GBT23A-344

Observing HI column densities to measure HVC metallicities

Abstract

Over 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, as infalling clouds are expected to have relatively low metallicity, while Fountain clouds have near-solar metallicity. We are working on a project to derive OI and SII column densities toward 400 sightlines observed by the COS instrument on HST. In order to derive a metallicity a HI reference column density is needed. We have deep GBT data for 90 sightlines, and in about 150 sightlines the HVC/IVC HI is sufficiently bright to get a good measurement from the HI4PI all-sky survey. We request 155 hours of GBT time to obtain accurate HI column densities for the remaining 133 sightlines.

Investigators

Name	Institution
April Horton	Texas Christian University; Macalester College
Jo Vazquez	Texas Christian University
Elena D'Onghia	Wisconsin at Madison, University of
Nicolas Lehner	University of Notre Dame
Bart Wakker *	Wisconsin at Madison, University of
Jay Lockman	Green Bank Observatory
Kathleen Barger	Texas Christian University
Philipp Richter	Bonn, Universität; Potsdam, Universität
Joel Bregman	Michigan at Ann Arbor, University of

* indicates the PI