Stellar-H I scaling relations. Galaxies are color-coded by Hubble type. In each panel, the dashed line shows a linear fit. Top left: M_{H I} vs. R_{H I} . The dotted line shows the expected relation for H I   disks with a constant mean surface density of 3.5 M_⊙ pc⁻². Top right: M_{H I} vs. L_[3.6]. The dotted line shows M_⋆ = M_gas for ϒ_⋆ = 0.5 M_⊙/L_⊙. Bottom: R_{H I} vs. R_eff (left) and R_d (right).