Tartalom
Képek
Kép feltöltése
DSS Images Other Images
Kapcsolódó cikkek
FLASH redshift survey - I. Observations and catalogue
The FLAIR Shapley-Hydra (FLASH) redshift survey catalogue consists of4613 galaxies brighter than bJ= 16.7 (corrected for Galacticextinction) over a 700-deg2 region of sky in the generaldirection of the Local Group motion. The survey region is a70°× 10° strip spanning the sky from the ShapleySupercluster to the Hydra cluster, and contains 3141 galaxies withmeasured redshifts. Designed to explore the effect of the galaxyconcentrations in this direction (in particular the Supergalactic planeand the Shapley Supercluster) upon the Local Group motion, the 68 percent completeness allows us to sample the large-scale structure betterthan similar sparsely-sampled surveys. The survey region does notoverlap with the areas covered by ongoing wide-angle (Sloan or 2dF)complete redshift surveys. In this paper, the first in a series, wedescribe the observation and data reduction procedures, the analysis forthe redshift errors and survey completeness, and present the surveydata.
| HYPERLEDA. I. Identification and designation of galaxies
We present the new catalog of principal galaxies (PGC2003). Itconstitutes the framework of the HYPERLEDA database that supersedes theLEDA one, with more data and more capabilities. The catalog is stillrestricted to confirmed galaxies, i.e. about one million galaxies,brighter than ~18 B-mag.In order to provide the best possible identification for each galaxy wegive: accurate coordinates (typical accuracy better than 2 arcsec),diameter, axis ratio and position angle. Diameters and axis ratios havebeen homogenized to the RC2 system at the limiting surface brightness of25 B-mag arcsec-2, using a new method, the EPIDEMIC method.In order to provide the best designation for each galaxy, we collectedthe names from 50 catalogues. The compatibility of the spelling istested against NED and SIMBAD, and, as far as possible we used aspelling compatible with both. For some cases, where no consensus existsbetween NED, SIMBAD and LEDA, we propose some changes that could makethe spelling of names fully compatible.The full catalog is distributed through the CDS and can be extractedfrom HYPERLEDA.Full Tables 1 and 2 are available in electronic form athttp://www.edpsciences.orgFull Table 5 is available in electronic form at CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?/A+A/412/45
| Seeing Galaxies through Thick and Thin. IV. The Superposed Spiral Galaxies of NGC 3314
The superposed pair of spiral galaxies making up NGC 3314 offers aunique opportunity to trace the dust properties in a spiral galaxy. Weanalyze multicolor Hubble Space Telescope imaging, supported byground-based near-IR imaging and fiber-array spectroscopy, to measuredust extinction in the foreground Sc galaxy NGC 3314A, which is backlitby the Sb system NGC 3314B. The superposition allows us to measureextinctions over a wide range of galactocentric radii in the foregroundgalaxy from 0.4-4.5 kpc. In the outer half of the disk, the extinctionis strongly localized in discrete dust lanes, including some patcheswhose galactic setting is clear only because of associated Hαemission at the foreground velocity. These dust features show anextinction curve with a slope close to the Galactic mean (R=3.5+/-0.3)over a range in galactocentric radius from 1.6 to 3.8 kpc, with noradial trend. Using the I-K color of the background nucleus, we derivean extinction of AI=3.3 through the disk at a projecteddistance of 400 pc from the nucleus of NGC 3314A. The extinction in eventhe inner disk of NGC 3314A is quite patchy, since background Hαemission is detected from all parts of the system. Localanticorrelations between foreground and background line emissiondemonstrate that the dust is concentrated in star-forming regions, ashas been found for the blue light in several systems. The colors of thedust lanes in NGC 3314A that are projected only partially against thebackground disk indicate that the dust scale height in the foregrounddisk is substantially smaller than that of the stars. Thecolor-intensity behavior of the net light in these regions tracks thepredictions of a thin-layer model closely. Based on observations withthe NASA/ESA Hubble Space Telescope obtained at the Space TelescopeScience Institute, which is operated by the Association of Universitiesfor Research in Astronomy, Inc., under NASA contract NAS 5-26555.
| Possible Nova in NGC 3314
IAUC 7388 available at Central Bureau for Astronomical Telegrams.
