the haze

Greg Dobler (UCSB) gave the astro seminar today, on the WMAP, Fermi, and now Planck haze at the center of the Milky Way. My take-away is that, energetically, it is not hard to explain, but specifically it has morphological features that are hard to explain. That's like so damned much in astrophysics!

Not much other work got done, except I shocked (shocked!) the crowd at stats school by saying that it is almost never the case that you want to select models based on chi-squared per degree of freedom. You can show that your models are bad fits that way, but you can't really choose among models that way. It is related to Gould's intemperate comment about accuracy vs precision: Model selection is a precision question, not an accuracy question.

inference talk

I thought about my IAS talk tomorrow; I am giving a talk I have never given before, about modeling the data, and the power that gives you. After our Brown Bag seminar (by Gabadadze, on the cosmological constant problem), I chatted with my various students about the possibility that we could re-reduce the WMAP data. With what I learned at Leiden, I am certain that it is possible to make a higher signal-to-noise map than the official map, and get better parameters. But that is a huge job I am not willing to take on. I also tried to talk Kazin (NYU) and Blanton into some homogeneity tests, with little effect. A scattered day, but there are lots of good ideas floating around. One issue I might mention tomorrow: There is no proper probabilistic approach (I know) for measuring two-point functions. Readers: Do you know anything?

New Directions in Modern Cosmology, day 2

Today was my first day at the meeting in Leiden, named above. It is an eclectic group, because the idea was to bring together outsiders and insiders in the whole cosmology thing and have people hash it out: A great idea. The talks were good, but I hope I will be forgiven for saying that (for my geeky self) I learned the most from the talk given by Hao Liu (Beijing), who is re-analyzing the WMAP data starting at the time stream. He is finding many very interesting things out about the calibration, attitude model, and map-making. It appears that the quadrupole amplitude is very soft. It is all about attitude and configuration modeling, just like Hipparcos, which is not surprising. Plus there are sidelobe issues. It appears that no-one, not Hou or the WMAP team, is building the full likelihood including all calibration parameters and then marginalizing out everything but the map (or the cosmological parameters). That is, there still is not an honest Bayesian analysis (if that is even possible!).

stars, pulsars, dark matter

I can't say I did much research today but I saw two beautiful talks, and going to talks does count as research.

At lunch time Dmitry Malyshev (NYU) gave a beautiful talk on millisecond-pulsar and dark-matter contributions to the observed haze at the Galactic Center from Fermi and WMAP. He showed specific pulsar-plus-DM models that explain the spectral properties of the haze beautifully, many of which are natural for both pulsars and the DM. In some, he had to make the electron–positron emission from pulsars very high, but it really is an unknown. He mentioned that 47 Tuc (globular cluster) is a key observable Fermi source for distinguishing these ideas. Malyshev was very cautious and made no strong claims, but my excitement about the possibility that dark matter annihilation is being observed grew during the presentation.

In the afternoon, Nathan Smith (Berkeley) gave an outstanding talk about extremely massive stars as observed in our own Galaxy and nearby galaxies, including their dramatic explosions and mass-loss episodes. These are incredibly rich in their kinematic and chemical properties and have implications for chemical abundance propagation, star formation, supernova prediction, and the evolution of the young universe. He made a comment at the end about extrapolating theories we don't understand into regimes where we have no data which made the astronomers laugh and the particle theorists ask And?.