Co-Authors: Matt Malkan, Juan Antonio Fernandez-Ontiveros, Suyash Kumar
SOFIA observations of far-IR fine-structure lines in galaxies to measure metallicity
We present new SOFIA FIFI-LS far-IR spectroscopic observations of the fine structure lines of [OIII]52μm and [NIII]57μm of a local sample of galaxies, together with observations of the same lines, and of the [OIII]88μm line, collected mainly with the Herschel-PACS spectrometer. In total we have analysed the spectra of 29 galaxies, including SOFIA archive observations. For 19 of these galaxies we have SOFIA detections of both the[OIII]52μm line and of the [NIII]57μm line, while for the remaining 10 galaxies we present detections of the [OIII]52μm line only. We use these data to assess the metallicity and compare these results with the estimates derived from optical spectroscopy. One of the preliminary findings of this study is the systematic difference of the N/O ratio derived from the IR lines compared to that one derived from optical emission lines. As opposite, the metallicities computed from the IR and optical lines, in terms of 12+log(O/H), agree within the errors. We discuss these findings using different methods and models.