A. Mazure

Luminosity Segregation and Anti-Segregation in Clusters of Galaxies

Gravitational systems and in particular clusters of galaxies seem to undergo various transient evolutionary phases: violent relaxation, two-body relaxation, secular evolution (Lightman & Shapiro, 1978) with different time scales. However uncertainties still exist concerning the estimate of these time scales as well as on the details of the evolution of these systems. Thus it seems well-advised to look for indications on their dynamical stage in observational data. Furthermore the presence of a large mass spectrum in a cluster of galaxies and the non-ponctual character of its constituents lead also to modify the conventional scenario of the evolution of stellar systems.

A comparison of X‐ray and optical wavelet maps in the central region of coma

We have applied a wavelet transform analysis on ROSAT images and on an optical catalouge of the Coma cluster of galaxies. The comparison of these two sets of images allows us a detection of X‐ray emitting galaxies as well as particular emitting regions.

Deep Redshift Surveys: The VIMOS VLT Deep Survey (Invited)

In this paper, the goals and methods of deep redshift surveys are reviewed and on-going projects are discussed. The requirements on instrumentation and observations methods are very stringent and call for a dedicated approach. Among the several on-going deep surveys, we are describing the VIMOS VLT Deep Survey (VVDS) which our team is conducting. It aims to obtain spectra in the redshift range 0 < z < 5, for a complete magnitude limited sample of more than 150000 galaxies. This will allow to quantify the evolution of the galaxy and AGN population over more than 90% of the current age of the universe, as a function of galaxy type, luminosity, or local environment.

VIRMOS: Deep Redshift Surveys with the VLT

We present the status of the feasibility study of the Visible InfraRed Multi Object Spectrograph, conducted under contract with ESO for the VLT. The aim of this study is to establish the scientific objectives, identify the opto-mechanical concepts, and predict the performances of a wide-field multi-object spectrograph dedicated to the deepest galaxy and AGN redshift surveys that will be possible with the VLT. We have identified that a concept based on a four quadrant imaging-spectrograph, using multi-slit aperture plates, is the most efficient concept in this context. The maximum number of slits 10 arcseconds in length, that can be observed simultaneously, is in excess of 800, offering a spectacular multiplexing gain in a field of 4 × 7 × 8 arcmin2, for a wavelength coverage from 0.37 to 1.8μm. We are proposing a dedicated wide-field deep redshift survey, to collect ~ 105 galaxies brighter than I = 24, in the redshift range 0.3 4 or more, in less than 200 nights at one Nasmyth focus of the VLT. The timescale of the instrument development is expected to be 4 years, with first light in early 2001, provided that the VIRMOS concept is selected by ESO early in 1997.

The VLT-VIRMOS Deep Redshift Survey

VIRMOS, the Visible InfraRed Multi Object Spectrograph, is being studied under contract with ESO, to identify the opto-mechanical concepts, and predict the performances of a wide-field multi-object spectrograph dedicated to the deepest galaxy, large scale

What does the Dynamical Analsis of Clusters of Galaxies Tell Us about Massive Neutrinos

It is often claimed that massive neutrinos (ν’s) can solve the “missing mass” problem, but it is not so clear in the particular case of clusters of galaxies (C.O.G.). Let us assume that the unseen matter is composed by massive ν’s only. If they are cosmological, the ν’s should obey Fermi-Dirac statistics with a density of ~ 100 ν/cm3/species. But if “relic,” the ν’s would be so slow (1) that they cannot exist in this form (because of the previous Jeans instability or because they are trapped in wells generated by baryonic matter). Since the time when the ν’s decoupled from the primeval mixture (T ~ 3–1 MeV), the ν’s can be considered as a “gravitational plasma,” so that violent relaxation occurs in inhomogeneous systems, leading to a Lynden-Bell distribution defined by three parameters: ην (numerical density), Vν (r.m.s. velocity) and the ν-mass, mν, all unknown. All three of these parameters are, in fact, necessary to define a state of ν-matter.

Multimass Models for Clusters of Galaxies

It is now a widely spread opinion that a ratio of 10:1 between dark and luminous matter exists. Supported by the existence of flat rotation curves at large radii for spirals, this fact reinforces cosmological scenarios with, for instance, massive neutrinos. This content of dark matter is often estimated from the dynamical analysis of clusters of galaxies based essentially on the application of the Virial theorem or the monomassive Emden sphere or deduced from numerical simulations. However, a careful examination shows crucial failures in such approaches, at least the lack of a mass spectrum and/or of a dynamically influent Intra Cluster Medium. This has been included in simple models1 together with other realistic features such as temperature gradient, isovelocity and/or isothermicity of the gravitational plasma. Our aim is thus to account simultaneously for all the available data concerning both galaxies and ICM; namely, the Nonisothermal Multimass Models1 allow us to fit jointly the numerical density profiles of galaxies, the luminosity function, the velocity dispersion profiles versus magnitude or radius, the luminosity segregation2, the X-ray temperature, luminosity and surface brightness profiles.