目录
图像
上传图像
DSS Images Other Images
相关文章
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.
| A sample of X-ray emitting normal galaxies from the BMW-HRI Catalogue
We obtained a sample of 143 normal galaxies with X-ray luminosity in therange 1038{-}1043 erg s-1 from thecross-correlation of the ROSAT HRI Brera Multi-scale Wavelet (BMW-HRI)Catalogue with the Lyon-Meudon Extragalactic Database (LEDA). We findthat the average X-ray properties of this sample are in good agreementwith those of other samples of galaxies in the literature. We selected acomplete flux limited serendipitous sample of 32 galaxies from which wederived the log N-log S distribution of normal galaxies in the fluxrange 1.1{-} 110 × 10-14 erg cm-2s-1. The resulting distribution is consistent with theEuclidean -1.5 slope. Comparisons with other samples, such as theExtended Medium Sensitivity Survey, the ROSAT All Sky Survey, theXMM-Newton/2dF survey, and the Chandra Deep Field Survey indicate thatthe log N -log S distribution of normal galaxies is consistent with aEuclidean slope over a flux range of about 6 decades.
| Quantitative Morphology of Galaxies in the Core of the Coma Cluster
We present a quantitative morphological analysis of 187 galaxies in aregion covering the central 0.28 deg2 of the Coma Cluster.Structural parameters from the best-fitting Sérsicr1/n bulge plus, where appropriate, exponential disk model,are tabulated here. This sample is complete down to a magnitude of R=17mag. By examining the recent compilation by Edwards et al. of galaxyredshifts in the direction of Coma, we find that 163 of the 187 galaxiesare Coma Cluster members and that the rest are foreground and backgroundobjects. For the Coma Cluster members, we have studied differences inthe structural and kinematic properties between early- and late-typegalaxies and between the dwarf and giant galaxies. Analysis of theelliptical galaxies reveals correlations among the structural parameterssimilar to those previously found in the Virgo and Fornax Clusters.Comparing the structural properties of the Coma Cluster disk galaxieswith disk galaxies in the field, we find evidence for an environmentaldependence: the scale lengths of the disk galaxies in Coma are 30%smaller. An analysis of the kinematics shows marginal differencesbetween the velocity distributions of elliptical galaxies withSérsic index n<2 (dwarfs) and those with n>2 (giants), thedwarf galaxies having a greater (cluster) velocity dispersion. Finally,our analysis of all 421 background galaxies in the catalog of Edwards etal. reveals a nonuniform distribution in redshift with contrasts indensity of ~3, characterized by a void extending from ~10,000 to ~20,000km s-1, and two dense and extended structures centered at~20,000 and ~47,000 km s-1.
| A Comparison of the Galaxy Populations in the Coma and Distant Clusters: The Evolution of k+a Galaxies and the Role of the Intracluster Medium
The spectroscopic properties of galaxies in the Coma Cluster arecompared with those of galaxies in rich clusters at z~0.5, toinvestigate the evolution of the star formation history in clusters.Luminous galaxies with MV<=-20 andpoststarburst/post-star-forming (k+a) spectra that constitute asignificant fraction of galaxies in distant cluster samples are absentin Coma, where spectacular cases of k+a spectra are found instead atMV>-18.5 and represent a significant proportion of thecluster dwarf galaxy population. A simple inspection of their positionson the sky indicates that this type of galaxy does not show apreferential location within the cluster, but the bluest and strongestlined group of k+a galaxies lie in projection toward the central 1.4 Mpcof Coma and have radial velocities significantly higher than the clustermean. We find a striking correlation between the positions of theseyoung and strong poststarburst galaxies and substructure in the hotintracluster medium (ICM) identified from XMM-Newton data, with thesegalaxies lying close to the edges of two infalling substructures. Thisresult strongly suggests that the interaction with the dense ICM couldbe responsible for the quenching of the star formation (thus creatingthe k+a spectrum) and, possibly, for any previous starburst. Theevolution with redshift of the luminosity distribution of k+a galaxiescan be explained by a ``downsizing effect,'' with the maximumluminosity/mass of actively star-forming galaxies infalling ontoclusters decreasing at lower redshift. We discuss the possible physicalorigin of this downsizing effect and the implications of our results forcurrent scenarios of environmental effects on the star formation ingalaxies.Based on observations made with the William Herschel Telescope operatedon the island of La Palma by the Isaac Newton Group in the SpanishObservatorio del Roque de los Muchachos of the Instituto de Astrofisicade Canarias.
