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|The HST/ACS Coma Cluster Survey. II. Data Description and Source Catalogs|
The Coma cluster, Abell 1656, was the target of an HST-ACS Treasuryprogram designed for deep imaging in the F475W and F814W passbands.Although our survey was interrupted by the ACS instrument failure inearly 2007, the partially completed survey still covers ~50% of the corehigh-density region in Coma. Observations were performed for 25 fieldsthat extend over a wide range of cluster-centric radii (~1.75 Mpc or1°) with a total coverage area of 274 arcmin2. Themajority of the fields are located near the core region of Coma (19/25pointings) with six additional fields in the southwest region of thecluster. In this paper, we present reprocessed images and SEXTRACTORsource catalogs for our survey fields, including a detailed descriptionof the methodology used for object detection and photometry, thesubtraction of bright galaxies to measure faint underlying objects, andthe use of simulations to assess the photometric accuracy andcompleteness of our catalogs. We also use simulations to performaperture corrections for the SEXTRACTOR Kron magnitudes based only onthe measured source flux and its half-light radius. We have performedphotometry for ~73,000 unique objects; approximately one-half of ourdetections are brighter than the 10? point-source detection limitat F814W = 25.8 mag (AB). The slight majority of objects (60%) areunresolved or only marginally resolved by ACS. We estimate that Comamembers are 5%-10% of all source detections, which consist of a largepopulation of unresolved compact sources (primarily globular clustersbut also ultra-compact dwarf galaxies) and a wide variety of extendedgalaxies from a cD galaxy to dwarf low surface brightness galaxies. Thered sequence of Coma member galaxies has a color-magnitude relation witha constant slope and dispersion over 9 mag (-21 < M F814W< -13). The initial data release for the HST-ACS Coma Treasuryprogram was made available to the public in 2008 August. The images andcatalogs described in this study relate to our second data release.Based on observations with the NASA/ESA Hubble Space Telescope obtainedat the Space Telescope Science Institute, which is operated by theassociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555. These observations are associated with programGO10861.
|Star formation, starbursts and quenching across the Coma supercluster|
We analyse Spitzer Multiband Imaging Photometer (MIPS) 24-?mobservations, and Sloan Digital Sky Survey Data Release 7 opticalbroad-band photometry and spectra, to investigate the star formation(SF) properties of galaxies residing in the Coma supercluster region. Wefind that SF in dwarf galaxies is quenched only in the high-densityenvironment at the centre of clusters and groups, but that passivelyevolving massive galaxies are found in all environments, indicating thatmassive galaxies can become passive via internal processes. TheSF-density relation observed for the massive galaxies is weaker relativeto the dwarfs, but both show a trend for the fraction of star-forminggalaxies (fSF) declining to ~0 in the cluster cores. We findthat active galactic nucleus activity is also suppressed among massivegalaxies residing in the cluster cores.We present evidence for a strong dependence of the mechanism(s)responsible for quenching SF in dwarf galaxies on the cluster potential,resulting in two distinct evolutionary pathways. First, we find asignificant increase (at the 3? level) in the mean equivalentwidth of H? emission among star-forming dwarf galaxies in theinfall regions of the Coma cluster and the core of Abell 1367 withrespect to the overall supercluster population, indicative of theinfalling dwarf galaxies undergoing a starburst phase. We identify thesestarburst galaxies as the precursors of the post-starburst k + Agalaxies. Extending the survey of k + A galaxies over the wholesupercluster region, we find 11.4 per cent of all dwarf (z mag >15)galaxies in the Coma cluster and 4.8 per cent in the Abell 1367 havepost-starburst like spectra, while this fraction is just 2.1 per centwhen averaged over the entire supercluster region (excluding theclusters). This points to a cluster-specific evolutionary process inwhich infalling dwarf galaxies undergo a starburst and subsequent rapidquenching due to their passage through the dense intracluster medium. Ingalaxy groups, the SF in infalling dwarf galaxies is instead slowlyquenched due to the reduced efficiency of ram-pressure stripping.We show that in the central ~2 h-170 Mpc of theComa cluster, the (24 - z) near-infrared/mid-infrared (MIR) colour ofgalaxies is correlated with their optical (g - r) colour and H?emission, separating all MIR-detected galaxies into two distinct classesof `red' and `blue'. By analysing the spatial and velocity distributionof galaxies detected at 24?m in Coma, we find that the (optically)red 24-?m detected galaxies follow the general distribution of `all'the spectroscopic members, but their (optically) blue counterparts (i)are almost completely absent in the central ~0.5h-170 Mpc of Coma and (ii) have a remarkable peakin their velocity distribution, corresponding to the mean radialvelocity of the galaxy group NGC 4839, suggesting that a significantfraction of the `blue' MIR galaxies are currently on their first infalltowards the cluster. The implications of adopting different SF-ratetracers for quantifying evolutionary trends like the Butcher-Oemlereffect are also discussed.
