The Interstellar Medium of the Most Luminous Galaxies, Near and Far

Galaxies spend most of their lives inhabiting what is called a main-sequence (MS) of star-formation, a peaceful and gentle state in which galaxies form stars and feed their central black holes in a steady manner. Most of the energy in the Universe at any cosmic epoch is generated within these galaxies. However, there is also a “obscured” galaxy population that, while very small in number (a few percent), still accounts for a significant fraction of the total energy production (up to 30%). The study of these incredibly luminous sources is therefore fundamental to our understanding of all the main physical processes that drive galaxy evolution. In this talk I will present results obtained from far-infrared observations of two samples of nearby and high-redshift luminous infrared galaxies, for which in-depth studies of their interstellar medium have only been made possible during the last years by the advent of state-of-the-art observatories such as Herschel or ALMA.