Collaborative Research: Establishing the Physical Picture for Rest-optical Emission Lines in Star-forming Galaxies from Cosmic Noon to Cosmic Dawn

Astronomers aim to measure several fundamental properties of galaxies across cosmic time. These include the rate at which new stars are being born, the proportion of so-called heavy elements (e.g., oxygen) relative to hydrogen, and the nature of the radiation field to which the interstellar medium (ISM) is exposed (be it light from massive stars or from accretion onto a supermassive black hole). These key galaxy properties are commonly inferred from the pattern of spectral emission lines produced by the ionized ISM. However, it has been shown that the translation between the spectrum of a galaxy and the underlying physical conditions prevailing in that galaxy may be qualitatively different in galaxies observed within the first few billion years of cosmic time, relative to what is observed in the universe today. Shapley and Sanders will analyze data from several hundred galaxies, observed roughly 10 billion years ago when the universe was forming stars at its peak level, to establish this essential translation between galaxy spectral and physical properties. They will also build a publicly available software tool for the community for modeling the spectra of galaxies all the way back to cosmic dawn within the first billion years after the Big Bang. Shapley and Sanders will also engage in several efforts in public outreach, partnering with the WorldWide Telescope Ambassadors Program to develop interactive tours across the night sky on topics such as astronomical spectroscopy. They will incorporate these pedagogical materials into ongoing outreach efforts at each of their respective campuses. There are important questions regarding the translation of rest-optical emission line properties to physical ones (e.g., star-formation rate, gas-phase oxygen abundance, ionization parameter) in distant galaxies. The co-PIs have assembled the definitive sample of z=1.5-2.5 star-forming galaxies from the Keck MOSFIRE Deep Evolution Field (MOSDEF) survey. They will use this sample to establish the translation between galaxy emission-line and physical properties, and build and publicly release a software tool for robust modeling of the rest-optical emission-line spectra of distant galaxies all the way back to cosmic dawn (z>6). The proposed products will provide a lasting legacy as we enter into a new era for near-IR spectroscopy with great observatories in space. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.