|The Hubble Space Telescope Advanced Camera for Surveys Coma Cluster Survey. I. Survey Objectives and Design|
We describe the HST ACS Coma Cluster Treasury survey, a deeptwo-passband imaging survey of one of the nearest rich clusters ofgalaxies, the Coma Cluster (Abell 1656). The survey was designed tocover an area of 740 arcmin2 in regions of different densityof both galaxies and intergalactic medium within the cluster. The ACSfailure of 2007 January 27 leaves the survey 28% complete, with 21 ACSpointings (230 arcmin2) complete, and partial data for afurther four pointings (44 arcmin2). The predicted surveydepth for 10 σ detections for optimal photometry of point sourcesis g'=27.6 in the F475W filter and IC=26.8 mag inF814 (AB magnitudes). Initial simulations with artificially injectedpoint sources show 90% recovered at magnitude limits ofg'=27.55 and IC=26.65. For extended sources, thepredicted 10 σ limits for a 1 arcsec2 region areg'=25.8 mag arcsec-2 and IC=25.0 magarcsec-2. We highlight several motivating science goals ofthe survey, including study of the faint end of the cluster galaxyluminosity function, structural parameters of dwarf galaxies, stellarpopulations and their effect on colors and color gradients, evolution ofmorphological components in a dense environment, the nature ofultracompact dwarf galaxies, and globular cluster populations of clustergalaxies of a range of luminosities and types. This survey will alsoprovide a local rich cluster benchmark for various well-known globalscaling relations and explore new relations pertaining to the nuclearproperties of galaxies.Based on observations with the NASA/ESA Hubble Space Telescope obtainedat the Space Telescope Science Institute, which is operated by theassociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS5-26555. These observations are associated with programGO10861.
|A catalogue of quasars and active nuclei: 12th edition|
Aims.This catalogue is aimed at presenting a compilation of all knownAGN in a compact and convenient form and we hope that it will be usefulto all workers in this field.Methods.Like the eleventh edition, itincludes position and redshift as well as photometry (U, B, V) and 6 cmflux densities when available. We now give 20 cm rather than 11 cm fluxdensities.Results.The present version contains 85 221 quasars,1122 BL Lac objects and 21 737 active galaxies (including 9628 Seyfert1s), almost doubling the number listed in the 11th edition. We also givea list of all known lensed and double quasars.
|Infrared Luminosity Function of the Coma Cluster|
Using mid-IR and optical data, we deduce the total infrared (IR)luminosities of galaxies in the Coma Cluster and present their IRluminosity function (LF). The shape of the overall Coma IR LF does notshow significant differences from the IR LFs of the general field, whichindicates the general independence of global galaxy star formation fromenvironment up to densities ~40 times greater than in the field (wecannot test such independence above LIR~1044 ergss-1). However, a shallower faint-end slope and a smallerL*IR are found in the core region (where thedensities are still higher) compared to the outskirt region of thecluster, and most of the brightest IR galaxies are found outside thecore region. The IR LF in the NGC 4839 group region does not show anyunique characteristics. By integrating the IR LF, we find a total starformation rate in the cluster of about 97.0 Msolaryr-1. We also studied the contributions of early- andlate-type galaxies to the IR LF. The late-type galaxies dominate thebright end of the LF, and the early-type galaxies, although only makingup a small portion (~15%) of the total IR emission of the cluster,contribute greatly to the number counts of the LF atLIR<1043 ergs s-1.
