The Absorption and Emission Kinematics in the z=0.7450 Mg II Absorber Towards Q1331+17

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Abstract
(Abridged) We present a comparative analysis of the galaxy emission and QSO absorption kinematics of a z~0.7450 MgII system and its candidate absorbing galaxy (G5) located 3.86 arcsecs (28.3 h-1 kpc) from the QSO. We have obtained a spectrum of the galaxy candidate, previously identified as a luminous edge-on disk, and detect the [OII] 3727 A doublet at a systemic redshift of z =0.7450. From slit spectroscopy of this galaxy, we find v_rot ~> 210 km/s, and possibly as large as 350 km/s. Plotted on the same velocity scale, the systemic redshift of the galaxy coincides with the center of the absorption system, although the absorption components span more than 100 km/s in either direction. However, once the sense of the rotation is taken into account, there is no absorbing gas at the projected velocity of the disk rotation curve. This implies incompatibility with a simple disk scenario. Moreover, a re-analysis of archival HST data reveals that the galaxy is only 0.3 L*, considerably less luminous than previously reported in the literature. Analysis of the absorption lines shows evidence for superbubbles in the interstellar medium (ISM) of the absorbing galaxy, based on the striking symmetry between components and large MgI/MgII and MgI/FeII ratios, indicative of large densities. The large velocity separations between line pairings, dv ~ 150 km/s indicates that these bubbles may be powered by OB associations comparable to the largest observed at z=0 and that the gas is probably enriched to at least 1/10 solar metallicity.

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