arXiv subjects

G. Mathez

Publications and source records attributed to G. Mathez.

31 records · Page 2Linked to original sources

arXiv2005

The VIMOS VLT Deep Survey: Evolution of the non-linear galaxy bias up to z=1.5

We present the first measurements of the Probability Distribution Function (PDF) of galaxy fluctuations in the VIMOS-VLT Deep Survey (VVDS) cone, covering 0.4x0.4 deg between 0.4 0.8; ii) the formation of bright galaxies is inhibited below a characteristic mass-overdensity threshold whose amplitude increases with redshift and luminosity; iii) the biasing function is non linear in all the redshift bins investigated with non-linear effects of the order of a few to 10% on scales >5Mpc.

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arXiv2004

The VLT-VIMOS Mask Preparation Software

VIMOS (VIsible Multi-Object Spectrograph) is a multi-object imaging spectrograph installed at the VLT (Very large Telescope) at the ESO (European Southern Observatory) Paranal Observatory, especially suited for survey work. VIMOS is characterized by its very high multiplexing factor: it is possible to take up to 800 spectra with 10 arcsec long slits in a single exposure. To fully exploit its multiplexing potential, we designed and implemented a dedicated software tool: the VIMOS Mask Preparation Software (VMMPS), which allows the astronomer to select the objects to be spectroscopically observed, and provides for automatic slit positioning and slit number maximization within the instrumental constraints. The output of VMMPS is used to manufacture the slit masks to be mounted in the instrument for spectroscopic observations.

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arXiv2004

The VVDS data reduction pipeline: introducing VIPGI, the VIMOS Interactive Pipeline and Graphical Interface

The VIMOS VLT Deep Survey (VVDS), designed to measure 150,000 galaxy redshifts, requires a dedicated data reduction and analysis pipeline to process in a timely fashion the large amount of spectroscopic data being produced. This requirement has lead to the development of the VIMOS Interactive Pipeline and Graphical Interface (VIPGI), a new software package designed to simplify to a very high degree the task of reducing astronomical data obtained with VIMOS, the imaging spectrograph built by the VIRMOS Consortium for the European Southern Observatory, and mounted on Unit 3 (Melipal) of the Very Large Telescope (VLT) at Paranal Observatory (Chile). VIPGI provides the astronomer with specially designed VIMOS data reduction functions, a VIMOS-centric data organizer, and dedicated data browsing and plotting tools, that can be used to verify the quality and accuracy of the various stages of the data reduction process. The quality and accuracy of the data reduction pipeline are comparable to those obtained using well known IRAF tasks, but the speed of the data reduction process is significantly increased, thanks to the large set of dedicated features. In this paper we discuss the details of the MOS data reduction pipeline implemented in VIPGI, as applied to the reduction of some 20,000 VVDS spectra, assessing quantitatively the accuracy of the various reduction steps. We also provide a more general overview of VIPGI capabilities, a tool that can be used for the reduction of any kind of VIMOS data.

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arXiv2004

Introducing BAX: a database for X-ray clusters and groups of galaxies

We present BAX, Base de Donnees Amas de Galaxies X (http://webast.ast.obs-mip.fr/bax), a multi-wavelength database dedicated to X-ray clusters and groups of galaxies allowing detailed information retrieval. BAX is designed to support astronomical research by providing access to published measurements of the main physical quantities and to the related bibliographic references: basic data stored in the database are cluster/group identifiers, equatorial coordinates, redshift, flux, X-ray luminosity (in the ROSAT band) and temperature, and links to additional linked parameters (in X-rays, such as spatial profile parameters, as well as SZ parameters of the hot gas, lensing measurements,and data at other wavelengths, such as optical and radio). The clusters and groups in BAX can be queried by the basic parameters as well as the linked parameters or combinations of these. We expect BAX to become an important tool for the astronomical community. BAX will optimize various aspects of the scientific analysis of X-ray clusters and groups of galaxies, from proposal planning to data collection, interpretation and publication, from both ground based facilities like MEGACAM (CFHT), VIRMOS (VLT) and space missions like XMM-Newton, Chandra and Planck.

