EDP Sciences
Free access
Volume 429, Number 2, January II 2005
Page(s) 477 - 487
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20041591

A&A 429, 477-487 (2005)
DOI: 10.1051/0004-6361:20041591

Abundances and kinematics of a candidate sub-damped Lyman $\alpha$ galaxy toward PHL 1226

L. Christensen1, R. E. Schulte-Ladbeck2, S. F. Sánchez1, T. Becker1, K. Jahnke1, A. Kelz1, M. M. Roth1 and L. Wisotzki1, 3

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)

The spectrum of the quasar PHL 1226 is known to have a strong $\ion{Mg}{ii}$ and sub-damped Lyman $\alpha$ (sub-DLA) absorption line system with $N(\ion{H}{i})=(5\pm2)\times10^{19}$ cm -2 at z=0.1602. Using integral field spectra from the Potsdam Multi Aperture Spectrophotometer (PMAS) we investigate a galaxy at an impact parameter of 6 $\farcs$4 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 $_{\normalsize\odot}$ $\>\rm yr^{-1}$ is inferred from the H $\alpha$ luminosity. Using nebular emission line ratios we find a solar oxygen abundance $12+\log\textrm{(O/H)}=8.7\pm0.1$ and a solar nitrogen to oxygen abundance ratio $\log\textrm{(N/O)}=-1.0\pm0.2$. 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 $\ion{Mg}{ii}$ absorption systems. These two categories can be reconciled if we assume an abundance gradient similar to local galaxies. Under that assumption we predict abundances $12+\log\textrm{(O/H)}=7.1$ and $\log\textrm{(N/O)}=-1.9$ 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.

Key words: galaxies: abundances -- galaxies: kinematics and dynamics -- quasars: individual: PHL 1226

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