|Nonthermal Hard X-Ray Emission in Galaxy Clusters Observed with the BeppoSAX PDS|
We study the X-ray emission in a sample of galaxy clusters using theBeppoSAX PDS instrument in the 20-80 keV energy band. We estimate thenonthermal hard X-ray (HXR) cluster emission by modeling the thermalcontribution from the cluster gas and the nonthermal contamination fromthe unobscured active galactic nuclei (AGNs) in the clusters. We alsoevaluate the systematic uncertainties due to the backgroundfluctuations. Assuming negligible contamination from the obscured AGNs,the resulting nonthermal component is detected at a 2 σ level in~50% of the nonsignificantly AGN-contaminated clusters: A2142, A2199,A2256, A3376, Coma, Ophiuchus, and Virgo. The data are consistent with ascenario whereby relaxed clusters have no hard X-ray component ofnonthermal origin, whereas merger clusters do, with a 20-80 keVluminosity of ~1043-1044h-250 ergs s-1. The co-added spectrumof the above clusters indicates a power-law spectrum for the HXRemission with a photon index of 2.8+0.3-0.4 in the12-115 keV band, and we find indication that it has extendeddistribution. These indications argue against significant contaminationfrom obscured AGNs, which have harder spectra and a centrallyconcentrated distribution. These results are supportive of theassumption of the merger shock acceleration of electrons in clusters,which has been proposed as a possible origin of the nonthermal hardX-ray emission models. Assuming that the cosmic microwave backgroundphotons experience inverse Compton scattering from themerger-accelerated relativistic electrons and thus produce the observedHXR, the measured hard X-ray slope corresponds to a differentialmomentum spectra of the relativistic electrons with a slope ofμ=3.8-5.0. In presence of cluster magnetic fields this relativisticelectron population produces synchrotron emission with a spectral indexof 1.4-2.1, consistent with radio halo observations of merger clusters.Thus both hard X-ray and radio observations of merger clusters areconsistent with the inverse Compton model. The observed slope of the HXRemission is also consistent with that predicted by the nonthermalbremsstrahlung, which thus cannot be ruled out by the fit to the currentdata, even though this model requires an extreme, untenable clusterenergetics. Assuming a centrally concentrated distribution of HXRemission, the data require a harder slope for the HXR spectrum, which isconsistent with secondary electron models, but this model yields a worsefit to the PDS data and thus seems to be disfavored over the primaryelectron inverse Compton model.
|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.
|Radio emission from AGN detected by the VLA FIRST survey|
Using the most recent (April 2003) version of the VLA FIRST survey radiocatalog, we have searched for radio emission from >2800 AGN takenfrom the most recent (2001) version of the Veron-Cetty and Veron AGNcatalog. These AGN lie in the 9033 square degrees of sky alreadycovered by the VLA FIRST survey. Our work has resulted in positivedetection of radio emission from 775 AGN of which 214 are new detectionsat radio wavelengths.Tables 3 and 4 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (18.104.22.168) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/416/35
|CAIRNS: The Cluster and Infall Region Nearby Survey. I. Redshifts and Mass Profiles|
The CAIRNS (Cluster and Infall Region Nearby Survey) project is aspectroscopic survey of the infall regions surrounding eight nearby,rich, X-ray-luminous clusters of galaxies. We have collected 15,654redshifts (3471 new or remeasured) within ~5-10 h-1 Mpc ofthe centers of the clusters, making it the largest study of the infallregions of clusters. We determine cluster membership and the massprofiles of the clusters based on the phase-space distribution of thegalaxies. All of the clusters display decreasing velocity dispersionprofiles. The mass profiles are fitted well by functional forms based onnumerical simulations but exclude an isothermal sphere. Specifically,NFW and Hernquist models provide good descriptions of cluster massprofiles to their turnaround radii. Our sample shows that the predictedinfall pattern is ubiquitous in rich, X-ray-luminous clusters over alarge mass range. The caustic mass estimates are in excellent agreementwith independent X-ray estimates at small radii and with virialestimates at intermediate radii. The mean ratio of the caustic mass tothe X-ray mass is 1.03+/-0.11, and the mean ratio of the caustic mass tothe virial mass (when corrected for the surface pressure term) is0.93+/-0.07. We further demonstrate that the caustic technique providesreasonable mass estimates even in merging clusters.
