A physical model for the [CII]-FIR deficit in luminous galaxies

Understand

Observations of ionised carbon at 158 micron ([CII]) from luminous star-forming galaxies at z~0 show that their ratios of [CII] to far infrared (FIR) luminosity are systematically lower than those of more modestly star-forming galaxies.

• In this paper, we provide a theory for the origin of this so called "[CII] deficit" in galaxies.
• Our model treats the interstellar medium as a collection of clouds with radially-stratified chemical and thermal properties, which are dictated by the clouds' volume and surface densities, as well as the interstellar radiation and cosmic ray fields to which they are exposed.
• [CII] emission arises from the outer, HI dominated layers of clouds, and from regions where the hydrogen is H2 but the carbon is predominantly C+.