Thermalized components/virialized

[ChrisVer]

I am trying to understand what does someone mean when he or she says that a particle component (eg for CDM) is thermalized/virialized in the galactic halo...
What happens during thermalization and what's the difference between virialized/unvirialized components?

Thanks...

 

[PeterDonis]

The Wikipedia page on the virial theorem may help, particularly the section on "in astrophysics".

 

[ChrisVer]

I think that the wiki article is just referring to the fact that matter in galaxies subject to gravitational potential, can have some statistical dispersion in velocities (the sigma), and this is related to the gravitational potential...

However it doesn't make any distinction between thermalized/non-thermalized or virialized/unvirialied or how the transition is being happening...

In case you have some cloud of CDM in the galactic halo, is that cloud virialized or not? If it is not thermalized, how does it get thermalized?

 

[Chalnoth]

The idea is that over time, a galaxy will eventually relax into a state that follows the virial theorem. But when there has been a significant recent disturbance (e.g. a merger between similar-sized galaxies), the galaxy is not well-described by the virial theorem at all.