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On the emergent system mass function: the contest between accretion and fragmentation

Clark, Paul C. ORCID: and Whitworth, Anthony P. ORCID: 2021. On the emergent system mass function: the contest between accretion and fragmentation. Monthly Notices of the Royal Astronomical Society 500 (2) , 1697–1707. 10.1093/mnras/staa3176

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We propose a new model for the evolution of a star cluster’s system mass function (SMF). The model involves both turbulent fragmentation and competitive accretion. Turbulent fragmentation creates low-mass seed proto-systems (i.e. single and multiple protostars). Some of these low-mass seed proto-systems then grow by competitive accretion to produce the high-mass power-law tail of the SMF. Turbulent fragmentation is relatively inefficient, in the sense that the creation of low-mass seed proto-systems only consumes a fraction, ∼23 per cent (at most ∼50 per cent⁠), of the mass available for star formation. The remaining mass is consumed by competitive accretion. Provided the accretion rate on to a proto-system is approximately proportional to its mass (dm/dt ∝ m), the SMF develops a power-law tail at high masses with the Salpeter slope (∼−2.3). If the rate of supply of mass accelerates, the rate of proto-system formation also accelerates, as appears to be observed in many clusters. However, even if the rate of supply of mass decreases, or ceases and then resumes, the SMF evolves homologously, retaining the same overall shape, and the high-mass power-law tail simply extends to ever higher masses until the supply of gas runs out completely. The Chabrier SMF can be reproduced very accurately if the seed proto-systems have an approximately lognormal mass distribution with median mass ∼0.11M⊙ and logarithmic standard deviation σlog10(M/M⊙)∼0.47⁠).

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Publisher: Oxford University Press
ISSN: 0035-8711
Date of First Compliant Deposit: 5 January 2021
Date of Acceptance: 17 August 2020
Last Modified: 06 May 2023 01:03

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