%0 Generic %1 Ballesteros-Paredes2011 %A Ballesteros-Paredes, Javier %A Vazquez-Semadeni, Enrique %A Gazol, Adriana %A Hartmann, Lee W. %A Heitsch, Fabian %A Colin, Pedro %D 2011 %K gmc gravity turbulence %T Gravity or turbulence? II. Evolving column density PDFs in molecular clouds %U http://arxiv.org/abs/1105.5411 %X It has been recently shown that molecular clouds do not exhibit a unique shape for the column density probability distribution function (Npdf). Instead, clouds without star formation seem to possess a lognormal distribution, while clouds with active star formation develope a power-law tail at high column densities. The lognormal behavior of the Npdf has been interpreted in terms of turbulent motions dominating the dynamics of the clouds, while the power-law behavior 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 Npdf, and later, in a power-law Npdf. We thus suggest that the observed Npdf 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.

@misc{Ballesteros-Paredes2011, abstract = { It has been recently shown that molecular clouds do not exhibit a unique shape for the column density probability distribution function (Npdf). Instead, clouds without star formation seem to possess a lognormal distribution, while clouds with active star formation develope a power-law tail at high column densities. The lognormal behavior of the Npdf has been interpreted in terms of turbulent motions dominating the dynamics of the clouds, while the power-law behavior 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 Npdf, and later, in a power-law Npdf. We thus suggest that the observed Npdf 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. }, added-at = {2011-05-30T18:54:41.000+0200}, author = {Ballesteros-Paredes, Javier and Vazquez-Semadeni, Enrique and Gazol, Adriana and Hartmann, Lee W. and Heitsch, Fabian and Colin, Pedro}, biburl = {https://www.bibsonomy.org/bibtex/2e954e375e2c449e64016ecef009a7acc/miki}, description = {[1105.5411] Gravity or turbulence? II. Evolving column density PDFs in molecular clouds}, interhash = {709c0c140a73897b8c68353727ac7f20}, intrahash = {e954e375e2c449e64016ecef009a7acc}, keywords = {gmc gravity turbulence}, note = {cite arxiv:1105.5411Comment: 9 pages, 4 figures. MNRAS, accepted}, timestamp = {2011-05-30T18:54:41.000+0200}, title = {Gravity or turbulence? II. Evolving column density PDFs in molecular clouds}, url = {http://arxiv.org/abs/1105.5411}, year = 2011 }