JWST is transforming our view of star formation and supermassive black hole growth in the first billion years. NIRCam imaging has revealed an unexpected abundance of bright z>9 galaxy candidates. NIRSpec prism spectroscopy has shown several of the brightest sources show extremely high ionization emission lines and peculiar abundance patterns, implying the presence of very massive stars and/or AGN, and detections of Lyman-alpha emission at z>10 suggest these hard ionizing sources may drive an earlier start to reionization than we had expected.
However, our understanding has been limited to sources with the brightest rest-frame UV emission lines.
The critical next step is ultra-deep high resolution rest-frame UV spectroscopy of galaxies at our redshift frontier to: confidently distinguish between massive stars and AGN powering galaxies' ionizing spectra, reveal direct emission from very massive stars, uncover the growth mode of high-redshift AGN, measure the physical conditions which facilitate early star formation and black hole growth, and constrain the onset of reionization.
We propose SPURS: The SPectroscopic Ultra-deep Reionization-era Survey (GO-9214) - 160 hrs of R~1000 NIRSpec spectroscopy of >150 z~5-14 galaxies, selected primarily from the deepest public spectroscopic surveys, including the majority of spectroscopically confirmed z>9 galaxies, with 30 hr depths in G140M. SPURS will provide the community with a vital legacy dataset for understanding the properties of the first galaxies and AGN, and what drove the reionization process.
