is not adequately described by a single-βmodel fit because of an increase in the density at the center(r<17h-170kpc, <12"), but it is well fittedby either a double-β model, or a ``cusped'' β model. Thetemperature data increase as a function of radius and are well fitted bya Bertschinger & Meiksin profile and may be approximated by apower-law T(r)~rαT, withαT=0.27+/-0.01.Using the fitted profiles to obtain smooth functions of density andtemperature, we employed the equation of hydrostatic equilibrium tocompute the total enclosed mass as a function of radius. We report atotal mass of 9.15+/-0.25×1013h-170Msolar within260h-170kpc, using the chosen parameterization ofgas density and temperature. The mass profile is remarkably welldescribed down to 0.002rvir by the Navarro, Frenk, &White (NFW) profile, or a Hernquist profile, over two decades of radiusand three decades of mass. For the NFW model, we measure a scale radiusrs=540+/-90h-170kpc(~0.2rvir) and concentration parameter c=4.4+/-0.9. The massprofile is also well approximated by a simple power-law fit[M(
| The Hamburg/RASS Catalogue of optical identifications. Northern high-galactic latitude ROSAT Bright Source Catalogue X-ray sources
We present the Hamburg/RASS Catalogue (HRC) of optical identificationsof X-ray sources at high-galactic latitude. The HRC includes all X-raysources from the ROSAT Bright Source Catalogue (RASS-BSC) with galacticlatitude |b| >=30degr and declination delta >=0degr . In thispart of the sky covering ~ 10 000 deg2 the RASS-BSC contains5341 X-ray sources. For the optical identification we used blue Schmidtprism and direct plates taken for the northern hemisphere Hamburg QuasarSurvey (HQS) which are now available in digitized form. The limitingmagnitudes are 18.5 and 20, respectively. For 82% of the selectedRASS-BSC an identification could be given. For the rest either nocounterpart was visible in the error circle or a plausibleidentification was not possible. With ~ 42% AGN represent the largestgroup of X-ray emitters, ~ 31% have a stellar counterpart, whereasgalaxies and cluster of galaxies comprise only ~ 4% and ~ 5%,respectively. In ~ 3% of the RASS-BSC sources no object was visible onour blue direct plates within 40\arcsec around the X-ray sourceposition. The catalogue is used as a source for the selection of(nearly) complete samples of the various classes of X-ray emitters.
| Magnetic fields in the Centaurus cluster
We present multifrequency Very Large Array (VLA) observations of theradio galaxy PKS 1246-410 at the centre of the Centaurus cluster, andcompare these results with recent Chandra observations. The unusualradio morphology of PKS 1246-410 probably results from interactions withthe hot, X-ray-emitting gas. This gas, along with cluster magneticfields, also produces substantial Faraday rotation measures towards PKS1246-410. We discuss these observations in the context of a sample of 14luminous X-ray clusters with embedded radio galaxies and possiblecooling flows. A correlation is found between the cooling flow rate andthe maximum Faraday rotation measures. Magnetic fields of strength 10-40μG are found to be common to the centres of clusters with strongcooling flows, and somewhat lower field strengths of 2-10 μG arefound in the non cooling-flow clusters.
