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Kinematic properties and stellar populations of faint early-type galaxies - I. Velocity dispersion measurements of central Coma galaxies
We present velocity dispersion measurements for 69 faint early-typegalaxies in the core of the Coma cluster, spanning -22.0<~MR<~-17.5 mag. We examine the L-σ relation forour sample and compare it to that of bright elliptical galaxies (Es)from the literature. The distribution of the the faint early-typegalaxies in the L-σ plane follows the relationL~σ2.01+/-0.36, which is significantly shallower fromL~σ4 as defined for the bright Es. While increasedrotational support for fainter early-type galaxies could account forsome of the difference in slope, we show that it cannot explain it. Wealso investigate the colour-σ relation for our Coma galaxies.Using the scatter in this relation, we constrain the range of galaxyages as a function of their formation epoch for different formationscenarios. Assuming a strong coordination in the formation epoch offaint early-type systems in Coma, we find that most had to be formed atleast 6 Gyr ago and over a short 1-Gyr period.
| The Epochs of Early-Type Galaxy Formation as a Function of Environment
The aim of this paper is to set constraints on the epochs of early-typegalaxy formation through the ``archaeology'' of the stellar populationsin local galaxies. Using our models of absorption-line indices thataccount for variable abundance ratios, we derive ages, totalmetallicities, and element ratios of 124 early-type galaxies in high-and low-density environments. The data are analyzed by comparison withmock galaxy samples created through Monte Carlo simulations taking thetypical average observational errors into account, in order to eliminateartifacts caused by correlated errors. We find that all threeparameters, age, metallicity, and α/Fe ratio, are correlated withvelocity dispersion. We show that these results are robust againstrecent revisions of the local abundance pattern at high metallicities.To recover the observed scatter we need to assume an intrinsic scatterof about 20% in age, 0.08 dex in [Z/H], and 0.05 dex in [α/Fe].All low-mass objects withM*<~1010Msolar (σ<~130kms-1) show evidence for the presence of intermediate-agestellar populations with low α/Fe ratios. About 20% of theintermediate-mass objects with1010<~M*/Msolar<~1011[110<~σ/(kms-1)<~230 both elliptical andlenticular galaxies] must have either a young subpopulation or a bluehorizontal branch. On the basis of the above relationships, valid forthe bulk of the sample, we show that the Mg-σ relation is mainlydriven by metallicity, with similar contributions from the α/Feratio (23%) and age (17%). We further find evidence for an influence ofthe environment on the stellar population properties. Massive early-typegalaxies in low-density environments seem on average ~2 Gyr younger andslightly (~0.05-0.1 dex) more metal-rich than their counterparts inhigh-density environments. No offsets in the α/Fe ratios areinstead detected. With the aid of a simple chemical evolution model, wetranslate the derived ages and α/Fe ratios into star formationhistories. We show that most star formation activity in early-typegalaxies is expected to have happened between redshifts ~3 and 5 inhigh-density environments and between redshifts 1 and 2 in low-densityenvironments. We conclude that at least 50% of the total stellar massdensity must have already formed at z~1, in good agreement withobservational estimates of the total stellar mass density as a functionof redshift. Our results suggest that significant mass growth in theearly-type galaxy population below z~1 must be restricted to lessmassive objects, and a significant increase of the stellar mass densitybetween redshifts 1 and 2 should be present, caused mainly by the fieldgalaxy population. The results of this paper further imply the presenceof vigorous star formation episodes in massive objects at z~2-5 andevolved elliptical galaxies around z~1, both observationally identifiedas SCUBA galaxies and extremely red objects, respectively.
| The Bologna Complete Sample of Nearby Radio Sources
We present a new, complete sample of 95 radio sources selected from theB2 Catolog of Radio Sources and the Third Cambridge Revised Catalog(3CR), with z<0.1. Since no selection effect on the core radio power,jet velocity, or source orientation is present, this sample is wellsuited for statistical studies. In this first paper we present theobservational status of all sources on the parsec (milliarcsecond) andkiloparsec (arcsecond) scale; we give new parsec-scale data for 28sources and discuss their parsec-scale properties. By combining thesedata with those in the literature, information on the parsec-scalemorphology is available for a total of 53 radio sources with differentradio power and kiloparsec-scale morphologies. We investigate theirproperties. We find a dramatically higher fraction of two-sided sourcesin comparison with that of previous flux-limited VLBI surveys.
