Садржај
Слике
Уплоадјуј своје слике
DSS Images Other Images
Везани чланци
The cluster relic source in A 521
We present high sensitivity radio observations of the merging cluster A521, at a mean redshift z = 0.247. The observations were carried outwith the GMRT at 610 MHz and cover a region of 1 square degree,with a sensitivity limit of 1σ = 35 μJy b‑1.The most relevant result of these observations is the presence of aradio relic at the cluster periphery, at the edge of a region wheregroup infalling into the main cluster is taking place. Thanks to thewealth of information available in the literature in the optical andX-ray bands, a multi-band study of the relic and its surroundings wasperformed. Our analysis is suggestive of a connection between thissource and the complex ongoing merger in the A 521 region. The relicmight be “revived’ fossil radio plasma through adiabaticcompression of the magnetic field or shock re-acceleration due to themerger events. We also briefly discussed the possibility that thissource is the result of induced ram pressure stripping of radio lobesassociated with the nearby cluster radio galaxy J0454 1016a. Allowingfor the large uncertainties due to the small statistics, the number ofradio emitting early-type galaxies found in A 521 is consistent with theexpectations from the standard radio luminosity function for local (z⩽ 0.09) cluster ellipticals.
| Study of the Structure of the Coma Cluster Based on a Hierarchical Force Clustering Method
Six subclusters in the Coma cluster have been selected on the basis of ahierarchical clustering method that takes the gravitational interactionamong galaxies into account. Of these, 3 central subclusters around thegalaxies NGC 4889, NGC 4874, and NGC 4839 have been singled out. We haveused the objective statistical criterion applied by Vennik and Anosovain studies of close groups of galaxies to evaluate each member includedin a subcluster with a high probability. Galaxies with a significantdeficit of hydrogen HI, including objects from the Bravo-Alfaro list,have been identified with members of the subclusters, with the greatestnumber of them in the subclusters around NGC 4874 and NGC 4839. Aquantitative estimate of the hydrogen deficit using the HI index in theRCG3 catalog reveals a statistically significant excess value for thosegalaxies that are members of the subclusters compared to galaxies with ahydrogen deficit in the overall Coma cluster field. A substantial numberof the spiral galaxies with a hydrogen deficit in the subclusters turnedout to be radio galaxies as well.
| The build-up of the Coma cluster by infalling substructures
We present a new multiwavelength analysis of the Coma clustersubclustering based on recent X-ray data and on a compilation of nearly900 redshifts. We characterize subclustering using the Serna &Gerbal (1996, A&A, 309, 65) hierarchical method, which makes use ofgalaxy positions, redshifts, and magnitudes, and identify 17 groups. Oneof these groups corresponds to the main cluster, one is the well knowngroup associated with the infalling galaxy NGC 4839, and one isassociated with NGC 4911/NGC 4926. About one third of the 17 groups havevelocity distributions centered on the velocities of the very brightcluster galaxies they contain (magnitudes R < 13). In order to searchfor additional substructures, we made use of the isophotes of X-raybrightness residuals left after the subtraction of the best-fitβ-model from the overall X-ray gas distribution (Neumann et al.2003, A&A, 400, 811). We selected galaxies within each of theseisophotes and compared their velocity distributions with that of thewhole cluster. We confirm in this way the two groups associated,respectively, with NGC 4839, and with the southern part of the extendedwestern substructure visible in X-rays. We discuss the group propertiesin the context of a scenario in which Coma is built by the accretion ofgroups infalling from the surrounding large-scale structure. We estimatethe recent mass accretion rate of Coma and compare it with hierarchicalmodels of cluster evolution.
