Using [CII] 158 micron Emission from Isolated ISM Phases as an Improved Star-Formation Rate Indicator

The brightest observed emission line in many normal star-forming galaxies is the [CII] 158 $\mu$m line, making it detectable in up to z$\sim$6 galaxies. It is thus imperative that we have the tools to fully understand how this emission line could be utilized as a tracer of galactic properties like star formation rate. There are two main challenges to using the[CII] 158 $\mu$m lineline as a star formation rate indicator, its multiphase origins and the decrease in [CII] to infrared luminosity in more active galaxies often referred to as the ` [CII] deficit'. In order to better understand and quantify the [CII] emission as a tracer of star-formation, the theoretical ratio between the [NII] 205 $\mu$m line emission and the [CII] 158 $\mu$m line emission has been employed to empirically determine the fraction of \CII\ emission that originates from the ionized and neutral phases of the ISM. Sub-kiloparsec measurements of the [NII] 205 $\mu$m line line in nearby galaxies have recently become available as part of the \textit{Herschel} KINGFISH program. With the information from these two far-infrared lines along with the multi-wavelength suite of KINGFISH data, an improved calibration of the [CII] emission line as a star formation rate indicator and better understanding the cause of the [CII] deficit are investigated. We find that the [CII] emission originating in the neutral phase of the ISM does not exhibit a deficit with respect to the infrared luminosity and is therefore preferred over the total [CII] 158 $\mu$m line emission as a star formation rate indicator for the galaxies included in this sample