| 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.
| Are radio galaxies and quiescent galaxies different? Results from the analysis of HST brightness profiles
We present a study of the optical brightness profiles of early typegalaxies, using a number of samples of radio galaxies and opticallyselected elliptical galaxies. For the radio galaxy samples - B2 ofFanaroff-Riley type I and 3C of Fanaroff-Riley type II - we determined anumber of parameters that describe a "Nuker-law" profile, which werecompared with those already known for the optically selected objects. Wefind that radio active galaxies are always of the "core" type (i.e. aninner Nuker law slope γ < 0.3). However, there are core-typegalaxies which harbor no significant radio source and which areindistinguishable from the radio active galaxies. We do not find anyradio detected galaxy with a power law profile (γ > 0.5). Thisdifference is not due to any effect with absolute magnitude, since in aregion of overlap in magnitude the dichotomy between radio active andradio quiescent galaxies remains. We speculate that core-type objectsrepresent the galaxies that have been, are, or may become, radio activeat some stage in their lives; active and non-active core-type galaxiesare therefore identical in all respects except their eventualradio-activity: on HST scales we do not find any relationship betweenboxiness and radio-activity. There is a fundamental plane, defined bythe parameters of the core (break radius rb and breakbrightness μ_b), which is seen in the strong correlation betweenrb and μ_b. The break radius is also linearly proportionalto the optical Luminosity in the I band. Moreover, for the few galaxieswith an independently measured black hole mass, the break radius turnsout to be tightly correlated with MBH. The black hole masscorrelates even better with the combination of fundamental planeparameters rb and μ_b, which represents the centralvelocity dispersion.
| A dichotomy in the orientation of dust and radio jets in nearby low-power radio galaxies
We examine the properties of central dust in nearby quiescent and activeearly-type galaxies. The active galaxies are low-power radio galaxieswith Fanaroff & Riley type I or I/II radio jets. We focus on (a) thecomparison of the dust distributions in the active and quiescent galaxysamples; and (b) the relation between the radio jet and dustorientations. Our main observational conclusions are: (i) in line withprevious studies, the dust detection rate is higher in radio-jetgalaxies than in non radio-jet galaxies; (ii) radio galaxies contain ahigher fraction of regular dust “ellipses” compared toquiescent galaxies which contain more often irregular dustdistributions; (iii) the morphology, size and orientation of dustellipses and lanes in quiescent early-types and active early-types withkpc-scale radio jets is very similar; (iv) dust ellipses are alignedwith the major axis of the galaxy, dust lanes do not show a preferredalignment except for large (>kpc) dust lanes which are aligned withthe minor axis of the galaxy; and (v) as projected on the sky, jets donot show a preferred orientation relative to the galaxy major axis (andhence dust ellipses), but jets are preferentially perpendicular to dustlanes. We show that the dust ellipses are consistent with being nearlycircular thin disks viewed at random viewing angles. The lanes arelikely warped dust structures, which may be in the process of settlingdown to become regular disks or are being perturbed by anon-gravitational force. We use the observed dust-jet orientations toconstrain the three-dimensional angle θDJ between jetand dust. For dust-lane galaxies, the jet is approximately perpendicularto the dust structure, while for dust-ellipse galaxies there is a muchwider distribution of θDJ. We discuss two scenariosthat could explain the dust/jet/galaxy orientation dichotomy. If lanesare indeed settling, then the jet orientation apparently is roughlyaligned with the angular momentum of the dust before it settles. Iflanes are perturbed by a jet-related force, it appears that it causesthe dust to move out of its equilibrium plane in the galaxy into a planewhich is perpendicular to the jet.
