Protogalactic Disk Models of Damped Lya Kinematics

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Abstract
We present new observational results on the kinematics of the damped lya systems. Our full sample is now comprised of 31 low-ion profiles and exhibits similar characteristics to the sample from Paper I. The primary exception is that the new distribution of velocity widths includes values out to a maximum of nearly 300 km/s, approx 100 km/s greater than the previous maximum. These high velocity width systems will significantly leverage models introduced to explain the damped lya systems. Comparing the characteristics from low-redshift and high-redshift sub-samples, we find no evidence for significant evolution in the kinematic properties of protogalaxies from z = 2.0 - 3.3. The new observations give greater statistical significance to the main conclusions of our first paper. In particular, those models inconsistent with the damped lya observations in Paper I are ruled out at even higher levels of confidence. At the same time, the observations are consistent with a population of rapidly rotating, thick disks (the TRD model) at high redshift. Buoyed by the success of the TRD model, we investigate it more closely by considering more realistic disk properties. Our goal is to demonstrate the statistical power of the damped lya observations by investigating the robustness of the TRD model. In particular, we study the effects of warping, realistic rotation curves, and photoionization on the kinematics of disks in the TRD model. The principal results are: (1) disk warping has only minimal effect on the kinematic results, primarily influencing the effective disk thickness, (2) the TRD model is robust to more realistic rotation curves; (3) the effects of photoionization require thicker disks to give consistent velocity width distributions. [abridged]

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