In this letter, the author distinguishes between morphology (i.e. early- vs. late-type) and structure (quantified using Sersic index). Although these two properties are correlated with each other, it turns out that it is meaningful to consider them separately. In the scheme used in this letter, a galaxy is classified as early-type if it has a smooth light distribution, even
if the Sersic index is small. Conversely, a galaxy is classified as late-type if the light distribution is clumpy even if it has a high Sersic index.
The bottom panels show a strong relationship between galaxy structure (Sersic index) and stellar mass, with little residual dependence on environmental density. The top panels show a relationship between morphology (i.e. smoothness) and environmental density, with essentially no residual dependence on mass.
The key to interpreting these results is to realize that star formation tends to make the light distibution clumpy. So (specific) star formation rate depends on environmental density, while structure depends only on stellar mass.
I found this interesting because it seems to imply that whatever processes are responsible for reducing the star formation in dense regions are ~independent of the processes that determine galaxy structure.