|The Hamburg/RASS Catalogue of optical identifications. Northern high-galactic latitude ROSAT Bright Source Catalogue X-ray sources|
We present the Hamburg/RASS Catalogue (HRC) of optical identificationsof X-ray sources at high-galactic latitude. The HRC includes all X-raysources from the ROSAT Bright Source Catalogue (RASS-BSC) with galacticlatitude |b| >=30degr and declination delta >=0degr . In thispart of the sky covering ~ 10 000 deg2 the RASS-BSC contains5341 X-ray sources. For the optical identification we used blue Schmidtprism and direct plates taken for the northern hemisphere Hamburg QuasarSurvey (HQS) which are now available in digitized form. The limitingmagnitudes are 18.5 and 20, respectively. For 82% of the selectedRASS-BSC an identification could be given. For the rest either nocounterpart was visible in the error circle or a plausibleidentification was not possible. With ~ 42% AGN represent the largestgroup of X-ray emitters, ~ 31% have a stellar counterpart, whereasgalaxies and cluster of galaxies comprise only ~ 4% and ~ 5%,respectively. In ~ 3% of the RASS-BSC sources no object was visible onour blue direct plates within 40\arcsec around the X-ray sourceposition. The catalogue is used as a source for the selection of(nearly) complete samples of the various classes of X-ray emitters.
|The Color-Magnitude Relation in Coma: Clues to the Age and Metallicity of Cluster Populations|
We have observed three fields of the Coma Cluster of galaxies with anarrowband (modified Strömgren) filter system. Observed galaxiesinclude 31 in the vicinity of NGC 4889, 48 near NGC 4874, and 60 nearNGC 4839, complete to M5500=-18 in all three subclusters.Spectrophotometric classification finds all three subclusters of Coma tobe dominated by red, E-type (elliptical/S0) galaxies with a mean bluefraction, fB, of 0.10. The blue fraction increases to fainterluminosities, possible remnants of dwarf starburst population or theeffects of dynamical friction removing bright, blue galaxies from thecluster population by mergers. We find the color-magnitude (CM) relationto be well defined and linear over the range of M5500=-13 to-22. The observational error is lower than the true scatter around theCM relation, indicating that galaxies achieve their final positions inthe mass-metallicity plane by stochastic processes. After calibration tomultimetallicity models, bright elliptical galaxies are found to haveluminosity-weighted mean [Fe/H] values between -0.5 and +0.5, whereaslow-luminosity elliptical galaxies have [Fe/H] values ranging from -2 tosolar. The lack of CM relation in our continuum color suggests that asystematic age effect cancels the metallicity effects in this bandpass.This is confirmed with our age index Δ(bz-yz), which finds a weakcorrelation between luminosity and mean stellar age in ellipticalgalaxies such that the stellar populations of bright elliptical galaxiesare 2-3 Gyrs younger than low-luminosity elliptical galaxies. Withrespect to environmental effects, there is a slight decreasingmetallicity gradient with respect to distance to each subcluster center,strongest around NGC 4874. Since NGC 4874 is the dynamic and X-raycenter of the Coma Cluster, this implies that environmental effects onlow-luminosity elliptical galaxies are strongest at the cluster corecompared with outlying subgroups.
|The Multiwavelength Quasar Survey. II. Quasars in the Coma Cluster|
This is the second paper of the series about our Multiwavelength QuasarSurvey. We present the observational results for the X-ray candidates inthe field of the Coma Cluster. Nine new X-ray active galactic nuclei arediscovered.
