Computer Science
Scientific paper
Jan 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005esasp.576..687h&link_type=abstract
"Proceedings of the Gaia Symposium "The Three-Dimensional Universe with Gaia" (ESA SP-576). Held at the Observatoire de Paris-Me
Computer Science
Galaxies Formation, Evolution, M31
Scientific paper
In this work, we have established an inside-out infall bulge-disc formation model by assuming that the disc begins to form at different times at different radii, and the bulge forms by the disc instabilities. A radial dependent star formation prescription was adopted. It is found that no matter how the model parameters are adjusted, the M31 disc gas profile in the outer part could not be reproduced. This is different from situations in the Milky Way disc, in which the same SFR law can fairly reproduce a large number of observables. The model also predicts a steeper abundance gradient compared with observations. In order to alleviate these inconsistencies, the star formation efficiency in the outer M31 disc could be higher than that in the Milky Way disc. Furthermore, we found that to form a bulge mass comparable to what is observed in M31, the stability criterion must be less than 0.30. In this case, the model can also fairly reproduce the M31 disc rotational curve. It is possible that two giant spirals, the Milky Way and M31, in the Local Group, may form in a different way. For M31, our model calculations imply that disc instability is not an efficient mechanism for its bulge formation. We argue that fast accretion or early merger could be the alternative. Also, the outer part of the M31 disc may have been influenced by early interaction with satellite dwarfs. The Gaia satellite will certainly provide more insights into formation processes of M31 disc and bulge by resolving the underlying stellar populations.
Chang Rui-Xiang
Chen Leon L.
Hou Lu-Jing
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