| Radio-selected Galaxies in Very Rich Clusters at z <= 0.25. I. Multiwavelength Observations and Data Reduction Techniques
Radio observations were used to detect the ``active'' galaxy populationwithin rich clusters of galaxies in a nonbiased manner that is notplagued by dust extinction or the K-correction. We present wide-fieldradio, optical (imaging and spectroscopy), and ROSAT All-Sky Survey(RASS) X-ray data for a sample of 30 very rich Abell (R>=2) clusterswith z<=0.25. The VLA radio data samples the ultrafaint radio(L1.4>=2×1022 W Hz-1) galaxypopulation within these extremely rich clusters for galaxies withMR<=-21. This is the largest sample of low-luminosity 20cm radio galaxies within rich Abell clusters collected to date.The radio-selected galaxy sample represents the starburst (starformation rate >=5 Msolar yr-1) and activegalactic nuclei populations contained within each cluster. Archival andnewly acquired redshifts were used to verify cluster membership for most(~95%) of the optical identifications. Thus, we can identify all thestarbursting galaxies within these clusters, regardless of the level ofdust obscuration that would affect these galaxies being identified fromtheir optical signature. Cluster sample selection, observations, anddata reduction techniques for all wavelengths are discussed.
| A new catalogue of ISM content of normal galaxies
We have compiled a catalogue of the gas content for a sample of 1916galaxies, considered to be a fair representation of ``normality''. Thedefinition of a ``normal'' galaxy adopted in this work implies that wehave purposely excluded from the catalogue galaxies having distortedmorphology (such as interaction bridges, tails or lopsidedness) and/orany signature of peculiar kinematics (such as polar rings,counterrotating disks or other decoupled components). In contrast, wehave included systems hosting active galactic nuclei (AGN) in thecatalogue. This catalogue revises previous compendia on the ISM contentof galaxies published by \citet{bregman} and \citet{casoli}, andcompiles data available in the literature from several small samples ofgalaxies. Masses for warm dust, atomic and molecular gas, as well asX-ray luminosities have been converted to a uniform distance scale takenfrom the Catalogue of Principal Galaxies (PGC). We have used twodifferent normalization factors to explore the variation of the gascontent along the Hubble sequence: the blue luminosity (LB)and the square of linear diameter (D225). Ourcatalogue significantly improves the statistics of previous referencecatalogues and can be used in future studies to define a template ISMcontent for ``normal'' galaxies along the Hubble sequence. The cataloguecan be accessed on-line and is also available at the Centre desDonnées Stellaires (CDS).The catalogue is available in electronic form athttp://dipastro.pd.astro.it/galletta/ismcat and at the CDS via anonymousftp to\ cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/405/5
| The diffuse radio emission from the Coma cluster at 2.675 GHz and 4.85 GHz
We present new measurements of the diffuse radio halo emission from theComa cluster of galaxies at 2.675 GHz and 4.85 GHz using the Effelsberg100-m telescope. After correction for the contribution from pointsources we derive the integrated flux densities for the halo source(Coma C), S2.675 GHz=(107+/- 28) mJy and S4.85GHz=(26+/- 12) mJy. These values verify the strong steepening of theradio spectrum of Coma C at high frequencies. Its extent stronglydepends on frequency, at 4.85 GHz it is only marginally visible. Themeasurement at 4.85 GHz is the first flux density determination for ComaC at this high frequency. In order to quantify the spectral steepeningwe compare the expectations for the spectrum of Coma C with theobservations, resorting to basic models for radio halo formation. Thein-situ acceleration model provides the best fit to the data. Fromequipartition assumptions we estimate a magnetic field strengthBeq=0.57 (1+k)0.26 mu G in the intracluster mediumof Coma, where k is the energy ratio of the positively and negativelycharged particles. \ As a by-product of the 2.675 GHz observation wepresent a new flux density for the diffuse emission of the extendedsource 1253+275 (S2.675GHz=112+/- 10). This measurementprovides a smaller error range for the power-law fit to the spectrum(alpha =1.18+/- 0.02) compared to previous investigations and yields anequipartition magnetic field strength of Beq=0.56(1+k)0.24 mu G.
