Left: sky distribution of the subsample of galaxies observed by Herschel. Red, green, and blue symbols are used to indicate galaxies belonging to the red sequence, green valley, and blue cloud, respectively. Filled dots indicate dust-rich galaxies, while empty symbols are undetected objects. The size of the symbols is proportional to the stellar mass of galaxies: medium size symbols are for objects with 10^8.5<M_star ≤ 10^9.5M_⊙, small size symbols for 10⁸ ≤ M_star ≤ 10^8.5M_⊙. Centre: sky distribution of the subsample of galaxies observed in spectroscopic mode by the SDSS. Filled dots indicate galaxies with an equivalent width in the Hα emission line EW Hα_emi> 3 Å (and S/N> 5), witnessing a nuclear star-forming activity. Right: same as central plot but where filled dots indicate PSB galaxies. In these last two plots, medium size symbols are for objects with 10^8.5<M_star ≤ 10^9.5M_⊙; small size symbols are for M_star ≤ 10^8.5M_⊙.