Disentangling the Causes and the Consequences of the [CII] Deficit

The 158 micron emission line of singly ionized carbon has become a frequent choice for studies of the most distant galaxies. The long wavelength of this far-infrared fine structure line allows for passage through gas and dust with minimal attenuation and its ability to cool both the neutral and ionized phases of the ISM make it often the brightest observed emission line in star-forming galaxies. One potential shortcoming of the [CII] line is the effect known as the [CII] deficit, in which galaxies with increased star formation often see a drop in the ratio of [CII]-to-infrared luminosity. As many programs propose to use [CII] as an indicator of star formation rates, this decreasing ratio is a worrisome sign for these studies. In order to overcome this obstacle and find the best uses for the slew of high-z [CII] detections, it is essential a complete understanding of the cause of this deficit is determined. In pursuit of this goal, observations of [CII] along with a full suite of panchromatic data from 28 nearby galaxies has been put to use. Based on preliminary results it seems the thermalization of the [CII] line in the ionized phases of the ISM is a major cause of the observed [CII] deficit.