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2011MNRAS.413.1899P - Mon. Not. R. Astron. Soc., 413, 1899-1912 (2011/May-3)
From the molecular-cloud- to the embedded-cluster-mass function with a density threshold for star formation.
PARMENTIER G.
Abstract (from CDS):
Adopting power-law volume density profiles of index p for spherically symmetric molecular clouds (clumps), we define two zones within each cloud (clump): a central cluster-forming region, actively forming stars by virtue of a local number density higher than nth, and an outer envelope inert in terms of star formation. We map how much the slope of the cluster-forming region mass function differs from that of their host clouds (clumps) as a function of their respective mass–radius relations and of the cloud (clump) density index. We find that for constant surface density clouds with density index p ≃ 1.9, a cloud mass function of index β0= 1.7 gives rise to a cluster-forming region mass function of index β ≃ 2. Our model equates with defining two distinct star formation efficiencies (SFEs): a global mass-varying SFE averaged over the whole cloud (clump), and a local mass-independent SFE measured over the central cluster-forming region. While the global SFE relates the mass function of clouds to that of embedded clusters, the local SFE rules cluster evolution after residual star-forming gas expulsion. That the cluster mass function slope does not change through early cluster evolution implies a mass-independent local SFE and, thus, the same mass function index for cluster-forming regions and embedded clusters, that is β=β*. Our model can therefore reproduce the observed cluster mass function index β* ≃ 2.
For the same model parameters, the radius distribution also steepens from clouds (clumps) to embedded clusters, which contributes to explaining observed cluster radius distributions.
Abstract Copyright: 2011 The Author Monthly Notices of the Royal Astronomical Society2011 RAS
Journal keyword(s): stars: formation - stars: kinematics and dynamics - ISM: clouds - galaxies: star clusters: general
Simbad objects: 10
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