Оглавление
Изображения
Загрузить ваше изображение
DSS Images Other Images
Публикации по объекту
Mergers of Close Primordial Binaries
We study the production of main-sequence mergers of tidally synchronizedprimordial short-period binaries. The principal ingredients of ourcalculation are the angular momentum loss rates inferred from thespin-down of open cluster stars and the distribution of binaryproperties in young open clusters. We compare our results with theexpected number of systems that experience mass transfer in thepost-main-sequence phases of evolution and compute the uncertainties inthe theoretical predictions. We estimate that main-sequence mergers canaccount for the observed number of single blue stragglers in M67.Applied to the blue straggler population, this implies that such mergersare responsible for about one-quarter of the population of halo bluemetal-poor stars and at least one-third of the blue stragglers in openclusters for systems older than 1 Gyr. The observed trends as a functionof age are consistent with a saturated angular momentum loss rate forrapidly rotating tidally synchronized systems. The predicted number ofblue stragglers from main-sequence mergers alone is comparable to thenumber observed in globular clusters, indicating that the net effect ofdynamical interactions in dense stellar environments is to reduce ratherthan increase the blue straggler population. A population of subturnoffmergers of order 3%-4% of the upper main sequence population is alsopredicted for stars older than 4 Gyr, which is roughly comparable to thesmall population of highly Li-depleted halo dwarfs. Other observationaltests are discussed.
| CIRS: Cluster Infall Regions in the Sloan Digital Sky Survey. I. Infall Patterns and Mass Profiles
We use the Fourth Data Release of the Sloan Digital Sky Survey (SDSS) totest the ubiquity of infall patterns around galaxy clusters and measurecluster mass profiles to large radii. The Cluster and Infall RegionNearby Survey (CAIRNS) found infall patterns in nine clusters, but thecluster sample was incomplete. Here we match X-ray cluster catalogs withSDSS, search for infall patterns, and compute mass profiles for acomplete sample of X-ray-selected clusters. Very clean infall patternsare apparent in most of the clusters, with the fraction decreasing withincreasing redshift due to shallower sampling. All 72 clusters in awell-defined sample limited by redshift (ensuring good sampling) andX-ray flux (excluding superpositions) show infall patterns sufficient toapply the caustic technique. This sample is by far the largest sample ofcluster mass profiles extending to large radii to date. Similar toCAIRNS, cluster infall patterns are better defined in observations thanin simulations. Further work is needed to determine the source of thisdifference. We use the infall patterns to compute mass profiles for 72clusters and compare them to model profiles. Cluster scaling relationsusing caustic masses agree well with those using X-ray or virial massestimates, confirming the reliability of the caustic technique. Weconfirm the conclusion of CAIRNS that cluster infall regions are wellfitted by Navarro-Frenk-White (NFW) and Hernquist profiles and poorlyfitted by singular isothermal spheres. This much larger sample enablesnew comparisons of cluster properties with those in simulations. Theshapes (specifically NFW concentrations) of the mass profiles agree wellwith the predictions of simulations. The mass in the infall region istypically comparable to or larger than that in the virial region.Specifically, the mass inside the turnaround radius is on average2.19+/-0.18 times that within the virial radius. This ratio agrees wellwith recent predictions from simulations of the final masses of darkmatter halos.
