Comparing direct and IR fine-structure metallicity measurements

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Understanding the processes regulating the heavy element content ('metallicity') of galaxies is one of the most important problems in astrophysics. Many studies in recent years have had great success in developing our understanding of metallicity, both in the local Universe and at high redshift. These studies have resulted in a great advance in our knowledge of the physics underlying galaxy evolution. It is, however, critical to note that essentially all of these findings were conducted using optical light, and are therefore likely to be strongly biased. Optical lines are poor probes of highly dusty regions: optical metallicity tracers can therefore fail to probe the very regions which are driving galaxy evolution. We are contacting a matched study, comparing metallicity relations derived both in the optical and the infra-red for a sample of dusty galaxies. These galaxies have existing Herschel far-IR spectroscopy (and far-IR-derived metallicities), which are minimally affected by dust. This observing trip is undertaken in order to conduct a program of optical spectroscopy to derive 'direct' optical metallicities for this sample, to enable a comparison between metallicities derived using traditional optical methods, and IR line methods.