SCYON Abstract

Received on July 20 2011

Volume Density Thresholds for Overall Star Formation imply Mass-Size Thresholds for Massive Star Formation

AuthorsGeneviéve Parmentier (1,2), Jens Kauffmann (3), Thushara Pillai (4), and Karl M. Menten (1)
Affiliation(1) Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
(2) Argelander-Institut für Astronomie, Bonn Universität, Auf dem Hügel 71, D-53121 Bonn, Germany
(3) Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
(4) California Institute of Technology, MC 249-17, 1200 East California Boulevard, Pasadena, CA 91125, USA
Accepted byMonthly Notices of the Royal Astronomical Society
Contactgparm@mpifr-bonn.mpg.de
URLhttp://xxx.lanl.gov/abs/1106.1173
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Abstract

We aim at understanding the massive star formation (MSF) limit m(r) = 870 M(sun) (r/pc)1.33 in the mass-size space of molecular structures recently proposed by Kauffmann & Pillai (2010). As a first step, we build on the hypothesis of a volume density threshold for overall star formation and the model of Parmentier (2011) to establish the mass-radius relations of molecular clumps containing given masses of star-forming gas. Specifically, we relate the mass mclump, radius rclump and density profile slope -p of molecular clumps which contain a mass mth of gas denser than a volume density threshold ρth. In a second step, we use the relation between the mass of embedded-clusters and the mass of their most-massive star to estimate the minimum mass of star-forming gas needed to form a 10 M(sun) star. Assuming a star formation efficiency of SFE ≅ 0.30, this gives mth,crit ≅ 150 M(sun). In a third step, we demonstrate that, for sensible choices of the clump density index (p ≅ 1.7) and of the cluster formation density threshold (nth ≅ 104 cm-3), the line of constant mth,crit ≅ 150 M(sun) in the mass-radius space of molecular structures equates with the MSF limit for spatial scales larger than 0.3 pc. Hence, the observationally inferred MSF limit of Kauffmann & Pillai is consistent with a threshold in star-forming gas mass beyond which the star-forming gas reservoir is large enough to allow the formation of massive stars. For radii smaller than 0.3 pc, the MSF limit is shown to be consistent with the formation of a 10 M(sun) star out of its individual pre-stellar core of density threshold nth ≅ 105 cm-3. The inferred density thresholds for the formation of star clusters and individual stars within star clusters match those previously suggested in the literature.