I worked out one possible null hypothesis to test in my fossil groups
project: I compare the distribution of magnitude differences (second brightest minus brightest) to the distribution you get if you randomize the galaxies at fixed group multiplicity. You have to randomize within / among groups of the same multiplicity or else you will find an effect just because the luminosity distribution is a strong function of environment.
I also worked out the most conservative possible assumptions to make about galaxies with no measured redshift (a few percent of the SDSS sample from which our group catalog is built).
Maybe a bit late to ask (haven't been able to check if there's any more recent post on that).
ReplyDeleteWhich kind of groups are you using? Are they loose ones? Are there compact ones there?
How does this Delta(M_12) looks like? If I'm not mistaken there's a Hickson paper with this distribution for his catalogues groups (there's only 2 fossil groups there). Not sure also if de Carvalho published this same distribution to his DPOSS compact groups. They can be compared to yours, depending if the selection criteria used in all the cases are compatible.