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Chloe Bosomworth (Hertfordshire)

Multi-object spectroscopy of HII Regions in M31 and a direct test of the metallicity dependence of alpha CO
When Dec 05, 2022
from 10:35 AM to 10:55 AM
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Giant Molecular Clouds (GMCs) are the main sites of star formation in galaxies and are home to the majority of HII regions - typically small regions of the molecular clouds that have been photoionized by newly formed massive stars. The gas-phase metallicities of such HII regions are tracing the latest phase of a galaxy’s chemical evolution. We have conducted a spectroscopic survey of HII regions in the Andromeda galaxy (M31) with the MMT/Hectospec, complemented by a novel dust continuum and CO survey of GMCs, conducted with the Submillimeter Array. Using a BPT diagram we classified our sources as HII regions or otherwise from their emission line ratios. We have calculated metallicities from strong-line diagnostics for around 250 HII regions, values ranging from solar to super-solar. From these, we have calculated a value for the radial gradient of oxygen abundance, which is consistent with literature values within error. We investigate the significant scatter around this radial trend, occurring especially within the 12 kpc ring where the majority of star-forming regions are found, suggesting that this environment is not well-mixed. This is not due to galaxy-scale trends but occurs even between nearby clouds. Furthermore, by combining the MMT and SMA results of the same GMCs, we obtain a unique direct test of the metallicity dependence of the SMA-derived alpha CO factor, i.e., the crucial factor to convert CO emission to mass. Preliminary results suggest that there is no directly observable trend of the alpha CO factor with metallicity, in spite of a considerable dynamic range of metallicities covered in this experiment.