star-galaxy separation, substructure

Ross Fadely and Beth Willman (Haverford) came in for two days, making my visitor list pretty long! We discussed Fadely's early-days results on star–galaxy separation. He has some strange objects that are obviously stars but are better fit by galaxies. We tasked him with giving more detail on a few of these cases to see if there is something simple wrong (or too general) with the galaxy models we are using, or too restrictive about the star models we are using.

In the afternoon, Willman gave the physics colloquium about the ultra-faint galaxies. What a rich and successful field this has been! And (in my humble view) it all started here at NYU with a pair (here and here) of papers. Now these galaxies are found to be incredibly numerous, observed to contain dark matter (Willman focused on the velocity measurements of Simon & Geha), possible sites for observable dark-matter annihilation (though Willman didn't discuss that at all), and promise to increase in observed number dramatically in the next decade.

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