| Obscuration and Origin of Nuclear X-Ray Emission in FR I Radio Galaxies
We present X-ray observations of the nuclear region of 25 Fanaroff-Rileytype I (FR I) radio galaxies from the 3CRR and B2 catalogs, using datafrom the Chandra and XMM-Newton archives. We find the presence of aX-ray central compact core (CCCX) in 13/25 sources; in 3/25 sources thedetection of a CCCX is uncertain, while in the remaining 9/25 sources noCCCX is found. All the sources are embedded in a diffuse soft X-raycomponent, generally on kiloparsec scales, which is in agreement withthe halo of the host galaxy and/or with the intracluster medium. TheX-ray spectra of the cores are described by a power law with photonindices Γ=1.1-2.6. In eight sources excess absorption over theGalactic value is detected, with rest-frame column densitiesNzH~1020-1021cm-2 thus, we confirm the previous claim, based on opticaldata, that most FR I radio galaxies lack a standard optically thicktorus. We find significant correlations between the X-ray coreluminosity and the radio and optical luminosities, suggesting that atleast a fraction of the X-ray emission originates in a jet; however, theorigin of the X-rays remains ambiguous. If the X-ray emission isentirely attributed to an isotropic, accretion-related component, wefind very small Eddington ratios,Lbol/LEdd~10-3to10-8, and wecalculate the radiative efficiency to beη~10-2to10-6 on the basis of the Bondiaccretion rates from the spatial analysis. This suggests thatradiatively inefficient accretion flows are present in the cores oflow-power radio galaxies.
| The Extreme-Ultraviolet Emission in the Coma Cluster of Galaxies and the Underlying Source of this Radiation
Observations with the Extreme Ultraviolet Explorer (EUVE) have shown theComa Cluster to be a source of EUV emission in excess of that producedby X-ray gas in the cluster. We have reexamined the EUVE data on thiscluster in an attempt to obtain clues as to the origin of this emission.We find two important new results. First, the ratio between theazimuthally averaged EUV excess emission and the ROSAT hard X-ray fluxis constant as a function of distance from the cluster center outward.Second, a correlation analysis between the EUV excess emission and theX-ray emission shows that on a detailed level the EUV excess isspatially closely related to the X-ray emission. These findingscontradict previous suggestions as to the underlying source of thediffuse EUV emission in Coma and provide important information in regardto the true source of this emission. We propose a new explanation forthe source of this emission: inverse Compton scattering of microwavebackground photons by secondary electrons and positrons. We explore thispossibility in some detail and show that it is consistent with all ofthe available observational evidence. The parent cosmic-ray protons mayhave been produced by any of a number of sources, including supernovae,active galaxies, galactic winds, and cluster formation shocks, but webelieve that the most likely source is cluster formation shocks. If theEUV emission in the Coma Cluster is, in fact, the result of secondaryelectrons, this may be the only direct evidence for secondary electronsin the intracluster medium of a cluster of galaxies, since recent worksuggests that secondary electrons may not be the cause of radio halos.
| Radio and Far-Infrared Emission as Tracers of Star Formation and Active Galactic Nuclei in Nearby Cluster Galaxies
We have studied the radio and far-infrared (FIR) emission from 114galaxies in the seven nearest clusters (<100 Mpc) with prominentX-ray emission to investigate the impact of the cluster environment onthe star formation and active galactic nucleus (AGN) activity in themember galaxies. The X-ray selection criterion is adopted to focus onthe most massive and dynamically relaxed clusters. A large majority ofcluster galaxies show an excess in radio emission over that predictedfrom the radio-FIR correlation, the fraction of sources with radioexcess increases toward cluster cores, and the radial gradient in theFIR/radio flux ratio is a result of radio enhancement. Of theradio-excess sources, 70% are early-type galaxies, and the same fractionhost an AGN. The galaxy density drops by a factor of 10 from thecomposite cluster center out to 1.5 Mpc, yet galaxies show no change inFIR properties over this region and show no indication of masssegregation. We have examined in detail the physical mechanisms thatmight impact the FIR and radio emission of cluster galaxies. Whilecollisional heating of dust may be important for galaxies in clustercenters, it appears to have a negligible effect on the observed FIRemission for our sample galaxies. The correlations between radio and FIRluminosity and radius could be explained by magnetic compression fromthermal intracluster medium pressure. We also find that simple delayedharassment cannot fully account for the observed radio, FIR, and mid-IRproperties of cluster galaxies.
