#4, final for sure. 915985971 Assigned ID: 1279 ----- Attempting Submission 1 (Thu Feb 28 20:22:23 GMT 2013) ----- HST Phase I Proposal 1279 (cosmicHI.apt) successfully submitted. ----- Attempting Submission 2 (Fri Mar 01 05:14:41 GMT 2013) ----- HST Phase I Proposal 1279 (cosmicHI.apt) successfully submitted. ----- Attempting Submission 3 (Fri Mar 01 20:34:32 GMT 2013) ----- HST Phase I Proposal 1279 (cosmicHI.apt) successfully submitted. ----- Attempting Submission 4 (Fri Mar 01 23:16:03 GMT 2013) ----- We propose a rigorous exploration of cosmic HI using state-of-the-art SPH simulations with advanced particle tracking capabilities to confront the rapidly expanding inventory of Lyman-limit system (LLS) and damped Lyman-alpha absorber (DLA) observations extending over a Hubble time. Unlike metals, hydrogen has the advantage of being a simple element understand that ubiquitously traces accretion (pristine and enriched), star formation, and outflows. We will address two main questions about cosmic HI: 1) Why do the number and mass density of DLAs stay nearly flat over 13 Gyrs of cosmic time, while star formation declines by a factor of 20?, and 2) Is the observed LLS metallicity bimodality an outcome of two distinct physical mechanisms driving galaxy formation? This project will use existing and new state-of-the-art simulations that match observed galaxy properties, process outputs identically to real observations, and distill the fundamental physical mechanisms regulating galaxy formation. Our assembled team includes theorists capable of running simulations and analyzing them, leading experts in the understanding of cosmic hydrogen, and an observer with access to and knowledge of the relevant COS data. QUASAR ABSORPTION LINES AND IGM Default Medium false true false false true SUPPORTED