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29 March 2024 |
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Article overview
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The Origin and Kinematics of Cold Gas in Galactic Winds: Insight from Numerical Simulations | Akimi Fujita
; Crystal L. Martin
; Mordecai-Mark Mac Low
; Kimberly C. B. New
; Robert Weaver
; | Date: |
19 Mar 2008 | Abstract: | We study the origin of Na I absorbing gas in ultraluminous infrared galaxies
motivated by the recent observations by Martin of extremely superthermal
linewidths in this cool gas. We model the effects of repeated supernova
explosions driving supershells in the central regions of molecular disks with
M_d=10^{10} M_{odot}, using cylindrically symmetric gas dynamical simulations
run with ZEUS-3D. The shocked swept-up shells quickly cool and fragment by
Rayleigh-Taylor instability as they accelerate out of the dense, stratified
disks. The numerical resolution of the cooling and compression at the shock
fronts determines the peak shell density, and so the speed of Rayleigh-Taylor
fragmentation. We identify cooled shells and shell fragments as Na I absorbing
gas and study its kinematics along various sightlines across the grid. We find
that simulations with a numerical resolution of le 0.2 pc produce multiple
Rayleigh-Taylor fragmented shells in a given line of sight that appear to
explain the observed kinematics. We suggest that the observed wide Na I
absorption lines, <v> = 320pm120 km s^{-1} are produced by these multiple
fragmented shells traveling at different velocities. We also suggest that some
shell fragments can be accelerated above the observed average terminal velocity
of 750 km s^{-1} by the same energy-driven wind with an instantaneous starburst
of ~10^9 M_{odot}. The mass carried by these fragments is only a small
fraction of the total shell mass, while the bulk of mass is traveling with
velocities consistent with the observed average shell velocity 330pm100 km
s^{-1}. Our results show that an energy-driven bubble causing Rayleigh-Taylor
instabilities can explain the kinematics of cool gas seen in the Na I
observations without invoking momentum conservation. (abridged) | Source: | arXiv, 0803.2892 | Services: | Forum | Review | PDF | Favorites |
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