Probing Interstellar Turbulence in the Warm Ionized Medium using Emission Lines
S. L. Tufte;
In Interstellar Turbulence, 1998, Puebla, Mexico, Cambridge University Press, Franco, J.; Carraminana, A., p. 42
ABSTRACT:The nature of turbulence in the warm ionized component of the interstellar medium (WIM) can be investigated using Fabry-Perot spectroscopy of
optical emission lines.
The Halpha intensity provides the emission measure
(EM) along a line of sight, which is used in conjunction with the scattering
measure, rotation measure, and dispersion measure in many studies of
interstellar turbulence.
Observing at high spectral resolution (about 10 km/s)
allows the measurement of the bulk velocity structure of the emitting gas, and
investigation of thermal and non-thermal (turbulent) broadening mechanisms
through the line widths.
By measuring the widths of the Halpha line and an
emission line from a heavier atom (e.g.
the SII 6716AA line), one can separate
the thermal and non-thermal contributions to the line width.
Preliminary studies using this method have shown that the broad range of Halpha line
widths (typically 15 -- 50 km/s) is mostly due to differences in the
non-thermal component of the width and that along many lines of sight this component
dominates.
The Wisconsin Halpha Mapper (WHAM) is in the process of producing a very
sensitive kinematic map of the northern sky in Halpha at 1deg angular resolution
and 12 km/s spectral resolution.
WHAM is also mapping emission lines from
heavier atoms such as sulfur and nitrogen for selected regions of the sky.
This
data set will provide a wealth of new information concerning turbulence in
the WIM.
PERSOKEY:turbulence, halpha, optical, milky way, h+, ,
CODE: tufte98