Speaker:	Allison Strom (Carnegie Observatories)
Title:	Rethinking metallicity: the quest to measure abundance scaling relations at cosmic noon
Date (JST):	Thu, Nov 07, 2019, 13:30 - 14:30
Place:	Seminar Room A
Related File:	2384.pdf
Abstract:	Large near-infrared spectroscopic surveys have confirmed that star-forming galaxies at cosmic noon (z~2-3) exhibit nebular spectra that are distinct from their local counterparts. These differences reflect important changes in the characteristic physical conditions and chemical enrichment patterns of galaxies at early times, correlated with differences in their star formation histories relative to most present-day galaxies: at z~2, almost all galaxies have nearly constant or rising star formation histories, but by z~0, galaxies overall have lower specific star formation rates and many have largely finished forming stars. Using spectra from the Keck Baryonic Structure Survey (KBSS) and photoionization models designed to reconcile the joint rest-UV-optical spectra of high-z star-forming galaxies, I have shown that the majority of z~2-3 KBSS galaxies have moderate oxygen enrichment but sub-solar iron enrichment as a result of their rapid assembly histories. I will argue that this marked alpha-enhancement means that it is imperative to consider abundance patterns rather than a single "metallicity" when describing galaxies' chemical enrichment. I will also report new measurements of the correlation between galaxy stellar mass and multiple chemical tracers (inluding O/H and Fe/H) at z~2-3 using my photoionization model method and discuss extant challenges to comparing metallicity scaling relations with predictions from cosmological simulations. These comparisons are critical for understanding the way in which energetic feedback acts to regulate galaxy assembly across redshift, which remains an open question in modern astrophysics and will be one of the key science drivers of upcoming facilities such as the James Webb Space Telescope and the ELTs.

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