The spatial, ionization, and kinematic conditions of the z=1.39 damped Lyα absorber in Q0957+561A, B

We examined the kinematics, ionization conditions, and physical size of the absorption clouds in a z = 1.3911 damped Lyalpha absorber (DLA) in the double-image lensed quasar Q0957+561A, B (separation 135 h(75)(-1) pc at the absorber redshift). Using HIRES/Keck spectra (FWHM similar or equal to 6.6 km s(-1)), we studied the Mg II lambdalambda2796, 2803 doublet, Fe II multiplet, and Mg I lambda2853 transition in absorption. Based on the Fe II profiles (the Mg II suffers from saturation), we defined six "clouds'' in the system of sight line A and seven clouds in the system of sight line B. An examination of the N(upsilon) profiles, using the apparent optical depth method, reveals no clear physical connection between the clouds in A and those in B. The observed column density ratios of all clouds are log N(Mg I)/N(F II) similar or equal to -2 across the full similar to300 km s(-1) velocity range in both systems and also spatially (in both sight lines). This is a remarkable uniformity not seen in Lyman limit systems. The uniformity of the cloud properties suggests that the multiple clouds are not part of a "halo.'' Based on photoionization modeling, using the N(Mg I)/N(Fe II) ratio in each cloud, we constrain the ionization parameters in the range -6.2 less than or equal to log U less than or equal to -5.1, where the range brackets known abundance ratio and dust depletion patterns. The inferred cloud properties are densities of 2 less than or equal to n(H) less than or equal to 20 cm(-3) and line-of-sight sizes of 1 less than or equal to D less than or equal to 25 pc. The masses of the clouds in system A are 10 less than or equal to M/M. less than or equal to 1000 and in system B are 1 less than or equal to M/M. less than or equal to 60 for spherical clouds. For planar clouds, the upper limits are 400 and 160 h(75)(-2) M. for A and B, respectively. We favor a model of the absorber in which the DLA region itself is a single cloud in this complex, which could be a parcel of gas in a galactic interstellar medium. We cannot discern whether the H I in this DLA cloud is in a single, cold phase or in cold+ warm phases. A spherical cloud of similar to10 pc would be limited to one of the sight lines (A) and imply a covering factor less than 0.1 for the DLA complex. We infer that the DLA cloud properties are consistent with those of lower density, cold clouds in the Galactic interstellar medium.