Coffee+Discussions


 * Coffee Discussions and outcomes:**

Every morning (except Tue) we meet for informal discussion in the Founders Room about an interesting paper (astro-ph or otherwise) or topic related to the program. Below are listed the topics thus far discussed and those discussed next time. Discussion leader should write a small summary of their conclusions (if any) from these discussion below:

1) Wed. Feb.22: Louis Strigari discussed Jardel & Gebhardt, Astrophys.J. 746 (2012) 89 ( arXiv:1112.0319 [astro-ph.CO]). The theme of the discussion was whether Schwarzschild models confirm previous dynamical analysis that the Vmax of Fornax is 20 km/s (assuming ``CDM priors"). The paper indicated that the M300 is down by a factor of 3 relative to the canonical 10^7 Msun value, and that a core in the DM profile is favored over a cusp. However, there are two issues that came up with this later interpretation: 1) the authors should explore whether a cusp in the stellar distribution provides the same results for a core in the dark matter, and 2) the model appears to be over-constrained so it's not clear how to interpret the chi2 values that are reported in the paper. Regarding the Vmax (mass) measurement, if doesn't seem that it's possible to put Fornax in a more massive halo, so on the surface this confirms previous analysis and doesn't do much to alleviate the classical satellites issue.

2) Thu. Feb.23: Laura Sales discussed the impact of reionization in dwarf galaxies. The discussion aimed at pinning down observational consequences of reionization in the star formation histories of Local Group dwarfs.

3). Fri. Feb 24: Frank van den Bosch discussed self-interacting dark matter, in particular the papers by Loeb & Weiner (arXiv:1011.6374) and Vogelsberger et al. (arXiv:1201.5892). In these papers a Yukawa like potential is adopted for the interaction, resulting in a velocity dependent interaction cross-section. By having the cross-section suppressed at high velocities, cores can be created in low mass haloes without effecting much the structure of more massive dark matter haloes. The simulations by Vogelsberger indicate that SIDM with a Yukawa-interaction may help (though probably not completely solve) the ``too big to fail problem'' of the MW dwarf galaxies.

4). Mon Feb. 27: Discussion about the issue whether dIrr can be the progenitors of dEs. A particular issue that is discussed is the specific frequency of globular clusters. It is concluded that data is too poor to draw firm conclusions, although input from GC experts would be appreciated.

5). Wed. Feb. 29: This is when Nick & Stacy wanted to discuss re-ionization and baryon fractions. Slides from Stacy's Tuesday talk

6). Thu. Mar. 1: Carlos on the "too big too fail" problem.

7). Fri. Mar. 2: Oleg on the mass of the Milky Way.

8). Wed. Mar 7: Stefania talked about First Stars and First Galaxies, discussing the results of the paper //Ultra faint dwarfs: probing early cosmic star formation//, Salvadori & Ferrara 2009, MNRAS Letters, Vol. 395, Issue 1, pp. L6-L10