| 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.
| M/L, Hα Rotation Curves, and H I Measurements for 329 Nearby Cluster and Field Spirals. I. Data
A survey of 329 nearby galaxies (redshift z<0.045) has been conductedto study the distribution of mass and light within spiral galaxies overa range of environments. The 18 observed clusters and groups span arange of richness, density, and X-ray temperature and are supplementedby a set of 30 isolated field galaxies. Optical spectroscopy taken withthe 200 inch (5 m) Hale Telescope provides separately resolved Hαand [N II] major-axis rotation curves for the complete set of galaxies,which are analyzed to yield velocity widths and profile shapes, extents,and gradients. H I line profiles provide an independent velocity widthmeasurement and a measure of H I gas mass and distribution. I-bandimages are used to deconvolve profiles into disk and bulge components,to determine global luminosities and ellipticities, and to checkmorphological classification. These data are combined to form a unifieddata set ideal for the study of the effects of environment upon galaxyevolution.
| The ISOPHOT 170 μm Serendipity Survey II. The catalog of optically identified galaxies%
The ISOPHOT Serendipity Sky Survey strip-scanning measurements covering≈15% of the far-infrared (FIR) sky at 170 μm were searched forcompact sources associated with optically identified galaxies. CompactSerendipity Survey sources with a high signal-to-noise ratio in at leasttwo ISOPHOT C200 detector pixels were selected that have a positionalassociation with a galaxy identification in the NED and/or Simbaddatabases and a galaxy counterpart visible on the Digitized Sky Surveyplates. A catalog with 170 μm fluxes for more than 1900 galaxies hasbeen established, 200 of which were measured several times. The faintest170 μm fluxes reach values just below 0.5 Jy, while the brightest,already somewhat extended galaxies have fluxes up to ≈600 Jy. For thevast majority of listed galaxies, the 170 μm fluxes were measured forthe first time. While most of the galaxies are spirals, about 70 of thesources are classified as ellipticals or lenticulars. This is the onlycurrently available large-scale galaxy catalog containing a sufficientnumber of sources with 170 μm fluxes to allow further statisticalstudies of various FIR properties.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries: France, Germany, TheNetherlands and the UK) and with the participation of ISAS and NASA.Members of the Consortium on the ISOPHOT Serendipity Survey (CISS) areMPIA Heidelberg, ESA ISO SOC Villafranca, AIP Potsdam, IPAC Pasadena,Imperial College London.Full Table 4 and Table 6 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/422/39
| UV and FIR selected samples of galaxies in the local Universe. Dust extinction and star formation rates
We have built two samples of galaxies selected at 0.2 μm (hereafterUV) and 60 μm (hereafter FIR) covering a sky area of 35.36deg2. The UV selected sample contains 25 galaxies brighterthan AB0.2=17. All of them, but one elliptical, are detectedat 60 μm with a flux density larger or equal to 0.2 Jy. The UV countsare significantly lower than the Euclidean extrapolation towardsbrighter fluxes of previous determinations. The FIR selected samplecontains 42 galaxies brighter than f60=0.6 Jy. Except fourgalaxies, all of them have a UV counterpart at the limiting magnitudeAB0.2=20.3 mag. The mean extinction derived from the analysisof the FIR to UV flux ratio is 1 mag for the UV selected sample and2 mag for the FIR selected one. For each sample we compare severalindicators of the recent star formation rate (SFR) based on the FIRand/or the UV emissions. We find linear relationships with slopes closeto unity between the different SFR indicator, which means that, over thewhole converting offset. Various absolute calibrations for both samplesare discussed in this paper. A positive correlation between extinctionand SFR is found when both samples are considered together although witha considerable scatter. A similar result is obtained when using the SFRnormalized to the optical surface of the galaxies.Tables 3, 4 and Fig. 1 are only available in electronic form athttp://www.edpsciences.org
| 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.