|The First Hour of Extragalactic Data of the Sloan Digital Sky Survey Spectroscopic Commissioning: The Coma Cluster|
On 1999 May 26, one of the Sloan Digital Sky Survey (SDSS) fiber-fedspectrographs saw astronomical first light. This was followed by thefirst spectroscopic commissioning run during the dark period of 1999June. We present here the first hour of extragalactic spectroscopy takenduring these early commissioning stages: an observation of the Comacluster of galaxies. Our data samples the southern part of this cluster,out to a radius of 1.5d (1.8 h-1 Mpc, approximately to thevirial radius) and thus fully covers the NGC 4839 group. We outline inthis paper the main characteristics of the SDSS spectroscopic systemsand provide redshifts and spectral classifications for 196 Comagalaxies, of which 45 redshifts are new. For the 151 galaxies in commonwith the literature, we find excellent agreement between our redshiftdeterminations and the published values, e.g., for the largesthomogeneous sample of galaxies in common (63 galaxies observed byColless & Dunn) we find a mean offset of 3 km s -1 and anrms scatter of only 24 km s -1. As part of our analysis, wehave investigated four different spectral classification algorithms:measurements of the spectral line strengths, a principal componentdecomposition, a wavelet analysis and the fitting of spectral synthesismodels to the data. We find that these classification schemes are inbroad agreement and can provide physical insight into the evolutionaryhistories of our cluster galaxies. We find that a significant fraction(25%) of our observed Coma galaxies show signs of recent star formationactivity and that the velocity dispersion of these active galaxies(emission-line and poststarburst galaxies) is 30% larger than theabsorption-line galaxies. We also find no active galaxies within thecentral (projected) 200 h-1 kpc of the cluster. The spatialdistribution of our Coma active galaxies is consistent with that foundat higher redshift for the CNOC1 cluster survey. Beyond the core region,the fraction of bright active galaxies appears to rise slowly out to thevirial radius and are randomly distributed within the cluster with noapparent correlation with the potential merger or postmerger of the NGC4839 group. We briefly discuss possible origins of this recent galaxystar formation.
|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-Infrared Emission from E+A Galaxies in the Coma Cluster|
We have used ISO to observe at 12 μm seven E+A galaxies plus anadditional emission-line galaxy, all in the Coma Cluster. E+A galaxieslacking narrow emission lines have 2.2-12 μm flux density ratios orlimits similar to old stellar populations (typical of early-typegalaxies). Only galaxies with emission lines have enhanced 12 μm fluxdensity. Excess 12 μm emission is therefore correlated with thepresence of ongoing star formation or an active galactic nucleus (AGN).From the mid- and far-infrared colors of the brightest galaxy in oursample, which was detected at longer wavelengths with IRAS, we estimatethe far-infrared luminosity of these galaxies. By comparing the currentstar formation rates with previous rates estimated from the Balmerabsorption features, we divide the galaxies into two groups: those forwhich star formation has declined significantly following a dramaticpeak ~1 Gyr ago; and those with a significant level of ongoing starformation or/and an AGN. There is no strong difference in the spatialdistribution on the sky between these two groups. However, the firstgroup has systemic velocities above the mean cluster value and thesecond group has systemic velocities below that value. This suggeststhat the two groups differ kinematically. Based on surveys of the ComaCluster in the radio, the IRAS sources, and galaxies detected inHα emission, we sum the far-infrared luminosity function ofgalaxies in the cluster. We find that star formation in late-typegalaxies is probably the dominant component of the Coma Clusterfar-infrared luminosity. The presence of significant emission fromintracluster dust is not yet firmly established. The member galaxiesalso account for most of the far-infrared output from nearby richclusters in general. We update estimates of the far-infraredluminosities of nearby, rich clusters and show that such clusters arelikely to undergo luminosity evolution from z=0.4 at a rate similar to,or faster than, field galaxies.
|The Universality of the Fundamental Plane of E and S0 Galaxies: Sample Definition and I-Band Photometric Data|
As part of a project to compare the fundamental plane and Tully-Fisherdistance scales, we present here I-band CCD photometry for 636early-type galaxies in eight clusters and groups of galaxies. These arethe A262, A1367, Coma (A1656), A2634, Cancer and Pegasus Clusters, andthe NGC 383 and NGC 507 Groups. Sample selection, cluster properties,and cluster membership assignment criteria are discussed. We presentphotometric parameters that are used in the fundamental plane relation,the effective radius r_e, and the effective surface brightness mu_e, asderived from a r^1/4 fit to the observed radial photometric profile ofeach galaxy. A comparison with similar data found in the literature forthe Coma Cluster shows that large systematic uncertainties can beintroduced in the measurement of r_e and mu_e by the particular methodused to derive those parameters. However, the particular combination ofthese two parameters that enters in the fundamental plane relation is aquantity that can be measured with high accuracy.
