MIfa Colloquium - Naveen Reddy (UC Riverside)

Title: he Ionization States and Dust Contents of High-Redshift Galaxies from Keck and JWST Spectroscopy

Abstract: A key goal of JWST is to explore the connection between massive stars and the state and contents of the ISM across cosmic history.  First, I will discuss the dependence of ionization parameter on metallicity and gas density.  Recent analyses using Keck and JWST spectroscopy demonstrate the importance of gas density in setting the physical conditions of the ISM at high redshift, and suggest a redshift invariance of the connection between gas density and ionization parameter between redshift z~2 to z~6, and possibly up to z~9.  Second, I will present new constraints on the shapes of the nebular dust attenuation curves and dust covering fractions from JWST/NIRSpec spectroscopy of HI Balmer and Paschen emission lines in z=2-4 galaxies.  I will discuss a few implications of the dust attenuation curves, including their affect on star-formation rates and some common emission lines ratios used to determine chemical abundances at high redshift.