| 1.65-μm (H -band) surface photometry of galaxies - VIII. The near-IR κ space at z =0
We present the distribution of a statistical sample of nearby galaxiesin the κ -space (κ 1 ~logM , κ 2~logI e 3 M /L , κ 3 ~logM /L ).Our study is based on near-IR (H -band: λ =1.65μm)observations, for the first time comprising early- and late-typesystems. Our data confirm that the mean effective dynamicalmass-to-light ratio M /L of the E+S0+S0a galaxies increases withincreasing effective dynamical mass M , as expected from the existenceof the Fundamental Plane relation. Conversely, spiral and Im/BCDgalaxies show a broad distribution in M /L with no detected trend of M/L with M , the former galaxies having M /L values about twice largerthan the latter, on average. For all the late-type galaxies, the M /Lincreases with decreasing effective surface intensity I e ,consistent with the existence of the Tully-Fisher relation. Theseresults are discussed on the basis of the assumptions behind theconstruction of the κ -space and their limitations. Our study iscomplementary to a previous investigation in the optical (B -band:λ =0.44μm) and allows us to study wavelength dependences ofthe galaxy distribution in the κ -space. As a first result, wefind that the galaxy distribution in the κ 1 -κ2 plane reproduces the transition from bulgeless tobulge-dominated systems in galaxies of increasing dynamical mass.Conversely, it appears that the M /L of late-types is higher (lower)than that of early-types with the same M in the near-IR (optical). Theorigins of this behaviour are discussed in terms of dust attenuation andstar formation history.
| On the formation of cluster radio relics
In several merging clusters of galaxies so-called cluster radio relicshave been observed. These are extended radio sources which do not seemto be associated with any radio galaxies. Two competing physicalmechanisms to accelerate the radio-emitting electrons have beenproposed: (i) diffusive shock acceleration and (ii) adiabaticcompression of fossil radio plasma by merger shock waves. Here thesecond scenario is investigated. We present detailed three-dimensionalmagneto-hydrodynamical simulations of the passage of a radio plasmacocoon filled with turbulent magnetic fields through a shock wave.Taking into account synchrotron, inverse Compton and adiabatic energylosses and gains, we evolved the relativistic electron population toproduce synthetic polarization radio maps. On contact with the shockwave the radio cocoons are first compressed and finally torn intofilamentary structures, as is observed in several cluster radio relics.In the synthetic radio maps the electric polarization vectors are mostlyperpendicular to the filamentary radio structures. If the magnetic fieldinside the cocoon is not too strong, the initially spherical radiococoon is transformed into a torus after the passage of the shock wave.Very recent, high-resolution radio maps of cluster radio relics seem toexhibit such toroidal geometries in some cases. This supports thehypothesis that cluster radio relics are fossil radio cocoons that havebeen revived by a shock wave. For a late-stage relic the ratio of itsglobal diameter to the filament diameter should correlate with the shockstrength. Finally, we argue that the total radio polarization of a radiorelic should be well correlated with the three-dimensional orientationof the shock wave that produced the relic.
| Redshift-Distance Survey of Early-Type Galaxies. I. The ENEARc Cluster Sample
This paper presents data on the ENEARc subsample of the larger ENEARsurvey of nearby early-type galaxies. The ENEARc galaxies belong toclusters and were specifically chosen to be used for the construction ofa Dn-σ template. The ENEARc sample includes newmeasurements of spectroscopic and photometric parameters (redshift,velocity dispersion, line index Mg2, and the angular diameterdn), as well as data from the literature. New spectroscopicdata are given for 229 cluster early-type galaxies, and new photometryis presented for 348 objects. Repeat and overlap observations withexternal data sets are used to construct a final merged catalogconsisting of 640 early-type galaxies in 28 clusters. Objectivecriteria, based on catalogs of groups of galaxies derived from completeredshift surveys of the nearby universe, are used to assign galaxies toclusters. In a companion paper, these data are used to construct thetemplate Dn-σ distance relation for early-typegalaxies, which has been used to estimate galaxy distances and derivepeculiar velocities for the ENEAR all-sky sample. Based on observationsat Complejo Astronomico El Leoncito, operated under agreement betweenthe Consejo Nacional de Investigaciones Científicas de laRepública Argentina and the National Universities of La Plata,Córdoba, and San Juan; Cerro Tololo Inter-American Observatory,National Optical Astronomical Observatory, which is operated by theAssociation of Universities for Research in Astronomy, Inc., undercooperative agreement with the National Science Foundation; the EuropeanSouthern Observatory (ESO), partially under the ESO-ON agreement; theFred Lawrence Whipple Observatory; the Observatório do Pico dosDias, operated by the Laboratório Nacional de Astrofísicaand the MDM Observatory at Kitt Peak.
