Contenuti
Immagini
Carica la tua immagine
DSS Images Other Images
Articoli relazionati
The UZC-SSRS2 Group Catalog
We apply a friends-of-friends algorithm to the combined Updated ZwickyCatalog and Southern Sky Redshift Survey to construct a catalog of 1168groups of galaxies; 411 of these groups have five or more members withinthe redshift survey. The group catalog covers 4.69 sr, and all groupsexceed the number density contrast threshold, δρ/ρ=80. Wedemonstrate that the groups catalog is homogeneous across the twounderlying redshift surveys; the catalog of groups and their membersthus provides a basis for other statistical studies of the large-scaledistribution of groups and their physical properties. The medianphysical properties of the groups are similar to those for groupsderived from independent surveys, including the ESO Key Programme andthe Las Campanas Redshift Survey. We include tables of groups and theirmembers.
| The Nuclear Activity of Galaxies in the Hickson Compact Groups
In order to investigate the nuclear activity of galaxies residing incompact groups of galaxies, we present results of our opticalspectroscopic program made at Okayama Astrophysical Observatory. We haveperformed optical spectroscopy of 69 galaxies belonging to 31 Hicksoncompact groups (HCGs) of galaxies. Among them, three galaxies havediscordant redshifts and, moreover, spectral quality is too poor toclassify another three galaxies. Therefore, we describe our results forthe remaining 63 galaxies. Our main results are summarized as follows:(1) We have found in our sample 28 active galactic nuclei (AGNs), 16 HII nuclei, and 19 normal galaxies showing no emission line. We used thisHCG sample for statistical analyses. (2) Comparing the frequencydistributions of activity types between the HCGs and the field galaxieswhose data are taken from Ho, Filippenko, & Sargent (382 fieldgalaxies), we find that the frequency of H II nuclei in the HCGs issignificantly less than that in the field. However, this difference maybe due to selection bias to the effect that our HCG sample contains moreearly-type galaxies than the field, because it is known that H II nucleiare rarer in early-type galaxies than in later ones. (3) Applying acorrection to this morphological bias to the HCG sample, we find thatthere is no statistically significant difference in the frequency ofoccurrence of emission-line galaxies between the HCGs and the field.This implies that the dense galaxy environment in the HCGs does notaffect the triggering of either the AGN activity and the nuclearstarburst. We discuss some implications on the nuclear activity in theHCG galaxies.
| An H_alpha catalogue of galaxies in Hickson compact groups. I. The sample
We present H_alpha photometry for a sample of 95 galaxies in HicksonCompact Groups obtained from observations of 31 groups. The Cataloguelists isophotal and adaptive aperture (Kron aperture) flux measurementsfor about 75% of the accordant galaxies inside the observed HCGs, 22 outof which are upper limits. Non standard data reduction procedures havebeen used to obtain the continuum subtracted H_alpha images for each HCGof the target sample. Flux calibration has also been performed in orderto obtain H_alpha luminosities for the whole sample. Both the datareduction and calibration procedures are carefully described in thispaper. The new data listed in this Catalogue are of great importance inunderstanding the star formation rate inside HCG galaxies and in givingnew insights on its dependence on galaxy interactions. Tables 3 to 10and Figs. 6 to 11 are only available in electronic version athttp://www.edpsciences.com Tables 7, 8, 9 are also available inelectronic version form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Far infrared properties of Hickson compact groups of galaxies. I. High resolution IRAS maps and fluxes.
