SCYON Abstract

Received on January 30 2010

The IMF of stellar clusters: effects of accretion and feedback

Authors	Sami Dib (¹), Mohsen Shadmehri (²), Paolo Padoan (³), G. Maheswar (⁴), D.K. Ojha (⁵), and Fazeleh Khajenabi (⁶)
Affiliation	(¹) Service d'Astrophysique, DSM/Irfu, CEA/Saclay, F-91191, Gif-sur-Yvette, Cedex, France (²) Department of Mathematical Physics, National University Ireland, Co kildare, Maynooth, Ireland (³) ICREA-ICC, University of Barcelona, Spain (⁴) Aryabhatta Research Institute of Observational Sciences, Manora Peak, Nainital 263129, India (⁵) Tata Institute for Fundamental Research (TIFR), Homi Bhabha Road, Mumbai-400005, India (⁶) School of Physics, University College Dublin, Belfield, Dublin 4, Ireland
Accepted by	Monthly Notices of the Royal Astronomical Society
Contact	sami.dib@gmail.com
URL	http://arxiv.org/abs/0908.4522
Links	Orion Nebula Cluster

Abstract

We have developed a model which describes the co-evolution of the mass function of dense gravitationally bound cores and of the stellar mass function in a protocluster clump. In the model, dense cores are injected, at a uniform rate, at different locations in the clump and evolve under the effect of gas accretion. Gas accretion onto the cores follows a time-dependent accretion rate that describes accretion in a turbulent medium. Once the accretion timescales of cores of a given age, of a given mass, and located at a given distance from the protocluster clumps center exceed their contraction timescales, they are turned into stars. The stellar initial mass function (IMF) is thus built up from successive generations of cores that undergo this accretion-collapse process. We also include the effect of feedback by the newly formed massive stars through their stellar winds. A fraction of the wind's energy is assumed to counter gravity and disperse the gas from the protocluster and as a consequence, quench further star formation. The latter effect sets the final IMF of the cluster. We apply our model to a clump that is expected to resemble the progenitor clump of the Orion Nebula Cluster (ONC). The ONC is the only known cluster for which a well determined IMF exists for masses ranging from the sub-stellar regime to very massive stars. Our model is able to reproduce both the shape and normalization of the ONC's IMF and the mass function of dense submillimeter cores in Orion. The complex features of the ONC's present day IMF, namely, a shallow slope in the mass range ~ [0.3-2.5] M(sun), a steeper slope in the mass range ~ [2.5-12] M(sun), and a nearly flat tail at the high mass end are reproduced. The model predicts a 'rapid' star formation process with an age spread for the stars of 2.3x10⁵yr which is consistent with the fact that 80 percent of the ONC's stars have ages of ~<0.3 Myr. The model also predicts a primordial mass segregation with the most massive stars being born in the region between 2 and 4 times the core radius of the cluster. In parallel, the model also reproduces, at the time the IMF is set and star formation quenched, the mass distribution of dense cores in the Orion star forming complex. We study the effects of varying some of the model parameters on the resulting IMF and we show that the IMF of stellar clusters is expected to show significant variations, provided variations in the clumps and cores physical properties exist.