|Morphological classification and structural parameters of galaxies in the Coma and Perseus clusters|
We present the results of an isophotal shape analysis of galaxies in theComa and Perseus clusters. These data, together with those of twoprevious papers, provide two complete samples of galaxies with reliableHubble types in rich clusters: 1) all galaxies brighter than m_b = 16.5falling within one degree (=2.3 Mpc) from the center of the Coma cluster(187 galaxies), 2) all galaxies brighter than m_Zwicky=15.7 in a regionof 5 degr 3' times 5 degr 27' around the center of the Perseus cluster(139 galaxies). These two complete samples cover 5 orders of magnitudein galaxy density and span areas of 91 and 17 Mpc^2, clustercentricradii up to 6.4 and 2.3 Mpc, for Perseus and Coma respectively. Theywill be used in subsequent papers to study the dependence of galaxytypes on cluster environment and as reference samples in comparisonswith distant clusters. Based on observations made with the 2-meterTelescope Bernard Lyot of Pic-du-Midi Observatory, operated by INSU(CNRS) and the Schmidt telescope at the Calern Observatory (OCA). Alltables are only available in electronic form at the CDS anonymous ftp tocdsarc.u-strasbg.fr (22.214.171.124) or viahttp://cdsweb.u-strasbg.fr/Abstract.html.
|1.65μm (H-band) surface photometry of galaxies. II. Observations of 297 galaxies with the TIRGO 1.5m telescope.|
We present near-infrared H-band (1.65μm) surface photometry of 297galaxies (mostly) in the Coma Supercluster obtained with the ArcetriNICMOS3 camera, ARNICA, mounted on the Gornergrat Infrared Telescope.Magnitudes and diameters within the 21.5mag/arcsec^2^ isophote,concentration indices, and total H magnitudes are derived. Combiningthese observations with those obtained similarly using the Calar Altotelescopes (Paper I, 1996A&AS..120..489G) we find a strong positivecorrelation between the near-infrared concentration index and the galaxyH-band luminosity, and we analyze the consequent dependence ofnear-infrared growth-curves on H-band luminosity.
|An image database. II. Catalogue between δ=-30deg and δ=70deg.|
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
|Morphological classification and structural parameters for early-type galaxies in the Coma cluster.|
We present the results of an isophotal shape analysis of three samplesof galaxies in the Coma cluster. Quantitative morphology, together withstructural and photometric parameters, is given for each galaxy. Specialemphasis has been placed on the detailed classification of early-typegalaxies. The three samples are: i) a sample of 97 early-type galaxiesbrighter than m_B_=17.00 falling within one degree from the center ofthe Coma cluster; these galaxies were observed with CCD cameras, mostlyin good to excellent resolution conditions; ii) a magnitude completesample of 107 galaxies of all morphological types down to m_B_=17.00falling in a circular region of 50arcmin diameter, slightly offcenteredto the North-West of the cluster center; the images for this and thenext sample come from digitized photographic plates; iii) a completecomparison sample of 26 galaxies of all morphological types down tom_R_=16.05 (or m_B_=~17.5), also in a region of 50arcmin diameter, butcentered 2.6degrees West of the cluster center. The reliability of ourmorphological classifications and structural parameters of galaxies,down to the adopted magnitude limits, is assessed by comparing theresults on those galaxies for which we had images taken with differentinstrumentation and/or seeing conditions, and by comparing our resultswith similar data from other observers.
|Spatial Distribution of the Starbursts in Post-Starburst Coma Cluster Galaxies|
We present long-slit spectra and multicolor CCD images which demonstratethat the strong star formation episodes that occurred in the post-starburst galaxies in the Coma Cluster and two field galaxies were notrestricted to the central regions of the galaxies. Rather, the remnantyoung stars from the starbursts are found to be distributed over a largeradius, though changes in the relative strength of the old and youngcomponents with radius are evident in a few cases. The Coma galaxies areshown to have exponential disk profiles, and the spectra provide furtherkinematical evidence that the galaxies are rotating systems, indicatingthat the galaxies are not ellipticals. The starburst material alsoappears to be distributed in disks. Such information places constraintson models for the starbursts that involve mergers. Population models arediscussed in a companion paper, which show that the post-starburstspectra in these particular galaxies can not be reproduced by normalspiral-like star formation which simply ceased, but rather are due to aburst of star formation which ceased ~1 Gyr ago and which presentlyaccount for ~60% of the light at 4000 A. Curiously, an on-goingstarburst galaxy, previously identified in Caldwell et al. [AJ,106,413(1993)] and also observed here, has its vigorous star formationisolated to its bulge region. The associated ionized gas shows peculiarkinematics, when compared to the gas located in the disk. Of four otherComa early-type galaxies with ionized gas studied here, two are shown tohave emission spectra characteristic of active galactic nuclei, whiletwo have spectra showing a mixture of H II region and AGN spectra.
