期刊
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
卷 416, 期 2, 页码 1436-1442出版社
OXFORD UNIV PRESS
DOI: 10.1111/j.1365-2966.2011.19141.x
关键词
turbulence; stars: formation; ISM: clouds; ISM: general; ISM: kinematics and dynamics
资金
- UNAM/DGAPA [IN110409]
- CONACYT [102488]
- NSF [AST-0807305]
- Division Of Astronomical Sciences
- Direct For Mathematical & Physical Scien [0807305] Funding Source: National Science Foundation
It has been recently shown that molecular clouds do not exhibit a unique shape for the column density probability distribution function (N-PDF). Instead, clouds without star formation seem to possess a lognormal distribution, while clouds with active star formation develop a power-law tail at high column densities. The lognormal behaviour of the N-PDF has been interpreted in terms of turbulent motions dominating the dynamics of the clouds, while the power-law behaviour occurs when the cloud is dominated by gravity. In the present contribution, we use thermally bi-stable numerical simulations of cloud formation and evolution to show that, indeed, these two regimes can be understood in terms of the formation and evolution of molecular clouds: a very narrow lognormal regime appears when the cloud is being assembled. However, as the global gravitational contraction occurs, the initial density fluctuations are enhanced, resulting, first, in a wider lognormal N-PDF, and later, in a power-law N-PDF. We thus suggest that the observed N-PDF of molecular clouds are a manifestation of their global gravitationally contracting state. We also show that, contrary to recent suggestions, the exact value of the power-law slope is not unique, as it depends on the projection in which the cloud is being observed.
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