Interpretation of the Spatial Power Spectra of Neutral Hydrogen in the Galaxy and in the Small Magellanic Cloud
I. Goldman;
ApJ, 2000, 541, 701
ABSTRACT:Recent 21 cm radio observations of H I regions in the Small Magellanic Cloud have revealed spatial power spectra of the intensity that are quite
similar in shape to those previously deduced for the Galaxy.
The similarity,
in spite of the differences in the physical parameters between the Galaxy
and the SMC, suggests that the shape of the power spectra reflects some
underlying mechanism that is not too sensitive to the environmental
specifics.
In this paper we present an interpretation for the observational power
spectra in terms of a large-scale turbulence in the interstellar medium in
which the emitting H I regions are embedded.
The turbulence gives rise to
density fluctuations that lead to the observed intensity fluctuations in the H
I regions.
The observational power spectra are used to deduce the
turbulence spectral function.
In the SMC, the turbulence's largest eddies are
comparable in scale to the SMC itself.
This implies that turbulent mixing should
have smoothed out any large-scale abundance gradients.
Indeed, this
seems to be the case, observationally.
The turbulence is also expected to
amplify and shape up the large-scale magnetic field.
Indeed, the
observational data indicate the existence of a large-scale disordered field of the
strength expected from energy equilibrium with the turbulent velocity
field.
The large-scale turbulence is most probably generated by instabilities
in the large-scale flows induced by the tidal close encounter with the LMC
~2×108 yr ago.
The lifetime of the largest eddies is
~4×108 yr, so the turbulence has not yet had enough time to decay and persists
even though the energy source is no longer there.
KEYWORDS: ism: kinematics and dynamics, ism: structure, turbulence
PERSOKEY:statistical analysis, h_i, 21 cm, turbulence, ,
CODE: goldman2000