| Magnetic fields and Faraday rotation in clusters of galaxies
We present a numerical approach to investigate the relationship betweenmagnetic fields and Faraday rotation effects in clusters of galaxies. Wecan infer the structure and strength of intra-cluster magnetic fields bycomparing our simulations with the observed polarization properties ofextended cluster radio sources such as radio galaxies and halos. We findthe observations require a magnetic field which fluctuates over a widerange of spatial scales (at least one order of magnitude). If severalpolarized radio sources are located at different projected positions ina galaxy cluster, as is the case for A119, detailed Faraday rotationimages allow us to constrain both the magnetic field strength and theslope of the power spectrum. Our results show that the standard analyticexpressions applied in the literature overestimate the cluster magneticfield strengths by a factor of 2. We investigate the possibleeffects of our models on beam depolarization of radio sources whoseradiation traverses the magnetized intracluster medium. Finally, wepoint out that radio halos may provide important information about thespatial power spectrum of the magnetic field fluctuations on largescales. In particular, different values of the index of the powerspectrum produce very different total intensity and polarizationbrightness distributions.
| The X-ray luminosity function of galaxies in the Coma cluster
The XMM-Newton survey of the Coma cluster of galaxies covers an area of1.86 square degrees with a mosaic of 16 pointings and has a total usefulintegration time of 400 ks. Detected X-ray sources with extent less than10'' were correlated with cataloged galaxies in the Comacluster region. The redshift information, which is abundant in thisregion of the sky, allowed us to separate cluster members frombackground and foreground galaxies. For the background sources, werecover a typical Log N-Log S in the flux range10-15-10-13 ergs s-1 cm-2 inthe 0.5-2.0 keV band. The X-ray emission from the cluster galaxiesexhibits X-ray colors typical of thermal emission. The luminosities ofComa galaxies lie in the 1039-1041 ergss-1 interval in the 0.5-2.0 keV band. The luminosity functionof Coma galaxies reveals that their X-ray activity is suppressed withrespect to the field by a factor of 5.6, indicating a lower level ofX-ray emission for a given stellar mass.
| Unifying B2 radio galaxies with BL Lacertae objects
In an earlier paper we presented nuclear X-ray flux densities, measuredwith ROSAT, for the B2 bright sample of nearby low-luminosity radiogalaxies. In this paper we construct a nuclear X-ray luminosity functionfor the B2 radio galaxies, and discuss the consequences of our resultsfor models in which such radio galaxies are the parent population of BLLacertae (BL Lac) objects. Based on our observations of the B2 sample,we use Monte Carlo techniques to simulate samples of beamed radiogalaxies, and use the selection criteria of existing samples of BL Lacobjects to compare our simulated results to what is observed. We findthat previous analytical results are not applicable since the BL Lacsamples are selected on beamed flux density. A simple model in which BLLacs are the moderately beamed (γ~ 3) counterparts of radiogalaxies, with some random dispersion (~0.4 decades) in the intrinsicradio-X-ray relationship, can reproduce many of the features of theradio-selected and X-ray-selected BL Lac samples, including their radioand X-ray luminosity functions and the distributions of theirradio-to-X-ray spectral indices. In contrast, models in which the X-rayand radio emission have systematically different beaming parameterscannot reproduce important features of the radio-galaxy and BL Lacpopulations, and recently proposed models in which the radio-to-X-rayspectral index is a function of source luminosity cannot in themselvesaccount for the differences in the slopes of the radio- andX-ray-selected BL Lac luminosity functions. The redshift distributionand number counts of the X-ray-selected Einstein Medium SensitivitySurvey (EMSS) sample are well reproduced by our best models, supportinga picture in which these objects are beamed Fanaroff-Riley type I radiogalaxies with intrinsic luminosities similar to those of the B2 sample.However, we cannot match the redshift distribution of the radio-selected1-Jy sample, and it is likely that a population of Fanaroff-Riley typeII radio galaxies is responsible for the high-redshift objects in thissample, in agreement with previously reported results on the sample'sradio and optical emission-line properties.
| 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.
