Galaxies
The study of the content, distribution and kinematics of interstellar gas is a key to understand the origin and maintenance of both star formation and nuclear activity in galaxies. In most Active Galactic Nuclei (AGN) the activity of the nucleus is powered by the accretion of matter onto a super- massive black hole. The processes involved in AGN fueling encompass a wide range of scales, both spatial and temporal, which have to be studied. Probing the gas flow from the outer disk down to the central engine of an AGN host, requires the use of specific tracers of the interstellar medium adapted to follow the change of phase of the gas as a function of radius. Current mm-interferometers like NOEMA and ALMA can provide a sharp view of the distribution and kinematics of molecular gas in the circumnuclear disks of galaxies through extensive CO line mapping.
On the other hand, the use of specific molecular tracers of the dense gas phase can probe the feedback influence of activity on the chemistry and energy balance/redistribution in the interstellar medium of nearby galaxies. Millimeter interferometers are able to unveil the strong chemical differentiation present in the molecular gas disks of nearby starbursts and AGNs (Figure 1). High-resolution observations are required to quantify the impact of AGN and star formation feedback on their host galaxies through the study of molecular outflows and to characterize the properties of the obscuring material around actively accreting super-massive black holes.
The formation of stars out of molecular interstellar gas is a major driver of galaxy evolution. Current Astrophysics strives to understand the different aspects of this complex process that involves physical mechanisms operating in a wide range of spatial scales. Observations of very distant galaxies conducted with mm-interferometers like IRAM NOEMA and ALMA are used to investigate the role of molecular gas in shaping the epoch of most active formation of stars in the Universe, around 10 Gyrs ago. These observations are instrumental to assess the balance between gas inflows and outflows in different populations of galaxies, as well as the feedback from accreting supermassive black holes and star formation activity. Nowadays, the latter is a cornerstone of galaxy formation models in the cosmological context. By scrutinizing closer galaxies in great detail, mm radiotelescopes also help us understand how galaxies have self-regulated their growth along their evolution (Figure 2) . In particular, the observations of molecular spectral lines inform most theoretical models of star formation. These observations reveal how the environment of the molecular clouds conditions their physical properties and, ultimately, their ability to form stars.
