The Planck era: a new perspective on the magnetized interstellar medium

Investigating the physics of the interstellar medium (ISM) is key to understand how our Galaxy works and evolves. The ISM is the fuel of the Galactic engine, the matter reservoir of the Milky Way to allow for new star formation. This interstellar plasma is a melting pot of cosmic rays, multiphase gas, and dust particles, all tightly coupled with magnetic fields. It is through their interactions that a complex cycle, involving gravity, several phase transitions, and magneto-hydrodynamic turbulence, leads diffuse/warm matter to condense into denser/colder regions, where stars eventually form. However, the detailed processes of this matter cycle are still unclear. For decades, one of the most difficult challenges of observational astrophysics has been the characterization of magnetic fields along this evolutionary sequence.
Today, thanks to the technological breakthrough of new experiments, such as the Planck satellite, we are now entering a new era to probe the magnetic properties of the ISM.

In this talk, after reviewing the state-of-the-art investigation of magnetic fields in the Milky Way, I will give an overview of the recent Planck results on the magnetized ISM. Using all-sky maps of linear polarization at sub-millimeter wavelengths, for the first time, we were able to trace the magnetic field structure of our own Galaxy with unprecedented statistics. I will focus on several aspects of the data analysis to show the relevance of magnetic fields in the Galactic environment, from the diffuse medium to the regions where early star formation takes place.

I will conclude with interesting perspectives for the future to study the magnetic properties of the Milky Way by combining multiple probes of the ISM with existing and upcoming experiments, such as Planck, LOFAR, and SKA.