A weak lensing study of the Coma cluster

Due to observational constraints, dark matter determinations in nearby clusters based on weak lensing are still extremely rare, in spite of their importance for the determination of cluster properties independent of other methods. We present a weak lensing study of the Coma cluster (redshift 0.024) based on deep images obtained at the CFHT. After obtaining photometric redshifts for the galaxies in our field based on deep images in the u (1x1 deg2), and in the B, V, R and I bands (42'x52'), allowing us to eliminate foreground galaxies, we apply weak lensing calculations on shape measurements performed in the u image. We derive a map of the mass distribution in Coma, as well as the radial shear profile, and the mass and concentration parameter at various radii. We obtain M_200c = 5.1+4.3-2.1 x10^14 Msun and c_200c=5.0+3.2-2.5, in good agreement with previous measurements. With deep wide field images it is now possible to analyze nearby clusters with weak lensing techniques, thus opening a broad new field of investigation

Evidence of Substructure in the Cluster of Galaxies A3558

We investigate the dynamical properties of the cluster of galaxies A3558 (Shapley 8). Studying a region of one square degree ($\sim$ 3 Mpc$^2$) centered on the cluster cD galaxy, we have obtained a statistically complete photometric catalog with positions and magnitudes of 1421 galaxies (down to a limiting magnitude of $B \sim 21$). This catalog has been matched to the recent velocity data obtained by Mazure et al. (1997) and from the literature, yielding a radial velocity catalog containing 322 galaxies. Our analysis shows that the position/velocity space distribution of galaxies shows significant substructure. A central bimodal core detected previously in preliminary studies is confirmed by using the Adaptive Kernel Technique and Wavelet Analysis. We show that this central bimodal subtructure is nevertheless composed of a projected feature, kinematically unrelated to the cluster, plus a group of galaxies probably in its initial merging phase into a relaxed core. The cD velocity offset with respect to the average cluster redshift, reported earlier by several authors, is completely eliminated as a result of our dynamical analysis. The untangling of the relaxed core component also allows a better, more reliable determination of the central velocity dispersion, which in turn eliminates the ``$\beta$-problem'' for A3558. The cluster also shows a ``preferential'' distribution of subclumps coinciding with the direction of the major axis position angle of the cD galaxy and of the central X-ray emission ellipsoidal distribution, in agreement with an anisotropic merger scenario.Comment: 35 pages in latex, 17 figures in Postscript, accepted for publication in the Astrophysical Journa

The XMM-LSS survey. Survey design and first results

We have designed a medium deep large area X-ray survey with XMM - the XMM Large Scale Structure survey, XMM-LSS - with the scope of extending the cosmological tests attempted using ROSAT cluster samples to two redshift bins between 0<z<1 while maintaining the precision of earlier studies. Two main goals have constrained the survey design: the evolutionary study of the cluster-cluster correlation function and of the cluster number density. The results are promising and, so far, in accordance with our predictions as to the survey sensitivity and cluster number density. The feasibility of the programme is demonstrated and further X-ray coverage is awaited in order to proceed with a truly significant statistical analysis. (Abridged)Comment: Published in Journal of Cosmology and Astroparticle Physic

Exploding superstars: understanding supernovae and gamma-ray bursts

The exceptional cosmic history and the fabulous destinies of exploding stars – supernovae and gamma-ray bursters – are highly fertile areas of research and are also very special tools to further our understanding of the universe. In this book, cosmologists Dr Alain Mazure and Dr Stéphane Basa throw light on the assemblage of facts, hypotheses and cosmological conclusions and show how these ‘beacons’ illuminate their immediate surroundings and allow us to study the vast cosmos, like searchlights revealing the matter comprising our universe

