A multiscale regularized restoration algorithm for XMM-Newton data

We introduce a new multiscale restoration algorithm for images with few photons counts and its use for denoising XMM data. We use a thresholding of the wavelet space so as to remove the noise contribution at each scale while preserving the multiscale information of the signal. Contrary to other algorithms the signal restoration process is the same whatever the signal to noise ratio is. Thresholds according to a Poisson noise process are indeed computed analytically at each scale thanks to the use of the unnormalized Haar wavelet transform. Promising preliminary results are obtained on X-ray data for Abell 2163 with the computation of a temperature map.Comment: To appear in the Proceedings of `Galaxy Clusters and the High Redshift Universe Observed in X-rays', XXIth Moriond Astrophysics Meeting (March 2001), Eds. Doris Neumann et a

Superconducting gap variations induced by structural supermodulation in BSCCO

We discuss the possibility that the strain field introduced by the structural supermodulation in Bi-2212 and certain other cuprate materials may modulate the superconducting pairing interaction. We calculate the amplitude of this effect, visible in scanning tunneling spectroscopy experiments, and thereby relate a change in the local superconducting gap with the change in the local dopant displacements induced by the supermodulation. In principle, since this modulation is periodic, sufficiently accurate x-ray measurements or ab initio calculations should enable one to determine which atomic displacements enhance pairing and therefore T_c.Comment: 4 pages, 3 figure

Unveiling hidden structures in the Coma cluster

We have assembled a large data-set of 613 galaxy redshifts in the Coma cluster, the largest presently available for a cluster of galaxies. We have defined a sample of cluster members complete to b$_{26.5}=20.0$, using a membership criterion based on the galaxy velocity, when available, or on the galaxy magnitude and colour, otherwise. Such a data set allows us to define nearly complete samples within a region of 1~\Mpc\ radius, with a sufficient number of galaxies per sample to make statistical analyses possible. Using this sample and the {\em ROSAT} PSPC X--ray image of the cluster, we have re-analyzed the structure and kinematics of Coma, by applying the wavelet and adaptive kernel techniques. A striking coincidence of features is found in the distributions of galaxies and hot intracluster gas. The two central dominant galaxies, NGC4874 and NGC4889, are surrounded by two galaxy groups, mostly populated with galaxies brighter than b$_{26.5}=17$ and well separated in velocity space. On the contrary, the fainter galaxies tend to form a single smooth structure with a central peak coinciding in position with a secondary peak detected in X--rays, and located between the two dominant galaxies; we suggest to identify this structure with the main body of the Coma cluster. A continuous velocity gradient is found in the central distribution of these faint galaxies, a probable signature of tidal interactions rather than rotation. There is evidence for a bound population of bright galaxies around other brightest cluster members. Altogether, the Coma cluster structure seems to be better traced by the faint galaxy population, the bright galaxies being located in subclusters. We discuss this evidence in terms of an ongoing accretion of groups onto the cluster.Comment: to appear in A&A, 19 pages, uuencoded gzipped postscript fil

On the galaxy luminosity function in the central regions of the Coma cluster

We have obtained new redshifts for 265 objects in the central 48~$\times$~25~arcmin$^2$ region of the Coma cluster. When supplemented with literature data, our redshift sample is 95~\% complete up to a magnitude b$_{26.5}$=18.0 (the magnitudes are taken from the photometric sample of Godwin et al. 1983). Using redshift-confirmed membership for 205 galaxies, and the location in the colour-magnitude diagram for another 91 galaxies, we have built a sample of cluster members which is complete up to b$_{26.5}$=20.0. We show that the Coma cluster luminosity function cannot be adequately fitted by a single Schechter (1976) function, because of a dip in the magnitude distribution at b$_{26.5}$$\sim$17. The superposition of an Erlang (or a Gauss) and a Schechter function provides a significantly better fit. We compare the luminosity function of Coma to those of other clusters, and of the field. Luminosity functions for rich clusters look similar, with a maximum at $M_{b} \simeq -19.5 + 5 \times \log h_{50}$, while the Virgo and the field luminosity functions show a nearly monotonic behaviour. These differences may be produced by physical processes related to the environment which affect the luminosities of a certain class of cluster galaxies.Comment: 7 pages, uuencoded postscript file (figures included) Accepted for publication on A&

Paleohydrology, Sedimentology, and Geochemistry of Two Meromictic Saline Lakes in Southern Saskatchewan

