2,136 research outputs found

    Star Formation and AGN in the Core of the Shapley Supercluster: A VLA Survey of A3556, A3558, SC1327-312, SC1329-313, and A3562

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    The core of the Shapley supercluster (A3556, A3558, SC1327-312, SC1329-313, and A3562) is an ideal region in which to study the effects of cluster mergers on the activity of individual galaxies. This paper presents the most comprehensive radio continuum investigation of the region, relying on a 63-pointing mosaic obtained with the Very Large Array yielding an areal coverage of nearly 7 square degrees. The mosaic provides a typical sensitivity of about 80 uJy at a resolution of 16", enabling detection of galaxies with star formation rates as low as 1 solar mass per year. The radio data are complemented by optical imaging in B and R, producing a catalog of 210 radio-detected galaxies with m_R <= 17.36 (M_R <= -19). At least 104 of these radio-detected galaxies are members of the supercluster on the basis of public velocity measurements. Across the entire core of the supercluster, there appears to be a significant deficit of radio galaxies at intermediate optical magnitudes (M_R between -21 and -22). This deficit is offset somewhat by an increase in the frequency with which brighter galaxies (M_R less than -22) host radio sources. More dramatic is the highly significant increase in the probability for fainter galaxies (M_R between -20 and -21) in the vicinity of A3562 and SC1329-313 to be associated with radio emission. The radio and optical data for these sources strongly suggest that these active galaxies are powered by star formation. In conjunction with recent X-ray analysis, this is interpreted as young starbursts related to the recent merger of SC1329-313 with A3562 and the rest of the supercluster.Comment: Accepted by AJ; 50 pages, including 16 figures (for full resolution PDF, see http://mywebpages.comcast.net/nealamiller2/Shapley_pp.pdf

    New Structure In The Shapley Supercluster

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    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

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    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

    A global occurrence database of the Atlantic blue crab Callinectes sapidus

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    The Atlantic blue crab Callinectes sapidus is a portunid native to the western Atlantic, from New England to Uruguay. The species was introduced in Europe in 1901 where it has become invasive; additionally, a significant northward expansion has been emphasized in its native range. Here we present a harmonized global compilation of C. sapidus occurrences from native and non-native distribution ranges derived from online databases (GBIF, BISON, OBIS, and iNaturalist) as well as from unpublished and published sources. The dataset consists of 40,388 geo-referenced occurrences, 39,824 from native and 564 from non-native ranges, recorded in 53 countries. The implementation of quality controls imposed a severe reduction, in particular from online databases, of the records selected for inclusion in the dataset. In addition, a technical validation procedure was used to flag entries showing identical coordinates but different year of record, in-land occurrences and those located close to the coast. Similarly, a flagging system identified entries outside the known distribution of the species, or associated with unsuccessful introductions

    Spectral properties and origin of the radio halo in A3562

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    We present a new detailed multiband study of the merging cluster A3562, in the core of the Shapley Concentration Supercluster. We analyzed new, low frequency radio data performed at 240 MHz, 332 MHz and 610 MHz with the Giant Metrewave Radio Telescope (GMRT). The new GMRT data allowed us to carry out a detailed study of the radio halo at the centre of A3562, as well as of the head--tail radio galaxy J1333--3141 embedded in it, and of the extended emission around the peripheral cluster galaxy J1332--3146a. Thanks to the present observations we could derive the integrated spectrum of the radio halo with five data points in the frequency range 240 MHz -- 1.4 GHz. Our data show a clear steepening of the total spectrum in this frequency range. Furthermore, by comparing the GMRT 332 MHz image with a previously published VLA 1.4 GHz image, we produced an image of the halo spectral index distribution. The image shows a very complex structure, with an average value of α332MHz1.4GHz∼1.5\alpha^{1.4GHz}_{332MHz} \sim 1.5 and a number of knots steepening up to ∼2\sim 2. We performed a combined morphological and statistical analysis using the radio images and the quantities derived from XMM--Newton and {\it Chandra} observations. We discuss our results in the light of particle re--acceleration processes in galaxy clusters. In particular, we outline an overall picture, consistent with the available radio and X-ray data, in which the cluster merger kinematics, the injection of turbulence and B--amplification induced by the merger between A 3562 and SC 1329--313 are jointly taken into account.Comment: 14 pages, 13 figures, A&A in press Paper with high quality figures can be downloaded from http://www.ira.cnr.it/~tventuri/pa

    Excavation at Aguas Buenas, Robinson Crusoe Island, Chile, of a gunpowder magazine and the supposed campsite of Alexander Selkirk, together with an account of early navigational dividers

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    Excavations were undertaken of a ruined building at Aguas Buenas, identified as an 18th-century Spanish gunpowder magazine. Evidence was also found for the campsite of an early European occupant of the island. A case is made that this was Alexander Selkirk, a castaway here from 1704 to 1709. Selkirk was the model for Defoe’s Robinson Crusoe. A detailed discussion is given of a fragment of copper alloy identifi ed as being from a pair of navigational dividers
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