| Seeing Galaxies through Thick and Thin. I. Optical Opacity Measures in Overlapping Galaxies
We describe the use of partially overlapping galaxies to provide directmeasurements of the effective absorption in galaxy disks, independent ofassumptions about internal disk structure. The nonoverlapping parts ofthe galaxies and symmetry considerations are used to reconstruct, viadifferential photometry, how much background galaxy light is lost inpassing through the foreground disks. Extensive catalog searches andfollow-up imaging yield ~15-25 nearby galaxy pairs suitable for varyingdegrees of our analysis; 11 of the best such examples are presentedhere. From these pairs, we find that interarm extinction is modest,declining from AB~1 mag at 0.3RB25 toessentially zero by RB25; the interarm dust has ascale length consistent with that of the disk starlight. In contrast,dust in spiral arms and resonance rings may be optically thick(AB>2) at virtually any radius. Some disks have flatterextinction curves than the Galaxy, with AB/AI~1.6this is probably the signature of clumpy dust distributions. Even thoughtypical spirals are not optically thick throughout their disks, wherethey are optically thick is correlated with where they are mostluminous: in spiral arms and inner disks. This correlation betweenabsorption and emission regions may account for their apparent surfacebrightness being only mildly dependent on inclination, erroneouslyindicating that spirals are generally optically thick. Taken as anensemble, the opacities of spiral galaxies may be just great enough tosignificantly affect QSO counts, though not enough to cause theirhigh-redshift cutoff. Based in part on archival observations with theNASA/ESA Hubble Space Telescope (HST) obtained at the Space TelescopeScience Institute, which is operated by the Association of Universitiesfor Research in Astronomy, Inc., under NASA contract NAS5-26555.
| Hα objective prism survey of Abell 1060
As part of a continuing study of the effect of cluster environment onthe star formation properties of galaxies, we have undertaken anHα objective prism survey of the nearby cluster, Abell 1060. Wedetect 33 galaxies in emission, 24 of which are cluster members. Wepresent new radial velocity measurements and Hα + [N Ii]equivalent widths and fluxes for a number of these galaxies. Wedistinguish between galaxies with diffuse and compact emission, thelatter having been associated in previous work with a disturbedmorphology of the galaxy and most likely resulting from tidally-inducedstar formation from galaxy-galaxy or cluster-galaxy interactions. Thefraction of cluster spirals in Abell 1060 detected with compact emissionagrees with the expected fraction for a cluster of its richness, asderived from results of a previous survey of 8 clusters. Some of thedetected cluster early-type spirals exhibit anomalously high globalHα equivalent widths, as compared to galaxies of similar type inthe field.
| Corrections and additions to the third reference catalogue of bright galaxies
List of corrections and additions to the Third Reference Catalogue ofBright Galaxies (RC3) are given. The corrected version of the catalogue(RC3.9b), dated April 1994, is currently available through the nationaldata centers.
| A measurement of the optical depth through a galaxy disk
The present approach to the controversy concerning the degree of dustobscuration of the disks of spiral galaxies notes that White and Keel's(1992) broadband color measurements of an overlapping galaxy pair wereunable to unambiguously separate the galaxies' respective contributions.Attention is accordingly given here to individual emission lines, whichare completely separated when the redshift difference between twogalaxies is sufficiently large. Significant optical depths are herenoted along three lines-of-sight through the foreground galaxy bycomparing H-alpha/H-beta ratios for the H II region in the backgroundgalaxy with those in isolated spiral galaxies, and then exploiting thewavelength dependence of extinction by dust.
| General study of group membership. II - Determination of nearby groups
We present a whole sky catalog of nearby groups of galaxies taken fromthe Lyon-Meudon Extragalactic Database. From the 78,000 objects in thedatabase, we extracted a sample of 6392 galaxies, complete up to thelimiting apparent magnitude B0 = 14.0. Moreover, in order to considersolely the galaxies of the local universe, all the selected galaxieshave a known recession velocity smaller than 5500 km/s. Two methods wereused in group construction: a Huchra-Geller (1982) derived percolationmethod and a Tully (1980) derived hierarchical method. Each method gaveus one catalog. These were then compared and synthesized to obtain asingle catalog containing the most reliable groups. There are 485 groupsof a least three members in the final catalog.
| H I imaging of NGC 3312 and NGC 3314a - A foreground group to the Hydra cluster?
