In composite astrophotography images, which emission, often rendered in blue or cyan, showcases the shock-heated gas structures?

Answer

OIII emission

The emission from doubly ionized oxygen, or OIII, is often represented using blue or cyan tones in composite images to highlight the structures heated by the shock front.

In composite astrophotography images, which emission, often rendered in blue or cyan, showcases the shock-heated gas structures?
SpaceastronomynebulaMilky WayVeil nebula