LOW VIRIAL PARAMETERS IN MOLECULAR CLOUDS: IMPLICATIONS FOR HIGH-MASS STAR FORMATION AND MAGNETIC FIELDS

By Jens Kauffmann, T. Pillai, Paul F. Goldsmith. 2013

161 citations recorded by the source corpus.

Whether or not molecular clouds and embedded cloud fragments are stable against collapse is of utmost importance for the study of the star formation process. Only “supercritical” cloud fragments are able to collapse and form stars. The virial parameter α = Mvir/M, which compares the virial mass to the actual mass, provides one way to gauge stability against collapse. Supercritical cloud fragments are characterized by α ≲ 2, as indicated by a comprehensive stability analysis considering perturbations in pressure and density gradients. Past research has suggested that virial parameters α ≳ 2 prevail in clouds. This would suggest that collapse toward star formation is a gradual and relatively slow process and that magnetic fields are not needed to explain the observed cloud structure. Here, we review a range of very recent observational studies that derive virial parameters ≪2 and compile a catalog of 1325 virial parameter estimates. Low values of α are in particular observed for regions of high-mass star formation (HMSF). These observations may argue for a more rapid and violent evolution during collapse. This would enable “competitive accretion” in HMSF, constrain some models of “monolithic collapse,” and might explain the absence of high-mass starless cores. Alternatively, the data could point at the presence of significant magnetic fields ∼1 mG at high gas densities. We examine to what extent the derived observational properties might be biased by observational or theoretical uncertainties. For a wide range of reasonable parameters, our conclusions appear to be robust with respect to such biases.

Subfields: Astronomy and Astrophysics, Fluid Flow and Transfer Processes, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/7f7fca54c9d764b162ed843ac24c65ac1f5f9c75

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Citations in the corpus

On the universality of interstellar filaments: theory meets simulations and observations (2015, background): “This leads to the dimensionless virial ratio αvir = 1.0 (also typical for molecular clouds in the Milky Way; see Falgarone et al. 1992; Kauffmann et al. 2013; Hernandez & Tan 2015) and to a plasma beta parameter (ratio of thermal to magnetic pressure) β = 0.33 or an Alfvén Mach number MA = 2.0.”
Global hierarchical collapse in molecular clouds. Towards a comprehensive scenario (2019, background): “…(e.g., Williams & Blitz 1998) (ii) Clouds appear to be close to equipartition between their kinetic and gravitational energies, except at low column densities, where large kinetic energy excesses are often found (e.g., Larson 1981; Heyer et al. 2009; Kauffmann et al. 2013; Leroy et al. 2015).”
ATLASGAL — towards a complete sample of massive star forming clumps ⋆ (2014, background): “A log–log linear regression fit to the distribution gives a slope of −0.53 ± 0.16, which is similar to values reported by Kauffmann et al. (2013) from their analysis of massive star formation studies in the literature (e.g. Sridharan et al. 2002; Wienen et al. 2012).”