Speed Found to be Key to Galaxy Formation

QuantumCrypto writes "The All-wavelength Extended Groth strip International Survey (AEGIS), a collaborative effort involving nearly 100 scientists in half a dozen countries, revealed a new principle in the formation of all galaxies, from disk-like spirals, cloud-like ellipticals, and just irregulars. In essence the morphology of the galaxies depends on total mass involved and the internal speed it generates. 'By defining a new speed indicator, their analysis has managed to make sense out of very chaotic-looking objects,' said Sandra Faber, professor of astronomy and astrophysics at the University of California, Santa Cruz."

Taking Tully-Fisher one more step

[TMB]

For those interested in more details, it looks like the preprint is available at http://arxiv.org/abs/astro-ph/0702643 [arxiv.org].

Originally TF was just a relationship between rotational speed and luminosity. Since luminosity is some measurement of stellar mass, it was proposed a few years ago that the true physical relationship was not with luminosity but with the total cooled baryonic mass (most of which is in the form of stars in most galaxies). So the Baryonic Tully Fisher relation was proposed, where they substituted the total mass of stars and gas instead of the luminosity. The relationship was tighter, indicating that this is closer to the fundamental relationship.

This work now takes it one more step and uses a more physical measurement for the other variable. Rotational speed of a disk galaxy tells you how deep the potential well is, assuming that all of the motion is in the form of rotation. But if there are also disordered motions, then it's really a combination of the disordered and ordered motion that tell you how deep the potential is. So they've replaced the rotation velocity with a combination of rotational velocity and velocity dispersion - and voila, the relationship is even tighter!

Very nice work.

[TMB]

Re:Simulations

[mdsolar]

I know Josh Barnes has produced some vidio of spirals rotating but I have not found it. Here are some more exciting merger simulation: http://www.ifa.hawaii.edu/~barnes/pressrel/mice/vi d301_04.mpg [hawaii.edu] and http://www.ifa.hawaii.edu/~barnes/pressrel/mice/v0 211d3.mpg [hawaii.edu] found at http://www.ifa.hawaii.edu/~barnes/research/interac tion_models/mice/index.html#modeling [hawaii.edu]. Models which concentrate on just rotation tend to be just two dimensional to save on computing. The are used to study secular evolution which could also lead from the Tully-Fisher to the Faber-Jackson relation.
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Fun with the Sun: http://mdsolar.blogspot.com/2007/01/slashdot-users -selling-solar.html [blogspot.com]

Re:Number of Turns of the Galaxy

[Anonymous Coward]

That's because the spiral is not caused by the rotation of the galaxy. It's caused by a (more slowly rotating) standing wave in spiral form in the disc. When the wave passes the matter in the disc, new bright young stars are formed and that's what you see.
This was discovered in the 60's I believe.

Tino Meinen