A COS Snapshot Survey for z < 1.25 Lyman Limit Systems

Details A COS Snapshot Survey for z < 1.25 Lyman Limit Systems A COS Snapshot Survey for z < 1.25 Lyman Limit Systems

Jul 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009hst..prop12289h&link_type=abstract

HST Proposal ID #12289. Cycle 18

Physics

Scientific paper

We propose a snapshot survey of z < 1.25 QSO sight lines to search for optically thick Lyman limit systems. These systems by their nature probe the interfaces between the diffuse IGM and the main bodies of galaxies; they are sensitive to matter accreting onto galaxies for the first time or being expelled in galactic feedback-driven winds. Our survey will probe a mostly-unexplored redshift regime for such systems, increasing the redshift survey path by a factor of 4 to 10 at z < 1. With our on-going SDSS, WFC3 and archival HST surveys for Lyman limit systems, our program will probe the number density and column density frequency distribution for LLSs over the redshift range 0.4 < z < 4.4. We will also provide a measure of the mean free path for ionizing photons in the universe over that same redshift regime. This is an important parameter for calculations of the extragalactic UV background, and our data will constrain the redshift at which the mean free path becomes larger than the horizon. Our proposed sample of 188 0.75 < z < 1.25 QSOs is drawn from a magnitude limited selection of spectroscopically confirmed SDSS QSOs. Using the COS G140L grating with short exposures will provide sufficient signal-to-noise observations to detect log N{H I} > 16.7 systems. These QSOs are bright enough to facilitate high-resolution follow-up spectroscopy from the ground or with higher dispersion COS observations. Our proposal will also provide a larger spectroscopic sample for the study of damped Lyman-alpha systems, metal line absorbers {e.g., O VI, C IV}, and studies of the higher column density Lyman-alpha forest.;

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