False three-color (red/green/blue) composite image of M 63 from Gil de Paz et al. (2007). The image was produced using the arcsinh function, which allows showing faint structures while simultaneously preserving brighter structures in the field, such as the spiral arms of large galaxies (Lupton et al. 2004). The green ellipse represents the B-band 25 mag arcsec^-2 isophote limit, r₂₅. The red solid line shows the CO mapping we performed along the major axis of M 63 from the center out to r_gal = 572″ = 1.6 r₂₅, where 27 single pointings were aligned with a spatial sampling of 22″. The red box encloses the bright UV region at r_gal = 483″ = 1.36 r₂₅ which we mapped with 6 × 2 = 12 pointings with the same spatial sampling. The CO(1–0) emission is observed out to the isophotal radius along the radial cut and in the bright UV region, while the CO(2–1) emission is confined to 0.68 r₂₅ (dashed green ellipse).