RMS sensitivities (σ) of the CO(3 − 2) maps converted into molecular mass surface densities (in M_⊙ pc⁻²) as a function of luminosity distance (in Mpc). For each galaxy we show two values, connected by a vertical bar: green squares correspond to the case r₃₁ = 0.7 (average value in galaxy centers, Israel 2020) combined with the standard Milky Way disk conversion factor X_CO = 2 × 10²⁰ mol cm⁻² (K km s⁻¹)⁻¹ (Bolatto et al. 2013); blue stars correspond to the case r₃₁ = 2.9 (measured at the AGN position in NGC 1068, Viti et al. 2014) combined with the recommended conversion factor for the nuclear region of the Milky Way X_CO = 0.5 × 10²⁰ mol cm⁻² (K km s⁻¹)⁻¹ (Bolatto et al. 2013).