GBT18B-307

Uncovering the hidden iceberg structure of the Milky Way halo

Abstract

How the Milky Way gets its gas and maintains its measured star formation rate is a long-standing mystery of Galactic studies, with important implications for galaxy evolution across the Universe. We recently reported the discovery of two populations of neutral hydrogen (HI) in the halo of the Milky Way (Moss+ 2017): 1) a narrow line-width population typical of bright high velocity cloud (HVC) components, and 2) a fainter, broad line-width population that aligns well with that found in the L02 survey (Lockman+ 2002). From existing data, we concluded that the diffuse population (almost unseen by surveys of HI) outweighs the dense HI by a factor of 3. This discovery of prevalent diffuse HI likely has significant overlap with the metal-line HVCs detected in UV absorption surveys (Lehner+ 2012; Fox+ 2014; Richter+ 2017), and may be key to understanding the bridge between the ionised and neutral Galactic halo. We will use the GBT to make deep maps of a sample of multiphase HVCs, especially those which also overlap with UV absorption sightlines. These extremely sensitive maps of interacting clouds will help to reveal the hidden structure of the multiphase Galactic halo in more detail than ever before.

Investigators

Name	Institution
Nickolas Pingel	Wisconsin at Madison, University of; Australian National University
Vanessa Moss *	Netherlands Institute for Radio Astronomy; Sydney, University of
Jay Lockman	Green Bank Observatory
D.J. Pisano	Cape Town, University of
Enrico Di Teodoro	Firenze, Università degli Studi di
Andrew Fox	Space Telescope Science Institute

* indicates the PI