| 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
| On the dependence of spectroscopic indices of early-type galaxies on age, metallicity and velocity dispersion
We investigate the Mg-σ and -σ relations in asample of 72 early-type galaxies drawn mostly from cluster and groupenvironments using a homogeneous data set which is well calibrated on tothe Lick/IDS system. The small intrinsic scatter in Mg at a givenσ gives upper limits on the spread in age and metallicity of 49and 32 per cent respectively, if the spread is attributed to onequantity only, and if the variations in age and metallicity areuncorrelated. The age/metallicity distribution as inferred from theHβ versus diagnostic diagram reinforces this conclusion,as we find mostly galaxies with large luminosity-weighted ages spanninga range in metallicity. Using Monte Carlo simulations, we show that thegalaxy distribution in the Hβ versus plane cannot bereproduced by a model in which galaxy age is the only parameter drivingthe index-σ relation. In our sample we do not find significantevidence for an anticorrelation of ages and metallicities which wouldkeep the index-σ relations tight while hiding a large spread inage and metallicity. As a result of correlated errors in theage-metallicity plane, a mild age-metallicity anticorrelation cannot becompletely ruled out by the current data. Correcting the line-strengthindices for non-solar abundance ratios, following the recent paper byTrager et al., leads to higher mean metallicity and slightly younger ageestimates while preserving the metallicity sequence. The [Mg/Fe] ratiois mildly correlated with the central velocity dispersion, and rangesfrom [Mg/Fe]=0.05 to 0.3 for galaxies withσ>100kms-1. Under the assumption that there is noage gradient along the index-σ relations, theabundance-ratio-corrected Mg-σ, Fe-σ and Hβ-σrelations give consistent estimates ofΔ[M/H]/Δlogσ~=0.9+/-0.1. The slope of theHβ-σ relation limits a potential age trend as a function ofσ to 2-3Gyr along the sequence.
| The Radio Galaxy Populations of Nearby Northern Abell Clusters
We report on the use of the NRAO VLA Sky Survey (NVSS) to identify radiogalaxies in 18 nearby Abell clusters. The listings extend from the coresof the clusters out to radii of 3 h-175 Mpc, whichcorresponds to 1.5 Abell radii and approximately 4 orders of magnitudein galaxy density. To create a truly useful catalog, we have collectedoptical spectra for nearly all of the galaxies lacking public velocitymeasurements. Consequently, we are able to discriminate between thoseradio galaxies seen in projection on the cluster and those that are inactuality cluster members. The resulting catalog consists of 329 clusterradio galaxies plus 138 galaxies deemed foreground or backgroundobjects, and new velocity measurements are reported for 273 of theseradio galaxies. The motivation for the catalog is the study of galaxyevolution in the cluster environment. The radio luminosity function is apowerful tool in the identification of active galaxies, as it isdominated by star-forming galaxies at intermediate luminosities andactive galactic nuclei (AGNs) at higher luminosities. The flux limit ofthe NVSS allows us to identify AGNs and star-forming galaxies down tostar formation rates less than 1 Msolar yr-1. Thissensitivity, coupled with the all-sky nature of the NVSS, allows us toproduce a catalog of considerable depth and breadth. In addition tothese data, we report detected infrared fluxes and upper limits obtainedfrom IRAS data. It is hoped that this database will prove useful in anumber of potential studies of the effect of environment on galaxyevolution. Based in part on observations obtained with the Apache PointObservatory 3.5 m telescope, which is owned and operated by theAstrophysical Research Consortium (ARC).
| Are all radio galaxies genuine ellipticals?
