Dr Marijke Haverkorn (Harvard Smithsonian Center for Astrophysics)

Turbulence in the warm ionized interstellar gas - Dr Marijke Haverkorn Colloquium

ATNF Marsfield Lecture Theatre

Abstract

Turbulence in the Galactic interstellar medium (ISM) has
been observed ubiquitously in the diffuse gas, molecular clouds, jets,
stellar winds etc. However, observations yield many different results
at different locations in the Milky Way, on different scales and in
different species. I will discuss several observations to give an
overview of what we know and don't know about turbulence in the ISM.

Furthermore, I will present results from the polarized continuum
observations done as part of the Southern Galactic Plane Survey
(SGPS). The SGPS is a radio survey in the fourth Galactic quadrant of
the neutral hydrogen line and full-polarization 1420 MHz continuum
emission, with a resolution of 1 arcmin. Analysis of rotation measures
(RMs) from the Test Region of the SGPS, combined with emission
measures (EMs) in the same field taken from the Southern H-Alpha Sky
Survey Atlas, yield information on the structure in the warm ISM on a
range of scales. Structure functions of RM and EM fluctuations in this
field show a shallow power law spectrum with a break at the scale of a
few parsec. I will show that the shallow spectrum and break can be
interpreted as contributions from the Local and Carina spiral arms,
which act as Faraday screens. From this, a typical outer scale of
structure of a few parsecs can be derived. We propose that this
structure is caused by H II regions from relatively low-mass stars,
whose characteristic scale size is similar to the outer scale of
turbulence inferred here and which are sufficiently abundant. These
sources may be the dominant source of density and velocity
fluctuations in warm ionized gas in the Galactic spiral arms.