Results 1 - 10 of 6208
Results 1 - 10 of 6208. Search took: 0.023 seconds
|Sort by: date | relevance|
[en] Two simple clustering prescriptions have provided useful comparisons for studies of the properties of the large-scale galaxy distribution: the power-law cluster model and the continuous hierarchy model. I propose another simple paradigm, inherently ''filamentary,'' whose correlation functions scale with size in a way indistinguishable at present from those of the continuous hierarchy. There exists a growing body of observational evidence for filaments
[en] We discuss the gravitational lens effect of the Virgo Supercluster, modelled by an axisymmetric, homogeneous ellipsoid. By numerical integration of the null geodesics we calculate the variation in the angular position and the brightness amplification ratio K of distant sources. The maximum angular displacement is found to be about 8 arcsec, occurring near the Supergalactic Poles. The maximum variation of K with respect to unity is about 3 10-4, occurring in the direction of Virgo, and corresponds to a negative amplification. The large-scale distribution of K in the celestial sphere is expanded in spherical harmonics, and its dipole and quadrupole amplitudes are found to be in magnitude about 6 10-5. All these effects are quite larger than the analogous ones calculated for the dark matter halo of our Galaxy
[en] The accurate determination of cluster total mass is crucial for their use as probes of cosmology. Recently, the Sunyaev-Zel'dovich effect (SZE) has been exploited in surveys to find galaxy clusters, but X-ray or lensing follow-up observations, or empirically determined scaling relations between SZE flux and total mass, have been required to estimate their masses. Here, we demonstrate a new method of mass determination from SZE observations, applicable in the absence of X-ray or lensing data. This method relies on the virial relation and a minimal set of assumptions, following an approach analogous to that used for stellar structure. By exploiting the virial relation, we implicitly incorporate an additional constraint from thermodynamics that is not used in deriving the equation of hydrostatic equilibrium. This allows us to relate cluster total mass directly to the robustly determined quantity, the integrated SZE flux.
[en] We identify new strong lensing clusters of galaxies from the Sloan Digital Sky Survey III (SDSS DR8) by visually inspecting color images of a large sample of clusters of galaxies. We find 68 new clusters showing giant arcs in addition to 30 known lensing systems. Among 68 cases, 13 clusters are 'almost certain' lensing systems with tangential giant arcs, 22 clusters are 'probable' and 31 clusters are 'possible' lensing systems. We also find two exotic systems with blue rings. The giant arcs have angular separations of 2.0-25.7 from the bright central galaxies. We note that the rich clusters are more likely to be lensing systems and the separations between the arcs and the central galaxies increase with cluster richness. (research papers)
[en] The relation between the spectral redshift of galaxies belonging to the Perseus supercluster and their morphological type on the basis of the complete sample given by Gregory et coll. is studied. It is shown that in the central core the Sb and Scd galaxies have a very significant redshift excess and that the Sbc and Sc galaxies have the same highly significant excess as a complete (for m<=13) of the Virgo I cluster
[fr]On etudie le lien entre le decalage spectral des galaxies du superamas de Persee et leur type morphologique d'apres les donnees de l'echantillon complet m<=14 de Gregory et coll. On montre que, dans l'amas central de Persee, les galaxies Sb a Scd presentent un exces tres significatif de decalage spectral et que les galaxies Sbc et Sc presentent le meme exces hautement significatif que dans un echantillon complet m<=13 de l'amas de Virgo I
[en] We use V-band time-series data to analyze the RR Lyrae (RRL) population of the Galactic globular cluster NGC 6101. Using template fitting, we have discovered seven new RRL stars and confirmed 10 candidates. We find unusually long mean periods for the RRL of (Pab ) = 0.803 days and (Pc ) = 0.393 days, and an atypically high ratio of n(c)/n(ab + c) = 0.82. Based on our derived mean properties of the RRL, NGC 6101 is Oosterhoff type II, consistent with the cluster metallicity but intriguing with respect to its kinematics.
[en] The compact groups of compact galaxies are studied. On the basis of the statistical analysis of these groups indicating that in most cases they are flattened out systems, a search was carried out (at high galaxy latitudes) for elongated (chainshaped) groups of objects including four of more than four members. Presented are the list and maps of identifications of 28 chain-shaped groups of galaxies, found on the maps of > 30 deg sones of the Palomar atlas. It appeared after the review of the Palomar maps that the members of the majority of the groups are compact galaxies
[en] We present the results of a Chandra study of the Hydra A galaxy cluster, where a powerful active galactic nucleus (AGN) outburst created a large-scale cocoon shock. We investigated possible azimuthal variations in shock strength and shape, finding indications for a weak shock with a Mach number in the range ∼1.2-1.3. We measured the temperature change across the shock front. However, the detection of a temperature rise in the regions immediately inside of the front is complicated by the underlying temperature profile of the cluster atmosphere. We measured the global temperature profile of the cluster up to 700 kpc, which represents the farthest measurement obtained with Chandra for this cluster. A plateauin the temperature profile in the range ∼70-150 kpc indicates the presence of cool gas, which is likely the result of uplift of material by the AGN outburst. After masking the cool filaments visible in the hardness ratio map, the plateau disappears and the temperature profile recovers a typical shape with a peak around 190 kpc, just inside the shock front. However, it is unlikely that such a temperature feature is produced by the shock as it is consistent with the general shape of the temperature profiles observed for relaxed galaxy clusters. We studied the spectral properties of the cool filaments finding evidence that ∼1011 Msun of low-entropy material has been dredged up by the rising lobes from the central 30 kpc to the observed current position of 75-150 kpc. The energy required to lift the cool gas is ∼> 2.2 x 1060 erg, which is comparable to the work required to inflate the cavities and is ∼25% of the total energy of the large-scale shock. Our results show that the AGN feedback in Hydra A is acting not only by directly heating the gas, but also by removing a substantial amount of potential fuel for the supermassive black hole.
[en] Gravitational lensing by a cluster of galaxies can distort a background galaxy so that it appears unusually elongated. It is found that if the observer's detection thresholds for measuring an unusually elongated galaxy are axial ratio ≥ 5 and z ≤ 1, then the probability of observation is about 1 in 50 clusters of velocity dispersion ≥ 1000 km/sec. It is also shown that such distorted galaxies are ≥ 10 times more likely than the currently observed giant arcs; the shorter arc, the more probable it is to occur. Observation of these elongated galaxies could serve as a measure of the velocity dispersion of clusters of galaxies
[en] We present a new detailed photometric mapping of 33 early-type galaxies belonging to the Virgo cluster. The study is based on B-band CCD and large-field photographic material. The final light profiles cover typically a range of ∼ 10 mag, with an overall accuracy of ±0.1 mag up to 26 B-mag arcsec-2. The geometrical characteristics of the isophotes have been studied with the purpose of disentangling the presence of a faint disk, if any. The contribution of the bulge alone has been separated from that of the whole galaxy. Comparisons with previous studies are presented and discussed