Jessica K. Werk
The Nature of Ionized Gas in the Milky Way Galactic Fountain
Werk, Jessica K.; Rubin, K.H.R.; Bish, H.V.; Prochaska, J.X.; Zheng, Y.; O’Meara, J.M.; Lenz, D.; Hummels, C.; Deason, A.J.
Authors
K.H.R. Rubin
H.V. Bish
J.X. Prochaska
Y. Zheng
J.M. O’Meara
D. Lenz
C. Hummels
Professor Alis Deason alis.j.deason@durham.ac.uk
Professor
Abstract
We address the spatial scale, ionization structure, mass, and metal content of gas at the Milky Way disk–halo interface detected as absorption in the foreground of seven closely spaced, high-latitude halo blue horizontal branch stars with heights z = 3–14 kpc. We detect transitions that trace multiple ionization states (e.g., Ca II, Fe II, Si IV, C IV) with column densities that remain constant with height from the disk, indicating that the gas most likely lies within z < 3.4 kpc. The intermediate ionization state gas traced by C IV and Si IV is strongly correlated over the full range of transverse separations probed by our sight lines, indicating large, coherent structures greater than 1 kpc in size. The low ionization state material traced by Ca II and Fe II does not exhibit a correlation with either NH I or transverse separation, implying cloudlets or clumpiness on scales less than 10 pc. We find that the observed ratio log(NSi IV/NC IV), with a median value of −0.69 ± 0.04, is sensitive to the total carbon content of the ionized gas under the assumption of either photoionization or collisional ionization. The only self-consistent solution for photoionized gas requires that Si be depleted onto dust by 0.35 dex relative to the solar Si/C ratio, similar to the level of Si depletion in DLAs and in the Milky Way interstellar medium. The allowed range of values for the areal mass infall rate of warm, ionized gas at the disk−halo interface is 0.0003 < dMgas/dtdA [Me kpc−2 yr−1 ] <0.006. Our data support a physical scenario in which the Milky Way is fed by complex, multiphase processes at its disk−halo interface that involve kiloparsec-scale ionized envelopes or streams containing parsec-scale, cool clumps.
Citation
Werk, J. K., Rubin, K., Bish, H., Prochaska, J., Zheng, Y., O’Meara, J., …Deason, A. (2019). The Nature of Ionized Gas in the Milky Way Galactic Fountain. Astrophysical Journal, 887(1), Article 89. https://doi.org/10.3847/1538-4357/ab54cf
Journal Article Type | Article |
---|---|
Acceptance Date | Nov 4, 2019 |
Online Publication Date | Dec 13, 2019 |
Publication Date | Dec 10, 2019 |
Deposit Date | Jan 15, 2020 |
Publicly Available Date | Jan 15, 2020 |
Journal | Astrophysical Journal |
Print ISSN | 0004-637X |
Publisher | American Astronomical Society |
Peer Reviewed | Peer Reviewed |
Volume | 887 |
Issue | 1 |
Article Number | 89 |
DOI | https://doi.org/10.3847/1538-4357/ab54cf |
Public URL | https://durham-repository.worktribe.com/output/1310067 |
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