Gravity or turbulence? Velocity dispersion–size relation

By J. Ballesteros-Paredes, Lee W. Hartmann Enrique V'azquez-Semadeni Fabian Heitsch, Manuel Zamora-Avil'es. 2010

178 citations recorded by the source corpus.

We discuss the nature of the velocity dispersion versus size relation for molecular clouds. In particular, we add to previous observational results showing that the velocity dispersions in molecular clouds and cores are not purely functions of the spatial scale but involve surface gas densities as well. We emphasize that hydrodynamic turbulence is required to produce the first condensations in the progenitor medium. However, as the cloud is forming, it also becomes bound, and gravitational accelerations dominate the motions. Energy conservation in this case implies |Eg |∼ Ek, in agreement with observational data, and providing an interpretation for two recent observational results: the scatter in the δv–R plane, and the dependence of the velocity dispersion on the surface density δv 2 /R ∝ � . We argue that the observational data are consistent with molecular clouds in a state of hierarchical and chaotic gravitational collapse, i.e. developing local centres of collapse throughout the whole cloud while the cloud itself is collapsing, and making equilibrium unnecessary at all stages prior to the formation of actual stars. Finally, we discuss how this mechanism need not be in conflict with the observed star formation rate.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/1ddbf575439972ced447ae11014f9c1007dd6636

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In Astronomy and Astrophysics

1. E. Ostriker
2. Mark R. Krumholz
3. Ralf Klessen
4. N. Murray
5. S. Glover
6. T. Dame
7. M. Heyer
8. A. Leroy

Citations in the corpus

• Modeling UV Radiation Feedback from Massive Stars. II. Dispersal of Star-forming Giant Molecular Clouds by Photoionization and Radiation Pressure (2018, background): “…processes to support them against gravitational collapse without dispersal (Krumholz et al. 2006; Goldbaum et al. 2011), while this kind of finely calibrated turbulent driving is not needed if GMCs are dispersed rapidly (Elmegreen 2000; Ballesteros-Paredes 2006; Ballesteros-Paredes et al. 2011).”
• 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.”
• PHYSICAL PROPERTIES OF MOLECULAR CLOUDS FOR THE ENTIRE MILKY WAY DISK (2016, background): “This increase can be explained by contraction of innerGalaxy GMCs (e.g., Ballesteros-Paredes et al. 2011; IbáñezMejı́a et al. 2016); this is the solution we advocate here.”
• 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).”
• Molecular Clouds in the Milky Way (2015, methodology): “Ballesteros-Paredes et al. (2011) interpret the displacement and correlation of σv/R 1/2 MC with 1/2 MC as collapsing clouds so that σ v reflects infalling motion of gas toward a local potential minimum rather than turbulent flows.”
• Gravity or turbulence? II. Evolving column density PDFs in molecular clouds (2011, background): “In addition, Ballesteros-Paredes et al. (2011), based on observations of massive dense cores (Caselli & Myers 1995; Plume et al. 1997; Shirley et al. 2003; Gibson et al. 2009; Wu et al. 2010), showed that the Larson (1981) relationship between velocity dispersion and size arises naturally if…”
• The CO-to-H2 Conversion Factor (2013, background): “The existence of a narrow range of proportionality coefficients, corresponding to a small interval of GMC average surface densities, is less well understood (for an alternative view on this point, see Ballesteros-Paredes et al. 2011).”