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

Bish, Hannah V.; Werk, Jessica K.; Prochaska, J. Xavier; Rubin, Kate H.R.; Zheng, Yong; O’Meara, John M.; Deason, Alis J.

doi:10.3847/1538-4357/ab3414

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

Bish, Hannah V.; Werk, Jessica K.; Prochaska, J. Xavier; Rubin, Kate H.R.; Zheng, Yong; O’Meara, John M.; Deason, Alis J.

Authors

Hannah V. Bish

Jessica K. Werk

J. Xavier Prochaska

Kate H.R. Rubin

Yong Zheng

John M. O’Meara

Dr Alis Deason alis.j.deason@durham.ac.uk
Associate Professor

Abstract

We present a novel absorption-line survey using 54 blue horizontal branch stars in the Milky Way halo as background sources for detecting gas flows at the disk–halo interface. Distance measurements to high-latitude (b > 60°) background stars at 3.1–13.4 kpc, combined with unprecedented spatial sampling and spectral resolution, allow us to examine the 3D spatial distribution and kinematics of gas flows near the disk. We detect absorption signatures of extraplanar Ca ii and Na i 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 Ca ii = 63%, f Na i = 26%, and f H i = 52%, consistent with a picture of the circumgalactic medium (CGM) that includes multiphase 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 <0.5 kpc. Ca ii and Na i absorption features exhibit an intermediate-velocity (IV) component inflowing at velocities of −75 km s−1

Citation

Bish, H. V., Werk, J. K., Prochaska, J. X., Rubin, K. H., Zheng, Y., O’Meara, J. M., & Deason, A. J. (2019). Galactic Gas Flows from Halo to Disk: Tomography and Kinematics at the Milky Way’s Disk–Halo Interface. Astrophysical Journal, 882(2), Article 76. https://doi.org/10.3847/1538-4357/ab3414

Journal Article Type	Article
Acceptance Date	Jul 20, 2019
Online Publication Date	Sep 4, 2019
Publication Date	Sep 10, 2019
Deposit Date	Sep 13, 2019
Publicly Available Date	Sep 13, 2019
Journal	Astrophysical Journal
Print ISSN	0004-637X
Publisher	American Astronomical Society
Peer Reviewed	Peer Reviewed
Volume	882
Issue	2
Article Number	76
DOI	https://doi.org/10.3847/1538-4357/ab3414