Gravity or turbulence? - II. Evolving column density probability distribution functions in molecular clouds

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 c...

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Vydáno v:	Monthly notices of the Royal Astronomical Society Ročník 416; číslo 2; s. 1436 - 1442
Hlavní autoři:	Ballesteros-Paredes, Javier, Vázquez-Semadeni, Enrique, Gazol, Adriana, Hartmann, Lee W., Heitsch, Fabian, Colín, Pedro
Médium:	Journal Article
Jazyk:	angličtina
Vydáno:	Oxford, UK Blackwell Publishing Ltd 01.09.2011 Wiley-Blackwell Oxford University Press
Témata:	Astronomy Astrophysics Earth, ocean, space Exact sciences and technology ISM: clouds ISM: general ISM: kinematics and dynamics Numerical analysis Star & galaxy formation stars: formation turbulence stars: formation ISM: clouds ISM: general turbulence ISM: kinematics and dynamics Turbulence Gravitational contraction High density Molecular clouds Digital simulation Column density Log normal distribution Star formation Dynamics Kinematics Probability density function Density fluctuation Power law Gravity
ISSN:	0035-8711, 1365-2966
On-line přístup:	Získat plný text
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Popis
Shrnutí:	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.
Bibliografie:	ark:/67375/WNG-SHSRMQ2D-M istex:19B6AFF062BF20A4E50072921F50089654B8C505 ArticleID:MNR19141 ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 14 content type line 23
ISSN:	0035-8711 1365-2966
DOI:	10.1111/j.1365-2966.2011.19141.x