| Spectrophotometry of galaxies in the Virgo cluster. II. The data
Drift-scan mode (3600-6800 Å) spectra with 500
| Gamma-ray line emission from galaxy clusters
We report first results of a study dedicated to a search for γ-rayline emission from rich galaxy clusters, finding traces of emission fromthe region of Virgo and Coma near the Northern Galactic Pole (NGP). Thestudy is based on the 6 years of COMPTEL data collected during theextended observational programme of the Compton Gamma Ray Observatory(CGRO) monitoring of the Virgo and 3C273 region. We point out theadvantages of performing this study using an energy range that containsthe strongest excitation γ-ray lines of 16O at 6.13,6.9 and 7.1 MeV, as well as lines at 6.175 MeV(15O*) and 6.322 MeV (15N*)of the spallation products of the cosmic ray interactions with16O. We discuss a generation mechanism for γ-ray lineemission in merging clusters via excitation of the abundant element(s)of the intracluster matter at the merger shock by the subrelativisticprotons accelerated to energies of 10 MeV to 100 MeV/n in themerger process.The COMPTEL project is supported by the BMBF through DLR grant 50 QV9096 8. AFI acknowledges financial support from the BMBF through the DLRgrant 50 OR 0002.
| 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.
| Detection of Nonrandom Galaxy Orientations in X-Ray Subclusters of the Coma Cluster
This study on the Coma Cluster suggests that there are deviations from acompletely random galaxy orientation on small scales. Since we found asignificant coincidence of hot-gas features identified in the latestX-ray observations of Coma with these local anisotropies, they mayindicate regions of recent mutual interaction of member galaxies withinsubclusters that are currently falling in on the main cluster.
| 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 dynamical state of the Coma cluster with XMM-Newton
We present in this paper a substructure and spectroimaging study of theComa cluster of galaxies based on XMM-Newton data. XMM-Newton performeda mosaic of observations of Coma to ensure a large coverage of thecluster. We add the different pointings together and fit ellipticalbeta-models to the data. We subtract the cluster models from the dataand look for residuals, which can be interpreted as substructure. Wefind several significant structures: the well-known subgroup connectedto NGC 4839 in the South-West of the cluster, and another substructurelocated between NGC 4839 and the centre of the Coma cluster.Constructing a hardness ratio image, which can be used as a temperaturemap, we see that in front of this new structure the temperature issignificantly increased (higher or equal 10 keV). We interpret thistemperature enhancement as the result of heating as this structure fallsonto the Coma cluster. We furthermore reconfirm the filament-likestructure South-East of the cluster centre. This region is significantlycooler than the mean cluster temperature. We estimate the temperature ofthis structure to be equal or below 1 keV. A possible scenario toexplain the observed features is stripping caused by the infall of asmall group of galaxies located around the two galaxies NGC 4921 and NGC4911 into the Coma cluster with a non-zero impact parameter. We also seesignificant X-ray depressions North and South-East of NGC 4921, whichmight either be linked to tidal forces due to the merger with theWestern structure or connected to an older cluster merger.Table 1 is only available in electronic form at\http://www.edpsciences.org
| A New Empirical Method for Estimating the Far-Infrared Flux of Galaxies
We propose a new empirical method to estimate the total far-infraredflux of galaxies from the spectral energy distribution (SED) atwavelengths of λ <= 100 μm. It is difficult to derive thetotal far-infrared luminosity from only the IRAS data, though it is oneof the most important properties of galaxies. Observations by InfraredTelescope in Space (IRTS) indicate that the SED of the diffuse emissionfrom the Galactic plane in this wavelength region can be derived fromthe 60 μm to 100 μm color. This empirical SED relation wasimproved in order to obtain a better fit to the Galactic plane data forIν(60 μm) / Iν(100 μm) > 0.6, andapplied to 96 IRAS galaxies for which ISOPHOT and KAO data are availableat λ > 100 μm. As a result, the empirical relation welldescribes the far-infrared (FIR) SED for a majority of galaxies.Additionally, the total FIR flux for λ >= 40 μm was derivedfrom the flux densities at 60 and 100 μm by using this model. For the96 IRAS galaxies, the uncertainty in the total far-infrared flux of thepresent method is 26%. The present method is more accurate than theprevious one widely used to derive the total infrared flux from the IRAS60 and 100 μm data.
