Thursday, August 16, 2012

Bulges and ellipticals

I read an interesting article on the train, Galaxy Bulges and Elliptical Galaxies, lecture notes by D. Gadotti. Dimitri had helped us a lot with the MICE decomposition.
He sums up a great deal of recent research regarding the structure of galaxies. A few main points:
  • the components that we call bulges are not necessarily old 'scaled down' ellipticals as we often hear: there are classical bulges, disk-like bulges, 'box-peanuts', which may coexist or overlap.
  • 'box-peanuts' are thought to be the inner parts of bars, not separate components
  • classical bulges are kinematically hot, i.e. supported by their velocity dispersion. disk-like bulges are kinematically cold, i.e. supported by their rotation velocity.
  • there's an interesting section on photometric bulge recognition, and why the arbitrary cut on n=2 is what it is, arbitrary. I tend to believe that any classification has to be data-driven, so I'll keep the alternative suggestions in mind.
  • another interesting part is about the scaling relations, i.e. the fundamental plane and F-J relation. I didn't know that the FP can be derived directly from the virial theorem!
  • F-J and L-size relations seem to be nonlinear, according to the data.
The only thing I'm not sure about is the use of 2D K-S test, an enlightening read otherwise.

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