Based on 19 high-resolution N-body/gasdynamical galaxy formation simulations in the \Lambda CDM cosmology it is shown , that for a galaxy like the Milky Way , in addition to the baryonic mass of the galaxy itself , about 70 % extra baryonic mass should reside around the galaxy ( inside of the virial radius ) , chiefly in the form of hot gas .
Averaging over the entire field galaxy population , this ‘ ‘ external ’ ’ component amounts to 64-85 % of the baryonic mass of the population itself .
These results are supported by the recent detection of very extended , soft X-ray emission from the halo of the quiescent , massive disk galaxy NGC 5746 .
Some of the hot gas may , by thermal instability , have condensed into mainly pressure supported , warm clouds , similar to the Galactic High Velocity Clouds ( HVCs ) .
Based on an ultra-high resolution cosmological test simulation of a Milky Way like galaxy ( with a gas particle mass and gravity softening length of only 7.6x10 ^ { 3 } h ^ { -1 } M _ { \odot } and 83 h ^ { -1 } pc , respectively ) , it is argued , that the hot gas phase dominates over the warm gas phase , in the halo .
Finally , an origin of HVCs as ‘ ‘ leftovers ’ ’ from filamentary , ‘ ‘ cold ’ ’ accretion events , mainly occurring early in the history of galaxies , is proposed .