| The GEMS project: X-ray analysis and statistical properties of the group sample
The Group Evolution Multiwavelength Study (GEMS) involves amultiwavelength study of a sample of 60 galaxy groups, chosen to span awide range of group properties. Substantial ROSAT Position SensitiveProportional Counter (PSPC) observations, available for all of thesegroups, are used to characterize the state of the intergalactic mediumin each. We present the results of a uniform analysis of these ROSATdata and a statistical investigation of the relationship between X-rayand optical properties across the sample. Our analysis improves inseveral respects on previous work: (i) we distinguish between systems inwhich the hot gas is a group-scale medium and those in which it appearsto be just a hot halo associated with a central galaxy; (ii) weextrapolate X-ray luminosities to a fixed overdensity radius(r500) using fitted surface brightness models, in order toavoid biases arising from the fact that cooler systems are detectable tosmaller radii, and (iii) optical properties have been rederived in auniform manner from the NASA Extragalactic Database, rather than relyingon the data in the disparate collection of group catalogues from whichour systems are drawn.The steepening of the LX-TX relation in the groupregime reported previously is not seen in our sample, which fits well onto the cluster trend, albeit with large non-statistical scatter. Anumber of biases affect the fitting of regression lines under thesecircumstances, and until the impact of these has been thoroughlyinvestigated it seems best to regard the slope of the groupLX-TX relation as being poorly determined. Asignificant problem in comparing the properties of groups and clustersis the derivation of system radii, to allow different systems to becompared within regions having the same overdensity. We find evidencethat group velocity dispersion (σv) provides a veryunreliable measure of system mass (and hence radius), with a number ofgroups having remarkably low values of σv, given thatthey appear from their X-ray properties to be collapsed systems. Weconfirm that the surface brightness profiles of groups are significantlyflatter than those of clusters - the maximum value of theβfit parameter for our sample is 0.58, lower than thetypical value of 0.67 seen in clusters - however, we find no significanttendency within our sample for cooler groups to show flatter profiles.This result is inconsistent with simple universal pre-heating models.The morphology of the galaxies in the GEMS groups is correlated to theirX-ray properties in a number of ways: we confirm the very strongrelationship between X-ray emission and a dominant early-type centralgalaxy, which has been noted since the early X-ray studies of groups,and also find that spiral fraction is correlated with the temperature ofthe hot gas and hence the depth of the gravitational potential. A classof spiral-rich groups with little or no X-ray emission probablycorresponds to groups that have not yet fully collapsed.
| K-band Properties of Galaxy Clusters and Groups: Brightest Cluster Galaxies and Intracluster Light
We investigate the near-infrared K-band properties of the brightestcluster galaxies (BCGs) in a sample of 93 X-ray galaxy clusters andgroups, using data from the Two Micron All Sky Survey. Our clustersample spans a factor of 70 in mass, making it sensitive to any clustermass-related trends. We derive the cumulative radial distribution forthe BCGs in the ensemble and find that 70% of the BCGs are centered inthe cluster to within 5% of the virial radius r200; thisquantifies earlier findings that BCG position coincides with the clustercenter as defined by the X-ray emission peak. We study the correlationsbetween the luminosity of the BCGs (Lb) and the mass and theluminosity of the host clusters, finding that BCGs in more massiveclusters are more luminous than their counterparts in less massivesystems and that the BCGs become less important in the overall clusterlight (L200) as cluster mass increases. By examining a largesample of optically selected groups, we find that these correlationshold for galactic systems less massive than our clusters(<3×1013 Msolar). From the differencesbetween luminosity functions in high- and low-mass clusters, we arguethat BCGs grow in luminosity mainly by merging with other luminousgalaxies as the host clusters grow hierarchically; the decreasing BCGluminosity fraction (Lb/L200) with cluster massindicates that the rate of luminosity growth in BCGs is slow compared tothe rate at which clusters acquire galaxy light from the field or othermerging clusters. Utilizing the observed correlation between the clusterluminosity and mass and a merger tree model for cluster formation, weestimate that the amount of intracluster light (ICL) increases withcluster mass; our calculations suggest that in 1015Msolar clusters more than 50% of total stellar mass is inICL, making the role of ICL very important in the evolution andthermodynamic history of clusters. The cluster baryon fractionaccounting for the ICL is in good agreement with the value derived fromcosmic microwave background observations. The inclusion of ICL reducesthe discrepancy between the observed cluster cold baryon fraction andthat found in hydrodynamical simulations. Based on the observed ironabundance in the intracluster medium, we find that the ICL predicted byour model, together with the observed galaxy light, match the ironmass-to-light ratio expected from simple stellar population models,provided that the Salpeter initial mass function is adopted. The ICLalso makes it easier to produce the ``iron excess'' found in the centralregions of cool-core clusters.
