2,057 research outputs found
Abell 3560, a galaxy cluster at the edge of a major merging event
In this paper we study A3560, a rich cluster at the southern periphery of the
A3558 complex, a chain of interacting clusters in the central part of the
Shapley Concentration supercluster.
From a ROSAT-PSPC map we find that the X-ray surface brightness distribution
of A3560 is well described by two components, an elliptical King law and a more
peaked and fainter structure, which has been modeled with a Gaussian. The main
component, corresponding to the cluster, is elongated with the major axis
pointing toward the A3558 complex. The second component, centered on the
Dumb-bell galaxy which dominates the cluster, appears significantly offset (by
about 0.15 Mpc) from the cluster X-ray centroid.
From a Beppo-SAX observation we derive the radial temperature profile,
finding that the temperature is constant (at kT~3.7 keV) up to 8 arcmin,
corresponding to 0.3 Mpc: for larger distances, the temperature significantly
drops to kT~1.7 keV. We analyze also temperature maps, dividing the cluster in
4 sectors and deriving the temperature profiles in each sector: we find that
the temperature drop is more sudden in the sectors which point towards the
A3558 complex.
From VLA radio data, at 20 and 6 cm, we find a peculiar bright extended radio
source (J1332-3308), composed by a core (centered on the northern component of
the Dumb-bell galaxy), two lobes, a "filament" and a diffuse component. The
morphology of the source could be interpreted either with a strong interaction
of the radio source with the intracluster medium or with the model of
intermittency of the central engine.Comment: 8 pages with encapsulated figures, A&A in pres
New Structure In The Shapley Supercluster
We present new radial velocities for 189 galaxies in a 91 sq. deg region of
the Shapley supercluster measured with the FLAIR-II spectrograph on the UK
Schmidt Telescope. The data reveal two sheets of galaxies linking the major
concentrations of the supercluster. The supercluster is not flattened in
Declination as was suggested previously and it may be at least 30 percent
larger than previously thought with a correspondingly larger contribution to
the motion of the Local Group.Comment: LaTex: 2 pages, 1 figure, includes conf_iap.sty style file. To appear
in proceedings of The 14th IAP Colloquium: Wide Field Surveys in Cosmology,
held in Paris, 1998 May 26--30, eds. S.Colombi, Y.Mellie
A substructure analysis of the A3558 cluster complex
The "algorithm driven by the density estimate for the identification of
clusters" (DEDICA, Pisani 1993, 1996) is applied to the A3558 cluster complex
in order to find substructures. This complex, located at the center of the
Shapley Concentration supercluster, is a chain formed by the ACO clusters
A3556, A3558 and A3562 and the two poor clusters SC 1327-312 and SC 1329-313.
We find a large number of clumps, indicating that strong dynamical processes
are active. In particular, it is necessary to use a fully three-dimensional
sample(i.e. using the galaxy velocity as third coordinate) in order to recover
also the clumps superimposed along the line of sight. Even if a great number of
detected substructures were already found in a previous analysis (Bardelli et
al. 1998), this method is more efficient and faster when compared with the use
of a wide battery of tests and permits the direct estimate of the detection
significance. Almost all subclusters previously detected by the wavelet
analyses found in the literature are recognized by DEDICA.
On the basis of the substructure analysis, we also briefly discuss the origin
of the A3558 complex by comparing two hypotheses: 1) the structure is a
cluster-cluster collision seen just after the first core-core encounter; 2)
this complex is the result of a series of incoherent group-group and
cluster-group mergings, focused in that region by the presence of the
surrounding supercluster. We studied the fraction of blue galaxies in the
detected substructures and found that the bluest groups reside between A3562
and A3558, i.e. in the expected position in the scenario of the cluster-cluster
collision.Comment: 10 pages with 12 encapsulated figures; MNRAS in pres
XMM-Newton observation of the interacting cluster Abell 3528
We analyze the XMM dataset of the interacting cluster of galaxies Abell 3528
located westward in the core of the Shapley Supercluster, the largest
concentration of mass in the nearby Universe. A3528 is formed by two
interacting clumps (A3528-N at North and A3528-S at South) separated by 0.9
Mpc at redshift 0.053. XMM data describe these clumps as relaxed
structure with an overall temperature of and
keV in A3528-N and A3528-S, respectively, and a core cooler by a factor
1.4--1.5 and super-solar metal abundance in the inner 30 arcsec. These clumps
are connected by a X-ray soft, bridge-like emission and present asymmetric
surface brightness with significant excess in the North--West region of A3528-N
and in the North--East area of A3528-S. However, we do not observe any evidence
of shock heated gas, both in the surface brightness and in the temperature map.
Considering also that the optical light distribution is more concentrated
around A3528-N and makes A3528-S barely detectable, we do not find support to
the originally suggested head-on pre-merging scenario and conclude that A3528
is in a off-axis post-merging phase, where the closest cores encounter happened
about 1--2 Gyrs ago.Comment: 15 pages, 16 figures (10 in colors), accepted for publication on A&A.
For a Poscript version with high resolution figures see
http://www.mi.iasf.cnr.it/~gasta/www/a3528.htm
Second fundamental form of the Prym map in the ramified case
In this paper we study the second fundamental form of the Prym map in the ramified case .
We give an expression of it in terms of the second fundamental form of the
Torelli map of the covering curves. We use this expression to give an upper
bound for the dimension of a germ of a totally geodesic submanifold, and hence
of a Shimura subvariety of , contained in the
Prym locus.Comment: To appear in Galois Covers, Grothendieck-Teichmueller Theory and
Dessins d'Enfants - Interactions between Geometry, Topology, Number Theory
and Algebra. Springer Proceedings in Mathematics & Statistics. arXiv admin
note: text overlap with arXiv:1711.0342
Radio halos in merging clusters of galaxies
We present the preliminary results of 235 MHz, 327 MHz and 610 MHz
observations of the galaxy cluster A3562 in the core of the Shapley
Concentration. The purpose of these observations, carried out with the Giant
Metrewave Radio Telescope (GMRT, Pune, India) was to study the radio halo
located at the centre of A3562 and determine the shape of its radio spectrum at
low frequencies, in order to understand the origin of this source. In the
framework of the re--acceleration model, the preliminary analysis of the halo
spectrum suggests that we are observing a young source (few yrs) at the
beginning of the re--acceleration phase.Comment: 3 pages, 2 figures. Proceedings of IAU Colloquium 195 - Outskirts of
Galaxy Clusters: intense life in the suburb
- âŠ