February 11, 2010: Galactic Sleuthing Lecture and Public Observing

This past Friday, Dr. Allyson Sheffield, a current post-doc of the Columbia Astronomy department, gave a talk entitled, ''Galactic Sleuthing: Unraveling the Milky Way’s Past.'' In her talk, Allyson described two prevailing models for galactic formation. First, 'monolithic collapse' posits that a galactic-sized gas reservoir (of Hydrogen and Helium) collapses all at once, creating an old population halo of stars first and then flattens out into a disk composed of younger stars. Second, she presented the theory of 'hierarchical merging' that posits that galaxies are built up from the accretion of smaller galaxies and the merging of bigger ones.

Allyson then talked about how we can determine which scenario better describes the evolutionary path of our own galaxy by looking at both the group motions of stars and their shared chemical abundances. By showing us data and simulations by Rodrigo Ibata and his collaborators and by our very own Prof. Kathryn Johnston, respectively, she showed us how the merging Sagittarius dwarf galaxy was discovered by surveying stellar velocities in the galaxy along with models that describe how the dwarf galaxy would currently look which were later confirmed by additional chemical abundance observations.

Finally, she showed us how one can merge the two indicators of common ancestry to look at moving groups closer to us and determine if evidence for other accreted dwarf galaxy remnants remain in the galaxy by looking at the spectra of stars with similar peculiar velocities. She found that she could likely link certain groups to larger ones seen in the galactic halo stellar streams by models that would predict the location of these peculiar stars. Given her research and the other research she presented, we learned that merging plays a significant role in galaxy evolution and that one can recount this evolution based on remnants of past accretion events.

We had a great turn out and our attendees made full use of our facilities by watching astronomy visualizations on our 3-D wall, ran by graduate student Jana Grcevich, and by going to the roof to stargaze. It's cool to think that many of the stars we observed, including our own, exhibit group origins or movements that were probably even more defined in the past.

Thanks to the 8 volunteers and the 130 people who attended our lecture and observing night!