|Galaxy Properties at the North Galactic Pole. I. Photometric Properties on Large Spatial Scales|
A two-color study of the galaxies detected on POSS-I in a 289 squaredegree region centered on the North Galactic Pole is presented. We use avariety of mapping techniques to characterize the large-scale spatialdistribution of galaxies. The depth and sample size of this new surveyallows, for the first time, the isolation of large photometricsubsamples of galaxies in high- and low-density environments on thescale of superclusters. Our principal finding is a statisticallysignificant difference between the mean photometric properties of thesesubsamples in the sense that galaxies in the high-density Coma andfilament environments have redder colors and larger concentrationindices than galaxies drawn from low-density interfilament regions.These results are in accord with the known morphology-density relation.Thus, appropriately chosen photometric and morphological parameters, inconcert with a galaxy surface density map, can be used to selectstructures from the projected galaxy distribution which correspond toregions of high density. An illustration of this point is our discoveryof a concentration of blue galaxies identified in our maps near the coreof the Coma cluster. This feature is comprised of early-type galaxieswhich exhibit signs of current or recent star formation. These resultsare predicated on relations between morphological type and photometricparameters derived from APS scans of POSS-I. We therefore discuss theimage calibration procedures used to compile our catalog of physicallysignificant photometric parameters. We demonstrate the morphologicaltype dependence among quantities such as mean color and imageconcentration index, and the lack of such a dependence for mean surfacebrightness.
|Ultraviolet observations of galaxies in nearby clusters. III. Star-forming galaxies in the Coma cluster.|
In a field of 1deg radius centered in the Coma cluster of galaxies, UV(λ=2000A) observations with a 40-cm balloon-borne imagingtelescope (FOCA) have provided a list of 442 UV sources brighter thanm_UV_=18, which are identified in the Godwin et al. (1983) catalogue.254 are identified as galaxies, 178 as star-like objects and 10 asgalaxy-star pairs, unresolved in the UV image. The 254 galaxies fallinto two sub-groups. The galaxies brighter than b=17 define a sequencein the (b-r,m_UV_-b) color-color diagram which is well fitted by themodels of Bruzual & Charlot (1993); most are cluster members. Thegalaxies fainter than b=17 show distinctly (m_UV_-b) colors bluer thanthe former group at the same (b-r); most of them are likely backgroundlate-type galaxies. Notably, a significant fraction of the 178 star-likeobjects have UV magnitudes and colors similar to that of the secondgroup of galaxies; ground-based spectroscopy is required to determinetheir nature and/or membership. In the UV sample, 61 galaxies haveradial velocities consistent with cluster membership. Among them, nearlyhalf are blue (m_UV_-b<1), star-forming galaxies. Their cumulated UVfluxes lead to a star formation rate of ~23h^-2^Msun_/yr.Their velocity distribution shows an unexpected concentration near 7500km/s and a void in the 6000-7000km/s range. The other half contains redgalaxies (m_UV_-b>1) with little or no recent star formation. Allearly-type galaxies brighter than b=14.5 are detected in UV and have amedian color (m_UV_-b)=3.0 in agreement with the representative spectraldistribution of an elliptical compiled from IUE. 17 early-types galaxieswhich have spectroscopic data in the sample of Caldwell et al. (1993)show a correlation between the (m_UV_-b) color and the Hδ(absorption line) equivalent width; some, with (m_UV_-b)<1, wouldimply that the last starburst event is younger than 1 Gyr or that aresidual star-formation is still present. The median UV flux and thefraction of blue star-forming galaxies which are cluster members show anenhancement at ~25'(0.5h^-1^Mpc) from the cluster center, suggestingthat a global physical process might induce star formation in a richcluster such as Coma.
