Thursday, August 17, 2006

L. Portinari: Cosmological formation of disk galaxies and the Tully-Fischer relation

The Tully-Fischer relation (TFR) for disk galaxies relates the absolute luminosity to its rotation speed. The angular momentum in simulations however is difficult to match with observed values and this is most probably due to the simplified treatment of baryons and thereby, again, feedback.

The question if the disk forms from a cooling flow from hot gas (at virial temperature) or by cold accretion is adressed and X-ray observations can give important clues here. Birnmoim & Dekel 2003 found less than 10% of the expected amount of hot gas, so cold accretion might be favorable. Gas does not need to be heated to virial temperature and there can be cold gas accreting along filaments.

They found an offset in the TFR for certain models but it was hard to grasp which objects they were, but one solution is claimed to be dynamical friction, i.e. the galaxy rotates slower than it should for the same luminosity.

Portinari et al. 2006 look at the evolution of the TFR from z=1 and find no significant mass evolution, while the individual objects gets to almost twice its mass.

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