Archive for thin disk

thick disc formation scenario of the Milky Way evaluated by ABC

Posted in Statistics, University life with tags , , , , , , , on July 9, 2014 by xi'an

“The facts that the thick-disc episode lasted for several billion years, that a contraction is observed during the collapse phase, and that the main thick disc has a constant scale height with no flare argue against the formation of the thick disc through radial migration. The most probable scenario for the thick disc is that it formed while the Galaxy was gravitationally collapsing from well-mixed gas-rich giant clumps that were sustained by high turbulence, which prevented a thin disc from forming for a time, as proposed previously.”

Following discussions with astronomers from Besancon on the use of ABC methods to approximate posteriors, I was associated with their paper on assessing a formation scenario of the Milky Way, which was accepted a few weeks ago in Astronomy & Astrophysics. The central problem (was there a thin-then-thick disk?) somewhat escapes me, but this collaboration started when some of the astronomers leading the study contacted me about convergence issues with their MCMC algorithms and I realised they were using ABC-MCMC without any idea that it was in fact called ABC-MCMC and had been studied previously in another corner of the literature… The scale in the kernel was chosen to achieve an average acceptance rate of 5%-10%. Model are then compared by the combination of a log-likelihood approximation resulting from the ABC modelling and of a BIC ranking of the models.  (Incidentally, I was impressed at the number of papers published in Astronomy & Astrophysics. The monthly issue contains dozens of papers!)