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STScI Webcast

2016 Fall Science Colloquia

Reconciling the Massive Stars and Nebular Emission in High Redshift Galaxies

Presented by: Charles Steidel (California Institute of Technology)
Category: Science Colloquia   Duration: 1 hour   Broadcast date: October 05, 2016
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Massive stars produce the most readily-observed signatures of forming galaxies at high redshift -- the FUV stellar continuum and the nebular/recombination emission excited by stellar EUV radiation field. Encoded in these spectra, which can be observed from the ground in the observed-frame optical and near-IR, are details of the stellar and gas-phase chemical abundances, the physical conditions in the galaxy ISM, and the nature of the massive stellar populations. Most of the efforts to understand the rapidly-improving observations of high-redshift star-forming galaxies have used low-redshift samples as both statistical baseline and to establish calibrations for extracting physical insight from comparatively crude data such as that available at high redshift. I will discuss why this type of approach is dangerous, and may lead to incorrect conclusions for galaxies observed at high redshift. Using data obtained as part of the Keck Baryonic Structure Survey (KBSS), I will show that the simultaneous analysis of FUV stellar and FUV/optical nebular spectra of the same galaxies can be used successfully to ``close the loop'' with internally consistent models of high redshift galaxies -- without reference to low-redshift, where the conditions that once prevailed at high redshift have become extremely rare. I will discuss what one can hope to measure reliably, and what will remain challenging, using current and future surveys based on rest-frame UV/optical spectra of high redshift galaxies.