| Dynamical Evolution of Galaxies in Clusters
Tidal forces acting on galaxies in clusters lead to a strong dynamicalevolution. In order to quantify the amount of evolution, I runself-consistent N-body simulations of disk galaxies for a variety ofmodels in the hierarchically forming clusters. The tidal field along thegalactic orbits is extracted from the simulations of cluster formationin the Ω0=1, 0.4, and 0.4,ΩΛ=0.6 cosmological scenarios. For large spiralgalaxies with a rotation speed of 250 km s-1, tidalinteractions truncate massive dark matter halos at 30+/-6 kpc andthicken stellar disks by a factor of 2-3, increasing Toomre's parameterto Q>~2 and halting star formation. Low-density galaxies, such as thedwarf spheroidals with a circular velocity of 20 km s-1 andthe extended low surface brightness galaxies with a scale length of10-15 kpc, are completely disrupted by tidal shocks. Their debriscontribute to the diffuse intracluster light. The tidal effects aresignificant not only in the core but throughout the cluster and can beparametrized by the critical tidal density. The tidally inducedevolution results in the transformation of the infalling spirals into S0galaxies and in the depletion of the low surface brightness galaxypopulation. In the low-Ω0 cosmological models, clustersform earlier and produce stronger evolution of galaxies.
| Redshift-Distance Survey of Early-Type Galaxies: Circular-Aperture Photometry
We present R-band CCD photometry for 1332 early-type galaxies, observedas part of the ENEAR survey of peculiar motions using early-typegalaxies in the nearby universe. Circular apertures are used to tracethe surface brightness profiles, which are then fitted by atwo-component bulge-disk model. From the fits, we obtain the structuralparameters required to estimate galaxy distances using theDn-σ and fundamental plane relations. We find thatabout 12% of the galaxies are well represented by a pure r1/4law, while 87% are best fitted by a two-component model. There are 356repeated observations of 257 galaxies obtained during different runsthat are used to derive statistical corrections and bring the data to acommon system. We also use these repeated observations to estimate ourinternal errors. The accuracy of our measurements are tested by thecomparison of 354 galaxies in common with other authors. Typical errorsin our measurements are 0.011 dex for logDn, 0.064 dex forlogre, 0.086 mag arcsec-2 for<μe>, and 0.09 for mRC,comparable to those estimated by other authors. The photometric datareported here represent one of the largest high-quality and uniformall-sky samples currently available for early-type galaxies in thenearby universe, especially suitable for peculiar motion studies.Based on observations at Cerro Tololo Inter-American Observatory (CTIO),National Optical Astronomy Observatory, which is operated by theAssociation of Universities for Research in Astronomy, Inc., undercooperative agreement with the National Science Foundation (NSF);European Southern Observatory (ESO); Fred Lawrence Whipple Observatory(FLWO); and the MDM Observatory on Kitt Peak.
| Spatially resolved spectroscopy of Coma cluster early-type galaxies. III. The stellar population gradients
Based on Paper I of this series (Mehlert et al. \cite{Mehlert00}), wederive central values and logarithmic gradients for the Hβ, Mg andFe indices of 35 early-type galaxies in the Coma cluster. We find thatpure elliptical galaxies have on average slightly higher velocitydispersions, lower Hβ, and higher metallic line-strengths thangalaxies with disks (S0). The latter form two families, one comparableto the ellipticals and a second one with significantly higher Hβ,and weaker metallic lines. Our measured logarithmic gradients within theeffective radius are ~ -0.037, ~ -0.029, ~ +0.017 and ~ -0.063. The gradients strongly correlate with the gradientsof sigma , but only weakly with the central index values and galaxyvelocity dispersion. Using stellar population models with variableelement abundance ratios from Thomas et al. (\cite{Thomas03a}) we deriveaverage ages, metallicities and [α/Fe] ratios in the center and atthe effective radius. We find that the α/Fe ratio correlates withvelocity dispersion and drives 30% of the Mg-sigma relation, theremaining 70% being caused by metallicity variations. We confirmprevious findings that part of the lenticular galaxies in the Comacluster host very young ( ~ 2 Gyr) stellar populations, hence must haveexperienced relatively recent star formation episodes. Again inaccordance with previous work we derive negative metallicity gradients (~ -0.16 dex per decade) that are significantly flatter than what isexpected from gaseous monolithic collapse models, pointing to theimportance of mergers in the galaxy formation history. Moreover, themetallicity gradients correlate with the velocity