Damped Ly Alpha Absorber Kinematics And Outflows From Starburst Galaxies

We present results from a numerical study of the multiphase interstellar medium in sub-Lyman-break galaxy protogalactic clumps. Such clumps are abundant at z = 3 and are thought to be a major contributor to damped Ly alpha absorption. We model the formation of winds from these clumps and show that during star formation (SF) episodes they feature outflows with neutral gas velocity widths up to several hundred km s(-1). Such outflows might, in principle, produce the high velocity dispersion observed in damped Ly alpha absorbers (DLAs). Since the majority of DLAs have low SF rates, and only a small fraction of them might host a starburst at any given time, our median velocity width v(90) still falls short of the observed value. This discrepancy with observations could indicate that at l = 12 pc grid resolution the efficiency of conversion of feedback energy into hydrodynamical flows is less than optimal, even though these models show a remarkable improvement compared to the lower resolution runs. At l = 24 pc, the first signs of the multiphase medium are spotted; however, at this low resolution thermal injection of feedback energy cannot yet create hot expanding bubbles around star-forming regions-instead feedback tends to erase high-density peaks and suppress SF. At l = 12 pc, we see the formation of cold (less than or similar to 300 K), dense (greater than or similar to 100 M(circle dot) pc(-3)) clouds that maintain SF while being compressed by the hot medium; at the same time a large fraction of feedback energy is channeled into low-density bubbles and winds. These winds often entrain compact neutral clumps which produce multi-component metal absorption lines.