More confirmed damped Lyman-Alpha systems from the Las Campanas/Palomar survey

Astronomy and Astrophysics – Astronomy

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Astronomical Catalogs, Lyman Alpha Radiation, Lyman Spectra, Quasars, Red Shift, Galactic Evolution, Radio Astronomy

Scientific paper

We present moderate-resolution spectra of six high-redshift quasars which contain nine candidate damped Lyman alpha absorption systems identified in the Las Campanas/Palomar survey of Lanzetta et al. (ApJS, 77, 1 (1991)). Eight of the nine candidate damped Lyman alpha absorption systems are confirmed (one tentative), including seven with N(H I) greater than or equal to 2 x 1020 /sq cm. The remaining one turns out to be due to blending of many narrow absorption lines. Accurate absorption redshifts, H I column densities, and metal-line equivalent widths are provided for these systems in order to facilitate future studies of detailed physical condition and chemical abundances. We briefly discuss the 18 other metal-line systems identified along these sight lines. The zabs = 2.6527 system toward Q 2231-00 is interesting in that it shows strong O VI (lambda) (lambda) 1031, 1037 absorption. The O VI ion is one of the best diagnostics of hot gas, and high resolution studies of the O VI absorption is likely to yield important clues regarding the ionization mechanism of the metal-line systems. Another system, at zabs = 2.3771 toward Q 2239-38, shows relatively strong Zn II and Cr II absorption, clearly indicating that it belongs to the same class absorbers as the damped Lyman systems. We have not obtained metal abundances for this system because the HI column density is not available. We also find a Lyman limit absorption system at zabs= 3.5090 toward Q 2239-38 which does not show obvious metal absorption lines. More sensitive observations are required to check on this interesting possibility.

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