Gaia Challenge 2014

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End of October, I was in Heidelberg to attend the Gaia Challenge workshop at the Max Planck Institute for Astronomy (MPIA). This workshop series was initiated last year by Justin Read, Mark Gieles and Daisuke Kawata at the University of Surrey (Guilford, south of London). This year we came together again, but this time the meeting was organized by Glenn van de Ven, who is a research-group leader at the MPIA. Glenn booked the Haus der Astronomie (house of astronomy) for us, which is a public outreach building on the premises of MPIA. The cool thing about it is that it’s shaped like a spiral galaxy (see photo above). The bulge of the Haus der Astronomie is a large auditorium and the spiral arms consist of seminar rooms and a child day care center. It’s quite a unique place! 

About 80 participants came together to work on modeling problems related to the Gaia mission. We formed five groups with significant overlap between each other:

  1. spherical & triaxial systems (like dwarf galaxies),
  2. disks (meaning mainly the Galactic disk),
  3. streams & halo stars (everything which is not in the Galactic bulge or the disk),
  4. collisional systems (i.e. star clusters),
  5. astrophysical parameters (covering everything non-dynamical Gaia is going to measure).

I had the fun role of being the coordinator of the streams & halo stars group. Together with Andreaa Font, I organized our daily meetings, lead the discussions in the group, focussed our modeling efforts, and summarized our progress. Our mission is to identify streams (i.e. groups of stars that are coherent in phase space) in survey data like Gaia’s first data release (expected early 2017) and then find fitting dynamical models for it. Sounds simple, but it’s absolutely not. With still 2.5 years to go until Gaia data release 1, we are still struggling with the most basic problems. But the workshop gives the stream & halo stars community a great forum to come together and figure out how to address these issues.

The concept of the workshop is to pose challenges in form of numerical simulations (which can be downloaded from the Gaia Challenge wiki). These we take as idealized survey data. The modelers apply their respective methods to this idealized data and try to recover the underlying (known) model parameters of the simulation. For the streams group this means that we make a numerical simulation of a dissolving Galactic satellite, like Palomar 5 or the Sagittarius dwarf galaxy, and let it form a stream. The modelers then get the stream stars’ positions and velocities and have to figure out what the parameters of the Galactic model are, which was used in the simulation. A first attempt of collectively solving one specific challenge is the Palomar 5 challenge that I posted. Several people are trying to model it right now, and we are collectively writing a paper about the results using github. It’s all open science, and everybody is invited to join!

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