GBT26A-548

Deep 21-cm Measurements to Constrain the Physics of HVCs in the Galactic CGM

Abstract

Galaxy evolution depends upon the interplay of inflows and outflows of gas such that accretion of pristine gas from the intergalactic medium is required to form new stars, while feedback processes driven by supermassive black holes and star formation push gas outward from the interstellar medium. This turbulent drama is staged within the circumgalactic medium (CGM). How gas flows through the CGM, and what physical conditions exist that allow these processes to occur, remain open questions. To address these questions, new high-resolution ultraviolet spectra of high-velocity clouds (HVCs) in the Milky Way's CGM, along with a suite of absorption line analysis and ionization modeling techniques, are employed to reveal the previously-obscured component structures and internal physics of the clouds. However, because 21-cm emission is not detected in the presently-available data of our targets, and because hydrogen column density is required to constrain the gas metallicities and sizes of the clouds - necessary measures in testing CGM gas physics theory - we propose 1-hour GBT observations of four QSO sightlines with exposure times providing 10 times deeper sensitivity compared to existing 21-cm data. These deep 21-cm observations will complement the high-resolution ultraviolet spectra and enable much-needed tests of CGM gas physics.

Investigators

Name	Institution
D.J. Pisano	Cape Town, University of
Darren Stroupe *	Massachusetts at Amherst, University of
Todd Tripp	Massachusetts at Amherst, University of

* indicates the PI