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arXiv2003

Early results from the VIMOS VLT Deep Survey

The VIMOS VLT Deep Survey (VVDS) is underway to study the evolution of galaxies, large scale structures and AGNs, from the measurement of more than 100000 spectra of faint objects. We present here the results from the first epoch observations of more than 20000 spectra. The main challenge of the program, the redshift measurements, is described, in particular entering the ``redshift desert'' in the range $1.5<z<3$ for which only very weak features are observed in the observed wavelength range. The redshift distribution of a magnitude limited sample brighter than $I_{AB}=24$ is presented for the first time, showing a peak at a low redshift $z\sim0.7$, and a tail extending all the way above $z=4$. The evolution of the luminosity function out to $z=1.5$ is presented, with the LF of blue star forming galaxies carrying most of the evolution, with L* changing by more than two magnitudes for this sub-sample.

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arXiv2001

The VIRMOS-VLT Deep Survey

The aim of the VIRMOS VLT Deep Survey (VVDS) is to study of the evolution of galaxies, large scale structures and AGNs from a sample of more than 150,000 galaxies with measured redshifts in the range 0<z<5+. The VVDS will rely on the VIMOS and NIRMOS wide field multi-object spectrographs, which the VIRMOS consortium is delivering to ESO. Together, they offer unprecedented multiplex capability in the wavelength range 0.37-1.8microns, allowing for large surveys to be carried out. The VVDS has several main aspects: (1) a deep multi-color imaging survey over 18deg^2 of more than one million galaxies, (2) a "wide" spectroscopic survey with more than 130,000 redshifts measured for objects brighter than IAB=22.5 over 18deg^2, (3) a "deep" survey with 50,000 redshifts measured to IAB=24, (4) ultra-deep" surveys with several thousand redshifts measured to IAB=25, (5) multi-wavelength observations with the VLA and XMM.

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arXiv2000

Hierarchical Clustering and Active Galaxies

The growth of Super Massive Black Holes and the parallel development of activity in galactic nuclei are implemented in an analytic code of hierarchical clustering. The evolution of the luminosity function of quasars and AGN will be computed with special attention paid to the connection between quasars and Seyfert galaxies. One of the major interests of the model is the parallel study of quasar formation and evolution and the History of Star Formation.

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arXiv2000

Quasar Candidate Multicolor Selection Technique: a different approach

We present a quasar candidate identification technique based on multicolor photometry. The traditional multi-dimensional method (2 $\times$ N dimensions, where N is the number of the color-color diagrams) is reduced to a one-dimensional technique, which consists in a standard fitting procedure, where the observed spectral energy distributions are compared to quasar simulated spectra and stellar templates. This new multicolor approach is firstly applied to simulated catalogues and its {\it efficiency} is examined in various redshift ranges, as a function of the filter combination and the available observing time for spectroscopy. We conclude that this method is better suited than the usual multicolor selection techniques to quasar identification, especially for high-redshift quasars. The application of the method to real quasar samples found in the literature results in an {\it efficiency} comparable to the one obtained from the use of color-color diagrams. The major advantage of the new method is the estimation of the {\it photometric} redshift of quasar candidates, enabling, in almost all cases, spectroscopy to be targeted to best suited wavelength ranges.

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arXiv1998

What can we learn from VIRMOS quasars?

Large, homogeneous quasar samples are necessary tools for the study of QSO statistics, cosmological tests, large scale structure and AGN evolution. These samples must be complete within well defined flux limits at all redshifts. An observational strategy without previous photometric selection of quasar candidates is described, based essentially on the VIRMOS Survey spectroscopy.