Classical double radio sources are believed to be powered by a strongrelativistic jet due to the presence of a rapidly spinning black hole inthe center of a giant E galaxy formed by the merging of two galaxies. Ifthis is true, no radio source should have been found in spiral or S0galaxies. A number of radio S0s have been reported, but most of them areprobably misclassified Es. However, our own observations confirm thatNGC 612 is an S0 although it is associated with the FR II radio sourcePKS 0131-36. We conclude that S0s can be classical radio sources, butthat such occurences are extremely rare. Partly based on observationsobtained with the ESO 3.6 m telescope, La Silla, Chile.
| Reviving fossil radio plasma in clusters of galaxies by adiabatic compression in environmental shock waves
We give for a plasma with a history of several expansion and contractionphases an analytical model of the evolution of a contained relativisticelectron population under synchrotron, inverse Compton and adiabaticenergy losses or gains. This is applied to different scenarios forevolution of radio plasma inside the cocoons of radio galaxies, afterthe activity of the central engine has ceased. It is demonstrated thatfossil radio plasma with an age of even up to 2 Gyr can be revived bycompression in a shock wave of large-scale structure formation, causedduring the merging events of galaxy clusters, or by the accretion ontogalaxy clusters. We argue, that this is a highly plausible explanationfor the observed cluster radio relics, which are the regions of diffuseradio emission found in clusters of galaxies, without any likely parentradio galaxy seen nearby. An implication of this model is the existenceof a population of diffuse, ultra-steep spectrum, very low frequencyradio sources located inside and possibly outside of clusters ofgalaxies, tracing the revival of aged fossil radio plasma by the shockwaves associated with large-scale structure formation.
| Spectroscopic constraints on the stellar population of elliptical galaxies in the Coma cluster
Near-infrared spectra for a sample of 31 elliptical galaxies in the Comacluster are obtained. The galaxies are selected to be ellipticals (nolenticulars), with a large spatial distribution, covering both the coreand outskirts of the cluster (i.e. corresponding to regions with largedensity contrasts). COsp (2.3-μm) absorption indices,measuring the contribution from intermediate-age red giant andsupergiant stars to the near-infrared light of the ellipticals, are thenestimated. It is found that the strength of COsp features inelliptical galaxies increases from the core (r<0.2°) to theoutskirts (r>0.2°) of the Coma cluster. Using the Mg2strengths, it is shown that the observed effect is not caused bymetallicity and is mostly caused by the presence of a younger population(giant and supergiant stars) in ellipticals in the outskirts(low-density region) of the cluster. Using the COsp features,the origin of the scatter on the near-infrared Fundamental Plane (therelation between the effective diameter, effective surface brightnessand velocity dispersion) of elliptical galaxies is studied. Correctingthis relation for contributions from the red giant and supergiant stars,the rms scatter reduces from 0.077 to 0.073dex. Although measurable, thecontribution from these intermediate-age stars to the scatter on thenear-infrared Fundamental Plane of ellipticals is only marginal. Arelation is found between the COsp and V-K colours ofellipticals, corresponding to a slope of 0.036+/-0.016, significantlyshallower than that from the Mg2-(V-K) relation. This isstudied using stellar synthesis models.
| Luminosity versus Phase-Space-Density Relation of Galaxies Revisited
We reexamined the correlation between the BTmagnitude and the phase-space-density parameterw=(D225vc)-1 of galaxies forthe Virgo, the Coma, the Fornax, and the Perseus clusters in an effortto better understand the physical underpinning of the fundamental plane.A tight correlation (BT=alog w+b) common to differentmorphological types of galaxies (E, S0, S) was found for the Virgo andthe Coma clusters, with a=1.87+/-0.10 and 1.33+/-0.11, respectively. Aninvestigation using only E galaxies was made for the four clusters. Theresults indicated that the empirical linear relation might be commonamong the Coma, the Fornax, and the Perseus clusters, with the VirgoCluster showing deviation. This relation, which is another way toproject the fundamental plane, has an expression insensitive to themorphology and may be suitable for treating galaxies of differentmorphological types collectively.