| K-Band Properties of Galaxy Clusters and Groups: Luminosity Function, Radial Distribution, and Halo Occupation Number
We explore the near-infrared (NIR) K-band properties of galaxies within93 galaxy clusters and groups using data from the Two Micron All SkySurvey. We use X-ray properties of these clusters to pinpoint clustercenters and estimate cluster masses. By stacking all these systems, westudy the shape of the cluster luminosity function and the galaxydistribution within the clusters. We find that the galaxy profile iswell described by the Navarro, Frenk, & White (NFW) profile with aconcentration parameter c~3, with no evidence for cluster massdependence of the concentration. Using this sample, whose masses spanthe range from 3×1013 to2×1015Msolar, we confirm the existence of atight correlation between total galaxy NIR luminosity and clusterbinding mass, which indicates that NIR light can serve as a cluster massindicator. From the observed galaxy profile, together with cluster massprofile measurements from the literature, we find that the mass-to-lightratio is a weakly decreasing function of cluster radius and that itincreases with cluster mass. We also derive the mean number of galaxieswithin halos of a given mass, the halo occupation number. We find thatthe mean number scales as N~M0.84+/-0.04 for galaxiesbrighter than MK=-21, indicating that high-mass clusters havefewer galaxies per unit mass than low-mass clusters. Using publishedobservations at high redshift, we show that higher redshift clustershave higher mean occupation numbers than nearby systems of the samemass. By comparing the luminosity function and radial distribution ofgalaxies in low-mass and high-mass clusters, we show that there is amarked decrease in the number density of galaxies fainter thanM* as one moves to higher mass clusters; in addition,extremely luminous galaxies are more probable in high-mass clusters. Weexplore several processes, including tidal interactions and merging, asa way of explaining the variation in galaxy population with clustermass.
| Dust and Ionized Gas in Nine Nearby Early-Type Galaxies Imaged with the Hubble Space Telescope Advanced Camera for Surveys
We present V and I continuum images and Hα+[N II] maps of nineearly-type galaxies observed with the Wide Field Channel of the AdvancedCamera for Surveys on the Hubble Space Telescope. Dust and ionized gasare detected in all galaxies. The optical nebulae are primarilyconcentrated on the nuclei and extend out to radii of a few hundredparsecs in compact clumps, filaments, or disks. Two galaxies, NGC 6166and NGC 6338, also possess diffuse, ionized filaments on kiloparsecscales. The ionized gas is entirely contained within the nuclear disksof ESO 208-G021, NGC 3078, and NGC 7720. In the radio-loud galaxy NGC6166, emission-line filaments are detected along the radio lobes,possibly as a result of shock ionization. A wide range of ionized gasmasses, Mg~7×102-3×106Msolar, are calculated from the observed fluxes. Even in thissmall sample, the orientation of the ionized material correlates wellwith the major or minor axis of the galaxies, consistent with anexternal origin for the dust and gas.Based on observations made with the NASA/ESA Hubble Space Telescope,which is operated by the Association of Universities for Research inAstronomy (AURA), Inc., under NASA contract NAS 5-26555.
| The Birmingham-CfA cluster scaling project - II. Mass composition and distribution
We investigate the spatial distribution of the baryonic and non-baryonicmass components in a sample of 66 virialized systems. We have used X-raymeasurements to determine the deprojected temperature and densitystructure of the intergalactic medium and have employed these to map theunderlying gravitational potential. In addition, we have measured thedeprojected spatial distribution of galaxy luminosity for a subset ofthis sample, spanning over two decades in mass. With this combinedX-ray/optical study, we examine the scaling properties of the baryonsand address the issue of mass-to-light (M/L) ratio in groups andclusters of galaxies.We measure a median mass-to-light ratio of 249h70(M/L)solar in the rest frame BJband, in good agreement with other measurements based on X-raydetermined masses. There is no trend in M/L with X-ray temperature andno significant trend for mass to increase faster than luminosity:M~L1.08 +/- 0.12BJ. This implied lackof significant variation in star formation efficiency suggests that gascooling cannot be greatly enhanced in groups, unless it drops out toform baryonic dark matter. Correspondingly, our results indicate thatnon-gravitational heating must have played a significant role inestablishing the observed departure from self-similarity in low-masssystems. The median baryon fraction for our sample is 0.162h-3/270, which allows us to place an upper limiton the cosmological matter density, Ωm<= 0.27h-170, in good agreement with the latest resultsfrom WMAP.We find evidence of a systematic trend towards higher central densityconcentration in the coolest haloes, indicative of an early formationepoch and consistent with hierarchical formation models.
