Input from stellar population models; other data
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by
mlpeck
I'm going to present a few graphs from my own modelling that show some interesting differences between the program and control samples. I have to emphasize that none of these should be used for any purpose except perhaps to get some ideas for data that might usefully be fetched from SDSS. First is just a histogram of the EW of HdeltaA, which is one of the Lick Balmer line indices developed in the mid-90's (e.g. Worthey et al. 1994, Jones & Worthey 1995). There's a similar graph buried deep in Schawinski et al. (2009) paper on blue early type galaxies:
Not too surprisingly the quench sample has rather strong Balmer absorption, but if the limit of 5A mentioned by Schawinski et al. for E+A galaxies is applicable to my estimates only a modest fraction of the quench sample (~23%) are spectroscopically E+A galaxies.
HdeltaA and D4000 are both sensitive to both age and metallicity. Here's a plot of one against another (in all of these plots the gray points and contour lines are for the control group):
All of these plots show pretty strong bimodality in the control sample. In this plot the lower right cluster of points must be passively evolving old galaxies. I haven't gotten around to checking morphologies from the GZ classifications, but I bet almost all of these are early type galaxies.
Then finally are two results from population models. These plot first "mass weighted" mean age against D4000, and next "luminosity weighted" age. One thing that might be interesting is to see if anything useful can be said about star formation histories of recently quenched galaxies. This is a matter that is given considerable attention in a paper just posted on arxiv.org today by Torres-Papaqui et al. (http://arxiv.org/abs/1308.1915).
DR10 includes results from a variety of population models, and it might be worthwhile digging around there to see if there's anything useful (certainly things like luminosity weighted ages will be estimated in most if not all of the models).
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