2009年02月27日

Galaxies made simple

At farst glance a galaxy looks pretty complex : each contains bilions of stars subject to many influences including gravity, rotation and radiation.

The hierarchical theory of galaxy formation - currently fashinoable - holds that they are assembled from smaller pieces, through many mergers of cold dark matter, and that the properties of individual galaxies are determinied by six independent parameters.

Now a survey of 200 individual galaxies suggests that things are simpler than that, and that galactic structure is controlled by a single parameter. Though frustratingly, it is not yet clear which parameter that is.

This lebel of organization is at odds with hierarchical galaxy formation and the predictions of cold dark matter cosmology.


### DataBace ###
nature Vol.455 1007-1148 Issue no.7216 23 October 2008
News and Vews p.1049/ ASTROPHYSICS : How do galaxies from? / Sidney van den
Letter p.1082 / Galaxies appear simpler than expected M J Disney et al. (cardiff University)

Galaxies are complex systems the evolution of which apparently results from the interplay of dynamics, star formation, chemical enrichment and feedback from supernova explosions and supermassive black holes.(de Jong,R.S.Island Universes: Structure and Evolution of Disk Galaxies - Astrophys. Space Sci. Proc., Springer,2007)

the hierarchical theory of galaxy formation holds that galaxies are assembled from samller pieces, through numerous mergers of cold dark matter.(Baugh,C.M.A primer on hierarchical galaxy formation: the semi-analytical approach.Rep.Prog.Phys. 69,3101-3156/2006)(Dalcanton,J.J, Spergel,D.N. & Summers,I.J. The formation of disk galaxies. Astrophys. J. 482,659-676/1997)(Mo,H.J., Mao,S & White, S.D.M. The formation of galactic discs. Mon. Not. R.Astron. Soc. 295,319-336/1998)

The properties of an individual galaxy should be controlled by six independent parameters including mass, angular momentum, baryon fraction, age and size, as well as by the accudents of its recent haphazard merger history.

Here we report that a sample of galaxies that were first detected through their neutral hydrogen radio-frequency emission, and are thus free from optical selection effects (Disney,M.J. in The Low Surface Brightness Universe - eds Davies,J.I., Impey,C & Phillipps,S.-/9-18/-IAU Symp. 171, Astoron.Soc.Pacif. Conf. Ser.170,Astronomical Society of the Pacific,1999) , shows five independent crrelations among six independent observables, despitehaving a wide range of properties.(Blumenthal,G.R., Faber,S.M., Primack,J.R., & Rees,M.J. Formation of galaxies and large-scale structure with cold dark matter. Nature 311,517-525/1984)

This implies that the structure of these galxies must be controlled by a single parameter, although we cannot identifi this parameter fromour data set.

Such a degree of organization appears to be odds with hierarchical galaxy formation, a central tenet of the cold dark matter model in cosmology.

posted by 0≠素子 at 23:10| Comment(0) | cosmos | このブログの読者になる | 更新情報をチェックする
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