| The Birmingham-CfA cluster scaling project - I. Gas fraction and the M-TX relation
We have assembled a large sample of virialized systems, comprising 66galaxy clusters, groups and elliptical galaxies with high-quality X-raydata. To each system we have fitted analytical profiles describing thegas density and temperature variation with radius, corrected for theeffects of central gas cooling. We present an analysis of the scalingproperties of these systems and focus in this paper on the gasdistribution and M-TX relation. In addition to clusters andgroups, our sample includes two early-type galaxies, carefully selectedto avoid contamination from group or cluster X-ray emission. We comparethe properties of these objects with those of more massive systems andfind evidence for a systematic difference between galaxy-sized haloesand groups of a similar temperature.We derive a mean logarithmic slope of the M-TX relationwithin R200 of 1.84 +/- 0.06, although there is some evidenceof a gradual steepening in the M-TX relation, with decreasingmass. We recover a similar slope using two additional methods ofcalculating the mean temperature. Repeating the analysis with theassumption of isothermality, we find the slope changes only slightly, to1.89 +/- 0.04, but the normalization is increased by 30 per cent.Correspondingly, the mean gas fraction within R200 changesfrom (0.13 +/- 0.01) h-3/270 to (0.11+/- 0.01) h-3/270, for the isothermalcase, with the smaller fractional change reflecting different behaviourbetween hot and cool systems. There is a strong correlation between thegas fraction within 0.3R200 and temperature. This reflectsthe strong (5.8σ) trend between the gas density slope parameter,β, and temperature, which has been found in previous work.These findings are interpreted as evidence for self-similarity breakingfrom galaxy feedback processes, active galactic nuclei heating orpossibly gas cooling. We discuss the implications of our results in thecontext of a hierarchical structure formation scenario.
| X-ray bright groups and their galaxies
Combining X-ray data from the ROSAT PSPC and optical data drawn from theliterature, we examine in detail the relationship between the X-ray andoptical properties of X-ray bright galaxy groups. We find a relationshipbetween optical luminosity and X-ray temperature consistent with thatexpected from self-similar scaling of galaxy systems,LB~T1.6+/-0.2. The self-similar form andcontinuity of the LB : T relation from clusters to groups andthe limited scatter seen in this relation, implies that the starformation efficiency is rather similar in all of these systems. We findthat the bright extended X-ray components associated with many centralgalaxies in groups appear to be more closely related to the group thanthe galaxy itself, and we suggest that these are group cooling flowsrather than galaxy haloes. In addition we find that the optical light inthese groups appears to be more centrally concentrated than the light inclusters.We also use the optical and X-ray data to investigate whether early- orlate-type galaxies are primarily responsible for pre-heating in groups.Using three different methods, we conclude that spiral galaxies appearto play a comparable role to early types in the pre-heating of theintragroup medium. This tends to favour models in which the pre-heatingarises primarily from galaxy winds rather than active galactic nucleiand implies that spirals have played a significant role in the metalenrichment of the intragroup medium.
| An X-Ray Atlas of Groups of Galaxies
A search was conducted for a hot intragroup medium in 109 low-redshiftgalaxy groups observed with the ROSAT PSPC. Evidence for diffuse,extended X-ray emission is found in at least 61 groups. Approximatelyone-third of these detections have not been previously reported in theliterature. Most of the groups are detected out to less than half of thevirial radius with ROSAT. Although some spiral-rich groups do contain anintragroup medium, diffuse emission is restricted to groups that containat least one early-type galaxy.
| 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.
| 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.
