Numerical simulations of radial heating in the Galaxy

It has long been known that older stellar populations have higher velocity dispersion in the Solar neighbourhood than the younger ones. This has been interpreted as a 'heating' of the stellar disk as a function of time. In a previous paper we examined this heating via numerical simulations. We concentrated on the heating due to the perturbations by giant molecular clouds (GMCs) and putative massive compact dark halo objects in the Solar neighbourhood. With an appropriate combination of massive halo objects and GMCs we could fit the observed heating of the stellar disk in the Solar neighbourhood within observational accuracy. In order to further explore the implications of the heating of the stellar disk by putative massive dark halo objects we have now examined via numerical simulations how the velocity dispersion evolves globally - not just in the Solar neighbourhood. We compare our results to the observational data by Lewis & Freeman (1989). We find that the stellar disk heating due to massive halo objects of mass 10(6) M-.(80% of the dark halo would be comprised of these objects) and the presently observed molecular gas distribution is not inconsistent with the observations.