Journal Article

Damped Lyman α systems in high-resolution hydrodynamical simulations

E. Tescari, M. Viel, L. Tornatore and S. Borgani

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 397, issue 1, pages 411-430
Published in print July 2009 | ISSN: 0035-8711
Published online July 2009 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.14943.x
Damped Lyman α systems in high-resolution hydrodynamical simulations

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We investigate the properties of damped Lyman α systems (DLAs) using high-resolution and large box-size cosmological hydrodynamical simulations of a Λ cold dark matter model. The numerical code used is a modification of gadget-2 with a self-consistent implementation of the metal enrichment mechanism. We explore the numerical convergence of some relevant physical quantities and we vary the parameters describing the properties of galactic winds, the initial stellar mass function, the linear dark matter power spectrum and the metal enrichment pattern of the intergalactic medium (IGM) around DLAs. We focus on the properties of dark matter haloes that are likely to be the hosts of DLAs systems: we predict relatively low star formation rates (∼0.01–0.1 M yr−1) and metallicities around 0.1 Z, at least for the bulk of our haloes of masses between 109 and 1010 h−1 M hosting DLAs. For more massive haloes metallicities and star formation rates depend on the specific wind model. We find that strong galactic winds with speed of about 600 km s−1, in an energy-driven wind scenario, are needed in order to match the observed column density distribution function for DLAs and the evolution of the neutral hydrogen content with redshift. The momentum-driven implementation of the galactic wind model, that relates the speed and mass load in the wind to the properties of the dark matter haloes, shows a behaviour which is intermediate between the energy-driven galactic winds of small (∼100 km s−1) and large (∼600 km s−1) velocities. At z= 3 the contribution of haloes of masses between 109 and 1010 h−1 M, for DLAs below 1020.8 cm−2, to the column density distribution function, is significant. By interpolating physical quantities along line-of-sights through massive haloes we qualitatively show how different galactic wind models impact on the IGM around DLAs. Furthermore, we analyse statistics related to the velocity widths of Si ii associated to DLAs: while the expanding shells of gaseous matter associated to the wind can account for the observed velocities, the metallicity in the wind seems to be rather clumpy and this produces an underestimation of the observed velocity widths. We outline possible solutions to this problem.

Keywords: methods: numerical; galaxies: formation; intergalactic medium; quasars: absorption lines; cosmology: theory

Journal Article.  15535 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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