The [CII] 158 μm line is a frequent target for studies of the interstellar medium (ISM) in galaxies near and far. Often the brightest observed emission line from star forming galaxies and an important cooling channel in photodissociation regions (PDRs), proposals have been made to use [CII] emission to trace a variety of phenomena in galaxies, including star formation, shocks, and CO-dark molecular gas. In order to better understand how the local environment affects the strength of this emission, we present a [CII] map of the galaxy NGC 7331 obtained with FIFI-LS on-board SOFIA. NGC 7331 is a highly-inclined spiral galaxy with an infrared-bright molecular ring and several visible spiral arms. Using this new FIFI-LS map along with the treasure trove of archival data spanning UV to millimeter wavelengths, we are able to probe the ISM conditions in isolated environments across NGC 7331. Through SED modeling the UV attenuation rate, FIR emission, and PAH emission can be estimated and compared to the [CII] emission to measure the heating and cooling rates across the ring, spiral arms, and disk. With these methods we find significant differences between the ISM heating efficiencies in the nucleus, ring, spiral arms, and disk of this galaxy. By comparing the [CII] emission across NGC 7331 to archival CO maps from HERACLES, we are able to use [CII] to search for CO dark molecular gas. The results of this in-depth analysis of NGC 7331 highlight how [CII] 158 μm emission can be affected by a wide variety of galaxy properties and helps to uncover the differences between galactic environments. Using the work we have done with NGC 7331 as a guide, we plan to expand our analysis of the environmental effects on [CII] emission using additional FIFI-LS and Herschel PACS maps of well-studied local universe galaxies.
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