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2018 Hot Sci @ STScI

Constraining AGB Extremes in Local Group Galaxies, To Grow a Supermassive Black Hole: Investigating the Connection Between Mergers and the Diverse Family of Active Galactic Nuclei

Presented by: Martha Boyer (Space Telescope Science Institute)
Category: Science Colloquia   Duration: 30 minutes   Broadcast date: July 25, 2018
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Carbon-rich Asymptotic Giant Branch (AGB) stars are important contributors of dust and chemical enrichment in galaxies. They form easily at low metallicity due to efficient dredge up and a low surface abundance of oxygen that leads to C/O>1 in their atmospheres, but they are much less common in metal-rich environments. Model predictions for carbon star formation vary significantly at high metallicity owing to a lack of calibration observations. I will discuss a new observing strategy that uses the WFC3/IR medium-band filters, which are a powerful and efficient tool for identifying carbon stars in distant galaxies by sampling key near-infrared molecular features. We have used this strategy in several fields across M31's disk, taking advantage of M31's metallicity gradient and diversity in stellar age. There is a clear effect at the highest metallicity, which shows an order of magnitude drop in the number of carbon stars. To further demonstrate the potential of this technique, I will also briefly discuss results from another program that uses the same observing strategy in nearby dwarf galaxies to identify dust-producing AGB stars. Finally, I will discuss how to do similar observations with JWST.