SCYON Abstract

Received on April 14 2011

Star formation efficiency as a function of metallicity: from star clusters to galaxies

Authors	Sami Dib (¹), Laurent Piau (²), Subhanjoy Mohanty (¹), and Jonathan Braine (³)
Affiliation	(¹) Astrophysics Group, Imperial College London, UK (²) LATMOS, France (³) LAB, Bordeaux, France
Accepted by	Monthly Notices of the Royal Astronomical Society
Contact	s.dib@imperial.ac.uk
URL	http://arxiv.org/abs/1102.3839
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Abstract

We explore how the star formation efficiency in a protocluster clump is regulated by metallicity dependent stellar winds from the newly formed massive OB stars (M(star) ≥ 5 M(sun)) on their main sequence. The model describes the co-evolution of the mass function of gravitationally bound cores and of the IMF in a protocluster clump. Dense cores are generated uniformly in time at different locations in the clump, and contract over lifetimes that are a few times their free fall times. The cores collapse to form stars that power strong stellar winds whose cumulative kinetic energy evacuates the gas from the clump and quenches further core and star formation. This sets the final star formation efficiency, SFE_f. Models are run with various metallicities in the range Z/Z(sun)=[0.1,2]. We find that the SFE_f decreases strongly with increasing metallicity. The SFE_f-metallicity relation is well described by a decaying exponential whose exact parameters depend weakly on the value of the core formation efficiency. We find that there is almost no dependence of the SFE_f-metallicity relation on the clump mass. This is due to the fact that an increase (decrease) in the clump mass leads to an increase (decrease) in the feedback from OB stars which is opposed by an increase (decrease) in the gravitational potential of the clump.The clump mass-cluster mass relations we find for all of the different metallicity cases imply a negligible difference between the exponent of the mass function of the protocluster clumps and that of the young clusters mass function. By normalizing the SFEs to their value for the solar metallicity case, we compare our results to SFE-metallicity relations derived on galactic scales and find a good agreement. As a by-product of this study, we also provide ready-to-use prescriptions for the power of stellar winds of main sequence OB stars in the mass range [5,80] M(sun) in the metallicity range we have considered.