Low-energy cosmic rays: regulators of the dense interstellar medium

Low energy cosmic rays (up to the GeV domain) play a crucial role in physics and chemistry of densest phase interstellar medium. Unlike ionising radiation, they can penetrate large column densities gas, reach molecular cloud cores. By maintaining there small but not negligible gas ionisation fraction, dictate coupling between plasma magnetic field, which turn affects dynamical evolution clouds impacts on process star planet formation. The cosmic-ray hydrogen also drives rich revealed by observations spectral lines broad region electromagnetic spectrum, spanning from submillimetre visual band. Some recent developments various branches astrophysics provide us with an unprecedented view low rays. Accurate measurements constraints intensity such particles are now available both for very local medium distant clouds. interpretation these data is currently debated, emerging picture calls reassessment scenario invoked describe origin and/or transport Galaxy.