interesting hints and set an observational path towards addressing the role of star formation and nuclear activity in forming galaxies.]{}

Introduction
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Modern scenarios of co-evolution between supermassive black holes (BHs) and their host galaxies envisage star formation and BH accretion to be in situ, time-coordinated processes (e.g., Lapi et al. 2006, 2011, 2014; Lilly et al. 2013; Aversa et al. 2015; Mancuso et al. 2016a,b), triggered by the early collapse of the host dark matter halos, but subsequently controlled by self-regulated baryonic physics and in particular by energy/momentum feedbacks from supernovae/stellar winds and AGNs. This results in a distinctive evolutionary pattern for the emission associated with the stellar and the nuclear component.

In a nutshell, during the early stages of a massive galaxy evolution, huge gas reservoirs can sustain violent, almost constant SFRs $\dot M_\star\ga 10^2\, M_\odot$ yr$^{−1}$, while the ambient medium is quickly enriched with metals and dust; in such conditions, the galaxy behaves as a bright sub-mm/far-IR source. After a time $\sim \hbox{several}\times10^8$ yr the SFR is abruptly quenched by the energy/momentum feedback from the central supermassive BH, and the environment is cleaned out; thereafter the stellar populations evolve passively and the galaxy becomes a red and 