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标题：A high-redshift quasar absorber without C IV. A galactic outflow caught in the act?
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作者：Anne Fox ; Anne Fox ; Philipp Richter 等
期刊名称：Astronomy & Astrophysics
印刷版ISSN：0004-6361
电子版ISSN：1432-0746
出版年度：2016
卷号：588
页码：1-10
DOI：10.1051/0004-6361/201527851
语种：English
出版社：EDP Sciences
摘要：We present a detailed analysis of a very unusual sub-damped Lyman α (sub-DLA) system at redshift z = 2.304 towards the quasar Q 0453−423, based on high signal-to-noise (S/N), high-resolution spectral data obtained with VLT/UVES. With a neutral hydrogen column density of log N(H i) = 19.23 and a metallicity of −1.61 as indicated by [O i/H i] the sub-DLA mimics the properties of many other optically thick absorbers at this redshift. A very unusual feature of this system is, however, the lack of any C iv absorption at the redshift of the neutral hydrogen absorption, although the relevant spectral region is free of line blends and has very high S/N. Instead, we find high-ion absorption from C iv and O vi in another metal absorber at a velocity more than 220 km s-1 redwards of the neutral gas component. We explore the physical conditions in the two different absorption systems using Cloudy photoionisation models. We find that the weakly ionised absorber is dense and metal-poor while the highly ionised system is thin and more metal-rich. The absorber pair towards Q 0453−423 mimics the expected features of a galactic outflow with highly ionised material that moves away with high radial velocities from a (proto)galactic gas disk in which star-formation takes place. We discuss our findings in the context of C iv absorption line statistics at high redshift and compare our results to recent galactic-wind and outflow models.
关键词：intergalactic medium;quasars: absorption lines;galaxies: high-redshift;cosmology: observations