|A catalogue of velocities in the central regions of the Coma cluster.|
We present a catalogue of velocities for 305 objects in a field of48x25arcmin^2^, centered between the galaxies NGC 4889 and NGC 4874, aswell as in a field of 10x10arcmin^2^ centered on NGC 4839, in the Comacluster. Of these velocities, 225 are new measurements, 78 of which forobjects with at least one velocity already available in the literaturebefore our survey. Our sample is 95% complete in redshift up to amagnitude b_26.5_=18.0.
|The nature of E and S0 galaxies: A study of magnitude-limited sample of galaxies in the Coma Cluster|
Differences and similarities of E and S0 galaxies have been investigatedon basis of new CCD surface photometry in Gunn r for 171 galaxies withinthe central square degree of the Coma Cluster; 146 of the galaxies areclassified as E or S0. The galaxies form a magnitude-limited sample withGunn r less than or equal to 15.3 mag. Together with the sample of Virgogalaxies compiled by Caon et al. (1993), this sample is one of the firstvolume-limited samples. The isophotal shapes of the galaxies have beenstudied in terms of ellipticity, c4 and c6. Thesample is deficit of apparently round S0 galaxies. The distribution ofthe apparent ellipticities for the S0 galaxies cannot be fittedsatisfactorily with any simple distribution of the intrinsicellipticities. This suggests that face-on S0 galaxies have beenclassified as ellipticals. It is shown that theellipticity-c4 diagram can be used for determination ofrelative disk luminosities, LD/Ltot. Thedistribution of LD/Ltot for galaxies fainter thanMB(sub T) = -22 mag is very broad (H0 = 50 km/(sMpc) is used). The distribution is best fitted by a model where 10% ofthe galaxies are diskless and 90% of the galaxies are drawn from adistribution which is uniform from zero to one. This model also predictsdistributions of apparent ellipticities, c4, and inclinationswhich are in agreement with the data. E galaxies brighter thanMB(sub T) = -22 mag do not show any evidence of disks and mayform another class. The sample contains no S0 galaxies brighter thanMB(sub T) = -22 mag. Our analysis implies that the E and S0galaxies fainter than MB(sub T) = -22 mag form one class ofgalaxies with a continuous change in LD/Ltot.Face-on members of this class are mostly classified as E galaxies whilemore edge-on members are classified as S0 galaxies. Further, it is foundthat only 12% of all the galaxies in the sample are truly disklesssystems. The diskless systems contribute approximately 30% to the totalluminosity of the sample, most of this originates from the six brightestgalaxies.
|Star formation in early-type galaxies in the Coma cluster|
The Hydra bench spectrograph on the 4 m telescope at Kitt Peak is usedto obtain multifiber spectra of 125 early-type galaxies in the Comacluster of galaxies. About one-third of all galaxies in a field locatedabout 40 arcmin SW of the center of the cluster exhibits enhanced Balmerabsorption lines or emission lines, indicative of recent star formationor nuclear activity. In contrast, very few such galaxies are found inthe central field of the cluster. It is argued that the anomalousspectral features cannot arise from morphological misidentifications. Itis suggested that an environmental process similar to that frequentlyfound in clusters at moderate redshift is occurring at the present epochin the outskirts of the Coma cluster.
|A catalog of 1268 radial velocities in 15 rich clusters|
Abstract image available at:http://adsabs.harvard.edu/abs/1988AJ.....95..284D
|The Coma Cluster - Part One - a Catalogue of Magnitudes Colours Ellipticities and Position Angles for 6724 Galaxies in the Field of the Coma Cluster|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1983MNRAS.202..113G&db_key=AST
|A catalog of morphological types in 55 rich clusters of galaxies|
Data are presented from a study of 55 rich clusters of galaxies. Thedata include positions, morphological types, estimated total magnitudes,bulge sizes, and ellipticities for about 6000 galaxies, as determinedfrom high scale photographic plates. Data reduction procedures aredescribed, and a brief analysis of cluster richness, which indicatesthat Abell richness classes are only rough indicators of total clustermembership, is included.
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