High Velocity Clouds and the Local Group

Abstract

It was proposed by Blitz et al. (1999) that High Velocity Clouds (HVCs) are remnants of Local Group formation and the average distance of HVCs is 1 Mpc, which is the result of a simple dynamical calculation leading to match the observed HVCs distributions. However, in this paper, we clearly show that fitting the observed HVCs distributions by a dynamical calculation cannot provide any constraints on the average distance of HVCs. With our choices of initial conditions, the observational results in Wakker & van Woerden (1991) are produced in our simulations for the models of both Galactic and extragalactic origins. Moreover, because Zwaan & Briggs (2000) reported that they failed to locate any extragalactic counterparts of the Local Group HVCs in a blind HI 21-cm survey of extragalactic groups, we propose to use ``remnants of galactic disc formation'' as the modification for the picture of ``remnants of galaxy group formation'' in Blitz et al. (1999) and thus reduce the possible average distances of HVCs to be about or less than a few hundred kpc.