Hot halos around high redshift protogalaxies*
Observations of and absorption in damped Lyman- systems
Institut d'Astrophysique de Paris, UMR 7095 CNRS, Université Pierre et Marie Curie, 98bis Boulevard Arago, 75014 Paris, France e-mail: firstname.lastname@example.org
2 LERMA, Observatoire de Paris, 61 Avenue de l'Observatoire, 75014 Paris, France
3 European Southern Observatory, Alonso de Córdova 3107, Casilla 19001, Vitacura, Santiago 19, Chile
4 IUCAA, Post Bag 4, Ganesh Khind, Pune 411 007, India
Accepted: 12 January 2007
Aims.We present a study of the highly ionized gas (plasma) associated with damped Lyman-α (DLA) systems at .
Methods.We search for absorption and corresponding , , and in a Very Large Telescope/Ultraviolet-Visible Echelle Spectrograph (VLT/UVES) sample of 35 DLA systems with data covering at . We then use optical depth profile comparisons and ionization modelling to investigate the properties, phase structure, and origin of the plasma.
Results.We report twelve DLAs (nine intervening and three at <5000 km s-1 from the QSO redshift) with detections of absorption. There are no clear non-detections, so the incidence of in DLAs is between 34% (12/35) and 100%. Among these 12 DLAs, and are seen whenever data is available, and is detected in 3 cases. Analysis of the line widths together with photoionization modelling suggests that two phases of DLA plasma exist: a hot, collisionally ionized phase (seen in broad components), and a warm, photoionized phase (seen just in narrow and components). The presence of inflows and/or outflows is indicated by individual and components displaced from the neutral gas (either blueshifted or redshifted) by up to 400 km s-1. We find tentative evidence (98% confidence) for correlations between the DLA metallicity (measured in the neutral gas) and high-ion column density, and between the DLA metallicity and high-ion line width, as would be expected if supernova-driven galactic outflows rather than accretion produced the high ions. Using conservative ionization corrections, we find lower limits to the total hydrogen column densities in the hot (-bearing) and warm (-bearing) phases in the range log >19.5 to >21.1, and log >19.4 to >20.9. On average, the hot and warm phases thus contain 40% and 20% of the baryonic mass of the neutral phase in DLAs, respectively.
Conclusions. If the temperature in the phase is ≈106 K and so , the plasma can make a significant contribution to the metal budget at high redshift. Additional searches for in Lyman Limit Systems (QSO absorbers with ) will be necessary to determine the total quantity of baryons and metals hidden in hot halos at .
Key words: quasars: absorption lines / cosmology: observations / galaxies: high-redshift / galaxies: halos / galaxies: ISM
© ESO, 2007