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

The spectrum of the quasar PHL 1226 is known to have a strong Mg  and sub-damped Lymanα (sub-DLA) absorp- tion line system with N(Hi) = (5 ± 2) × 10 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. 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 Myr −1 is inferred from the Hα luminosity. Using nebular emis- sion line ratios we find a solar oxygen abundance 12 + log (O/H) = 8.7 ± 0.1 and a solar nitrogen to oxygen abundance ratio log (N/O) = −1.0 ± 0.2. 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 respon- sible for strong Mg  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 (O/H) = 7. 1a nd log (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.

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