Abundances and kinematics of a candidate sub-damped Lymanα galaxy toward PHL 1226^*

¹ Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany e-mail: lchristensen@aip.de
² Department of Physics & Astronomy, University of Pittsburgh, 3941 O'Hara Street, Pittsburgh, PA 15260, USA
³ Institut für Physik, Universität Potsdam, Am Neuen Palais 10, 14469 Potsdam, Germany

Received: 3 July 2004
Accepted: 8 September 2004

Abstract

The spectrum of the quasar PHL 1226 is known to have a strong and sub-damped Lymanα (sub-DLA) absorption line system with cm^-2 at . Using integral field spectra from the Potsdam Multi Aperture Spectrophotometer (PMAS) we investigate a galaxy at an impact parameter of 64 which is most probably responsible for the absorption lines. A fainter galaxy at a similar redshift and a slightly larger distance from the QSO is known to exist, but we assume that the absorption is caused by the more nearby galaxy. From optical Balmer lines we estimate an intrinsic reddening consistent with 0, and a moderate star formation rate of 0.5 M is inferred from the Hα luminosity. Using nebular emission line ratios we find a solar oxygen abundance and a solar nitrogen to oxygen abundance ratio . This abundance is larger than those of all known sub-DLA systems derived from analyses of metal absorption lines in quasar spectra. On the other hand, the properties are compatible with the most metal rich galaxies responsible for strong absorption systems. These two categories can be reconciled if we assume an abundance gradient similar to local galaxies. Under that assumption we predict abundances and for the sub-DLA cloud, which is similar to high redshift DLA and sub-DLA systems. We find evidence for a rotational velocity of ~200 km s^-1 over a length of ~7 kpc. From the geometry and kinematics of the galaxy we estimate that the absorbing cloud does not belong to a rotating disk, but could originate in a rotating halo.