Galactic Gas Flows from Halo to Disk: Tomography and Kinematics at the Milky Way's Disk-Halo Interface

• Published in: arXiv.org 2019-07
• Main Authors: Bish, Hannah V, Werk, Jessica K, Prochaska, J Xavier, Rubin, Kate H R, Zheng, Yong, O'Meara, John M, Deason, Alis J
• Format: Article
• Language: English
• Subjects: Absorption; Clouds; Clumps; Cold gas; Distance measurement; Horizontal branch stars; Inflow; Kinematics; Milky Way Galaxy; Spatial distribution; Spectral resolution; Substructures; Velocity gradient
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1907.09459

We present a novel absorption line survey using 54 blue horizontal branch stars (BHBs) in the Milky Way halo as background sources for detecting gas flows at the disk-halo interface. Distance measurements to high-latitude (\(b\) > 60{\deg}) background stars at 3.1-13.4 kpc, combined with unprecedented spatial sampling and spectral resolution, allow us to examine the 3-dimensional spatial distribution and kinematics of gas flows near the disk. We detect absorption signatures of extraplanar CaII and NaI in Keck HIRES spectra and find that their column densities exhibit no trend with distance to the background sources, indicating that these clouds lie within 3.1 kpc of the disk. We calculate covering fractions of \(f_{CaII}\) = 63%, \(f_{NaI}\) = 26%, and \(f_{HI}\) = 52%, consistent with a picture of the CGM that includes multi-phase clouds containing small clumps of cool gas within hotter, more diffuse gas. Our measurements constrain the scale of any substructure within these cool clouds to