| X-ray luminosities of galaxies in groups
We have derived the X-ray luminosities of a sample of galaxies ingroups, making careful allowance for contaminating intragroup emission.The LX:LB and LX:LFIRrelations of spiral galaxies in groups appear to be indistinguishablefrom those in other environments, however the elliptical galaxies fallinto two distinct classes. The first class is central-dominant groupgalaxies, which are very X-ray luminous and may be the focus of groupcooling flows. All other early-type galaxies in groups belong to thesecond class, which populates an almost constant band ofLX/LB over the range9.8
| Redshifts of CLASS Radio Sources
Spectroscopic observations of a sample of 42 flat-spectrum radio sourcesfrom the Cosmic Lens All-Sky Survey (CLASS) have yielded a mean redshiftof =1.27 with an rms spread of 0.95, at a completeness level of64%. The sample consists of sources with a 5 GHz flux density of 25-50mJy, making it the faintest flat-spectrum radio sample for which theredshift distribution has been studied. The spectra, obtained with theWilliam Herschel Telescope, consist mainly of broad-line quasars atz>1 and narrow-line galaxies at z<0.5. Though the mean redshift offlat-spectrum radio sources exhibits little variation over more than 2orders of magnitude in radio flux density, there is evidence of adecreasing fraction of quasars at weaker flux levels. We present theresults of our spectroscopic observations and discuss the implicationsfor constraining cosmological parameters with statistical analyses ofCLASS.
| The peculiar motions of early-type galaxies in two distant regions - II. The spectroscopic data
We present the spectroscopic data for the galaxies studied in the EFARproject, which is designed to measure the properties and peculiarmotions of early-type galaxies in two distant regions. We have obtained1319 spectra of 714 early-type galaxies over 33 observing runs on 10different telescopes. We describe the observations and data reductionsused to measure redshifts, velocity dispersions and the Mgb and Mg_2Lick linestrength indices. Detailed simulations and intercomparison ofthe large number of repeat observations lead to reliable error estimatesfor all quantities. The measurements from different observing runs arecalibrated to a common zero-point or scale before being combined,yielding a total of 706 redshifts, 676 velocity dispersions, 676 Mgblinestrengths and 582 Mg_2 linestrengths. The median estimated errors inthe combined measurements are Delta cz=20 km s^-1, Delta sigma sigma=9.1 per cent, Delta Mgb Mgb=7.2 per cent and Delta Mg_2=0.015 mag.Comparison of our measurements with published data sets shows nosystematic errors in the redshifts or velocity dispersions, and onlysmall zero-point corrections to bring our linestrengths on to thestandard Lick system. We have assigned galaxies to physical clusters byexamining the line-of-sight velocity distributions based on EFAR andZCAT redshifts, together with the projected distributions on the sky. Wederive mean redshifts and velocity dispersions for these clusters, whichwill be used in estimating distances and peculiar velocities and to testfor trends in the galaxy population with cluster mass. The spectroscopicparameters presented here for 706 galaxies combine high-quality data,uniform reduction and measurement procedures, and detailed erroranalysis. They form the largest single set of velocity dispersions andlinestrengths for early-type galaxies published to date.
| Far-Ultraviolet Radiation from Elliptical Galaxies
Far-ultraviolet radiation is a ubiquitous, if unanticipated, phenomenonin elliptical galaxies and early-type spiral bulges. It is the mostvariable photometric feature associated with old stellar populations.Recent observational and theoretical evidence shows that it is producedmainly by low-mass, small-envelope, helium-burning stars in extremehorizontal branch and subsequent phases of evolution. These are probablydescendants of the dominant, metal rich population of the galaxies.Their lifetime UV outputs are remarkably sensitive to their physicalproperties and hence to the age and the helium and metal abundances oftheir parents. UV spectra are therefore exceptionally promisingdiagnostics of old stellar populations, although their calibrationrequires a much improved understanding of giant branch mass loss, heliumenrichment, and atmospheric diffusion.
| Arcsecond Positions of UGC Galaxies
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.
| Mass and Metallicity of Five X-Ray-bright Galaxy Groups
We present ASCA X-ray observations of a sample of five groups selectedfrom a cross-correlation of the ROSAT All-Sky Survey with the White etal. optical catalog of groups. These X-ray-bright groups significantlyincrease the number of known systems with temperatures between 2 and 3keV. They have element abundances of roughly 0.3solar, which are typicalof clusters, but their favored ratio of Si-to-Fe abundance is lower thanthe cluster value. Combining the ASCA results with ROSAT imaging data,we calculate total masses of a few to several times 10^13 M_solar, gasmass fractions of ~10%, and baryonic mass fractions of at least 15%-20%within a radius of 0.5 Mpc. Upper limits for the ratios of gas to galaxymass and of the iron mass to galaxy luminosity overlap with the rangeobserved in rich clusters and extend to lower values, but not to suchlow values as seen in much poorer groups. These results support the ideathat groups, unlike clusters, are subject to the loss of theirprimordial and processed gas and show that this transition occurs at themass scale of the 2-3 keV groups. A discussion of ASCA calibrationissues and a comparison of ROSAT and ASCA temperatures are included inan Appendix.