| 1.65 μm (H-band) surface photometry of galaxies. III. observations of 558 galaxies with the TIRGO 1.5 m telescope
We present near-infrared H-band (1.65 μm ) surface photometry of 558galaxies in the Coma Supercluster and in the Virgo cluster. This dataset, obtained with the Arcetri NICMOS3 camera ARNICA mounted on theGornergrat Infrared Telescope, is aimed at complementing, withobservations of mostly early-type objects, our NIR survey of spiralgalaxies in these regions, presented in previous papers of this series.Magnitudes at the optical radius, total magnitudes, isophotal radii andlight concentration indices are derived. We confirm the existence of apositive correlation between the near-infrared concentration index andthe galaxy H-band luminosity Based on observations taken at TIRGO(Gornergrat, Switzerland). TIRGO is operated by CAISMI-CNR, Arcetri,Firenze, Italy. Tables 1 and 2 are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 1.65 μm (H-band) surface photometry of galaxies. V. Profile decomposition of 1157 galaxies
We present near-infrared H-band (1.65 μm) surface brightness profiledecomposition for 1157 galaxies in five nearby clusters of galaxies:Coma, A1367, Virgo, A262 and Cancer, and in the bridge between Coma andA1367 in the ``Great Wall". The optically selected (mpg≤16.0) sample is representative of all Hubble types, from E to Irr+BCD,except dE and of significantly different environments, spanning fromisolated regions to rich clusters of galaxies. We model the surfacebrightness profiles with a de Vaucouleurs r1/4 law (dV), withan exponential disk law (E), or with a combination of the two (B+D).From the fitted quantities we derive the H band effective surfacebrightness (μe) and radius (re) of each component, theasymptotic magnitude HT and the light concentration indexC31. We find that: i) Less than 50% of the Ellipticalgalaxies have pure dV profiles. The majority of E to Sb galaxies is bestrepresented by a B+D profile. All Scd to BCD galaxies have pureexponential profiles. ii) The type of decomposition is a strong functionof the total H band luminosity (mass), independent of the Hubbleclassification: the fraction of pure exponential decompositionsdecreases with increasing luminosity, that of B+D increases withluminosity. Pure dV profiles are absent in the low luminosity rangeLH<1010 L\odot and become dominantabove 1011 L\odot . Based on observations taken atTIRGO, Gornergrat, Switzerland (operated by CAISMI-CNR, Arcetri,Firenze, Italy) and at the Calar Alto Observatory (operated by theMax-Planck-Institut für Astronomie (Heidelberg) jointly with theSpanish National Commission for Astronomy). Table 2 and Figs. 2, 3, 4are available in their entirety only in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The near-infrared Fundamental Plane of elliptical galaxies
Near-infrared (2.2 μm) observations of a sample of 48 ellipticalgalaxies in the Coma cluster have been carried out and used to study thenear-infrared Fundamental Plane (FP) of ellipticals in this cluster. Anrms scatter of 0.072 dex is found for this relation, similar to that ofits optical counterpart, using the same sample of galaxies. Thiscorresponds to an uncertainty of 18 per cent in distances to individualgalaxies derived from this relation. The sensitivity of thenear-infrared FP to the star formation or changes in metallicity andstellar population among the ellipticals is explored and found to besmall, although a likely source of scatter in this relation iscontributions from the asymptotic giant branch (AGB) population to thenear-infrared light. Allowing for observational uncertainties, we findan intrinsic scatter of 0.060 dex in the near-infrared FP. The clustergalaxies presented here provide the zero-point for the peculiar velocitystudies, using the near-infrared FP. Changes in the slopes of theD-sigma and L-sigma relations of ellipticals between the optical andnear-infrared wavelengths are investigated and found to be due tovariations in metallicity or age (or a combination of them). However, itis not possible to disentangle the effects of age and metallicity inthese relations. We find M/L~M^alpha with alpha=0.18+/-0.01 in thenear-infrared and alpha=0.23+/-0.01 at optical wavelengths, using thesame sample of galaxies. This relation is interpreted as being due to amass-metallicity effect or changes in age or the initial mass functionslope with mass. Using evolutionary population synthesis models, we findthat the effects of age and metallicity decouple in the (M/L)_K versusMg_2 and (M/L)_K versus (V-K) diagrams. The models suggest that theobserved trends in these relations may be due to an age sequence, whilemetallicity mainly contributes to the scatter.
| 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.
