Properties of high-z galaxies as seen through lensing clusters

We discuss the first results obtained on the study of a sample of high-z galaxies (2 < z < 7), using the gravitational amplification effect in the core of lensing clusters. Sources are located close to the critical lines in clusters with well constrained mass distributions, and selected through photometric redshifts, computed on a large wavelength domain, and lens inversion techniques.Comment: 5 pages, 3 figures, Conference Proceedings of the "Clustering at High Redshift" Conference, June 29 to July 2, 1999, Marseille (France

Delaunay based algorithm for finding polygonal voids in planar point sets

This paper presents a new algorithm to find under-dense regions called voids inside a 2D point set. The algorithm starts from terminal-edges (local longest-edges) in a Delaunay triangulation and builds the largest possible low density terminal-edge regions around them. A terminal-edge region can represent either an entire void or part of a void (subvoid). Using artificial data sets, the case of voids that are detected as several adjacent subvoids is analyzed and four subvoid joining criteria are proposed and evaluated. Since this work is inspired on searches of a more robust, effective and efficient algorithm to find 3D cosmological voids the evaluation of the joining criteria considers this context. However, the design of the algorithm permits its adaption to the requirements of any similar application.ENL009/15, VID2015, University of Chile, and Anillo Project Number ACT1122 financed by Conicy

Cusps in the center of galaxies: a real conflict with observations or a numerical artefact of cosmological simulations?

Galaxy observations and N-body cosmological simulations produce conflicting dark matter halo density pro files for galaxy central regions. While simulations suggest a cuspy and universal density pro file (UDP) of this region, the majority of observations favor variable profiles with a core in the center. In this paper, we investigate the convergency of standard N-body simulations, especially in the cusp region, following the approach proposed by [1]. We simulate the well known Hernquist model using the SPH code Gadget-3 and consider the full array of dynamical parameters of the particles. We find that, although the cuspy pro file is stable, all integrals of motion characterizing individual particles suffer strong unphysical variations along the whole halo, revealing an effective interaction between the test bodies. This result casts doubts on the reliability of the velocity distribution function obtained in the simulations. Moreover, we find unphysical Fokker-Planck streams of particles in the cusp region. The same streams should appear in cosmological N-body simulations, being strong enough to change the shape of the cusp or even to create it. Our analysis, based on the Hernquist model and the standard SPH code, strongly suggests that the UDPs generally found by the cosmological N-body simulations may be a consequence of numerical effects. A much better understanding of the N-body simulation convergency is necessary before a 'core-cusp problem' can properly be used to question the validity of the CDM model.CONICYT Anillo project ACT-1122 Center of Excellence in Astrophysics and Associated Technologies CATA PFB0

A 3D Voronoi+Gapper Galaxy Cluster Finder in Redshift Space to z ∼ 0.2. II. An Abundant Cluster Population Dominated by Late-type Galaxies Unveiled

We identify 1901 galaxy clusters (N-g >= 2) with the VoML+G algorithm (Paper I) on the Two-Degree Field Galaxy Redshift Survey. We present the 341 clusters with at least 10 galaxies that are within 0.009 = 0.5) with corresponding mean multiplicity and logarithmic virial mass (in units of M-circle dot) of 15.7 +/- 0.9 and 12.66 +/- 0.07, respectively. The statistical analysis of the late-type fraction distribution supports, with a 3 sigma confidence level, the presence of two population components. It is suggested that the late-type-poor galaxy systems reflect and extend the class of Abell-APM-EDCC clusters and that the late-type-rich systems (similar to one-third of the total) belong to a new, previously unappreciated class. The late-type-rich clusters, on average high mass-to-light ratio systems, appear to be more clustered on large scales than the late-type-poor clusters. A class of late-type-rich clusters is not predicted by current theory.Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT) CONICYT PIA/ANILLOS ACT-1122 CONICYT project Basal AFB-170002 Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT) CONICYT FONDECYT 1040499 704006