| CCD Photometry of Galactic Globular Clusters. IV. The NGC 1851 RR Lyrae Variables
The variable-star population of the Galactic globular cluster NGC 1851(C0512-400) has been studied by CCD photometry, from observations madein the B, V, and I bands during 1993-1994. Light curves are presentedfor 29 variables, seven of which are new discoveries. The behavior ofthe RR Lyrae stars in the period-temperature diagram appears normal whencompared with clusters that bracket the NGC 1851 metallicity. Reddeningand metallicity are reevaluated, with no compelling evidence being foundto change from the values of E(B - V) = 0.02 and [Fe/H] = -1.29 (Zinnscale) adopted in recent studies of the cluster. Photometry is providedfor stars in an annulus with radii 80" and 260" centered on NGC 1851. Toat least V = 18.5 there is excellent agreement with the extensiveearlier photometry for the brighter NGC 1851 stars, with systematicsless than 0.02 mag in all colors. Instability-strip boundary positionsfor several clusters show a trend for the red boundary to move to reddercolors as the metallicity increases.
| Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
| Bright galaxies from WENSS. I. The minisurvey
A search for bright galaxies associated with radio sources from theWENSS minisurvey has been carried out. A galaxy counterpart was foundfor 402 of almost 10,000 radio sources. Of these a radio and opticallycomplete sample, with a flux density limit at 325 MHz of 30 mJy and alimiting red magnitude of 16, can be constructed, which contains 119galaxies. This paper is the first step of a more general study, in whichwe aim to derive a bright galaxy sample from the entire WENSS survey(which is now available in the public domain) and thus to constructpractically definitive local radio luminosity functions of ellipticaland spiral galaxies. We briefly describe the WENSS minisurvey, and thesteps that are needed for the optical identification of its radiosources. Due to the large numbers of sources involved (over 200,000)completely automated procedures are obviously needed and we discussthese in some detail. It is shown that with modern utilities projects asdescribed here have become quite feasible. Some results (e.g. apreliminary determination of the local radio luminosity function) arepresented. Table 1 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The peculiar motions of early-type galaxies in two distant regions. III - The photometric data
We present R-band CCD photometry for 776 galaxies observed in the EFARproject. The photometry is compared with photoelectric data, showingthat a common zero-point good to better than 1 per cent and a precisionof 0.03 mag per zero-point have been achieved. We give the circularlyaveraged surface brightness profiles and the photometric parameters ofthe 762 program galaxies, D(n) diameters, half-luminosity radii, totalmagnitudes, and average effective surface brightnesses. More than 80percent of the profiles have a global S/N ratio larger than 300. Theextrapolation needed to derive total magnitudes is less than 10 percentfor 80 percent of the fits. More than 80 percent of the galaxies havemean effective surface brightness larger than the observed skybrightness. In 90 percent of the profiles the estimate of thecontamination of the sky by the galaxy light is less than 1 percent. Wederive total magnitudes and half-luminosity radii to better than 0.15mag and 25 percent, respectively, for 90 percent of our sample. Incontrast, external comparisons show that data in the literature can bestrongly affected by systematic errors due to large extrapolations,small radial range, sky subtraction errors, seeing effects, and the useof a simple R exp 1/4 fit. The resulting errors can easily amount tomore than 0.5 mag in the total magnitudes and 50 percent in thehalf-luminosity radii.
