**AAS 197, January 2001**

*Session 42. Dust and Theory of ISM*

Display, Tuesday, January 9, 2001, 9:30am-7:00pm, Exhibit Hall
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## [42.16] Turbulent Dissipation in the Interstellar Medium in the Presence of Discrete Energy Sources

*E. Vazquez-Semadeni, V. Avila-Reese (Instituto de Astronomia, UNAM)*

We explore the dissipative ability of numerical simulations
of compressible MHD turbulence that represent the
interstellar medium at intermediate-to-large scales.
Turbulent kinetic energy E_{k} is injected realistically
into the medium by means of randomly placed ``stars'', which
radially accelerate their surrounding medium. We
characterize the input sources by their size l_{f} and by
the rate \dot{E}_{i,s} at which each one injects energy
into the flow. A third important parameter is
\dot{\Sigma}_{OB}, the rate of formation of ``OB stars''.
The spatially-scattered, small-scale nature of the injection
(``forcing'') gives rise to the coexistence of both forced
and decaying turbulent regimes within the same flow.

In the forced regime, the global dissipation rate is always
very similar to the injection rate, implying that most of
the energy is dissipated in the vicinity of the sources. The
characteristic dissipation time is given approximately by
t_{i}\ge \langle\Sigma_g\rangle
u_{rms}^2/E_{i,s}\dot{\Sigma}_{OB}, where
\langle\Sigma_{g}\rangle is the average gas surface density,
u_{rms} is the rms velocity dispersion, and E_{i,s} is
the net kinetic energy input per source. Since u_{rms}
also depends on the other injection parameters, it turns out
that the dissipation time is nearly independent of
\dot{E}_{i,s} and of \dot{\Sigma}_{OB}, the dominant
parameter being l_{f}. Empirically, we find that t_{i}
\propto l_{f}^{0.7}. For realistic values of the parameters,
t_{i}\approx 15-25 Myr.

In the decaying regime, the kinetic energy decays with time
as ~t^{-0.8}. This time dependence can be translated
into a distance dependence. We discuss the implications of
our results for models of galaxy formation and evolution.

This research has received partial funding from Conacyt
grant 27752-E.

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

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