| Determination of the Dark Matter Profile of A2199 from Integrated Starlight
We have obtained deep, long-slit spectroscopy along the major axis ofNGC 6166, the cD galaxy in the cluster A2199, in order to measure thekinematics of intracluster stars at large radii. The velocity dispersioninitially decreases from the central value of 300 to 200 kms-1 within a few kiloparsecs and then steadily rises to 660km s-1 at a radius of 60 kpc (H0=75 kms-1 Mpc-1, Ωm=0.3,ΩΛ=0.7), nearly reaching the velocity dispersionof the cluster (σA2199=775+/-50 km s-1).These data suggest that the stars in the halo of the cD galaxy trace thepotential of the cluster and that the kinematics of these intraclusterstars can be used to constrain the mass profile of the cluster. Inaddition, we find evidence for systematic rotation (V/σ~0.3) inthe intracluster stars beyond 20 kpc. Such rotation is not seen in thekinematics of the cluster members. The surface brightness and velocitydispersion profiles can be fitted using a single-component mass modelonly by making unphysical assumptions about the level of anisotropy forboth the stars in the cD galaxy and the kinematics of the galaxies inthe cluster. Two-component mass models for the cD galaxy and its haloare subsequently explored using the kinematics of known cluster membersas an additional constraint on the total enclosed mass beyond the extentof the stellar kinematics. Under the assumption of isotropy, theobserved major-axis kinematics can be reproduced only if the halo,parameterized by a generalized Navarro-Frenk-White (NFW) profile, has asoft core, i.e., α<1 (a generalized NFW halo with α=1 isexcluded because of low implied stellar mass-to-light ratios). Thisresult is inconsistent with the predictions of current N-bodysimulations for dark matter halos. To test the consistency of our haloprofiles with those derived from strong lensing measurements inintermediate-redshift clusters, we calculate the critical radii fortangential arcs, assuming that our best-fit mass models for A2199 wereplaced at cosmological redshifts between 0.2<=z<=0.5. Thecalculated critical radii for our best-fit two-component isotropicmodels range from 5" to 40", depending on the assumed source redshift,consistent with the radii for gravitational arcs observed inintermediate-redshift clusters. We also present the results of MonteCarlo simulations testing the general reliability of velocity dispersionmeasurements in the regime of low signal-to-noise ratio and largeintrinsic Doppler broadening. Based on observations obtained at the W.M. Keck Observatory, which is operated jointly by the CaliforniaInstitute of Technology and the University of California.
| Chandra Observations of Abell 2029: No Cooling Flow and a Steep Abundance Gradient
We have obtained high spatial resolution temperature and abundanceprofiles for the galaxy cluster Abell 2029 with the Chandra ACIS-Sinstrument. Our observations reveal that the spectra are well fitted bya single-phase gas in each annulus. While the temperature of theintracluster medium drops from ~9 keV at 3' (260h-170 kpc) to 3 keV in the central 5" (5h-170 kpc) of the cluster, there is no evidence ofgas emitting at temperatures below 3 keV. The addition of a cooling flowcomponent does not improve the fits, despite previous claims for amassive cooling flow. There is also no evidence of excess absorptionabove the Galactic NH-value. We also observe a steep Feabundance gradient, such that ZFe>~2 Zsolar(assuming meteoritic solar Fe abundance) in the core, consistent withsignificant enrichment from Fe-rich Type Ia supernovae in the cD galaxy.The Fe abundance drops to ~0.5 Zsolar at 3' (260h-170 kpc), in good agreement with previousBeppoSAX measurements. The high-resolution image reveals neither astrong central point source nor any filamentary structure related to acooling flow or a merger. The absence of a strong merger signatureargues against the creation of the wide-angle-tailed radio sourcemorphology in a merger event.
| Magnetic Fields in Cluster Cores: Faraday Rotation in A400 and A2634
We present Faraday rotation data for radio sources in the centers of theAbell clusters A400 and A2634. These clusters contain large (>~100kpc), tailed radio sources, each attached to the central cD galaxy.These clusters do not have strong cooling cores. Our data extendprevious work on rotation measure in cluster centers to larger scalesand noncooling clusters. The rotation measure, and thus the magneticfield, is ordered on scales ~10-20 kpc in both clusters. The geometry ofthe rotation measure appears to be determined by the distribution of theX-ray-emitting gas, rather than by the radio tails themselves. Wecombine our data with previously published X-ray and radio data in orderto analyze the magnetic fields in all 12 clusters whose central radiosources have been imaged in rotation measure. We find that the fieldsare dynamically significant in most clusters. We argue that the Faradaydata measure fields in the intracluster medium, rather than in a skin ofthe radio source. Finally, we consider the nature and maintenance of themagnetic fields in these clusters and conclude that either thecluster-wide field exists at similar levels or a weaker cluster-widefield is amplified by effects in the core.
