GBT26A-054

The metallicity of high-velocity clouds

Abstract

TBDOver the past 30 years it has been shown that the high- and intermediate-velocity clouds (HVCs/IVCs) are tracers of several important Galactic processes - the infall of fresh material, tidal streams and the Galactic Fountain. The key to understanding the rate of the gas flows associatd with each of these processes is to measure the metallicities of many HVCs/IVCs. Infalling clouds are expected to have relatively low metallicity, while Fountain clouds have near-solar metallicity. We have been working on a project to derive OI and SII column densities toward about 500 sightlines observed by the COS instrument on HST. Deriving metallicities requires HI reference column densities. We have deep GBT data for 430 sightlines (detection limit logN(HI)~17.3), 280 of which come from our GBT project 23A-344. Since that program was approved, we have found more well-isolated HVCs in absorption from both new COS sightlines and our continuing analysis of the COS spectra. We request 38 hours of GBT time for 44 additional sightlines with well-separated HVC absorption, in order to obtain accurate HI column densities.

Investigators

Name	Institution
Michelle Berg	Texas Christian University; Texas at Austin, University of; University of Notre Dame
Andrew Tom	Texas Christian University
Kathleen Barger	Texas Christian University
Bart Wakker *	Eureka Scientific, Inc.
Philipp Richter	Bonn, Universität; Potsdam, Universität

* indicates the PI