The Northern Great Plains of western Canada contain numerous saline and hypersaline lakes. Most of these lakes are shallow (< 3 m) and exhibit playa characteristics. Some, however, are relatively deep, permanent water bodies. The sediment records of these deep perennial saline lakes offer an excellent opportunity to evaluate key paleohydrologic and hydrochemical parameters. Variations in these parameters may, in turn, be interpreted with respect to climatic fluctuations in the region. Waldsea and Deadmoose lakes, located in south-central Saskatchewan, are both presently meromictic, with saline Mg-Na-SO4-CI waters overlying denser hypersaline brines of similar composition. The modern sediments of the lakes consist of a mixture of organic matter, finegrained detrital elastics (mainly clay minerals, carbonate minerals, quartz, and feldspars), and finely crystalline endogenic/authigenic precipitates (aragonite, gypsum, calcite, pyrite, and mirabilite). Variations in mineralogy and chemistry of sediment cores from the morphologically simple Waldsea basin show that the lake was much shallower and more saline about 4000 years ago. Although water levels have since generally increased in the basin giving rise to higher organic productivity and greater inorganic carbonate precipitation, there is also evidence of several hydrologie reversals during the last 2000 years. The stratigraphy preserved in nearby Deadmoose Lake is much more complex because of the irregular basin morphology. Lower water levels about 1000 years ago created several isolated but still relatively deep lakes in the Deadmoose basin.Les grandes plaines du nord de l'ouest du Canada contiennent de nombreux lacs salés et hypersalés. La plupart de ces lacs sont peu profonds (< 3 m) et offrent les caractéristiques des playas. D'autres, par contre, sont des plans d'eau permanents relativement profonds. Les données sédimentologiques de ces derniers permettent d'évaluer certains paramètres clés de paléohydrologie et d'hydrochimie. Les variations qu'offrent ces paramètres peuvent à leur tour être interprétées en fonction des fluctuations climatiques qu'a connues la région. Les lacs Waldsea et Deadmoose, dans le centre-sud de la Saskatchewan, sont méromictiques et leurs eaux composées de Mg-Na-So4-Cl recouvrent une saumure hypersaline plus dense, mais de composition semblable. Les sédiments actuels de ces lacs consistent en un mélange de matière organique, de roches détritiques à grains fins (surtout des minéraux argileux et carbonates ainsi que des quartz et des feldspaths) et de calcaires de précipitation cristallins à grains fins endogènes et authigènes (aragonite, gypse, calcite, pyrite et mirabilite). La minéralogie et la chimie des sédiments contenus dans les carottes recueillies dans le bassin du lac Waldsea, de morphologie simple, montrent des variations qui indiquent que le lac était beaucoup moins profond et plus salé il y a 4000 ans. Bien que, de façon générale, les niveaux lacustres se soient haussés depuis, ce qui a donné lieu à une production accrue de matière organique et à une plus forte précipitation des carbonates inorganiques, on trouve les témoins de plusieurs inversions de nature hydrologique depuis les 2000 dernières années. Non loin, au lac Deadmoose, la stratigraphie est beaucoup plus complexe en raison de la morphologie irrégulière du bassin. Il y a 1000 ans environ, les bas niveaux lacustres ont été à l'origine de la formation de plusieurs lacs isolés et relativement profonds dans le bassin Deadmoose.den nôrdlichen groBen Ebenen von West-Kanada gibt es zahlreiche salzhaltige und hypersalzhaltige Seen. Die meisten dieser Seen sind seicht (< 3 m) und zeigen Pfannen Charakteristika. Einige hingegen sind relativ tiefe permanente Wasserspiegel. Die Sediment-Belege dieser tiefen, bestândigen Salz-Seen bieten eine ausgezeichnete Gelegenheit, die paleohydrologischen und hydrochemischen Schlùssel-Parameter zu bewerten. Variationen dieser Parameter kônnen ihrerseits interpretiert werden in Bezug auf die klimatischen Fluktuationen in dieser Region. Die Seen Waldsea und Deadmoose, die im sùdlichen Zentrum von Saskatchewan liegen, sind gegenwârtig beide meromiktisch, mit salinen Mg-Na-SO4-Cl Wassern, welche dichtere, hypersaline Salzlaken âhnlicher Zusammensetzung ùberlagern. Die gegenwàrtigen Sedimente dieser Seen bestehen aus einer Mischung von organischem Material, feinkôrnigen Trùmmergesteinen (hauptsàchlich Lehm-Minerale, Karbonat-Minerale, Quartz und Feldspate), und fein kristallinen endogenen/ authigenen Niederschlàgen (Aragonit, Gipsstein, Kalkspat, Pyrit und Mirabilit). Variationen in der Minéralogie und Chemie der Sediment-Keme von dem morphologisch einfachen Waldsea-Becken zeigen, dafî der See vor etwa 4000 Jahren viel seichter und saliner war. Obwohl die Wasserspiegel seitdem im Allgemeinen in dem Becken angestiegen sind, was zu hôherer organischer Produktivitàt und vestârktem inorganischem Karbonat-Niederschlag fùhrte, findet man auch Belege fur einige hydrologische Umschwùnge wâhrend der letzten 2000 Jahre. Die im nahegelegenen Deadmoose-See erhaltene Stratigraphie ist viel komplexer auf Grund der unregelmàfîigen Morphologie des Beckens. Niedrigere Wasserspiegel vor ungefâhr 1000 Jahren fùhrten zu einigen isolierten, aber immer noch relativ tiefen Seen im Deadmoose-Becken

A Population of Compact Elliptical Galaxies Detected with the Virtual Observatory

Compact elliptical galaxies are characterized by small sizes and high stellar densities. They are thought to form through tidal stripping of massive progenitors. However, only a handful of them were known, preventing us from understanding the role played by this mechanism in galaxy evolution. We present a population of 21 compact elliptical galaxies gathered with the Virtual Observatory. Follow-up spectroscopy and data mining, using high-resolution images and large databases, show that all the galaxies exhibit old metal-rich stellar populations different from those of dwarf elliptical galaxies of similar masses but similar to those of more massive early-type galaxies, supporting the tidal stripping scenario. Their internal properties are reproduced by numerical simulations, which result in compact dynamically hot remnants resembling the galaxies in our sample.Comment: 26 pages, 5 figures, 2 tables. Science in press, published in Science Express on 1/Oct/2009. Full resolution figures in the supplementary online material are available from the Science Magazine web-sit