| A new list of extra-galactic radio jets
A catalogue of extra-galactic jets is very useful both in observationaland theoretical studies of active galaxies. With the use of new powerfulradio instruments, the detailed structures of very compact or weak radiosources are investigated observationally and many new radio jets aredetected. In this paper, we give a list of 661 radio sources withdetected radio jets known to us prior to the end of December 2000. Allreferences are collected for the observations of jets in radio, IR,optical, UV and X-ray wave-bands. Table 1 and references to Table 1 areonly available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/381/757
| The origin of wide-angle tailed radio galaxies
To investigate the origins of wide-angle tailed radio sources (WATs), wehave compiled a sample of these systems in Abell clusters for whichX-ray data exist. Contrary to conventional wisdom, the WATs are found tobe significantly displaced from the X-ray centroids of their hostclusters. The bends in the radio jets of WATs are found to be orientedpreferentially such that they point directly away from or toward thecluster centre, with more of the former than the latter. If thismorphology is attributed to ram pressure, then the WATs are on primarilyradial orbits, with more approaching the X-ray centroid than receding.There is also some evidence that the incoming WATs are on averagefurther from the X-ray centroid than the outgoing ones. All of theseobservations strongly support a scenario in which WATs are created incluster mergers.
| Signatures of Interstellar-Intracluster Medium Interactions: Spiral Galaxy Rotation Curves in Abell 2029
We investigate the rich cluster Abell 2029 (z~0.08) using opticalimaging and long-slit spectral observations of 52 disk galaxiesdistributed throughout the cluster field. No strong emission-linegalaxies are present within ~400 kpc of the cluster center, a regionlargely dominated by the similarly shaped X-ray and low surfacebrightness optical envelopes centered on the giant cD galaxy. However,two-thirds of the galaxies observed outside the cluster core exhibitline emission. Hα rotation curves of 14 cluster members are usedin conjunction with a deep I-band image to study the environmentaldependence of the Tully-Fisher relation. The Tully-Fisher zero point ofAbell 2029 matches that of clusters at lower redshifts, although we doobserve a relatively larger scatter around the Tully-Fisher relation. Wedo not observe any systematic variation in the data with projecteddistance to the cluster center. We see no environmental dependence ofTully-Fisher residuals, R-I color, Hα equivalent width, or theshape and extent of the rotation curves.
| The evolution of the color gradients of early-type cluster galaxies
We investigate the origin of color gradients in cluster early-typegalaxies to probe whether pure age or pure metallicity gradients canexplain the observed data in local and distant (z ≍ 0.4) samples.We measure the surface brightness profiles of the 20 brightestearly-type galaxies of CL0949+44 (hereafter CL0949) at redshiftz=0.35-0.38 from HST WF2 frames taken in the filters F555W, F675W,F814W. We determine the color profiles (V - R)(r), (V - I)(r), and (R -I)(r) as a function of the radial distance r in arcsec, and fitlogarithmic gradients in the range -0.2 to 0.1 mag per decade. Thesevalues are similar to what is found locally for the colors (U -B), (U -V), (B-V ) which approximately match the (V -R), (V -I), (R-I) atredshift ≍ 0.4. We analyse the results with up to date stellarpopulation models. We find that passive evolution of metallicitygradients (≍ 0.2 dex per radial decade) provides a consistentexplanation of the local and distant galaxies' data. Invoking pure agegradients (with fixed metallicity) to explain local color gradientsproduces too steep gradients at redshifts z ≍ 0.4. Pure agegradients are consistent with the data only if large present day ages>= 15 Gyr are assumed for the galaxy centers. Based on observationswith the NASA/ESA Hubble Space Telescope, obtained at the SpaceTelescope Science Institute, which is operated by AURA, Inc., under NASAcontract NAS 5-26555.
