Talk:Faber–Jackson relation

Deletion of Theory Section
The theory section is an ex post facto justification of the Faber Jackson relationship that saw some currency in the 1970's after discovery of the relationship, but which is not rigorous nor fundamental. The assumption of constant surface brightness for galaxies is incorrect, in any case. The FJ relationship is now understood as a projection of the fundamental plane onto the luminosity and dispersion axes. The FP itself is understood to reflect the virial theorem with an intrinsic relationship between luminosity and mass/light ratio. In actuality the theory section adds nothing to understanding the FJ relationship and is actually misleading.

Lastly, deletion of this section addresses the "too technical" flag.

Todlauer (talk) 19:07, 25 December 2008 (UTC)

I want to add my voice to this suggestion. This 'Theory' doesn't rise to the level of scientific explanation. 1.) The assumption of a constant M/L ration is absurd. Throw in Dark Matter, and M/L ratios of 10 to 30 are not uncommon. 2.) The assumption of constant Surface brightness (as mentioned) flies in the face of all evidence. It's obvious that someone started with the relation, and worked backwards to make some unfounded assumptions. This section should be removed. There's no scientific theory to explain the FB relation.

Variation with galaxy luminosity
Currently, there is no reference for the statement that gamma varies between 3 and 15 for different galaxy masses. However, looking at, say, this paper (http://arxiv.org/abs/1004.5496) and converting from the slopes they get for magnitude to the corresponding slopes for luminosity, gamma seems to vary between 0.4 and 2.7 or so. Which is correct? —Preceding unsigned comment added by 78.60.119.219 (talk) 09:45, 24 April 2011 (UTC)