Cosmology

Abstract:

We present the Mock Map Facility, a powerful tool to generate mock catalogues or images from semi-analytically post-processed snapshots of cosmological N-body simulations. The paper describes in detail an efficient technique to create such mocks from the GALICS semi-analytic model, providing the reader with an accurate quantification of the artifacts it introduces at every step. We show that replication effects introduce a negative bias on the clustering signal -- typically peaking at less than 10 percent around the correlation length. We also thoroughly discuss how the clustering signal is affected by finite volume effects, and show that it vanishes at scales larger than about a tenth of the simulation box size. For the purpose of analysing our method, we show that number counts and redshift distributions obtained with GALICS and MOMAF compare well to K-band observations and to the 2dFGRS. Given finite volume effects, we also show that the model can reproduce the APM angular correlation function. The MOMAF results discussed here are made publicly available to the astronomical community through a public database. Moreover, a user-friendly Web interface (http://galics.iap.fr) allows any user to recover her/his own favourite galaxy samples through simple SQL queries. The flexibility of this tool should permit a variety of uses ranging from extensive comparisons between real observations and those predicted by hierarchical models of galaxy formation, to the preparation of observing strategies for deep surveys and tests of data processing pipelines.

Abstract:

We summarise the properties of the absorbing haloes around two high-redshift radio galaxies studied with the VLT-UVES echelle spectrograph. The absorbers in 0943 - 242 (z = 2.92) exhibit little further structure compared with previous data-the main absorber still has N(HI) similar or equal to 10(19) cm(-2)-reinforcing the picture in which the absorbing gas occupies a smooth shell beyond the emission line halo. In 0200+015 (z = 2.23) the main absorber now splits into two spatially-resolved systems with N(HI) = 4 x 10(14) cm(-2), one of which has strong CIV absorption, implying a metallicity of Z similar or equal to 10 Zcircle dot. We explain the differences between the two sources with an evolutionary scenario, invoking interaction with the expanding radio source and metal enrichment via a starburst superwind. (C) 2003 Elsevier B.V. All rights reserved.