A VLA neutral hydrogen image pointed toward the center of the Hydra I(Abell 1060) Galaxy Cluster, which is offset in velocity from thecluster mean is presented. The velocity range covers NGC 3312, NGC3314a, and a small ring galaxy. In contrast to an H I image of thespirals that are projected close to the center of Virgo, these threegalaxies are gas rich, have extended H I disks, and show signs of tidalinteractions. A comparison of the Einstein IPC data for Virgo and Hydrasuggests that the ICM density in Hydra is an order of magnitude higherthan at the location of the shrunken H I disks in Virgo. Althoughgalaxies with high relative velocities with respect to the cluster meanare expected to be close to the cluster center, the absence of anyeffects of the dense ICM on the H I distribution can most easily beunderstood if the three galaxies form a separate group, which is closeto the center of Hydra in projection only.
| Groups of galaxies within 80 Mpc. II - The catalogue of groups and group members
This paper gives a catalog of the groups and associations obtained bymeans of a revised hierarchical algorithm applied to a sample of 4143galaxies with diameters larger than 100 arcsec and redshifts smallerthan 6000 km/s. The 264 groups of galaxies obtained in this way (andwhich contain at least three sample galaxies) are listed, with the looseassociations surrounding them and the individual members of eachaggregate as well; moreover, the location of every entity among 13regions corresponding roughly to superclusters is specified. Finally,1729 galaxies belong to the groups, and 466 to the associations, i.e.,the total fraction of galaxies within the various aggregates amounts to53 percent.
| The Hydra I cluster of galaxies. V - A catalogue of galaxies in the cluster area
The available information for 581 galaxies in the area of the Hydra I (= Abell 1060) cluster is compiled into a catalog. Positions, magnitudes,diameters, position angles, radial velocities, and morphological typesare given. A first determination of the luminosity function of Hydra Iis attempted. An assessment of the photometric errors in the isophotalmagnitudes is included.
| Dynamics of the Hydra I galaxy cluster
This paper examines the dynamics of the Hydra I cluster. This clusterhas circularly symmetric galaxy and X-ray distributions, and a velocityhistogram that is close to Gaussian. However, the velocity distributionof galaxies near the cluster center is very flat. Using variousstatistical tests, the probability that the observed velocities weredrawn from a normal distribution, or from a set of spherical equilibriummodels is calculated. Based on several of the tests, the data areinconsistent with the models at the approximately 2.4 sigma level. Thepossibility that substructure is important in this cluster is thereforeconsidered. It is found that a model that is spherically symmetric atlarge radii, and clumpy at small radii, is more consistent with thekinematical data. The locations and the velocities of the brightercluster galaxies also lend support to this hypothesis. Such a model canalso explain why Hydra I does not lie along the L(x)-sigma relation forgalaxy clusters.
| The two superposed galaxies of NGC 3314
Spectroscopic data for the two superposed galaxies of NGC 3314 arepresented. The observations were carried out using the 4-meter telescopeof the Cerro Tololo Inter-American Observatory in the wavelength range6100-7000 A. Long-slit spectrograms show two sets of emission linesstemming from the superposed galaxies. The foreground galaxy, NGC 3314aappears to be a type SBbc or SBc spiral with an absolute magnitude of-20 mag and a radial velocity of 2835 + or - 15 km/s. The backgroundgalaxy, NGC 3314b, is probably an Sb type with an absolute magnitude of-20.5 mag and a radial velocity of 4641 + or - 6 km/s. It is suggestedon the basis of the observational data that at least NGC 3314a, andprobably also NGC 3314b, are members of the Hydra I cluster.
| The Hydra I cluster of galaxies. II - First results from H I observations
The number of known redshifts in the area of the Hydra I cluster hasbeen raised to 96, through the detection of 17 galaxies in the course ofH I 21-cm line observations of 42 galaxies in this field. Evidence isalso found for an increase of the H I deficiency factor radially inwardsto the center of the cluster. The cluster's distance modulus, relativeto the Virgo cluster from the blue magnitude Tully-Fisher relation is inagreement with other determinations and with the value that is based onthe ratio of cluster redshifts; a constraint to the infall velocity ofthe Local Group toward the Virgo cluster is therefore given to values ofless than 350 km/sec.
|
Új cikk hozzáadása
Kapcsolódó hivatkozások
- - (nincs kapcsolódó hivatkozás) -
Új link hozzáadása
Besorolás csoportokba:
|
Pozíciós és asztrometriai adatok
Katalógusok és elnevezések:
|
