SCYON Abstract

Received on May 29 2003

Formation of globular clusters in hierarchical cosmology

Authors	Andrey V. Kravtsov (¹), Oleg Y. Gnedin (²)
Affiliation	¹ Department of Astronomy and Astrophysics and Center for Cosmological Physics, The University of Chicago, Chicago, IL 60637 ² Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218
Submitted to	Astrophysical Journal
Contact	andrey@oddjob.uchicago.edu \| ognedin@stsci.edu
URL	http://arXiv.org/abs/astro-ph/0305199
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Abstract

We study the formation of globular clusters in a Milky Way-size galaxy using a high-resolution cosmological simulation. The clusters in our model form in the strongly baryon-dominated cores of supergiant molecular clouds in the gaseous disks of high-redshift galaxies. The properties of clusters are estimated using a physically-motivated subgrid model of the isothermal cloud collapse. The first clusters in the simulation form at z ~ 12, while the best conditions for globular cluster formation appear to be at z ~ 3-5. Most clusters form in the progenitor galaxies of the virial mass M_h 10⁹ Mo and the total mass of the cluster population is strongly correlated with the mass of its host galaxy: M_GC = 3.2 x 10⁶ Mo (M_h/10¹¹ Mo)^{1.13 ± 0.08}. This corresponds to a fraction ~ 2 x 10^-4 of the galactic baryons being in the form of globular clusters. In addition, the mass of the globular cluster population and the maximum cluster mass in a given region strongly correlates with the local average star formation rate. We find that the mass, size, and metallicity distributions of the globular cluster population identified in the simulation are remarkably similar to the corresponding distributions of the Milky Way globulars. We find no clear mass-metallicity or age-metallicity correlations for the old clusters. The zero-age mass function of globular clusters can be approximated by a power-law dN/dM ~ M^-alpha with alpha ~ 2, in agreement with the mass function of young stellar clusters in starbursting galaxies. However, the shape of the zero-age mass function may be better described by the high-mass tail of a log-normal distribution which peaks at ~ 10³ Mo. In particular, the logarithmic slope of the mass function alpha in the model steepens with increasing mass, suggesting the possible existence of a maximum cluster mass. We discuss in detail the origin, universality, and dynamical evolution of the globular cluster mass function. Our results indicate that globular clusters with properties similar to those of observed clusters can form naturally within young dense gaseous disks at z > 3 in the concordance Lambda CDM cosmology.