**Previous
abstract** **Next
abstract**

**Session 20 - Chemistry & Physical Process in the ISM.**

*Display session, Wednesday, January 07*

*Exhibit Hall, *

## [20.06] On the Density Distribution Function of Interstellar Gas

*E. Vázquez-Semadeni (Instituto de Astronomía, UNAM), J. Scalo, D. Chappell (Astronomy Dept., U. Texas at Austin), T. Passot (Obs. Nice)*
We investigate the form of the one-point probability
distribution function (pdf) for the density field of the
interstellar medium using numerical simulations that
successively reduce the number of physical processes
included. Two-dimensional simulations of self-gravitating
supersonic MHD turbulence, of supersonic self-gravitating
hydrodynamic turbulence, and of decaying Burgers turbulence,
produce in all cases filamentary density structures and
evidence for a power-law density pdf with logarithmic slope
around -1.7. This suggests that the functional form of
the pdf and the general filamentary morphology are the
signature of the nonlinear advection operator.

These results do not support previous claims that the pdf
is lognormal. A series of 1D simulations of forced
supersonic polytropic turbulence is used to resolve the
discrepancy. They suggest that the pdf is lognormal only
for effective polytropic indices \gamma=1 (or nearly
lognormal for \gamma\not=1 if the Mach number is
sufficiently small), while power laws develop for
densities larger than the mean if \gamma<1.

The author(s) of this abstract have provided an email address for comments about the abstract: enro@astroscu.unam.mx

**Program
listing for Wednesday**