| Evolution of Star-forming and Active Galaxies in Nearby Clusters
We have used optical spectroscopy to investigate the active galaxypopulations in a sample of 20 nearby Abell clusters. The targets wereidentified on the basis of 1.4 GHz radio emission, which identifies themas either active galactic nuclei (AGNs) or galaxies forming stars atrates comparable to or greater than that of the Milky Way. The spectrawere used to characterize the galaxies via their emission and absorptionfeatures. The spectroscopy results reveal a significant population ofstar-forming galaxies with large amounts of nuclear dust extinction.This extinction eliminates bluer emission lines such as [O II] from thespectra of these galaxies, meaning their star formation could easily beoverlooked in studies that focus on such features. Around 20% of thecluster star-forming galaxies have spectra of this type. The radialdistributions of active galaxies in clusters show a strong segregationbetween star-forming galaxies and AGNs, with star-forming galaxiesbroadly distributed and AGNs preferentially in the cluster cores. Theradial distribution of the dusty star-forming galaxies is more centrallyconcentrated than the star-forming galaxies in general, which arguesthat they are a consequence of some cluster environmental effect.Furthermore, we note that such galaxies may be identified using their4000 Å break strengths. We find that discrepancies in reportedradio luminosity functions for AGNs are likely the result ofclassification differences. There exists a large population of clustergalaxies whose radio fluxes, far-infrared fluxes, and optical magnitudessuggest their radio emission may be powered by stars yet whose spectralack emission lines. Understanding the nature of these galaxies iscritical to assessing the importance of AGNs in the radio luminosityfunction at low luminosities. We also find that regardless of thispopulation, the crossover point where the radio luminosity function iscomposed equally of star-forming galaxies and AGNs occurs at lowerluminosities in clusters than in the field. This is likely a simpleconsequence of the reduction in star formation in cluster galaxies andthe morphological mix in clusters compared with the field.Based in part on observations obtained with the Apache Point Observatory(APO) 3.5 m telescope, which is owned and operated by the AstrophysicalResearch Consortium.
| The UZC-SSRS2 Group Catalog
We apply a friends-of-friends algorithm to the combined Updated ZwickyCatalog and Southern Sky Redshift Survey to construct a catalog of 1168groups of galaxies; 411 of these groups have five or more members withinthe redshift survey. The group catalog covers 4.69 sr, and all groupsexceed the number density contrast threshold, δρ/ρ=80. Wedemonstrate that the groups catalog is homogeneous across the twounderlying redshift surveys; the catalog of groups and their membersthus provides a basis for other statistical studies of the large-scaledistribution of groups and their physical properties. The medianphysical properties of the groups are similar to those for groupsderived from independent surveys, including the ESO Key Programme andthe Las Campanas Redshift Survey. We include tables of groups and theirmembers.
