Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995aas...187.2002v&link_type=abstract
American Astronomical Society, 187th AAS Meeting, #20.02; Bulletin of the American Astronomical Society, Vol. 27, p.1313
Astronomy and Astrophysics
Astronomy
Scientific paper
We present preliminary results from a statistical study of clouds in two-dimensional numerical simulations of the interstellar medium (ISM). Clouds are defined as connected sets of pixels above an arbitrary density threshold. Similarly to real interstellar clouds, the clouds in the simulations exhibit a differential mass spectrum dN(M)/dM ~ M(-1.5) and a velocity dispersion-size relation Delta v ~ l(0.4) , although with correlation coefficients of only 0.6--0.7. The maximum-sized clouds at each velocity dispersion seem to be better described by Delta v ~ l(0.5) . However, the clouds do not follow a unique density-size relation. Instead, at a given mean density, clouds span a wide range of sizes from the smallest resolved scale up to a maximum given by a Larson-type relation l_max ~ rho (-1) , implying non-constant column densities. These results suggest that the Larson relations define the clouds of maximum size at a given mean density or velocity dispersion that can exist before collapsing gravitationally. However, low-column density clouds out of balance between gravity and velocity dispersion are apparently not uncommon, probably being transients induced by turbulence. Such clouds might tend to be missed observationally because of their low column density, as has been suggested by Scalo. Finally, we compare these results with recent observational data. We suggest that a result by Wood and collaborators in which nearly constant column densities for dark clouds are inferred from IRAS 100-mu m images may be an artifact of a temperature gradient within the clouds induced by external radiative heating.
Ballesteros-Paredes Javier
Rodriguez Luis F.
Vázquez-Semadeni Enrique
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