Density cusps: restrictions on non-axisymmetric models

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7 Citations (Scopus)

Abstract

Galactic nuclei are now generally thought to have density cusps in their centres, and the evidence is mounting that as a consequence they are unlikely to be triaxial. Self-consistent stellar dynamical models of non-axisymmetric cusps would be an interesting counterargument to this conclusion. We consider 2D analogues of triaxial cusps: a sequence of non-axisymmetric, cuspy discs first described by Sridhar & Touma. Scale-free models with potential Phi proportional to r(alpha) are examined in detail. It is shown analytically for 0 < alpha less than or similar to 0.43 that self-consistent models with positive phase-space density do not exist. Numerical solutions of the combined Vlasov and Poisson equations suggest that the whole sequence of models with 0 < alpha < 1 are also unphysical. Together with existing work on cusps, we conclude on purely theoretical grounds that galactic nuclei are not expected to be triaxial.

Original languageEnglish
Pages (from-to)407-413
Number of pages7
JournalMonthly Notices of the Royal Astronomical Society
Volume296
Issue number2
Publication statusPublished - 11 May 1998

Keywords

  • galaxies, kinematics and dynamics
  • SELF-CONSISTENT MODELS
  • DARK-MATTER HALOS
  • ELLIPTIC GALAXIES
  • SHAPES

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