RECALIBRATING STRONG-LINE METALLICITY DIAGNOSTICS WITH ELECTRON TEMPERATURE MEASUREMENTS FROM COMPOSITE SPECTRA OF STAR-FORMING GALAXIES
PublisherThe University of Arizona.
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AbstractGalaxy evolution is driven by the accretion of gas, the birth of stars, and the outflows of enriched gas from dying stars. We can understand how these processes behave with heavy element abundance measurements. Current studies of distant galaxies utilize “strong-line diagnostics” to determine these abundances. These measurements are not accurate as they are calibrated with nearby galaxies, which differ from galaxies seen in the early universe. One method for solving this problem is to calibrate these commonly used strong-line diagnostics for distant galaxies with a “direct” metallicity indicator that is sensitive to the electron temperature, [Oiii]λ4363. In my Honors thesis project, I analyzed data from the DEEP2 Survey with the goal of detecting this emission line. I explored different binning approaches to find the best technique to obtain optimal signal-to-noise for stacked spectra. Ultimately, I yielded seven detections and eight reliable limiting cases of [Oiii]λ4363 out of twenty-seven composite spectra. Using these measurements, I evaluated two recently published calibrations for high-redshift galaxies. Ifind that one calibration developed byJiang et al.  yielded more reliable estimates with a difference on the “R23” flux ratio of 0.03 dex with a dispersion of 0.07 dex. However, the calibration was not robust for low and high metallicities. Given these limitations, I plan to develop my own calibration that encompasses the broad range of metallicities seen for high-redshift galaxies.