2016MNRAS.459.3861C

We assemble a sample of disc star-forming galaxies from the Sloan Digital Sky Survey Data Release 7, studying the structure of Hα emission lines, finding a large fraction of this sample contains boxy Hα line profiles. This fraction depends on galaxy physical and geometric parameters in the following way: (1) it increases monotonically with star formation rate per unit area (Σ_SFR), and stellar mass (M_*), with the trend being much stronger with M_*, from ∼0 per cent at M_*=10¹⁰ M_☉ to about 50 per cent at M_*=10¹¹ M_☉; (2) the fraction is much smaller in face-on systems than in edge-on systems. It increases with galaxy inclination (i) while i