Gravity or turbulence? II. Evolving column density PDFs in molecular clouds

By J. Ballesteros-Paredes, E. Vázquez-Semadeni, A. Gazol, L. Hartmann, F. Heitsch, Pedro Colin Centro de Radioastronom'ia y Astrof'isica. D Astronomy, U. D. O. Physics, Astronomy, U. N. C. C. Hill. 2011

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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.

Subfields: Astronomy and Astrophysics, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/13b40466571a02e3aa7eff0961029e269d93598e

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Citations in the corpus

ON THE STAR FORMATION EFFICIENCY OF TURBULENT MAGNETIZED CLOUDS (2012, background): “…(Federrath et al. 2008a) and in pure grid simulations (Dib & Burkert 2005; Vázquez-Semadeni et al. 2008; Cho & Kim 2011; Kritsuk et al. 2011a; Ballesteros-Paredes et al. 2011; Collins et al. 2012; Safranek-Shrader et al. 2012), though with a significantly narrower parameter range than…”
Dispersal of molecular clouds by ionizing radiation (2012, background): “…from gravitational amplification of noise in the density field (Bonnell & Bate 2002) or from initial turbulence leading to density fluctuations which are subsequently enhanced by gravity (Heitsch et al. 2009; Ballesteros-Paredes et al. 2011,?; Walch et al. 2010, 2012; Girichidis et al. 2011, 2012).”
Global hierarchical collapse in molecular clouds. Towards a comprehensive scenario (2019, background): “(7) should not be confused with that followed by the component of the velocity driven by self-gravity, which, as pointed out in Ballesteros-Paredes et al. (2011a), is instead expected to follow a relation of the form σv/R 1/2 ∝ Σ1/2 (cf. Sec.”
The meaning and consequences of star formation criteria in galaxy models with resolved stellar feedback (2013, background): “This is precisely what is seen in detailed simulations of turbulent media, in the absence of “pumping” to unbind collapsing regions (Ballesteros-Paredes et al. 2011; Padoan & Nordlund 2011; Padoan et al. 2012).”
The structure of the interstellar medium of star‐forming galaxies (2011, background): “Indeed, even in these simulations, hints have often appeared of non-lognormal ‘tails’ in the distribution (see Ballesteros-Paredes et al. 2011).”
THE MAGELLANIC MOPRA ASSESSMENT (MAGMA). I. THE MOLECULAR CLOUD POPULATION OF THE LARGE MAGELLANIC CLOUD (2011, methodology): “A lognormal distribution in column density is predicted by numerical simulations of the turbulent interstellar medium (e.g., Ballesteros-Paredes et al. 2011), althoug an excess at low column densities, such as we find in Figure 4, is often seen as well, representing warmer or unperturbed gas (Wada…”
WHAT DETERMINES THE DENSITY STRUCTURE OF MOLECULAR CLOUDS? A CASE STUDY OF ORION B WITH HERSCHEL (2013, background): “…theory, a purely lognormal distribution is only expected if the cloud structure is shaped by supersonic, isothermal turbulence while deviations in the form of a power law for high column densities are predicted for self-gravitating clouds (Klessen et al. (2000), Ballesteros-Paredes et al. (2011)).”
THE STAR FORMATION RATE OF TURBULENT MAGNETIZED CLOUDS: COMPARING THEORY, SIMULATIONS, AND OBSERVATIONS (2012, background): “…at high densities (Klessen 2000; Dib & Burkert 2005; Federrath et al. 2008a; VázquezSemadeni et al. 2008; Cho & Kim 2011; Kritsuk et al. 2011a; Ballesteros-Paredes et al. 2011; Collins et al. 2012; Safranek-Shrader et al. 2012), which has been observed in the column density PDFs of clouds…”