C IV absorption in damped and sub-damped Lyman-alpha systems: correlations with metallicity and implications for galactic winds at z~2-3

Abstract

We present a study of C IV absorption in a sample of 63 damped Lyman-alpha (DLA) systems and 11 sub-DLAs in the redshift range 1.75<z_abs<3.61, using a dataset of high-resolution (6.6 km/s FWHM), high signal-to-noise VLT/UVES spectra. Narrow and broad C IV absorption line components indicate 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 C IV column density, the C IV total line width, and the maximum C IV velocity. We explore the effect on these correlations of the sub-DLAs, the proximate DLAs (defined as those within 5 000 km/s 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 C IV and sub-DLA C IV. In 25 DLAs and 4 sub-DLAs, covering 2.5 dex in [Z/H], we directly observe C IV moving above the escape speed, where v_esc is derived from the total line width of the neutral gas profiles. These high-velocity C IV 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 C IV 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 C IV absorbers show a median mass flow rate of ~22(r/40 kpc) solar masses per year, where r is the characteristic C IV radius. Their kinetic energy fluxes are large enough that a star formation rate (SFR) of ~2 solar masses per year is required to power them.Comment: 21 pages, accepted to A&A, Fig 1 downgraded, v2 with proof corrections made and improved Fig 1