| Kinematics, abundances and origin of brightest cluster galaxies
We present kinematic parameters and absorption line strengths for threebrightest cluster galaxies, NGC 6166, 6173 and 6086. We find that NGC6166 has a velocity dispersion profile which rises beyond 20arcsec fromthe nucleus, with a halo velocity dispersion in excess of 400kms^-1. Allthree galaxies show a positive and constant h_4 Hermite moment. Therising velocity dispersion profile in NGC 6166 thus indicates anincreasing mass-to-light ratio. Rotation is low in all three galaxies,and NGC 6173 and 6086 show possible kinematically decoupled cores. Allthree galaxies have Mg_2 gradients similar to those found in normalbright ellipticals, which are not steep enough to support simpledissipative collapse models, but these could be accompanied bydissipationless mergers which would tend to dilute the abundancegradients. The [Mg/Fe] ratios in NGC 6166 and 6086 are higher than thatfound in NGC 6173, and if NGC 6173 is typical of normal brightellipticals, this suggests that cDs cannot form from late mergers ofnormal galaxies.
| 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.
| Detailed Surface Photometry of Dwarf Elliptical and Dwarf S0 Galaxies in the Virgo Cluster
We analyze new V-band images of 14 dwarf S0 galaxies and 10 dwarfelliptical galaxies in the Virgo Cluster, in combination with R-bandimages of 70 dwarf elliptical galaxies from an earlier paper. We computethe intensity-weighted mean ellipticity, the mean deviations fromelliptical isophotes, and a newly defined parameter to measure isophotaltwists. We also fit each major-axis profile to a power lawSigma(a)~exp[-(a/a_s)^n], where n is allowed to vary. Consistent withother studies of the Virgo dwarf ellipticals, we find that the profileshapes for the entire sample is strongly peaked near n=1 (exponentialprofiles) and that no galaxies have n=1/4 (de Vaucouleurs profile). Thefaintest galaxies all have nearly exponential profiles, while thebrighter ones on average have n<1. The correlation betweenellipticity and the boxy/disky parameter is similar to that of largeelliptical galaxies, suggesting that dwarfs may also be divided into twogroups with differing internal dynamics. The Virgo dEs also show agreater degree of isophotal twisting than more luminous ellipticalgalaxies. There does not seem to be any combination of parameters fromthe surface photometry that statistically correlates with the dE/dS0designation: in particular, the dS0 galaxies do not, on average, havemore pointed (disky) isophotes than the dEs.
| Spectral gradients in central cluster galaxies: further evidence of star formation in cooling flows
We have obtained radial gradients in the spectral features of thelambda4000-Angstroms break (D_4000) and Mg_2 for a sample of 11 centralcluster galaxies (CCGs): eight in clusters with cooling flows and threein clusters without. After careful removal of the emission lines foundwithin the D_4000 and Mg_2 bandpasses for some objects, the new datastrongly confirm the correlations between line-strength indices and thecooling flow phenomenon found in our earlier study. We find that suchcorrelations depend on the presence and characteristics of emissionlines in the inner regions of the CCGs. The nuclear indices arecorrelated with the mass deposition rate (M^.) only when emission linesare found in the central regions of the galaxies. The central D_4000 andMg_2 indices in cooling flow galaxies without emission lines arecompletely consistent with the indices measured in CCGs in clusterswithout cooling flows. CCGs in cooling flow clusters exhibit a clearsequence in the D_4000-Mg_2 plane, with a neat segregation depending onemission-line type and blue morphology. This sequence can be modelled,using stellar population models with a normal initial mass function(IMF), by a recent (~0.1 Gyr old) burst of star formation, althoughmodel uncertainties do not allow us to completely discard continuousstar formation or a series of bursts over the last few Gyr. In CCGs withemission lines, the gradients in the spectral indices are flat orpositive inside the emission-line regions, suggesting the presence ofyoung stars. Outside the emission-line regions, and in cooling flowgalaxies without emission lines, gradients are negative and consistentwith those measured in CCGs in clusters without cooling flows and giantelliptical galaxies. Index gradients measured exclusively in theemission-line region correlate with M^.. Using the same populationmodels we have estimated the radial profiles of the mass transformedinto new stars. The derived profiles are remarkably parallel to theexpected radial behaviour of the mass deposition rate derived from X-rayobservations. Moreover, a large fraction ( probably most) of the coolingflow gas accreted into the emission-line region is converted into stars.In the light of these new data, we discuss the evolutionary sequencesuggested by McNamara, in which radio-triggered star formation burststake place several times during the lifetime of the cooling flow. Weconclude that this scenario is consistent with the availableobservations.
