Detection of two power-law tails in the probability distribution functions of massive GMCs

Schneider, N. and Bontemps, S. and Girichidis, P. and Rayner, T. and Motte, F. and Csengeri, Tímea (2015) Detection of two power-law tails in the probability distribution functions of massive GMCs. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 453 (1). ISSN 0035-8711

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Abstract

We report the novel detection of complex high-column density tails in the probabil-ity distribution functions (PDFs) for three high-mass star-forming regions (CepOB3,MonR2, NGC6334), obtained from dust emission observed with Herschel. The lowcolumn density range can be fit with a lognormal distribution. A first power-law tailstarts above an extinction (AV) of ∼6–14. It has a slope of α=1.3–2 for the ρ ∝ r−αprofile for an equivalent density distribution (spherical or cylindrical geometry), andis thus consistent with free-fall gravitational collapse. Above AV∼40, 60, and 140, wedetect an excess that can be fitted by a flatter power law tail with α >2. It correlateswith the central regions of the cloud (ridges/hubs) of size ∼1 pc and densities above104 cm−3. This excess may be caused by physical processes that slow down collapse andreduce the flow of mass towards higher densities. Possible are: 1. rotation, which intro-duces an angular momentum barrier, 2. increasing optical depth and weaker cooling, 3.magnetic fields, 4. geometrical effects, and 5. protostellar feedback. The excess/secondpower-law tail is closely linked to high-mass star-formation though it does not implya universal column density threshold for the formation of (high-mass) stars.

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