m(3.4 μm)−m(22 μm) vs. m(FUV)−r colour–colour diagram for a sample of emission-line galaxies detected in the WISE 3.4 μm (W1) and 22 μm (W4) bands and in the GALEX FUV band. Galaxies with Hβ equivalent width EW(Hβ) ≥ 50 Å and with L(Hβ) ≥ 3 × 10⁴⁰ erg s^-1 are shown by red filled circles, while galaxies with EW(Hβ) < 50 Å and with L(Hβ) < 3 × 10⁴⁰ erg s^-1 are depicted by blue open circles. Galaxies with m(3.4 μm)−m(4.6 μm)≥ 2 mag are shown by large black filled circles.