The Far Infrared (FIR) properties of galaxies which are members ofcompact groups bear relevant information on the dynamical status and thephysical properties of these structures. All studies published so farhave been undermined by the poor sensitivity and spatial resolution ofthe IRAS-PSC and IRAS Sky Survey data. We used the HIRAS softwareavailable at the IRAS server at the Laboratory for Space Research inGroningen to fully exploit the redundancy of the IRAS data and toapproach the theoretical diffraction limit of IRAS. Among the 97 groupswhich were observed by IRAS, 62 were detected in at least one band,while reliable upper limits were derived for all the others. Among thedetected groups, 49 were fully or partially resolved, i.e. it waspossible to discriminate which member or members emit most of the FIRlight. At 60μm, for instance, 87 individual sources were detected in62 groups. In order to ease the comparison with data obtained at otherwavelengths - and in particular in the X and radio domains - we giveco-added and HIRAS maps for all the detected groups.
| The CfA Redshift Survey: Data for the NGP +36 Zone
We have assembled redshifts for a complete sample of 719 galaxies withm_zw_ <= 15.5 in the declination range 32.5^deg^ <= δ <=38.5^deg^ and right ascension range 8^h^ <= α <= 17^h^. Wehave determined morphological types for all galaxies in the magnitudelimited sample by direct inspection of the POSS-O plates. 576 of theredshifts are measurements from Mount Hopkins, and 405 are newredshifts. We also include new redshifts for 77 fainter galaxies in thesame strip.
| Morphology of galaxies in compact groups
We present the results of an isophotal analysis of 140 early-typegalaxies and a visual inspection of images of an additional 202 galaxiesin compact groups. This is essentially the entire sample of galaxies inthe subset of 92 Hickson compact groups which have at least threeaccordant members. About 12% of the elliptical galaxies have largercharacteristic radii and shallower surface brightness profiles thangalaxies of the same luminosity in less dense environments. The averageellipticity of elliptical galaxies in compact groups is a slowlyincreasing function of the metric radius, as it is for field andloose-group galaxies. No alignment is found among the major axes of thegalaxies and the major axis of the group. When combined with previouslypublished morphological, kinematic, radio, infrared, and colorinformation on the same galaxies, our data show that 43% of the galaxiesin the compact group sample show morphological and/or kinematicaldistortions indicative of interactions and/or mergers. About 32% of thegroups have three or more galaxies which show some sign of interaction.This is a lower limit, since for the great majority of the galaxies inthe groups, only imaging and low-resolution spectra are available. Forthe subsample of 16 groups for which published detailed kinematical dataare also available, the fraction of groups with three or more galaxiesin interaction is 75%. No correlation is found between the number ofinteracting galaxies in a group and the group velocity dispersion orcrossing time. These observations strongly support the view that compactgroups are systems of physically associated galaxies and not chancealignments of field, loose-group, or cluster galaxies. They also confirmthe importance of compact groups for studies of interactions and galaxyevolution. While the lack of a good control sample makes it difficult tomake quantitative comparisons for some aspects of this study, it isclear that the fraction of galaxies showing evidence of interactions ismuch higher in compact groups than in other environments.
| Morphology of early-type galaxies in compact groups.
Investigations on the morphology of early-type galaxies in compactgroups should help us to understand if we are looking at objects whichhave jet experienced encounters and merging events. In this paper, wepresent geometrical and luminosity profiles of a sample of 55 early-typegalaxies belonging to 18 Hickson Compact Groups. Although acomprehensive discussion of the morphological properties of this classof objects cannot be tried at this stage, some morphological trends aresuggested by the data. In particular, an indication that boxyellipticals are less frequent in compact groups than in differentenvironments is found.
| Dynamical properties of compact groups of galaxies
Radial velocities are presented for 457 galaxies in the 100 Hicksoncompact groups. More than 84 percent of the galaxies measured havevelocities within 1000 km/s of the median velocity in the group.Ninety-two groups have at least three accordant members, and 69 groupshave at least four. The radial velocities of these groups range from1380 to 42,731 km/s with a median of 8889 km/s, corresponding to amedian distance of 89/h Mpc. The apparent space density of these systemsranges from 300 to as much as 10 exp 8 sq h/sq Mpc, which exceeds thedensities in the centers of rich clusters. The median projectedseparation between galaxies is 39/h kpc, comparable to the sizes of thegalaxies themselves. A significant correlation is found between crossingtime and the fraction of gas-rich galaxies in the groups, and a weakanticorrelation is found between crossing time and the luminositycontrast of the first-ranked galaxy.
