The neutral gas (HI) in spiral galaxies is commonly thought to be confined to a very thin disc. In the past decades the HI gas has been used as a tracer to study the mass distribution in the outer parts and to prove the existence of the dark matter halos. Although these dark matter halos have long been known to exist, their shape and kinematics are still controversial.
In particular, it is unclear whether they are nearly spherical or highly flattened because of the difficulty of tracing the galactic potential in the vertical direction. In recent years, very deep HI observations have been obtained for nearby spiral galaxies and a new picture of the vertical HI distribution is now emerging. The presence of HI gas has been discovered in the halo region of spiral galaxies at large distance from the plane.
Such halo gas show an anomalous kinematics and a slower rotation with respect to the gas in the disc. So far there has been no comprehensive theoretical study of this halo gas. The origin of the gas halo can be either internal (galactic fountain) or external (gas accretion) leading to two different evolutionary models in which a larger or smaller role is played by these processes. Moreover, such gas can be used as a tracer of the galactic potential outside the plane and give unique clues on the shape of dark halos.
The proposed research will combine the observational experience of the applicant with the theoretical expertise of Professor Binney and his group at Oxford University. It aims to investigate:
- the origin of the halo gas;
- the shape of dark matter halos;
- the role of gas accretion in galaxy evolution and in warp formation.
The applicant is expected, during this fellowship, to acquire skills in the interpretation of general astrophysical problems and the use of sophisticated numerical methods. This will offer extensive benefits to the development of his research career.
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