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Clouds in the Milky Way’s Nuclear Wind — Breaking the Speed Limit

Published onJun 01, 2020
Clouds in the Milky Way’s Nuclear Wind — Breaking the Speed Limit

Observations over the last few years have established the existence of significant amounts of gas entrained in the Milky Way's nuclear wind. The gas is found in all phases, from molecular and neutral atomic, tomoderately and highly ionized (1,2,3). The largest amount of information has come from HI emission studies in the 21cm line, which have detected ~200 discrete clouds whose kinematics imply a vertical acceleration away from the nucleus reaching outflow velocities ~330 km/s (4,5). Recent 21cm HI observations with the Green Bank Telescope (GBT) have now found clouds up to an LSR velocity +425 km/s implying that the acceleration may continue to even greater distances from the Galactic Center than previously thought. Also, the number of HI clouds is now large enough that asymmetries in their distribution — predicted from models of outflow — are now being observed. These data put new constraints on models for the nuclear wind, the total energetics, and mass outflow rate. The Green Bank Telescope is a facility of the National Science Foundation, operated by Associated Universities, Inc. References:(1) McClure-Griffiths, N.+ 2013, ApJ, 770, L4; (2) Fox, A.+ 2015, ApJL, 799, L7; (3) Savage, B.D.+ 2017, ApJS, 232, 25; (4) di Teodoro, E.+ 2018, ApJ, 855, 33; (5) Lockman, F.J.+ 2020, ApJ, 888, 51.

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