| Hα surface photometry of galaxies in the Virgo cluster. IV. The current star formation in nearby clusters of galaxies
Hα +[NII] imaging observations of 369 late-type (spiral) galaxiesin the Virgo cluster and in the Coma/A1367 supercluster are analyzed,covering 3 rich nearby clusters (A1367, Coma and Virgo) and nearlyisolated galaxies in the Great-Wall. They constitute an opticallyselected sample (mp<16.0) observed with ~ 60 %completeness. These observations provide us with the current(T<107 yrs) star formation properties of galaxies that westudy as a function of the clustercentric projected distances (Theta ).The expected decrease of the star formation rate (SFR), as traced by theHα EW, with decreasing Theta is found only when galaxies brighterthan Mp ~ -19.5 are considered. Fainter objects show no orreverse trends. We also include in our analysis Near Infrared data,providing information on the old (T>109 yrs) stars. Puttogether, the young and the old stellar indicators give the ratio ofcurrently formed stars over the stars formed in the past, or``birthrate'' parameter b. For the considered galaxies we also determinethe ``global gas content'' combining HI with CO observations. We definethe ``gas deficiency'' parameter as the logarithmic difference betweenthe gas content of isolated galaxies of a given Hubble type and themeasured gas content. For the isolated objects we find that b decreaseswith increasing NIR luminosity. In other words less massive galaxies arecurrently forming stars at a higher rate than their giant counterpartswhich experienced most of their star formation activity at earliercosmological epochs. The gas-deficient objects, primarily members of theVirgo cluster, have a birthrate significantly lower than the isolatedobjects with normal gas content and of similar NIR luminosity. Thisindicates that the current star formation is regulated by the gaseouscontent of spirals. Whatever mechanism (most plausibly ram-pressurestripping) is responsible for the pattern of gas deficiency observed inspiral galaxies members of rich clusters, it also produces the observedquenching of the current star formation. A significant fraction of gas``healthy'' (i.e. with a gas deficiency parameter less than 0.4) andcurrently star forming galaxies is unexpectedly found projected near thecenter of the Virgo cluster. Their average Tully-Fisher distance isfound approximately one magnitude further away (muo = 31.77)than the distance of their gas-deficient counterparts (muo =30.85), suggesting that the gas healthy objects belong to a cloudprojected onto the cluster center, but in fact lying a few Mpc behindVirgo, thus unaffected by the dense IGM of the cluster. Based onobservations taken at the Observatorio Astronómico Nacional(Mexico), the OHP (France), Calar Alto and NOT (Spain) observatories.Table \ref{tab4} is only available in electronic form athttp://www.edpsciences.org
| A deep Hα survey of galaxies in the two nearby clusters Abell 1367 and Coma. The Hα luminosity functions
We present a deep wide field Hα imaging survey of the centralregions of the two nearby clusters of galaxies Coma and Abell 1367,taken with the WFC at the INT 2.5 m telescope. We determine for thefirst time the Schechter parameters of the Hα luminosity function(LF) of cluster galaxies. The Hα LFs of Abell 1367 and Coma arecompared with each other and with that of Virgo, estimated using the Bband LF by Sandage et al. (\cite{Sandage85}) and a L(Hα ) vs.MB relation. Typical parameters of phi * ~100.00+/-0.07 Mpc-3, L* ~1041.25+/-0.05 erg s-1 and alpha ~ -0.70+/-0.10are found for the three clusters. The best fitting parameters of thecluster LFs differ from those found for field galaxies, showing flatterslopes and lower scaling luminosities L*. Since, however, ourHα survey is significantly deeper than those of field galaxies,this result must be confirmed on similarly deep measurements of fieldgalaxies. By computing the total SFR per unit volume of clustergalaxies, and taking into account the cluster density in the localUniverse, we estimate that the contribution of clusters like Coma andAbell 1367 is approximately 0.25% of the SFR per unit volume of thelocal Universe. Appendix a is only available in electronic form athttp://www.edpsciences.org
| The colour-magnitude relation for galaxies in the Coma cluster
We present a new photometric catalogue of the Coma galaxy cluster in theJohnson U and V bands. We cover an area of 3360arcmin2 ofsky, to a depth of \fontshape{it}{V}=20\hphantom{0} mag in a13-arcsec diameter aperture, and produce magnitudes for ~1400 extendedobjects in metric apertures from 8.8- to 26-arcsec diameters. The meaninternal rms scatter in the photometry is 0.014mag in V, and 0.026mag inU, for \fontshape{it}{V}13<17\hphantom{0}mag.We place new limits on the levels of scatter in the colour-magnituderelation (CMR) in the Coma cluster, and investigate how the slope andscatter of the CMR depend on galaxy morphology, luminosity and positionwithin the cluster. As expected, the lowest levels of scatter are foundin the elliptical galaxies, while the late-type galaxies have thehighest numbers of galaxies bluewards of the CMR. We investigate whetherthe slope of the CMR is an artefact of colour gradients within galaxies,and show that it persists when the colours are measured within adiameter that scales with galaxy size. Looking at the environmentaldependence of the CMR, we find a trend of systematically bluer galaxycolours with increasing projected radius from the centre of the cluster.Surprisingly, this is accompanied by a decreased scatter of the CMR. Weinvestigate whether this gradient could be caused by dust in the clusterpotential, however the reddening required would produce too large ascatter in the colours of the central galaxies. The gradient appears tobe better reproduced by a gradient in the mean galactic ages withprojected radius.
