Differential rotation and turbulence in extended H I disks

Citation
Ja. Sellwood et Sa. Balbus, Differential rotation and turbulence in extended H I disks, ASTROPHYS J, 511(2), 1999, pp. 660-665
Citations number
41
Categorie Soggetti
Space Sciences
Journal title
ASTROPHYSICAL JOURNAL
ISSN journal
0004637X → ACNP
Volume
511
Issue
2
Year of publication
1999
Part
1
Pages
660 - 665
Database
ISI
SICI code
0004-637X(19990201)511:2<660:DRATIE>2.0.ZU;2-C
Abstract
When present, extended disks of neutral hydrogen around spiral galaxies sho w a remarkably uniform velocity dispersion of similar to 6 km s(-1). Since stellar winds and supernovae are largely absent in such regions, neither th e magnitude nor the constancy of this number can be accounted for in the cl assical picture in which interstellar turbulence is driven by stellar energ y sources. Here we suggest that magnetic fields with strengths of a few mic rogauss in these extended disks allow energy to be extracted from galactic differential rotation through MHD-driven turbulence. The magnitude and cons tancy of the observed velocity dispersion may be understood if its value is Alfvenic. Moreover, by providing a simple explanation for a lower bound to the gaseous velocity fluctuations, MHD processes may account for the sharp outer edge to star formation in galaxy disks.