| X-Ray Spectral Properties of the Cluster Abell 2029
We have analyzed ASCA and ROSAT PSPC spectra and images of the galaxycluster Abell 2029. The ASCA spectra of the cluster indicate that thegas temperature declines with radius. The PSPC image shows that thecluster is very regular and smooth. Also, there is no significantevidence for any irregularities in the temperature distribution in thecluster, as would be produced by a subcluster merger. These resultssuggest that A2029 is a relaxed cluster and that the gas is inhydrostatic equilibrium. We use the assumption of equilibrium todetermine the gravitational mass of the cluster as a function of radius.At a radius of 16' (1.92 h^{-1}50 Mpc; H0 = 50 h50 km s-1Mpc-1), the gravitational mass is Mtot = (9.42 +/- 4.22) x 1014h^{-1}50 Mȯ, while the mass of gas is Mgas = (2.52 +/-0.77) x 1014 h^{-5/2}50 Mȯ. The gas fraction is found toincrease with radius; within a spherical radius of 16', the fraction isMgas/Mtot = (0.26 +/- 0.14) h^{-3/2}50 . The iron abundancein the gas is found to be 0.40 +/- 0.04 solar. There is no significantevidence for any variation in the abundance with position in thecluster. The global X-ray spectra, central X-ray spectra, and ROSATsurface brightness all require a cooling flow at the cluster center. Theglobal X-ray spectrum implies that the total cooling rate is363^{+79}_{-96} h^{-2}50 Mȯ yr-1. The global X-rayspectra are consistent with the Galactic value for the soft X-rayabsorption toward the cluster. White et al. and Allen & Fabian havesuggested that there is significant excess absorption associated withthe cooling flow in the cluster. The ROSAT PSPC spectra of the centralregions of the cluster are inconsistent with a large value of foregroundexcess absorption. The upper limit on excess foreground absorption is7.3 x 1019 cm-2. However, the spectra do not rule out a significantamount of intrinsic absorbing gas located within the cooling flowregion.
| 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
| A 20 Centimeter VLA Survey of Abell Clusters of Galaxies. VII. Detailed Radio Images
We present detailed radio images, and models, obtained with the VeryLarge Array at 20 cm for 199 radio galaxies in Abell clusters ofgalaxies.
| 21 CM H1 Line Spectra of Galaxies in Nearby Clusters
A compilation of HI line fluxes, systemic velocities and line widths ispresented for \Ndet detected galaxies, mostly in the vicinities of 30nearby rich clusters out to a redshift of z ~ .04, specifically for usein applications of the Tully-Fisher distance method. New 21 cm HI lineprofiles have been obtained for ~ 500 galaxies in 27 Abell clustersvisible from Arecibo. Upper limits are also presented for \Nnod galaxiesfor which HI emission was not detected. In order to provide ahomogeneous line width determination optimized for Tully-Fisher studies,these new data are supplemented by the reanalysis of previouslypublished spectra obtained both at Arecibo and Green Bank that areavailable in a digital archive. Corrections for instrumental broadening,smoothing, signal-to-noise and profile shape are applied, and anestimate of the error on the width is given. When corrected forturbulent broadening and viewing angle, the corrected velocity widthspresented here will provide the appropriate line width parameter neededto derive distances via the Tully-Fisher relation.
| A VLA survey of rich clusters of galaxies. III. The weaker sources: maps and identifications.