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arXiv1997

The ESO-Sculptor Faint Galaxy Redshift Survey: The Photometric Sample

We present the photometric sample of a faint galaxy survey carried out in the southern hemisphere, using CCDs on the 3.60m and NTT-3.5m telescopes at La Silla (ESO). The survey area is a continuous strip of 0.2 deg x 1.53 deg located at high galactic latitude (-83 deg) in the Sculptor constellation. The photometric survey provides total magnitudes in the bands B, V (Johnson) and R (Cousins) to limiting magnitudes of 24.5, 24.0, 23.5 respectively. To these limits, the catalog contains about 9500, 12150, 13000 galaxies in B, V, R bands respectively and is the first large digital multi-colour photometric catalog at this depth. This photometric survey also provides the entry catalog for a fully-sampled redshift survey of ~ 700 galaxies with R < 20.5 (Bellanger et al. 1995). In this paper, we describe the photometric observations and the steps used in the data reduction. The analysis of objects and the star-galaxy separation with a neural network are performed using SExtractor, a new photometric software developed by E. Bertin (1996). The photometric accuracy of the resulting catalog is ~ 0.05 mag for R < 22. The differential galaxy number counts in B, V, R are in good agreement with previously published CCD studies and confirm the evidence for significant evolution at faint magnitudes as compared to a standard non evolving model (by factors 3.6, 2.6, 2.1). The galaxy colour distributions B-R, B-V of our sample show a blueing trend of ~ 0.5 mag between 21 < R < 23.5 in contrast to the V-R colour distribution where no significant evolution is observed.

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arXiv1996

The Auto-Correlation Function of the extragalactic background light: I. Measuring gravitational shear

A new method for measuring the shear induced by gravitational light deflection is proposed. It is based on analyzing the anisotropy induced in the auto-correlation function (ACF) of the extragalactic background light which is produced by very faint distant galaxies. The ACF can be measured `locally', and its anisotropy is caused by the tidal gravitational field of the deflecting mass distribution in the foreground of these faint background galaxies. Since the method does not require individual galaxy detection, it can be used to measure the shear of extremely faint galaxies which are not detectable individually, but are present in the noise. The shear estimated from the ACF of the noise provides an independent measurement which can be compared to the shear obtained from the distortion of individual galaxy images. Combining these two independent estimates clearly increases the sensitivity of shear measurements. In addition, our method may allow to determine the local magnification caused by the deflector if the auto-correlation function is caused by a large number density of faint galaxies; in this case, the intrinsic ACF may provide a `standard source' with respect to which shear and magnification can be obtained. Applications to real and synthetic data are shown and the feasibility of our new method is demonstrated. In particular, we present the shear maps obtained with our method for the double QSO 2345+007 and the cluster Cl0024+16 and compare them to published shear maps.

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arXiv1995

V/Vmax statistic and Neo-Classic Cosmological Tests

A new cosmological test is derived, based on the distribution of individual V/Vmax in a complete redshift-limited sample of distant objects. The fundamental assumption is that, in any bin of absolute luminosity, individual V/Vmax are required to be uniformly spread over the [0,1] range. This condition of uniformity allows a likelihood function to be computed from the Kolmogorov- Smirnov probabilities of each bin. Monte-Carlo simulations show that the test is mostly sensitive to the density parameter, but under certain conditions, it also sets constraints on the space curvature and, to a lower extent, on the cosmological constant. The test is then applied to the UVX sample of Boyle et al. (1990). A low matter density, and a flat Universe without cosmological constant, are rejected: 0.2<Omega<0.8 within the 95% confidence level.

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arXiv1995

Pure Luminosity Evolution Hypothesis for QSOs: From Luminosity Functions to Synthetic Catalogues

This paper describes the simulation of realistic Monte-Carlo extragalactic catalogues, aimed at comparing the behaviour of cosmological tests versus input parameters. QSO catalogues are built on a Luminosity Function derived from data through suitable computation of individual maximum volumes in complete (but magnitude- and redshift-limited) samples requiring neither of redshift nor of apparent magnitude histogram. The values of the evolution parameter are derived for various cosmologies, corresponding to =1/2 in the sample of 400 Ultra-Violet Excess (UVX) QSOs (Boyle et al 1990). The various luminosity functions are compared, both for the whole sample and in redshift bins. An evolution characteristic time is defined and computed, depending strongly on the cosmology, but practically constant when expressed in terms of the age of the Universe. Algorithms are given for producing unbiased or biased catalogues based on the null hypothesis that the objects are uniformly distributed in volume but suffer Pure Luminosity Evolution.

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