| On the local radio luminosity function of galaxies. II. Environmental dependences among late-type galaxies
Using new extensive radio continuum surveys at 1.4 GHz (FIRST and NVSS),we derive the distribution of the radio/optical and radio/NIR luminosity(RLF) of late-type (Sa-Irr) galaxies (m_p<15.7) in 5 nearby clustersof galaxies: A262, Cancer, A1367, Coma and Virgo. With the aim ofdiscussing possible environmental dependences of the radio properties,we compare these results with those obtained for relatively isolatedobjects in the Coma supercluster. We find that the RLF of Cancer, A262and Virgo are consistent with that of isolated galaxies. Conversely weconfirm earlier claims that galaxies in A1367 and Coma have their radioemissivity enhanced by a factor ~ 5 with respect to isolated objects. Wediscuss this result in the framework of the dynamical pressure sufferedby galaxies in motion through the intra-cluster gas (ram-pressure). Wefind that the radio excess is statistically larger for galaxies in fasttransit motion. This is coherent with the idea that enhanced radiocontinuum activity is associated with magnetic field compression. TheX-ray luminosities and temperatures of Coma and A1367 imply that thesetwo clusters have significantly larger intracluster gas density than theremaining three studied ones, providing a clue for explaining the higherradio continuum luminosities of their galaxies. Multiple systems in theComa supercluster bridge (with projected separations smaller than 300kpc) have radio luminosities significantly larger than isolatedgalaxies. Table~1 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html}
| Groups of galaxies. III. Some empirical characteristics.
Not Available
| The Universality of the Fundamental Plane of E and S0 Galaxies: Spectroscopic Data
We present central velocity dispersion measurements for 325 early-typegalaxies in eight clusters and groups of galaxies, including newobservations for 212 galaxies. The clusters and groups are the A262,A1367, Coma (A1656), A2634, Cancer, and Pegasus Clusters and the NGC 383and NGC 507 Groups. The new measurements were derived frommedium-dispersion spectra that cover 600 Å centered on the Mg I btriplet at lambda ~ 5175 Å. Velocity dispersions were measuredusing the Tonry & Davis cross-correlation method, with a typicalaccuracy of 6%. A detailed comparison with other data sources is made.
| The Universality of the Fundamental Plane of E and S0 Galaxies: Sample Definition and I-Band Photometric Data
As part of a project to compare the fundamental plane and Tully-Fisherdistance scales, we present here I-band CCD photometry for 636early-type galaxies in eight clusters and groups of galaxies. These arethe A262, A1367, Coma (A1656), A2634, Cancer and Pegasus Clusters, andthe NGC 383 and NGC 507 Groups. Sample selection, cluster properties,and cluster membership assignment criteria are discussed. We presentphotometric parameters that are used in the fundamental plane relation,the effective radius r_e, and the effective surface brightness mu_e, asderived from a r^1/4 fit to the observed radial photometric profile ofeach galaxy. A comparison with similar data found in the literature forthe Coma Cluster shows that large systematic uncertainties can beintroduced in the measurement of r_e and mu_e by the particular methodused to derive those parameters. However, the particular combination ofthese two parameters that enters in the fundamental plane relation is aquantity that can be measured with high accuracy.
| 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.
| Cluster radio relics as a tracer of shock waves of the large-scale structure formation
We present evidence for the existence of shock waves caused by theformation of the large-scale structure. In some clusters of galaxiesperipherally located sources of extended diffuse radio emission exist,the so-called cluster radio relics. They have steep radio spectra but noapparent cutoff, as old remnants of radio galaxies usually have.Therefore particle acceleration has to take place within them. Wepropose that shock structures of the cosmological large-scale matterflows are responsible for the { acceleration of} relativistic electrons:cluster accretion shocks and bow shocks of merger events. We develop atheory of radio plasma having { traversed} these shocks and compare itto observational data of { nine} radio relics (0038-096, 0917+75,1140+203, 1253+275, { 1712+64, }1706+78, 2006-56, { 2010-57,} 1401-33)and their host clusters (A85, A786, A1367, Coma, A2255, A2256, A3667,S753). The necessary accretion power, the spectral index of the radiospectrum, the acceleration efficiency of the shock, the diffusioncoefficient in the post-shock region, and the predicted radiopolarization in all of our examples fit into a coherent interpretationof the observational data. Since polarization measurements are availableonly for four sources, the predictions of our theory can beindependently checked using other examples. The predicted values of theshock compression ratio, density and temperature of the infalling gas,magnetic field strength of the shocked and unshocked radio plasma arediscussed within the frame of structure formation theory.
