C IV absorption in damped and sub-damped Lyman-α systems^*,**,***

Correlations with metallicity and implications for galactic winds at z ≈ 2–3

¹ Institut d'Astrophysique de Paris, UMR7095 CNRS, Université Pierre et Marie Curie, 98bis Bd. Arago, 75014 Paris, France e-mail: fox@iap.fr
² European Southern Observatory, Alonso de Córdova 3107, Casilla 19001, Vitacura, Santiago 19, Chile
³ LERMA, Observatoire de Paris, 61 avenue de l'Observatoire, 75014 Paris, France
⁴ IUCAA, Post Bag 4, Ganesh Khind, Pune 411 007, India

Received: 13 April 2007
Accepted: 27 July 2007

Abstract

We present a study of  absorption in a sample of 63 damped Lyman-α (DLA) systems and 11 sub-DLAs in the redshift range , using a dataset of high-resolution (6.6 km s^-1 FWHM), high signal-to-noise VLT/UVES spectra. The complex absorption line profiles show both narrow and broad  components, indicating the presence of both warm, photoionized and hot, collisionally ionized gas. We report new correlations between the metallicity (measured in the neutral-phase) and each of the  column density, the  total line width, and the maximum  velocity. We explore the effect on these correlations of the sub-DLAs, the proximate DLAs (defined as those within 5000 km s^-1 of the quasar), the saturated absorbers, and the metal line used to measure the metallicity, and we find the correlations to be robust. There is no evidence for any difference between the measured properties of DLA  and sub-DLA . In 25 DLAs and 4 sub-DLAs, covering 2.5 dex in [Z/H], we directly observe  moving above the escape speed, where v_esc is derived from the total line width of the neutral gas profiles. These high-velocity  clouds, unbound from the central potential well, can be interpreted as highly ionized outflowing winds, which are predicted by numerical simulations of galaxy feedback. The distribution of  column density in DLAs and sub-DLAs is similar to the distribution in Lyman Break galaxies, where winds are directly observed, supporting the idea that supernova feedback creates the ionized gas in DLAs. The unbound  absorbers show a median mass flow rate of ~22 (r/40 kpc)  yr^-1, where r is the characteristic  radius. Their kinetic energy fluxes are large enough that a star formation rate (SFR) of ~2  yr^-1 is required to power them.