The Origin of the Initial Mass Function and Its Dependence on the Mean Jeans Mass in Molecular

Matthew R Bate, Ian Alexander Bonnell

Research output: Contribution to journalArticlepeer-review

250 Citations (Scopus)

Abstract

We investigate the dependence of stellar properties on the mean thermal Jeans mass in molecular clouds. We compare the results from the two largest hydrodynamical simulations of star formation to resolve the fragmentation process down to the opacity limit, the first of which was reported by Bate, Bonnell & Bromm. The initial conditions of the two calculations are identical except for the radii of the clouds, which are chosen so that the mean densities and mean thermal Jeans masses of the clouds differ by factors of 9 and 3, respectively. We find that the denser cloud, with the lower mean thermal Jeans mass, produces a higher proportion of brown dwarfs and has a lower characteristic (median) mass of the stars and brown dwarfs. This dependence of the initial mass function (IMF) on the density of the cloud may explain the observation that the Taurus star-forming region appears to be deficient in brown dwarfs when compared with the Orion Trapezium cluster. The new calculation also produces wide binaries (separations >20 au), one of which is a wide binary brown dwarf system. Based on the hydrodynamical calculations, we develop a simple accretion/ejection model for the origin of the IMF. In the model, all stars and brown dwarfs begin with the same mass (set by the opacity limit for fragmentation) and grow in mass until their accretion is terminated stochastically by their ejection from the cloud through dynamically interactions. The model predicts that the main variation of the IMF in different star-forming environments should be in the location of the peak (due to variations in the mean thermal Jeans mass of the cloud) and in the substellar regime. However, the slope of the IMF at high masses may depend on the dispersion in the accretion rates of protostars.

Original languageEnglish
Pages (from-to)1201
Number of pages1201
JournalMonthly Notices of the Royal Astronomical Society
Volume356
DOIs
Publication statusPublished - 1 Feb 2005

Keywords

  • accretion
  • accretion discs
  • hydrodynamics
  • binaries : general
  • stars : formation
  • stars : low-mass
  • brown dwarfs
  • stars : luminosity function
  • mass function
  • STAR-FORMING REGIONS
  • ORION NEBULA CLUSTER
  • SMOOTHED PARTICLE HYDRODYNAMICS
  • MAIN-SEQUENCE STARS
  • CLOSE BINARY-SYSTEMS
  • COSMIC GAS CLOUDS
  • STELLAR CLUSTERS
  • BROWN DWARFS
  • TAURUS-AURIGA
  • PROPER MOTIONS

Fingerprint

Dive into the research topics of 'The Origin of the Initial Mass Function and Its Dependence on the Mean Jeans Mass in Molecular'. Together they form a unique fingerprint.

Cite this