A Tale of Two Epochs -- Studying the Physical Conditions in Galaxies from Cosmic Dawn to Cosmic Noon

There is much we have yet to fully understand about the nature of star-forming galaxies across cosmic time.  In the distant, early Universe (z>5.5), the first galaxies are enshrouded in the neutral gas permeating in the intergalactic medium, shielding the first generations of stars within them from detection.  For decades, obtaining even a spectroscopic redshift for the majority of these galaxies at cosmic dawn was impossible. Contrarily, around the cosmic noon (z~2), clumps of star formation -- the fundamental building blocks of galaxies -- have long been known and deeply studied.  However, key properties such as stellar ages, sizes, and star formation rates, or physical properties such as gas density, metallicity, and ionization have remained largely unconstrained.  In both of these science cases, we have been limited by the instrumentation and technology available to us.

Now, with the advent of JWST, we have witnessed an explosion of science from both of these epochs, many of which are new discoveries that shed light on previously-unreachable observations.  Due to the advanced capabilities of JWST, we have not just obtained redshifts, but also begun to characterize the sources that exist deep within the heart of the reionization era.  That same improvement in resolution and sensitivity has enabled the study of individual clumps of star formation in lensed galaxies across cosmic time to exquisite spatial detail.

In this talk, I will highlight some of the exciting science that has emerged from these two epochs of cosmic history driven by JWST's spectroscopic capabilities.  I will share early characterizations of the physical conditions from integrated light of galaxies in the reionization era, highlighting the massive shift this subfield has undergone.  Additionally, I will visualize the power of spatially-resolved spectroscopy -- using JWST to map the physical conditions of galaxies on sub-kpc scales, tracing the spatial variation of key properties across the extent of individual galaxies and individual star-forming clumps.  I will share work from several ERS and Cy1 programs targeting distant galaxies and spatially-resolved spectroscopy of highly-magnified clumpy galaxies across the peak of cosmic star formation and into the reionization era.