Absorption systems at z similar to 2 as a probe of the circumgalactic medium: a probabilistic approach

We characterize the properties of the intergalactic medium (IGM) around a sample of galaxies extracted from state-of-the-art hydrodynamical simulations of structure formation in a cosmological volume of 25 Mpc comoving at z similar to 2. The simulations are based on two different subresolution schemes for star formation and supernova feedback: the Multi-Phase Particle Integrator (MUPPI) scheme and the Effective Model. We develop a quantitative and probabilistic analysis based on the apparent optical depth method of the properties of the absorbers as a function of impact parameter from their nearby galaxies: in such a way, we probe different environments from circumgalactic medium to low-density filaments. Absorbers' properties are then compared with a spectroscopic observational data set obtained from high-resolution quasar spectra. Our main focus is on the N-C IV-N-H I relation around simulated galaxies: the results obtained with MUPPI and the Effective model are remarkably similar, with small differences only confined to regions at impact parameters b = [1 - 3] x r(vir). Using C IV as a tracer of the metallicity, we obtain evidence that the observed metal absorption systems have the highest probability to be confined in a region of 150-400kpc around galaxies. Near-filament environments have instead metallicities too low to be probed by present-day telescopes, but could be probed by future spectroscopical studies. Finally, we compute C IV covering fractions which are in agreement with observational data

ESPRESSO: A High Resolution Spectrograph for the Combined Coud\ue9 Focus of the VLT

In the frame of the call for proposal for the E-ELT instrumentation studies, the CODEX team carried out the feasibility study for a spectrograph for extremely stable Doppler measurements. The CODEX project and its scientific goals are described in [L. Pasquini, S. Cristiani et al. in Messenger 122, 10 (2005)]. During the development of this study, the CODEX team recognized that a CODEX-like instrument would be of high scientific interest also on the VLT. The ESPRESSO concept was born. The contribution by J. Liske in this volume highlights the direct links between the two instruments (see also [J. Liske, A. Grazian, E. Vanzella et al. in 2008MNRAS.tmp..460L, in press])