MUSICA · Origin of Magnetic strUctureS in the ISM obscuring the Cosmic DAwn

Origin of Magnetic strUctureS in the ISM obscuring the Cosmic DAwn

Cosmic magnetism is among the biggest unknowns in the formation of structures in the Universe. Radio observations represent a unique window to explore magnetic fields from the most diffuse and tenuous intergalactic media to the turbulent interstellar medium (ISM) of the Milky Way. The ISM is the space that fills most of the Galaxy between already existing stars and planets. It constitutes the mass reservoir for the formation of new stars that partake to the life cycle of the Galaxy. The ISM is a dynamical system made of multiphase gas (with different thermodynamical equilibrium conditions), dust particles, cosmic rays, and magnetic fields. The complex interaction among its constituents regulates Galactic evolution as a whole determining the origin of cold-dense pockets of gas, called molecular clouds, where new solar systems are born. Thus, the study of structure formation in the ISM is intimately connected to societal fundamental questions about the origin of stars, planets, and life in the Universe and the place that human beings occupy in Nature. Moreover, a thorough understanding of the Galactic ISM represents a pivotal issue for accessing with high accuracy extragalactic and cosmological signals that unavoidably reach our telescopes through the magnetized ISM. The problems of structure formation in the ISM and that of Galactic foregrounds in the radio band were our two scientific pillars in the course of our MSCA-IF project, called MUSICA. We aimed to focus on one specific aspect of structure formation in the ISM, namely the role that magnetic fields play in the formation of cold gas in the Galaxy. Our goal was to deepen the understanding of unprecedented radio observations of the magnetized Milky Way at low frequency (< 200 MHz) from the LOFAR telescope. These data offered a completely new perspective to observing the diffuse ISM toward the formation of cold gas in the Galaxy. The low-frequency radio sky is dominated by synchrotron radiation resulting from the interaction of cosmic-ray electrons gyrating around interstellar magnetic fields. However, at these low frequencies synchrotron radiation is also heavily affected by a wavelength-dependent process called Faraday rotation. The longer the wavelength the stronger the effect. Because of Faraday rotation, synchrotron polarization is rotated depending on the amount of ionized and magnetized gas along any given sightline. Thanks to its broadband receivers and high sensitivity, the LOFAR telescope provided us with the finest-ever survey of the magneto-ionic medium of our Galaxy through Faraday rotation. We spotted regions in the sky where the polarization observed with LOFAR was strongly correlated with tracers of the cold neutral interstellar gas rather than with the fully ionized gas. This opened the unprecedented possibility of probing the mutual interaction of warm and cold gas phases in the diffuse ISM under the action of magnetic fields. Our overall objectives consisted in statistically quantifying the correlation between tracers of the multiphase and magnetized ISM based on multi-wavelength observational data and to start modelling the observed signals based on state-of-the-art numerical simulations of the magnetized Galaxy. Our goal was to identify the key physical processes that give origin to the sky brightness in polarization observed with LOFAR and to provide first a statistical description of the synchrotron sky at low frequency.

Data: CORDIS, © European Union