Martin, star-galaxy likelihoods

Nicolas Martin (Strasbourg) came in to NYU after the M31 Conference in Princeton. He gave an extended version of his conference talk on the substructure, streams, shells, and stellar halo discoveries they are making with their huge PAndAS survey of a large part of the M31–M33 virial region. Martin is also thinking a lot about star–galaxy separation, a subject close to my heart these days. We are both working in ways that we can combine results, in that we are both producing likelihoods or marginalized likelihoods that can be multiplied together, with his likelihood relating to magnitude and morphology, and our (heavily marginalized) likelihood relating to spectral energy distribution. Remember: Even if you and your friends are all Bayesians, you want to communicate via likelihood functions!