Modelling Galaxies with a 3D Multi-Phase ISM

We present a modified TREE-SPH code to model galaxies in three dimensions. The model includes a multi-phase description of the interstellar medium which combines two numerical techniques. A diffuse warm/hot gas phase is modelled by SPH, whereas a cloudy medium is represented by a sticky particle scheme. Interaction processes (such as star formation and feedback), cooling, and mixing by condensation and evaporation, are taken into account. Here we apply our model to the evolution of a Milky Way type galaxy. After an initial stage, a quasi-equilibrium state is reached. It is characterised by a star formation rate of ∼1 M⊙ yr–1. Condensation and evaporation rates are in balance at 0.1–1 M⊙ yr–1.

N63A: A Supernova Remnant in a Cloudy Medium

Our recently obtained HST WFPC2 images of N63A reveal shocked cloudlets in the SNR interior. The study of N63A helps us understand the structure and evolution of SNRs in a cloudy medium.

The Formation of the Galactic Bulge

The question is adressed whether the problem of the stellar metallicity distribution and the dynamics of the stellar components in the bulge as found out by refined observations during recent years can be understood within the context of the evolution of the whole Galaxy. A selfconsistent galaxy model has to explain the apparent differences in the effective yields of the enrichment of bulge, disk and halo. Moreover, it has to account for the observed age-metallicity distribution of the stellar components. It appears that chemo-dynamical infall models provide a consistent description of the bulge, in particular the metallicity distribution of the K giants. It should be emphasized that simple closed-box models are not appropriate, because during the bulge formation there is infall of cloudy medium (CM), as well as outflow of hot, ionized gas ejected by supernovae type II (SNII). Therefore dynamical processes have to be taken into account. For details of the chemo-dynamical description we refer to Samland & Hensler (1994) and references therein.

X-ray Emission from Supernova Remnants in a Cloudy Medium

Young SNRs expand to much larger radii in a cloudy ISM than in a homogeneous medium, and they can have large variations in the pressure. The collision between supernova ejecta and an ambient cloud can result in an expanding high pressure region (a “secondary blast wave”). Observations of MSH 15–52 can be accounted for in this manner. X-ray emission from both young and older SNRs can provide an important probe for inferring the structure of the ISM.