The two-component virial theorem and the acceleration-discrepancy relation

Abstract

We revisit the 'two-component virial theorem' (2VT) in the light of recent theoretical and observational results related to the 'dark matter problem'. This modification of the virial theorem offers a physically meaningful framework to investigate possible dynamical couplings between the baryonic and dark matter components of extragalactic systems. In particular, we examine the predictions of the 2VT with respect to the 'acceleration-discrepancy relation' (ADR). Considering the combined data (composed of systems supported by rotation and by velocity dispersion), we find the following: (i) The overall behaviour of the 2VT is consistent with the ADR. (ii) The 2VT predicts a nearly constant behaviour in the lower acceleration regime, as suggested in recent data on dwarf spheroidals. We also briefly comment on possible differentiations between the 2VT and some modified gravity theories.