Superstelle in esplosione: fare cosmologia con le supernovae e i gamma-ray burst

Le supernovae e i gamma-ray burst, gli eventi più catastrofici che si verificano nell’Universo, sono oggetto di studio nei campi più dinamici della moderna ricerca astronomica. Dei secondi ancora non conosciamo con precisione i meccanismi che li innescano e tuttavia forti indizi suggeriscono che, come nelle supernovae, la causa scatenante sia il collasso esplosivo di stelle di grande massa. Nell’ultimo decennio, questi fenomeni sono diventati strumenti molto efficaci nello studio dell’origine e dell’evoluzione dell’Universo. I cosmologi li utilizzano come "fari" cosmici che illuminano i loro immediati dintorni e anche come sonde per ricostruire la dinamica dell’espansione dell’Universo. Grazie ad essi, oggi sappiamo che circa il 70% del contenuto di energia-materia dell’Universo è costituito di un’energia oscura la cui natura ci è ancora completamente ignota. Questo libro getta un po’ di luce sui curiosi destini delle superstelle in esplosione e sulle affascinanti conclusioni cosmologiche che possiamo trarre dalla loro osservazione

Etude de la fonction de luminosité de l'amas de COMA

La fonction de luminosité (FL) est une description fondamentale de la population de galaxies. Au sein d'un amas tel que l'amas de COMA, elle permet de connaître le nombre de galaxies par intervalle de magnitude et ainsi d'étudier la population de faible luminosité. Je présenterai dans cette thèse un nouveau sondage profond de l'amas de COMA et les traitements des données effectués. L'analyse des images grand champ (40'X1ʿ) permettra d'étudier in situ les effets d'environnement et ses conséquences sur l'universalité de la fonction de luminosité. Trois parties seront consacrées aux différentes méthodes de décontamination des galaxies d'arrière plan : la soustraction statistique, la relation couleur magnitude (CMR) avec l'emploi de redshifts spectroscopiques connus, et enfin les redshifts photométriques. L'ensemble de ces résultats montre un accord, aux faibles magnitudes, entre la pente de la FL obtenue via la CMR et la pente de la FL obtenue par la méthode des redshifts photométriques. L'étude par région de la FL montre que les effets d'environnement sont partout présents au sein d'un amas aussi riche que celui de COMA. La ségrégation de type morphologique ainsi qu'un manque de galaxies faibles au cœur de l'amas sont confirmésAIX-MARSEILLE1-BU Sci.St Charles (130552104) / SudocSudocFranceF

Etude de l'environnement des supernovae de type IA (implications sur la mesure des paramètres cosmologiques)

AIX-MARSEILLE1-BU Sci.St Charles (130552104) / SudocSudocFranceF

Matter, Dark Matter, and Anti-Matter: In Search of the Hidden Universe /

For over ten years, the dark side of the universe has been headline news. Detailed studies of the rotation of spiral galaxies, and 'mirages' created by clusters of galaxies bending the light from very remote objects, have convinced astronomers of the presence of large quantities of dark (unseen) matter in the cosmos. Moreover, in the 1990s, it was discovered that some four to five billion years ago the expansion of the universe entered a phase of acceleration. This implies the existence of dark energy. The nature of these 'dark; ingredients remains a mystery, but they seem to comprise about 95 percent of the matter/energy content of the universe. As for ordinary matter, although we are immersed in a sea of dark particles, including primordial neutrinos and photons from 'fossil' cosmological radiation, both we and our environment are made of ordinary, baryonic matter. Strangely, even if 15-20 percent of matter is baryonic matter, this represents only 4-5 percent of the total matter/energy content of the cosmos. Here, authors Alain Mazure and Vincent Le Brun present the inventory of matter, both baryonic and exotic, and investigate the nature and fate of matter's twin, anti-matter. According to the standard model, matter and anti-matter should have been formed in equal quantities. Yet there seems to have been a very slight asymmetry, as yet unexplained, where 100,000,001 particles of matter formed for every 100,000,000 particles of anti-matter! The authors show how developments in technology have led to significant progress in scientific research and how, in tandem with the evolution of new ideas, these advances are helping to lift the cosmic veil