Assigned ID: 409 ----- Submission 1 (Fri Jan 21 21:40:46 GMT 2005) ----- We propose an archival HST program, surveying Si III absorption from high-velocity clouds (HVCs) in STIS E140M and G140M data for 70 AGN/QSO sight lines. The interstellar Si III line at 1206.50 Angstroms is the strongest metal line in the HST-STIS bandpass for HVC studies and is not often contaminated by IGM interlopers. At present, large surveys have been carried out for only the highest-column-density HVCs through studies of H I 21cm emission. This program will map the distribution, covering factor, and kinematics of HVCs down to a sensitivity of logN(H I)=15-16, an improvement of approximately 3 orders of magnitude over previous HVC surveys in H I emission. In addition, we will explore the ionization characteristics of the Si III-detected HVCs in order to assess models of HVCs and their role in structure formation scenarios. Despite the problems with current UV instruments and uncertainty surrounding future missions, this program presents new science through the use of existing HST data.

ISM AND CIRCUMSTELLAR MATTER 12 70500 false 0.0 false false false false false SUPPORTED