We present radio and optical parameters for 737 weak sources in 60 Abellcluster fields observed with the Very Large Array (VLA) using scaledarrays at 1.5 and 4.9 GHz. The measurements extend to a lower 1.5 GHzlimit of 1.0 mJy and comprise a complete sample with 1.5-GHz fluxdensity 2.5 < S_1.5 < 20 mJy. The combined sky area within thehalf-power circle on the maps is 3.5 x 10^-3 sr, and the cluster fieldsare distributed over 24 h of right ascension and between declinations+35deg and -30deg. Contour maps of the extended sources at 1.5 GHz arepresented and source parameters such as position, angular size andspectral index are tabulated. We also derive the emitted power andlinear size for those sources with published redshifts. We try toidentify the radio sources with optical images on the Palomar and SERCsurvey plates and give their accurate optical positions, morphologiesand apparent magnitudes.
| The Effects of Dust on Broadband Color Gradients in Elliptical Galaxies
In order to examine the possibility that dust effects cause colorgradients in elliptical galaxies, we have constructed a set ofelliptical galaxy models spanning a wide range of dust properties,including mass, spatial distribution, and spectral properties. Thesemodels are spherically symmetric and include the effects of scattering.We have calculated the emergent broadband colors from the far-UV bandsthrough K. These results were then compared with the color propertiesfor a sample of 52 galaxies taken from the literature. In the optical,we can reproduce the magnitude, morphology, and color gradient ratios[i.e., {DELTA}U - R)/{DELTA}(B - R)] observed in many of the galaxies.The best fits are found for distributions with ρ_d_ ~ r^-1^ andτT ~ 1, which corresponds to dust masses on the order of 10^6^M_sun_ within the central 10-30 kpc. More condensed dust profiles alsoproduce strong color gradients, but only in the central regions (r <0.5 kpc). For many of the objects in this sample, the implied dustmasses are in reasonable agreement with the dust masses inferred fromIRAS observations, although a number of objects require significantlyhigher dust masses than their IRAS observations imply if their colorproperties are to be attributed solely to reddening by dust. Our modelssuggest that a simple dusty elliptical galaxy scenario can reproduce themagnitude, morphology, and ratios of observed broadband color gradientsin many ellipticals. We find that currently available color gradientmeasurements are consistent with our model results but that thesemeasurements are not precise enough in many objects to provide tightconstraints on the models. Extended dust distributions will greatlycomplicate the interpretation of all broadband data. Any broadbandanalysis hindered by age-metallicity degeneracy will also be hindered bydust effects. In effect, all broadband observations of ellipticalgalaxies may be age-metallicity-dust degenerate. We also consider theeffects of dust on several global relationships in ellipticals, such asthe color-magnitude relation and various distance indicators.
| Accurate sky Subtraction of Long-Slit Spectra: Velocity Dispersions at Sigma(v) = 24.0 Mag/arcsec^2
We describe an observing strategy for obtaining accurate sky subtractionwhen observing with a long-slit spectrograph. The technique is achopping procedure in which the telescope is sequentially moved fromobject to sky on short time scales (~300 s), but instead of reading outthe CCD detector with each exposure, we repeatedly clock the charge onthe chip in the parallel direction in a manner that produces twocomplete exposures (one object+sky, one sky) on each CCD frame. Thebackground subtraction proceeds naturally by differencing these twoexposures. We show that this method provides superior results to moretraditional sky- subtraction methods that rely on measuring the skybrightness at the ends of the slit. We find that we can reach a V-bandsurface brightness of 24 mag arcsec^2^ in about 8 hours of observingtime on the 2.4-meter Hiltner telescope at the Michigan-Dartmouth-MITObservatory. We present some preliminary results obtained with thismethod for the stellar dynamics in the outer envelopes of threeelliptical galaxies (M87, NGC 5846, and IC 1101). We usecross-correlation and Fourier quotient techniques to derive radialvelocity and velocity dispersion profiles. We confirm that the velocitydispersion in the outer envelope of IC 1101 (the central galaxy in Abell2029) rises with distance from the center of the galaxy, as noted byDressler [APJ. 23,659 (1979)].
