Assigned ID: 877 ----- Attempting Submission 1 (Sat Mar 08 00:41:02 GMT 2008) ----- Phase I Proposal 877 (proplls.apt) successfully submitted. ----- Attempting Submission 2 (Sat Mar 08 00:51:54 GMT 2008) ----- Phase I Proposal 877 (proplls.apt) successfully submitted. ----- Attempting Submission 3 (Sat Mar 08 00:54:12 GMT 2008) ----- Lyman limit systems (LLS) are a key for understanding the transfer of ionizing radiation in the universe, the interactions between the galaxies and their environments, and the distribution of metals in the universe. Yet, they are the least understood and studied class of QSO absorbers both observationally and theoretically. This is especially true at z<2 (i.e. looking back over 75% of cosmic time), where they can only be observed in the UV. Progress toward a better understanding of these systems and improved theoretical models has been limited by the small statistical samples and few detailed analyses. We propose to use the 516 low resolution FOS and STIS spectra from the HST archive to determine the statistical properties of the z<2 LLS. Our analysis will span a total redshift path of ~200 and yield over 110 Lyman thick absorbers (17.2 =< log N(HI) < 20.3) at z<2, increasing their number by at least a factor of 7 over the current largest sample. We will undertake for the first time a systematic search for partial LLS (16.5 =< log N(HI) < 17.2) at z<2. The main goals of our survey are 1) to determine the redshift density and the column density frequency distribution of the LLS, and 2) to compare the partial LLS and LLS statistics to those of indirect tracers of high column density absorbers such as MgII systems. Currently, uncertainties in dN/dz and f[N(HI)] are among the greatest sources of uncertainty for inferring the shape and intensity of the UV background radiation field and constraining cosmological models. We will make high level data products available to the community, including co-added and calibrated spectra, and line identifications.

QUASAR ABSORPTION LINES AND IGM 12 50300 false 0.0 0.0 false false false false false SUPPORTED