| Optical properties and dynamics of galaxies in the Hickson compact groups
The way in which galaxy properties in dense galaxy environments comparewith the properties isolated in the field is presently evaluated inlight of broadband R and H-alpha images, as well as H-alpha long-slitspectroscopy, for a set of galaxies (in 21 Hickson compact groups) whoseobserved velocity patterns range from too peculiar for rotation-curveformation, to abnormal, to normal. A surprisingly high correlation isnoted between absolute magnitude and (log) maximum rotation velocity,especially in the case of galaxies with normal rotation curves. Theseobservations support a model in which the compact-group galaxies haveonly recently accumulated from the general galaxy distribution, and inwhich tidal interactions are frequent and persisting.
| The luminosity function of compact groups of galaxies
An analysis of the luminosity function of 68 compact groups of galaxiescataloged by Hickson (1982) is presented. The luminosities of compactgroup galaxies are consistent with their being drawn from a Schechterluminosity function. Individual morphological-type luminosity functionsare also determined. Both the total and morphological-type specificluminosity functions of compact group galaxies are significantlydifferent from those of field, loose-group, and cluster galaxies. Inparticular, the luminosity function of HCG elliptical galaxies has amean magnitude which is significantly brighter than the mean magnitudeof Virgo cluster elliptical galaxies. The mean luminosity density ofgalaxies in compact groups is estimated. The obtained result isconsistent with the conventional scenario in which compact groups mergeto form elliptical galaxies on a relatively short time scale.
| KISO survey for ultraviolet-excess galaxies. X.
Presented here are the tenth list and identification charts of theultraviolet-excess galaxies which have been detected on the multi-colorplates taken with the Kiso Schmidt telescope for 10 survey fields. Inthe sky area of some 300 square degrees 490 objects are catalogued downto the photographic magnitude of about 18.
| A photometric catalog of compact groups of galaxies
The paper presents astrometry, photometry, and morphological types,derived from CCD images, for 463 galaxies in the 100 compact groupsselected by Hickson. Some minor revisions to the membership of theoriginal catalog are made, based on these new images. The completenessof the catalog is considered as a function of group magnitude andGalactic latitude. At high Galactic latitude the catalog is estimated tobe 90 percent complete for groups with total B(T) magnitude 13.0 orless. It is less complete at lower Galactic latitude because ofobscuration and high stellar density.
| Groups of galaxies in the Center for Astrophysics redshift survey
By applying the Huchra and Geller (1982) objective group identificationalgorithm to the Center for Astrophysics' redshift survey, a catalog of128 groups with three or more members is extracted, and 92 of these areused as a statistical sample. A comparison of the distribution of groupcenters with the distribution of all galaxies in the survey indicatesqualitatively that groups trace the large-scale structure of the region.The physical properties of groups may be related to the details oflarge-scale structure, and it is concluded that differences among groupcatalogs may be due to the properties of large-scale structures andtheir location relative to the survey limits.
| Neutral hydrogen in compact groups of galaxies
Integrated H I profiles were detected for 34 of 51 Hickson compactgroups (HCGs) of galaxies, and sensitive upper limits to the H I fluxdensity were measured for the other 17. About 60 percent of the galaxieswithin compact groups are spirals, and a significant tendency exists forthe fraction of elliptical galaxies to increase with group surfacebrightness. The amount of dark matter within the compact group region isnegligibly small. An HCG on average contains half as much neutralhydrogen as a loose group with a similar spectrum of galaxy luminositiesand morphological types, implying that compact groups are independentdynamical entities and not transient or projected configurations ofloose groups. The observed fraction of galaxies which are luminousenough to be possible merger products of compact groups is smallcompared with the fraction required by the theory of dynamical friction.A clear discrepancy thus exists between solid empirical evidence and astraightforward prediction of Newtonian dynamical theory in a settingwhich does not permit a dark matter explanation.
|
Sottometti un nuovo articolo
Link relazionati
Sottometti un nuovo link
Membro dei seguenti gruppi:
|
Osservazione e dati astrometrici
Cataloghi e designazioni:
|