| Optical Spectroscopy of Radio Galaxies in Abell Clusters II. BL Lacs and FR I Unification
As part of our optical spectroscopic study of radio galaxies in Abellclusters, we report a search for BL Lac phenomena in our sample. As anindicator of possible nonthermal activity in the nuclei of our radiogalaxies, we report D(4000), a measure of the 4000 A break, for 190objects. None of the objects in our sample are found which meet thetions for BL Lac objects both for D(4000) and for weakness of emissionlines. We do find 15 objects which have diluted 4000 A breaks[D(4000)<= 1.8], and these are discussed individually. At least fourof them appear to have weak nonthermal activity which may be related tothe BL Lac phenomena. These results appear to be in conflict with thesimplest BL Lac/FR I unification model. Several ways out of this dilemmaare discussed. Perhaps the most likely change in this model is theinclusion of FR II radio galaxies as part of the parent population of BLLac objects.
| 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.
| Kinematics of 13 brightest cluster galaxies
Velocity dispersion profiles and rotation curves have been determinedfor a sample of 13 brightest cluster galaxies (BCGs) in order to studytheir internal stellar kinematics and investigate their relationship toellipticals. We find that BCGs generally display velocity dispersionprofiles with gradients similar to those found in normal brightellipticals. A rising velocity dispersion profile is found for the BCGIC 1101, the dominant member of Abell 2029, confirming Dressler's (1979)result. No other rising velocity dispersion profiles are found in oursample suggesting that they are not a feature common to brightestcluster galaxies. Significant rotation is found in only two of thegalaxies, a result in agreement with previous studies showing thedeclining importance of rotation with increasing luminosity forelliptical galaxies. Our data suggest that environment plays a role inthe kinematic characteristics of BCGs. We find a correlation between therotation of BCGs and the velocity dispersion of their parent clusters inthe sense that very slow rotating galaxies (Vm/(mean value ofsigma))* less than 0.1, are predominantly found in high velocitydispersion (sigmacL greater than 650 km/s) clusters. Thisrelation between the internal stellar kinematics of BCGs and the clustervelocity dispersion is in the sense expected if ellipticals formed bymerging. Brightest cluster galaxy mass-to-light ratios derived fromphotometric and kinematic modeling are found to be similar to normalelliptical M/L values. For the galaxy NGC 4073, the dominant galaxy inthe poor cluster MKW 4, we find that it contains a counterrotatingstellar core suggestive of the occurrence of an accretion event(s).
| A 20 CM Survey of Abell Clusters of Galaxies. V. Optical Observations and Surface Photometry
We present results from a program of optical imaging of 265 radiogalaxies in rich clusters. Using isophotal surface photometry, weinvestigate the optical properties such as the morphology, surface-brightness profiles, surface-brightness/size relationships,ellipticities, and the frequency of nonelliptical isophotes. The resultsare compared to a "normal" nonradio-selected sample of ellipticalgalaxies from the same clusters. The goal is to determine if the parentpopulation of FR I radio galaxies can be distinguished optically fromradio-quiet galaxies. The results of the analysis are that clusterellipticals are a very homogeneous class of objects. The opticalproperties are consistent with a one-parameter family, where the opticalluminosity is the fundamental parameter. In all tests considered, radio-loud FR I galaxies cannot be distinguished optically from radio-quietgalaxies selected from the same environment. The local density of nearbycompanions (<20 kpc) and the frequency of morphological peculiaritiesor tidal interactions are not statistically different between theradio-loud and quiet samples. There is some suggestion from comparisonto published samples of non-cluster radio galaxies, that the clusterenvironment is not condusive to long-lived tidal interactions, and thatsuch events may be more important to galaxy evolution in poor groups andlower density environments. Such events appear to have little influenceon the formation of FR I radio galaxies in rich clusters. The resultsare consistent with the idea that all elliptical galaxies may at sometime (or many times) contain powerful (rR I) radio sources.
|
Sottometti un nuovo articolo
Link relazionati
Sottometti un nuovo link
Membro dei seguenti gruppi:
|
Osservazione e dati astrometrici
Cataloghi e designazioni:
|