| A Photometric and Spectroscopic Study of Dwarf and Giant Galaxies in the Coma Cluster. II. Spectroscopic Observations
This is the second paper in a series studying the photometric andspectroscopic properties of galaxies of different luminosities in theComa Cluster. We present the sample selection, spectroscopicobservations, and completeness functions. To study the spectralproperties of galaxies as a function of their local environment, twofields were selected for spectroscopic observations to cover both thecore (Coma 1) and outskirts (i.e., southwest of the core and centered onNGC 4839; Coma 3) of the cluster. To maximize the efficiency ofspectroscopic observations, two subsamples were defined, consisting of``bright'' and ``faint'' galaxies, both drawn from magnitude-limitedparent samples. Medium-resolution spectroscopy (6-9 Å) was thencarried out for a total of 490 galaxies in both fields (302 in Coma 1and 188 in Coma 3), using the WYFFOS multifiber spectrograph on theWilliam Herschel Telescope. The galaxies cover a range of 122. The completeness functions for our sampleare calculated. These show that the bright sample is 65% complete atR<17 mag, becoming increasingly incomplete toward fainter magnitudes,while the faint sample follows a monotonically decreasing completenessfunction at R>19 mag. Based on observations made with the WilliamHerschel Telescope, operated on the island of La Palma by the IsaacNewton Group in the Spanish Observatorio del Roque de los Muchachos ofthe Instituto de Astrofisica de Canarias.
| 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).
| Homogenization of the Stellar Population along Late-Type Spiral Galaxies
We present a study of the broadband UBV color profiles for 257 Sbcbarred and nonbarred galaxies, using photoelectric aperture photometrydata from the literature. Using robust statistical methods, we haveestimated the color gradients of the galaxies, as well as the total andbulge mean colors. A comparative photometric study using CCD images wasdone. In our sample, the color gradients are negative (reddish inward)in approximately 59% of the objects, are almost null in 27%, and arepositive in 14%, considering only the face-on galaxies, which representapproximately 51% of the sample. The results do not change, essentially,when we include the edge-on galaxies. As a consequence of this study wehave also found that barred galaxies are overrepresented among theobjects having null or positive gradients, indicating that bars act as amechanism of homogenization of the stellar population. This effect ismore evident in the U-B color index, although it can also be detected inthe B-V color. A correlation between the total and bulge colors wasfound that is a consequence of an underlying correlation between thecolors of bulges and disks found by other authors. Moreover, the meantotal color is the same irrespective of the gradient regime, whilebulges are bluer in galaxies with null or positive gradients, whichindicates an increase of the star formation rate in the central regionsof these objects. We have also made a quantitative evaluation of theamount of extinction in the center of these galaxies. This was doneusing the Wide Field Planetary Camera 2 (WFPC2) and the Near InfraredCamera and Multi-Object Spectrometer (NICMOS) Hubble Space Telescope(HST) archival data, as well as CCD B, V, and I images. We show thatalthough the extinction in the V-band can reach values up to 2 mag inthe central region, it is unlikely that dust plays a fundamental role inglobal color gradients. We found no correlation between color and O/Habundance gradients. This result could suggest that the color gradientsare more sensitive to the age rather than to the metallicity of thestellar population. However, the absence of this correlation may becaused by dust extinction. We discuss this result by considering apicture in which bars are a relatively fast, recurrent phenomenon. Theseresults are not compatible with a pure classical monolithic scenario forbulge and disk formation. On the contrary, they favor a scenario inwhich both these components are evolving in a correlated process inwhich stellar bars play a crucial role. Based partly on observationsmade at the Pico dos Dias Observatory (PDO/LNA-CNPq), Brazil.