dispersion gradients,confirming empirically earlier suggestions that the metallicity gradientin ellipticals is produced by the local potential well. The gradients inage are negligible, implying that no significant residual star formationhas occurred either in the center or in the outer parts of the galaxies,and that the stellar populations at different radii must have formed ata common epoch. For the first time we derive the gradients of theα/Fe ratio and find them very small on average. Hence, α/Feenhancement is not restricted to galaxy centers but it is a globalphenomenon. Our results imply that the Mg-sigma local relation inside agalaxy, unlike the global Mg-sigma relation, must be primarily drivenby metallicity variations alone. Finally we note that none of thestellar population parameters or their gradients depend on the densityprofile of the Coma cluster, even though it spans 3 dex in density.Appendix A (Tables A.1-A.3) is only available in electronic form athttp://www.edpsciences.org
| The radio halo in the merging cluster A3562
We present new VLA observations at 1.4 GHz confirming the presence of aradio halo at the centre of the cluster A3562, in the core of theShapley Concentration. We also report a detailed multifrequency radiostudy of the head tail galaxy J1333-3141, which is completely embeddedin the halo emission. The radio halo has an irregular shape, and amaximum linear size of ~ 620 kpc, which is among the smallest found inthe literature. The source has a steep spectrum, i.e. alpha843MHz 1.4 GHz ~ 2, and its total radio power, P1.4GHz ~ 2 *E23 W Hz-1, is the lowest known todate. The radio power of the halo and the X-ray parameters of thecluster, such as LX and kT, nicely fit the correlations foundin the literature for the other halo clusters, extending them to lowradio powers. We found that the total number of electrons injected inthe cluster environment by the head-tail source is enough to feed thehalo, if we assume that the galaxy has been radio active over a largefraction of its crossing time. We discuss possible origins of the radiohalo in the light of the two-phase model (Brunetti et al.\cite{Brunetti2001}) and propose that the observed scenario is theresult of a young source at the beginning of the reacceleration phase.
| The black hole mass of low redshift radiogalaxies
We make use of two empirical relations between the black hole mass andthe global properties (bulge luminosity and stellar velocity dispersion)of nearby elliptical galaxies, to infer the mass of the central blackhole (CM MBH) in low redshift radiogalaxies. Using the mostrecent determinations of black hole masses for inactive early typegalaxies we show that the bulge luminosity and the central velocitydispersion are almost equally correlated (similar scatter) with thecentral black-hole mass. Applying these relations to two large andhomogeneous datasets of radiogalaxies we find that they host black-holeswhose mass ranges from ~ 5*E7 to ~ 6*E9CMMsun (average ~ 8.9). CMMBH is found to be proportional to the mass of the bulge (CMMbulge). The distribution of the ratio CM MBH/CMMbulge has a mean value of 8*E-4 and shows ascatter that is consistent with that expected from the associatederrors. At variance with previous claims no significant correlation isinstead found between CM MBH (or CM Mbulge) andthe radio power at 5 GHz.
| 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.
| Stellar populations in early-type Coma cluster galaxies - I. The data
We present a homogeneous and high signal-to-noise ratio data set (meanS/N ratio of ~60 Å-1) of Lick/IDS stellar populationline indices and central velocity dispersions for a sample of 132 bright(bj<= 18.0) galaxies within the central 1°(≡1.26h-1 Mpc) of the nearby rich Coma cluster (A1656). Ourobservations include 73 per cent (100 out of 137) of the totalearly-type galaxy population (bj<= 18.0). Observationswere made with the William Herschel 4.2-m telescope and theAUTOFIB2/WYFFOS multi-object spectroscopy instrument (resolution of~2.2-Å FWHM) using 2.7-arcsec diameter fibres (≡0.94h-1 kpc). The data in this paper have well-characterizederrors, calculated in a rigorous and statistical way. Data are comparedwith previous studies and are demonstrated to be of high quality andwell calibrated on to the Lick/IDS system. Our data have median errorsof ~0.1 Å for atomic line indices, ~0.008 mag for molecular lineindices and 0.015 dex for velocity dispersions. This work provides awell-defined, high-quality baseline at z~ 0 for studies of medium- tohigh-redshift clusters. Subsequent papers will use this data set toprobe the stellar populations (which act as fossil records of galaxyformation and evolution) and the spectrophotometric relations of thebright early-type galaxies within the core of the Coma cluster.
| 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.
