On the gravitational content of molecular clouds and their cores

Abstract

(Abridged) The gravitational term for clouds and cores entering in the virial theorem is usually assumed to be equal to the gravitational energy, since the contribution to the gravitational force from the mass distribution outside the volume of integration is assumed to be negligible. Such approximation may not be valid in the presence of an important external net potential. In the present work we analyze the effect of an external gravitational field on the gravitational budget of a density structure. Our cases under analysis are (a) a giant molecular cloud (GMC) with different aspect ratios embedded within a galactic net potential, and (b) a molecular cloud core embedded within the gravitational potential of its parent molecular cloud. We find that for roundish GMCs, the tidal tearing due to the shear in the plane of the galaxy is compensated by the tidal compression in the z direction. The influence of the external effective potential on the total gravitational budget of these clouds is relatively small, although not necessarily negligible. However, for more filamentary GMCs, the external effective potential can be dominant and can even overwhelm self-gravity, regardless of whether its main effect on the cloud is to disrupt it or compress it. This may explain the presence of some GMCs with few or no signs of massive star formation, such as the Taurus or the Maddalena's clouds. In the case of dense cores embedded in their parent molecular cloud, we found that the gravitational content due to the external field may be more important than the gravitational energy of the cores themselves. This effect works in the same direction as the gravitational energy, i.e., favoring the collapse of cores. We speculate on the implications of these results for star formation models.

Accepted for publication in MNRAS

References in corpus (5)

• Theory of Star Formation
• Star cluster disruption by giant molecular clouds
• Magnetic Fields in Dark Cloud Cores: Arecibo OH Zeeman Observations
• Six Myths on the Virial Theorem for Interstellar Clouds
• Remarks on Rapid vs. Slow Star Formation

Cited by in corpus (12)

• The Green Bank Ammonia Survey: Dense Cores Under Pressure in Orion A
• From diffuse gas to dense molecular cloud cores
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• WISDOM Project -- IX Giant Molecular Clouds in the Lenticular Galaxy NGC4429: Effects of Shear and Tidal Forces on Clouds
• Eventful Evolution of Giant Molecular Clouds in Dynamically Evolving Spiral Arms
• The dynamical evolution of molecular clouds near the Galactic Centre -- III. Tidally--induced star formation in protocluster clouds
• Tidal foces as a regulator of star formation in Taurus
• Bird's eye view of molecular clouds in the Milky Way: I. Column density and star formation from sub-pc to kpc scales
• Accretion and Diffusion Timescales in Sheets and Filaments
• Weather Forecast of the Milky Way: Shear and Stellar feedback determine the lives of Galactic-scale filaments
• The effect of tidal forces on the Jeans instability criterion in star-forming regions
• Why most molecular clouds are gravitationally dominated