| The Peculiar Motions of Early-Type Galaxies in Two Distant Regions. I. Cluster and Galaxy Selection
The EFAR project is a study of 736 candidate elliptical galaxies in 84clusters lying in two regions, toward Hercules-Corona Borealis andPerseus-Pisces-Cetus, at distances cz ~ 6000-15,000 km s^-1^. In thispaper (the first of a series), we present an introduction to the EFARproject and describe in detail the selection of the clusters andgalaxies in our sample. Fundamental data for the galaxies and clustersare given, including accurate new positions for each galaxy andredshifts for each cluster. The galaxy selection functions aredetermined by using diameters measured from Schmidt sky survey imagesfor 2185 galaxies in the cluster fields. Future papers in this serieswill present the spectroscopic and photometric observations of thissample, investigate the properties of the fundamental plane forelliptical galaxies, and determine the large- scale peculiar velocityfields in these two regions of the universe.
| The Einstein Slew Survey Sample of BL Lacertae Objects
We have used an efficient method of finding new BL Lacertae objects inthe Einstein Slew Survey suggested by Stocke et al. By exploiting theunique broadband (radio/optical/X-ray) spectra of X-ray-selected BL Lacobjects, we have identified 29 new BL Lac objects out of 32 candidatesobserved, effectively doubling the size of the Slew Survey BL Lacsample, which now includes 62 objects. Six more BL Lac candidates haveyet to be observed, and seven blank field radio sources cannot be ruledout as optically faint BL Lac objects, although this is unlikely. Thecorrect classification of one BL Lac candidate remains uncertain. Wepresent finding charts, optical spectroscopy, radio images, and opticalpolarimetry for these new BL Lac objects. Based upon nearly completeradio imaging and optical spectroscopy observations, we present thenorthern, high-latitude Slew Survey BL Lac sample, in the area boundedby δ >= -40^deg^ and |b_II| >= 15^deg^ and excluding theregion within 5^deg^ of M31. This sample contains 48 BL Lac objects,five BL Lac candidates, and five blank fields which may contain possibleBL Lac candidates. This is considerably larger than any previouscomplete sample of BL Lac objects. We compare this sample with theX-ray-selected Extended Medium-Sensitivity Survey (EMSS) sample of BLLac objects as well as the radio-selected 1 Jy sample.
| Integrated photoelectric magnitudes and color indices of bright galaxies in the Johnson UBV system
The photoelectric total magnitudes and color indices published in theThird Reference Catalogue of Bright Galaxies (RC3) are based on ananalysis of approximately equals 26,000 B, 25,000 B-V, and 17,000 U-Bmultiaperture measurements available up to mid 1987 from nearly 350sources. This paper provides the full details of the analysis andestimates of internal and external errors in the parameters. Thederivation of the parameters is based on techniques described by theVaucouleurs & Corwin (1977) whereby photoelectric multiaperture dataare fitted by mean Hubble-type-dependent curves which describe theintegral of the B-band flux and the typical B-V and U-B integrated colorgradients. A sophisticated analysis of the residuals of thesemeasurements from the curves was made to allow for the random andsystematic errors that effect such data. The result is a homogeneous setof total magnitudes BTA total colors(B-V)T and (U-B)T, and effective colors(B-V)e and (U-B)e for more than 3000 brightgalaxies in RC3.
| The ROSAT AGN content of the 87GB 5 GHz survey: bulk properties of previously optically identified sources.
The cross-correlation of the source list from the ROSAT All-Sky Surveywith the 5 GHz Green Bank survey yields a list of 2127 objects. Abouttwo thirds of them are optically unidentified. The majority of theobjects with known optical counterparts are quasars and radio galaxies,most of them detected in X-rays for the first time. In this paper wepresent a list of the previously optically identified objects with theirmain characteristics and discuss their general (bulk) properties. Wefind strong correlations between luminosities in the radio, optical, andX-ray bands which differ for quasars and radio galaxies. The fraction offlat radio spectrum sources increases with redshift and ~ 95% of allsources above z = 2 are of that type. In the relatively large group ofblazars, radio selected BL Lacs and highly polarized quasars show verysimilar properties while X-ray selected BL Lacs have markedly differentX-ray to radio flux ratios. The sample is large enough and ofsufficiently high quality to reveal clearly various detection biases andselection effects which strongly influence the physical interpretationof the correlations. Radio follow - up observations for thedetermination of the morphological and spectral properties as well asenvironmental conditions are needed for a statistically reliable studyof the sample. The very large group of sources with low radio fluxesremains to be optically identified.
