Evidence for dust reddening in damped Lyα absorbers identified through Ca ii (H&K) absorption

We present a new sample of 31 Ca ii (H&K) λλ3935, 3970 absorption-line systems with 0.84 99.99 per cent confidence. The discovery of significant amounts of dust in a subsample of DLAs has direct implications for studies of the metallicity evolution of the Universe and the nature of DLAs in relation to high-redshift galaxies. The gas:dust ratio is discussed. Our results suggest that at least ∼40 per cent of the Ca ii absorption systems are excluded from the magnitude-limited SDSS quasar sample as a result of the associated extinction, a fraction similar to the upper limit deduced at higher redshifts from radio-selected surveys.