| VLA HI Imaging of the brightest spiral galaxies in Coma. II. The HI Atlas and deep continuum imaging of selected early type galaxies
In the first paper of this series we used HI observations of the 19brightest spirals in Coma to analyze the dynamical state of the cluster.In this paper we present the detailed HI distribution and kinematics ofthe spirals that were detected in HI, and radio continuum data for asample of star forming and post starburst galaxies in Coma. We discussthe importance of ICM-ISM interactions to explain the observed HImorphology. A rough comparison of observed HI sizes with predicted HIsizes from simulations by Abadi et al. (\cite{Abadi99}) gives reasonableagreement. We use the results on radio continuum emission to estimatethe star formation rate in the PSB galaxies we pointed at. The radiocontinuum emission in the 11 so called post starburst galaxies,identified by Caldwell et al. (\cite{Caldwell93}) in the cluster, isweak. Eight of the 11 were not detected down to a 3 sigma upper limit of0.6 mJy. This sets an upper limit to the star formation rate in thesegalaxies of less than 0.2 Msun,yr-1. The threedetected post starburst galaxies have a star formation rate of less thanone solar mass per year. Thus none of the post starburst galaxies inComa are dust enshrouded starbursts. Appendix is only available inelectronic form at http://www.edpsciences.org
| XMM-Newton observation of the Coma Galaxy cluster. The temperature structure in the central region
We present a temperature map and a temperature profile of the centralpart (r < 20' or 1/4 virial radius) of the Coma cluster. We combined5 overlapping pointings made with XMM/EPIC/MOS and extracted spectra inboxes of 3.5'x3.5'. The temperature distribution around the two centralgalaxies is remarkably homogeneous (r<10'), contrary to previous ASCAresults, suggesting that the core is actually in a relaxed state. Atlarger distance from the cluster center we do see evidence for recentmatter accretion. We confirm the cool area in the direction of NGC 4921,probably due to gas stripped from an infalling group. We findindications of a hot front in the South West, in the direction of NGC4839, probably due to an adiabatic compression. Based on observationsobtained with XMM-Newton, an ESA science mission with instruments andcontributions directly funded by ESA Member States and the USA (NASA).EPIC was developed by the EPIC Consortium led by the PrincipalInvestigator, Dr. M. J. L. Turner. The consortium comprises thefollowing Institutes: University of Leicester, University of Birmingham,(UK); CEA/Saclay, IAS Orsay, CESR Toulouse, (France); IAAP Tuebingen,MPE Garching, (Germany); IFC Milan, ITESRE Bologna, IAUP Palermo, Italy.EPIC is funded by: PPARC, CEA, CNES, DLR and ASI.
| A mosaic of the Coma cluster of galaxies with XMM-Newton
The Coma cluster of galaxies was observed withXMM-Newton in 12 partially overlapping pointings. We present here theresulting X-ray map in different energy bands and discuss the largescale structure of this cluster. Many point sources were foundthroughout the observed area, at least 11 of them are coincident withbright galaxies. We also give a hardness ratio map at the so far highestangular resolution obtained for a cluster of galaxies. In this map wefound soft regions at the position of bright galaxies, little variationin the central 15 arcmin, but some harder regions north of the lineNGC 4874 - NGC 4889. Based onobservations with XMM-Newton, an ESA Science Mission with instrumentsand contributions directly funded by ESA Member States and the USA(NASA).
