MAGALOPS:
the magnetic field of the Galaxy, from optical starlight polarization.

What makes our Galaxy’s ecosystem so fascinating is the complex interactions between its components: stars, gas, dust, magnetic fields, and cosmic rays. Of these components, the Galactic magnetic field may well be the most enigmatic. Only partially observable through indirect means, its study relies heavily on modeling, almost exclusively using line-of-sight integrated radio-polarimetric data. Although much has been learned, many questions are still unanswered especially about the turbulent, small-scale field component and out-of-plane field.

The innovations in the ERC project MAGALOPS are large independent data sets with 3D (distance) information – which can only be provided by stars polarized due to differential absorption by interstellar dust, with known distances – and more advanced Bayesian statistics which allows including prior knowledge and enables quantitative model comparison.

MAGALOPS consists of three sub-projects:

  1. Optical polarimetric surveys: two new polarization surveys in the V (visual) band will result in polarimetry of millions of stars across the southern sky. With distance information provided by the GAIA satellite, this improves the current data situation by 3 orders of magnitude.
  2. Modeling the Galactic magnetic field using bayesian methods and statistics: this will make use of IMAGINE, a Bayesian inference software package which we are developing. Our optical polarimetric data will be included as a new tracer; the first tracer in a 3D grid instead of a 2D projection.
  3. Interstellar dust: In order to include optical polarimetry, we need to produce a 3D all-sky (out to absorption limits) dust distribution consistent with both UV/optical/near IR absorption and optical polarization.
We expect that MAGALOPS will result in a next-generation Galactic magnetic field model that includes heterogeneous observational tracers and can use informative priors. It will allow mapping out interstellar magnetized turbulence in the Galaxy, instead of providing averaged parameters only, and understanding the interplay between the local magnetic field, gas and dust. Its legacy is a 1000x increased stellar polarization catalog, an all-sky 3D dust model, a bayesian sampler for Galactic magnetic field models, and a superior Galactic magnetic field model for use in cosmic ray modeling or foreground subtraction.