| A catalogue and analysis of local galaxy ages and metallicities
We have assembled a catalogue of relative ages, metallicities andabundance ratios for about 150 local galaxies in field, group andcluster environments. The galaxies span morphological types from cD andellipticals, to late-type spirals. Ages and metallicities were estimatedfrom high-quality published spectral line indices using Worthey &Ottaviani (1997) single stellar population evolutionary models. Theidentification of galaxy age as a fourth parameter in the fundamentalplane (Forbes, Ponman & Brown 1998) is confirmed by our largersample of ages. We investigate trends between age and metallicity, andwith other physical parameters of the galaxies, such as ellipticity,luminosity and kinematic anisotropy. We demonstrate the existence of agalaxy age-metallicity relation similar to that seen for local galacticdisc stars, whereby young galaxies have high metallicity, while oldgalaxies span a large range in metallicities. We also investigate theinfluence of environment and morphology on the galaxy age andmetallicity, especially the predictions made by semi-analytichierarchical clustering models (HCM). We confirm that non-clusterellipticals are indeed younger on average than cluster ellipticals aspredicted by the HCM models. However we also find a trend for the moreluminous galaxies to have a higher [Mg/Fe] ratio than the lowerluminosity galaxies, which is opposite to the expectation from HCMmodels.
| Cluster Magnetic Fields
Magnetic fields in the intercluster medium have been measured using avariety of techniques, including studies of synchrotron relic and haloradio sources within clusters, studies of inverse Compton X-ray emissionfrom clusters, surveys of Faraday rotation measures of polarized radiosources both within and behind clusters, and studies of cluster coldfronts in X-ray images. These measurements imply that most clusteratmospheres are substantially magnetized, with typical field strengthsof order 1 μGauss with high areal filling factors out to Mpc radii.There is likely to be considerable variation in field strengths andtopologies both within and between clusters, especially when comparingdynamically relaxed clusters to those that have recently undergone amerger. In some locations, such as the cores of cooling flow clusters,the magnetic fields reach levels of 10-40 μG and may be dynamicallyimportant. In all clusters the magnetic fields have a significant effecton energy transport in the intracluster medium. We also review currenttheories on the origin of cluster magnetic fields.
| Active Galactic Nucleus Black Hole Masses and Bolometric Luminosities
Black hole mass, along with mass accretion rate, is a fundamentalproperty of active galactic nuclei (AGNs). Black hole mass sets anapproximate upper limit to AGN energetics via the Eddington limit. Wecollect and compare all AGN black hole mass estimates from theliterature; these 177 masses are mostly based on the virial assumptionfor the broad emission lines, with the broad-line region size determinedfrom either reverberation mapping or optical luminosity. We introduce200 additional black hole mass estimates based on properties of the hostgalaxy bulges, using either the observed stellar velocity dispersion orthe fundamental plane relation to infer σ these methods assumethat AGN hosts are normal galaxies. We compare 36 cases for which blackhole mass has been generated by different methods and find, forindividual objects, a scatter as high as a couple of orders ofmagnitude. The less direct the method, the larger the discrepancy withother estimates, probably due to the large scatter in the underlyingcorrelations assumed. Using published fluxes, we calculate bolometricluminosities for 234 AGNs and investigate the relation between blackhole mass and luminosity. In contrast to other studies, we find nosignificant correlation of black hole mass with luminosity, other thanthose induced by circular reasoning in the estimation of black holemass. The Eddington limit defines an approximate upper envelope to thedistribution of luminosities, but the lower envelope depends entirely onthe sample of AGNs included. For any given black hole mass, there is arange in Eddington ratio of up to 3 orders of magnitude.
| Radio Halo Formation through Magnetoturbulent Particle Acceleration in Clusters of Galaxies
We develop a magnetoturbulent model for the cosmic-ray (CR) electronsseen in the radio halo clusters of galaxies. Steady-state momentumdistribution functions of the CR electrons are calculated for givenspectra of the turbulent Alfvén waves. The radio spectrumproduced by the obtained CR electron distribution is compared to theobserved radio spectrum of the Coma radio halo. We find that theobserved radio spectrum of the Coma Cluster is well reproduced when thespectral index of the turbulent Alfvén waves is ~2.8. Theobtained energy spectrum of the turbulent Alfvén waves is steeperthan that expected from the turbulence theory, suggesting back-reactionof the particle acceleration. The fitting procedure constraints theamplitude of the turbulent Alfvén waves as well as the spectralindex. Then we estimate the dissipation of the turbulent Alfvénwaves, which is found to be less than the cooling rate by X-rayradiation. We suggest that the turbulence that is sufficient forparticle acceleration is developed in the clusters containing the radiohalo. It is most likely that cluster mergers create the turbulence andseed relativistic electrons.
