Generation of angular momentum in cold gravitational collapse
Abstract
During the violent relaxation of a selfgravitating system, a significant fraction of its mass may be ejected. If the timevarying gravitational field also breaks spherical symmetry, this mass can potentially carry angular momentum. Thus, starting initial configurations with zero angular momentum can, in principle, lead to a bound virialised system with nonzero angular momentum. Using numerical simulations we explore here how much angular momentum can be generated in a virialised structure in this way, starting from configurations of cold particles that are very close to spherically symmetric. For the initial configurations in which spherical symmetry is broken only by the Poissonian fluctuations associated with the finite particle number N, with N in range 10^{3} to 10^{5}, we find that the relaxed structures have standard "spin" parameters λ ~ 10^{3}, and decreasing slowly with N. For slightly ellipsoidal initial conditions, in which the finiteN fluctuations break the residual reflection symmetries, we observe values λ ~ 10^{2}, I.e. of the same order of magnitude as those reported for elliptical galaxies. The net angular momentum vector is typically aligned close to normal to the major semiaxis of the triaxial relaxed structure and of the ejected mass. This simple mechanism may provide an alternative, or complement, to the socalled tidal torque theory for understanding the origin of angular momentum in astrophysical structures.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 January 2016
 DOI:
 10.1051/00046361/201526756
 arXiv:
 arXiv:1505.03371
 Bibcode:
 2016A&A...585A.139B
 Keywords:

 methods: numerical;
 galaxies: elliptical and lenticular;
 cD;
 galaxies: formation;
 Astrophysics  Astrophysics of Galaxies;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 12 pages, 13 figures. Accepted for publication in Astronomy and Astrophysics