| Mid and Far IR properties of late-type galaxies in the Coma and A1367 clusters: ISOCAM and ISOPHOT observations
We present Mid (MIR) and Far (FIR) Infrared observations of 18spiral/irregular galaxies belonging to the Coma and A1367 clusters,carried out with the CAM and PHOT instruments on board the ISOsatellite. Complementary photometry from the UV to the Near Infrared(NIR) together with Hα imaging, HI and 12CO linemeasurements allow us to study the relationships between the IR emissionand the star formation properties of these galaxies. Most of theresolved galaxies show extended MIR emission throughout their disks evenwhere no Hα emission is present. This suggests that the Aromaticcarriers can be excited by the general interstellar radiation field(ISRF), i.e. by visible photons. Only close to HII regions the UVphotons are the principal sources of Aromatic carrier excitation.However, when the UV radiation field becomes intense enough thesecarriers can be destroyed. The average integrated 15/6.75 mu m ratio ofthe observed galaxies is ~ 1, i.e. the typical value for thephotodissociation regions (PDRs). This suggests that, despite the highstar formation rate (SFR) and the very luminous HII regions of thesegalaxies, their integrated MIR emission is dominated by PDR-like regionsrather than HII-like regions. A cold dust component with averagetemperature ~ 22 K exists in most of the target galaxies, probablyarising from big dust grains (BGs) in thermal equilibrium with the ISRF.The contribution to the BGs heating from the ionizing stars decreaseswith increasing wavelength. A warmer dust component whose emissiondominates the spectrum between 20 and 100 mu m is likely to exist. Thisis probably due to both Very Small Grains (VSGs) and warm BGs emission.The dust to gas ratio of the target galaxies is comparable to that ofthe solar neighborhood. There is a weak trend between the dust totalmass and both the atomic and molecular gas content. The MIR and FIRproperties of the analyzed galaxies do not seem to be affected by theenvironment despite the fact that most of the targets are interactingwith the Intra-Cluster-Medium. Based on observations with ISO, an ESAproject with instruments funded by ESA member states (especially the PIcountries: France, Germany, The Netherlands and the UK) and with theparticipation of ISAS and NASA.
| An Hα survey of eight Abell clusters: the dependence of tidally induced star formation on cluster density
We have undertaken a survey of Hα emission in a substantiallycomplete sample of CGCG galaxies of types Sa and later within 1.5 Abellradii of the centres of eight low-redshift Abell clusters (Abell 262,347, 400, 426, 569, 779, 1367 and 1656). Some 320 galaxies weresurveyed, of which 116 were detected in emission (39 per cent ofspirals, 75 per cent of peculiars). Here we present previouslyunpublished data for 243 galaxies in seven clusters. Detected emissionis classified as `compact' or `diffuse'. From an analysis of the fullsurvey sample, we confirm our previous identification of compact anddiffuse emission with circumnuclear starburst and disc emissionrespectively. The circumnuclear emission is associated either with thepresence of a bar, or with a disturbed galaxy morphology indicative ofongoing tidal interactions (whether galaxy-galaxy, galaxy-group, orgalaxy-cluster). The frequency of such tidally induced (circumnuclear)starburst emission in spirals increases from regions of lower to higherlocal galaxy surface density, and from clusters with lower to highercentral galaxy space density. The percentages of spirals classed asdisturbed and of galaxies classified as peculiar show a similar trend.These results suggest that tidal interactions for spirals are morefrequent in regions of higher local density and for clusters with highercentral galaxy density. The prevalence of such tidal interactions inclusters is expected from recent theoretical modelling of clusters witha non-static potential undergoing collapse and infall. Furthermore, inaccord with this picture, we suggest that peculiar galaxies arepredominantly ongoing mergers. We conclude that tidal interactions arelikely to be the main mechanism for the transformation of spirals to S0sin clusters. This mechanism operates more efficiently in higher densityenvironments, as is required by the morphological type-local surfacedensity (T-Σ) relation for galaxies in clusters. For regions ofcomparable local density, the frequency of tidally induced starburstemission is greater in clusters with higher central galaxy density. Thisimplies that, for a given local density, morphological transformation ofdisc galaxies proceeds more rapidly in clusters of higher central galaxydensity. This effect is considered to be the result of subclustermerging, and could account for the previously considered anomalousabsence of a significant T-Σ relation for irregular clusters atintermediate redshift.
|
提交文章
相关链接
提交链接
下列团体成员
|
观测天体数据
目录:
|
