| Type |
Journal Article |
| Names |
Alex S. Hill, Robert A. Benjamin, Grzegorz Kowal, Ronald J. Reynolds, L. Matthew Haffner, Alex Lazarian |
| Publication |
The Astrophysical Journal |
| Volume |
686 |
| Issue |
1 |
| Pages |
363-378 |
| Date |
October 1, 2008 |
| Short Title |
The Turbulent Warm Ionized Medium |
| URL |
http://adsabs.harvard.edu/abs/2008ApJ...686..363H |
| Library Catalog |
NASA ADS |
| Abstract |
We present an analysis of the distribution of Hα emission measures
for the warm ionized medium (WIM) of the Galaxy using data from the
Wisconsin Hα Mapper (WHAM) Northern Sky Survey. Our sample is
restricted to Galactic latitudes |b|>10deg. We removed
sight lines intersecting 19 high-latitude classical H II regions,
leaving only sight lines that sample the diffuse WIM. The distribution
of EMsin|b| for the diffuse WIM sample is poorly characterized by a
single normal distribution, but is extraordinarily well fit by a
lognormal distribution, with -6)-1>=0.146+/-0.001 and
standard deviation σlogEMsin|b|=0.190+/-0.001. The
value of drops from 0.260+/-0.002 at Galactic latitude 10<|b|<30
to 0.038+/-0.002 at Galactic latitude 60<|b|<90. The distribution
may widen slightly at low Galactic latitude. We compare the observed EM
distribution function to the predictions of three-dimensional
magnetohydrodynamic simulations of isothermal turbulence within a
nonstratified interstellar medium. We find that the distribution of
EMsin|b| is well described by models of mildly supersonic turbulence
with a sonic Mach number of ~1.4-2.4. The distribution is weakly
sensitive to the magnetic field strength. The model also successfully
predicts the distribution of dispersion measures of pulsars and Hα
line profiles. In the best fitting model the turbulent WIM occupies a
vertical path length of 400-500 pc within the 1.0-1.8 kpc scale height
of the layer. The WIM gas has a lognormal distribution of densities with
a most probable electron density npk~0.03 cm-3. We
also discuss the implications of these results for interpreting the
filling factor, the power requirement, and the magnetic field of the
WIM. |
| Tags |
ISM: structure, Magnetohydrodynamics: MHD, turbulence |