On radial anisotropy limits in stellar systems

A.J. Barber, H. Zhao

Research output: Contribution to journalArticlepeer-review

Abstract

Following earlier authors we re-examine the upper limits on the radial velocity anisotropy of general stellar systems; these constraints coming generically from phase-space density positivity, stability, and separability. Galaxy models almost always satisfy an inequality β <γ/2, i.e. the radial anisotropy is locally no greater than half of the logarithmic density slope. Some complex separable models are the only known cases which disobey this inequality and do so by having an exceptionally large anisotropy at the centre. Here we present newfamilies of non-separable but simple models which have β > γ/2. Such large, superthreshold anisotropy always occurs in a finite region in between an isotropic core and an isotropic outer boundary. Our models are always self-consistent and hence maintain the positivity of the phase-space density. Nevertheless, regions with superthreshold anisotropy are potentially subject to secular instability and may thus be observed in a short-lived phase of galaxies.
Original languageEnglish
Pages (from-to)3533-3543
Number of pages11
JournalMonthly Notices of the Royal Astronomical Society
Volume442
Issue number4
Early online date2 Jul 2014
DOIs
Publication statusPublished - 21 Aug 2014

Keywords

  • Methods: analytical
  • Galaxies: haloes

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