Geha and lucky

Marla Geha (Yale) gave the astrophysics seminar, on the star-formation properties of low-luminosity galaxies. She (with Blanton, Tinker, Yan at NYU) finds an incredibly strong environmental effect: Low-luminosity galaxies that are far from any massive parent galaxy are all star-forming, whereas those more nearby are in a mix of star-forming and non-star-forming. It is not just a trend: There really are no non-star-forming, isolated, low-luminosity galaxies. This makes these galaxies very valuable tools for cosmlogy and galaxy formation, as Geha noted and the crowd discussed. The seminar was just what I love: Lots of constructive and interesting interruptions and discussion, mainly because the results are so interesting and valuable; this really is a significant discovery. It is the strongest (in some sense) known environmental effect for galaxies, and it immediately rules out many simplistic ideas about low-mass galaxies, like that their star formation histories will be shut off by supernova feedback.

On the airplane to visit Bloom's CTDI at Berkeley, I worked more on our side project on Lucky Imaging. I got the code working (finally) and then handed it off to Foreman-Mackey. I have to get back to the things I am supposed to be doing! (Although one of the things that I love about my job is that procrastination like this is valuable in the long term.)


  1. I will constructively point out that there are at least a couple of known isolated, low-luminosity non-star forming galaxies in the Local Group: Cetus and Tucana (e,g., Monelli et al. 2010b, c). Based on their radial velocities, they could have interacted with the MW at fairly high redshifts, but such galaxies do actually exist. I still completely agree with the importance of low luminosity galaxies as tracers of environmental effects.

  2. @dweisz: The effect is strongest -- ie, the galaxies are all star forming -- at distances > 1.5 Mpc, which I think is farther than these two.