Gerhard Hensler (University of Vienna)

Shaping and Survival of High-velocity Clouds -- Gerhard Hensler Colloquium

Abstract

According to the hierarchical structure formation scenario in CDM
cosmology, our Milky Way should experience a continuous merging
with Dark Matter (DM) subhaloes which are expected to harbour
baryonic matter. Since our Milky Way is steadily bombarded by
high-velocity clouds (HVCs) which must partly originate from
the intergalactic medium, the question has to be addressed whether
these HVCs are embedded in DM subhalos.

During their approach to the Galaxy HVCs have to pass through the
galactic hot halo gas and should experience its ram pressure and
Kelvin-Helmholtz (KH) instability. To explore what extent of the
baryonic matter should be stripped off from the DM subhalos
and how the cloud shape and cloud disruption depend on the DM
existence, high-resolution hydrodynamical simulations of HVCs
passing the hot gas in the galactic gravitational potential
are performed in order to study their stripping properties and
differences of the cloud shapes with vs. without DM subhalos.

Since we can conclude that HVCs are DM-free objects, reasonable
simulations have to consider their survival without DM subhalos
for different HVC masses and densities. By this, we can prove that
the usually neglected process of thermal conduction between both
gas phases helps the HVCs to suppress KH instability and extent
their lives on their passage through the hot halo.
Further consequences will be debated.