| The Relative Distance Between the Clusters of Galaxies A2634 and Coma
The Tully-Fisher (TF) and Fundamental Plane (FP) relations are used toobtain two independent estimates of the relative distance between theclusters A2634 and Coma. Previously published studies of A2634 showed alarge discrepancy between the distance estimates obtained with the TFand the \dns\ relations, questioning the reliability ofredshift-independent distances obtained using these relations. Becauseof the importance of this issue, we have obtained new distance estimatesfor A2634, based on much larger samples than previously used, andselected according to rigorous membership criteria. New I band CCDphotometry for 175 galaxies, new 21 cm observations of 11 galaxies, andnew velocity dispersion measurements for 62 galaxies are used togetherwith previously published data in building these samples. As part of alarger project to compare the TF and FP distance-scales, we haveobtained a new FP template using for the first time I band photometry.The template is derived using a sample of 109 E and S0 galaxies that aremembers of the Coma cluster. Its parameters are in very good agreementwith recent determinations of the FP obtained at shorter wavelengths.The uncertainty with which the FP can provide peculiar velocityestimates for single galaxies is =~ 0.43 mag in the distance modulus, or20% of the distance. This uncertainty is slightly larger than thetypical uncertainty that characterizes TF estimates. However thisdisadvantage is partly compensated by the fact that the sampleincompleteness bias has a less severe effect on FP cluster distanceestimates than it has on the corresponding TF distance estimates. Also,cluster membership is more readily established for early-type objectsthan for spirals. After the appropriate corrections for sampleincompleteness have been taken into account, we find the TF and FPdistance estimates to be in good agreement, both indicating that A2634has a negligibly small peculiar velocity with respect to the CosmicMicrowave Background reference frame. Because of the high accuracy withwhich the two distance estimates have been obtained, their agreementstrongly supports the universality of the TF and FP relations, andtherefore their reliability for the estimate of redshift-independentdistances.
| Unveiling hidden structures in the Coma cluster.
We have assembled a large data-set of 613 galaxy redshifts in the Comacluster, the largest presently available for a cluster of galaxies. Wehave defined a sample of cluster members complete to b_26.5_=20.0, usinga membership criterion based on the galaxy velocity, when available, oron the galaxy magnitude and colour, otherwise. Such a data set allows usto define nearly complete samples within a region of 1h^-1^Mpc radius,with a sufficient number of galaxies per sample to make statisticalanalyses possible. Using this sample and the ROSAT PSPC X-ray image ofthe cluster, we have re-analyzed the structure and kinematics of Coma,by applying the wavelet and adaptive kernel techniques. A strikingcoincidence of features is found in the distributions of galaxies andhot intracluster gas. The two central dominant galaxies, NGC 4874 andNGC 4889, are surrounded by two galaxy groups, mostly populated withgalaxies brighter than b_26.5_=17 and well separated in velocity space.On the contrary, the fainter galaxies tend to form a single smoothstructure with a central peak coinciding in position with a secondarypeak detected in X-rays, and located between the two dominant galaxies;we suggest to identify this structure with the main body of the Comacluster. A continuous velocity gradient is found in the centraldistribution of these faint galaxies, a probable signature of tidalinteractions rather than rotation. There is evidence for a boundpopulation of bright galaxies around other brightest cluster members.Altogether, the Coma cluster structure seems to be better traced by thefaint galaxy population, the bright galaxies being located insubclusters. We discuss this evidence in terms of an ongoing accretionof groups onto the cluster.
| 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.
|
Додај нови чланак
Линкови у сродству са темом
Додај нови линк
Чланови следећих група \:
|
Посматрања и Астрометриски подаци
Каталог и designations:
|
