Stellar Populations in the Cosmological Context: Day 2

By Julianne Dalcanton | May 4, 2010 9:49 pm

Day 2 of the meeting finds us moving away from in depth studies of individual stellar clusters, to larger ensembles of stars — namely, systems of stellar clusters (in the morning), and dwarf galaxies + tidally shredded galaxy debris, left behind as streams in the halos of nearby galaxies (in the afternoon).

The morning talks featured an exceptionally clear talk by Dean McLaughlin discussing the scaling relations one expects to see among the properties of the globular cluster population, assuming that most globular clusters are destroyed by evaporation/relaxation after they form. (Mike Fall had recently sent me the relevant papers, and I hang my head in shame at confessing I had not yet read them, but now I will, I promise.)

Highlights of the morning also included two talks with different viewpoints on the dissolution of young stellar clusters. Rupali Chandar presented a simple empirical scaling law that does a nice job of describing their distribution of cluster ages and masses. Their data can be well described by a steady dissolution of clusters over 1 Gyr timescales, (and here’s the surprising bit) with no dependence on cluster mass. Nate Bastian then presented an equally well-motivated talk discussing cluster “infant mortality”, wherein young stellar clusters should dissolve on much faster timescales (~10Myr), due to expulsion of gas, which, as Jonathon Tan’s talk on the first day pointed out, should produce a dramatic change in the binding energy, due to the very low efficiency of conversion of gas into stars, even within very massive molecular clouds. There are a ton of observational and theoretical subtleties which one would have to master to understand why smart careful people disagree on these issues — but I haven’t yet. Lots of other good stuff in Nate’s talk as well.

The afternoon talks included a perfect pedagogical introduction by Kathryn Johnston to the expected enrichment patterns in stellar halos. Many of the observations were perplexing as they came out, but her analysis does a nice job of making them seem obvious and sensible.

David Martinez-Delgado presented his deep imaging of tidal features around nearby galaxies. While it’s going to be a while until we can extract far-reaching deep quantitative conclusions from these type of data, these features are just soooo freakin’ cool. Definitely some of my favorite images from the last couple of years, and if someone strung them together with music, they’d probably get a zillion hits on youtube.

In the same “just sit back and enjoy the show” vein was Alan McConnachie’s presentation of his super duper extra wide field imaging of the are out to a radius of many-hundreds-of-kiloparsecs around the Andromeda (M31) and Triangulum (M33) galaxies. It was the kind of data that makes you want to stand up and do the wave. A big parade of Awesome!

Alan’s talk was sandwiched between talks by Annette Ferguson and Marla Geha on detailed analysis of structures within M31 and M33 and their extended dwarf and globular cluster populations. (They too have awesome data, but not of the “that would look great on youtube variety”). I was particularly impressed with Marla’s analysis showing how the inferred mechanism for supporting dwarf ellipticals changed drastically once large radius stars were included.

Ok, my need to sleep is triumphing over my need to summarize more talks, so I’ll stop here. Here’s one of David’s pictures to sleep on:

NGC 5907

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