C IV absorption in damped and sub-damped Lyman-αsystems: Correlations with metallicity and implications for galactic winds at z ≈ 2-3

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 1.75 < z_abs <3.61, 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 CIV 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 CIV column density, the CIV total line width, and the maximum CIV 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 CIV and sub-DLA . In 25 DLAs and 4 sub-DLAs, covering 2.5 dex in [Z/H], we directly observe CIV moving above the escape speed, where v_escis derived from the total line width of the neutral gas profiles. These high-velocity CIV 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 CIV 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 CIV absorbers show a median mass flow rate of ∼22 (r/40 kpc) M_⊙ yr^-1, where r is the characteristic CIV radius. Their kinetic energy fluxes are large enough that a star formation rate (SFR) of ∼2 M_⊙ yr^-1 is required to power them.