| The Orientation of Jets Relative to Dust Disks in Radio Galaxies
We use Hubble Space Telescope broadband images and VLA and VLBIcontinuum data to study the three-dimensional orientation of jetsrelative to nuclear dust disks in 20 radio galaxies. The comparisonbetween the position angles of the jets and those of the dust disk majoraxes shows a wide distribution, suggesting that they are not alignedpreferentially perpendicular to each other. We use a statisticaltechnique to determine the three-dimensional distribution of anglesbetween jets and dust disk rotation axes. This analysis shows that theobservations are consistent with jets homogeneously distributed over alarge region, extending over polar caps of 55°-77° but seemingto avoid lying close to the plane of the dust disks. We argue that thelack of close alignment between jets and dust disks axes is not likelyto be caused by feeding the nucleus with gas from mergers originatedfrom random directions. We suggest that the misalignment can be due to awarping mechanism in the accretion disk, such as self-irradiationinstability or the Bardeen-Petterson effect, or that the gravitationalpotential in the inner regions of the galaxy is misaligned with respectto that of the dust disk. Based partly on observations made with theNASA/ESA Hubble Space Telescope, which is operated by the Association ofUniversities for Research in Astronomy, Inc., under NASA contractNAS5-26555.
| Constraints Imposed by a High Magnetic Field on Models for the Extreme-Ultraviolet Emission in the Coma Cluster
A variety of models have been explored in regard to the origin of theexcess extreme-ultraviolet (~0.1 keV) emission in the Coma cluster. Itis now established that the flux is nonthermal, and the only nonthermalsource mechanism that appears viable is inverse Compton emissionproduced by ~100 MeV electrons interacting with the cosmic microwavebackground photons. All but one of the models that have been proposedrequire a cluster magnetic field less than 1 μG. However, recentobservations strongly suggest that the magnetic field in the Comacluster is ~5 μG. We investigate the constraints on models imposed bya 5 μG cluster field and find a limited class of models that arecompatible with this constraint. We also investigate the possibilitythat the excess hard (40-60 keV) X-ray emission in the cluster isproduced by inverse Compton emission with the same electron populationthat produces the EUV excess. We find no scenarios that are compatiblewith a large cluster magnetic field, and consequently, in this case,these two components must be unrelated.
| 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.
| HST images of B2 radio galaxies: A link between circum-nuclear dust and radio properties?
Almost 60% of the B2 low luminosity radio galaxies have been observedwith the Hubble Space Telescope. We present an analysis of the dustfeatures, which are often present in the form of circum-nuclear disks orlanes, and show that there are correlations between radio source anddust properties. It is found that nearby radio sources in which a jethas been detected tend to have dust more often than sources withoutjets; the dust is often in the form of disks or lanes. Moreover theradio jets are close to perpendicular to the disk or lane in the weakerradio sources (with P < 1024 WHz-1). Instronger sources the orientation effect appears to be weak or evenabsent. Also the dust masses found in the weaker radio sources aresmaller than in the stronger ones (log M/Msun ~ 3 against 5respectively). More generally it appears that there is a correlationbetween dust mass and total radio power (for those sources in which dusthas been detected); we show that this correlation is not induced byredshift. Based on observations with the NASA/ESA Hubble SpaceTelescope, obtained at the Space Telescope Science Institute, which isoperated by AURA, Inc., under NASA contract NAS 5-26555 and by STScIgrant GO-3594.01-91A.
| Spatially resolved spectroscopy of Coma cluster early-type galaxies. II. The minor axis dataset
We present minor axis, offset major axis and one diagonal long slitspectra for 10 E and S0 galaxies of the Coma cluster drawn from amagnitude-limited sample studied before. We derive rotation curves,velocity dispersion profiles and the H3 and H4coefficients of the Hermite decomposition of the line of sight velocitydistribution. Moreover, we derive the line index profiles of Mg, Fe andHβ line indices and assess their errors. The data will be used toconstruct dynamical models of the galaxies and study their stellarpopulations. Tables 3 and 4 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/395/753
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