Volume 534, October 2011
|Number of page(s)||11|
|Published online||06 October 2011|
High-ion absorption in the proximate damped Ly-α system toward Q0841+129⋆
European Southern Observatory, Alonso de Córdova 3107, Casilla 19001, Vitacura, Santiago, Chile
2 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK
3 Institut d’Astrophysique de Paris, UMR7095 CNRS, UPMC, 98bis Blvd Arago, 75014 Paris, France
4 Inter-University Centre for Astronomy and Astrophysics, Post Bag 4, Ganesh Khind, Pune 411 007, India
5 Programa de Modelagem Computacional - SENAI - Cimatec, 41650-010 Salvador, Bahia, Brazil
Received: 31 March 2011
Accepted: 11 July 2011
We present VLT/UVES spectroscopy of the quasar Q0841+129, whose spectrum shows a proximate damped Ly-α (PDLA) absorber at z = 2.47621 and a proximate sub-DLA at z = 2.50620, both lying close in redshift to the QSO itself at zem = 2.49510 ± 0.00003. This fortuitous arrangement, with the sub-DLA acting as a filter that hardens the QSO’s ionizing radiation field, allows us to model the ionization level in the foreground PDLA, and provides an interesting case-study on the origin of the high-ion absorption lines Si iv, C iv, and O vi in DLAs. The high ions in the PDLA show at least five components spanning a total velocity extent of ≈ 160 km s-1, whereas the low ions exist predominantly in a single component spanning just 30 km s-1. We examine various models for the origin of the high ions. Both photoionization and turbulent mixing layer models are fairly successful at reproducing the observed ionic ratios after correcting for the non-solar relative abundance pattern, though neither model can explain all five components. We show that the turbulent mixing layer model, in which the high ions trace the interfaces between the cool PDLA gas and a hotter phase of shock-heated plasma, can explain the average high-ion ratios measured in a larger sample of 12 DLAs.
Key words: quasars: absorption lines / galaxies: high-redshift / galaxies: halos / galaxies: ISM
© ESO, 2011
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