dust lanes and AGN

In group meeting, Wu gave a nice summary of Julianne Dalcanton's result that low-mass disk galaxies don't appear to have dust lanes. Dalcanton et al suggest that this has to do with gravitational instability in a rotating disk; the large disks are unstable to gravitational collapse of dust and gas, while the small disks aren't. This hypothesis links the presence of dust lanes with metallicity evolution in a non-trivial way, because you get higher metallicity when the gas from early generations of stars collapses efficiently to make new stars. Wu and I are interested in whether this relates to the trends of PAH emission with luminosity (since PAH emission comes from illuminated, dusty regions).

After Wu, Renbin Yan (Berkeley) showed beautiful results on post-starburst galaxies, LINERs, and Seyferts in DEEP2 and SDSS. He finds that a lot of red galaxies contain LINERs, and many post-starburst galaxies contain LINERs. He has many punchlines, but among them are that certain emission-line ratio selections can reliably select red galaxies (because some kinds of weak AGN—or whatever they are—appear only in early-type galaxies), and that there aren't enough post-starburst galaxies in DEEP2 and SDSS to explain the evolution in the red sequence since a redshift of unity. This is great, because other paths to the red sequence are hard to find (given that red galaxies do not look like faded versions of blue galaxies).

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