| Multifrequency observations of ROSAT selected radio sources
We report on results of multifrequency radio continuum observations withthe Effelsberg 100-m telescope of 234 radio sources which havecounterparts in the ROSAT all-sky survey. Observations have been made at21 cm, 11 cm, 6 cm and 2.8 cm wavelength in the flux density range above20 mJy. We have determined the spectrum, size, linear polarization andimproved positions of these sources. We give the statistical propertiesof the ROSAT selected radio sources and compare them with results fromunbiased radio source surveys so far available. In general thedifferences are small. We find a weak excess of flat spectrum sourcesand a higher fraction of unresolved sources. Cumulative counts of theradio sources become incomplete already at a relatively high fluxdensity level. At 11 cm wavelength we have about three times lesssources at 100 mJy than expected and this deficit increases towardslower flux densities. The reason is the limited ROSAT all-sky surveysensitivity making cumulative counts of X-ray sources incomplete below10^-12^ erg/cm^2^/s. No global correlation is found between theintegrated radio flux densities and the X-ray flux densities for theentire sample. Our sample is not large enough and we do not have enoughoptical identifications for a general study of correlations for distinctgroups of radio sources. Differences are seen, however, between verysteep (α<-0.7 (Snu_{prop.to}ν^+α^)) andvery flat spectrum radio sources (α> -0.3). About 1/3 of thevery flat spectrum radio sources have an unusually small ratio of X-rayto radio emission. Most of them are quasars. The remaining flat spectrumsources show a significant correlation between their X-ray and radioflux densities. Nevertheless, the differences in the properties of radiosources, which have strong enough X-ray emission to be seen in the ROSATsurvey, and those which are not seen remain unclear.
| Spectral properties of X-ray loud extragalactic radio sources
The cross-correlation of a source catalog from the ROSAT All Sky Surveywith existing radio surveys resulted in a list of more than 2500extragalactic objects. Here, we present those X-ray objects from thecorrelations for which enough counts were accumulated in the Survey toallow for individual spectral fits. Many of them are well known X-rayemitters, others were detected in X-rays for the first time, and someremain optically unidentified. The soft X-ray spectral characteristicsof these prominent objects are discussed and compared to the statisticalproperties of the large sample of the corresponding weaker sources.
| Photoelectric and CCD photometry of E and S0 galaxies
We present BR photoelectric photometry for 352 E and S0 galaxies thatare part of a large survey of the properties and peculiar motions ofgalaxies in distant clusters. Repeat measurements show our internalerrors to be 2-3 percent in B and R and 1-2 percent in B-R. Comparisonsof BR and BVR reductions for 10 galaxies also observed in V show smallsystematic errors due to differences between the spectral energydistributions of stars and galaxies. External comparisons with B-Vcolors in the literature confirm that these colors are good to 1percent. We also describe R-band CCD observations for 95 of the galaxiesand place these on a BR photometric system for photoelectric and CCDphotomerry, with a common zero-point good to better than 1 percent. Wefind the rms precision of both our photoelectric and CCD R magnitudes tobe 2-3 percent for galaxies as faint as R = 15.
| The Einstein Slew Survey
A catalog of 819 sources detected in the Einstein IPC Slew Survey of theX-ray sky is presented; 313 of the sources were not previously known asX-ray sources. Typical count rates are 0.1 IPC count/s, roughlyequivalent to a flux of 3 x 10 exp -12 ergs/sq cm s. The sources havepositional uncertainties of 1.2 arcmin (90 percent confidence) radius,based on a subset of 452 sources identified with previously knownpointlike X-ray sources (i.e., extent less than 3 arcmin).Identifications based on a number of existing catalogs of X-ray andoptical objects are proposed for 637 of the sources, 78 percent of thesurvey (within a 3-arcmin error radius) including 133 identifications ofnew X-ray sources. A public identification data base for the Slew Surveysources will be maintained at CfA, and contributions to this data baseare invited.
|
Добавить новую статью
Внешние ссылки
- - Внешних ссылок не найдено -
Добавить внешнюю ссылку
Группы:
|
Наблюдательные данные и астрометрия
Каталоги и обозначения:
|
