SPURS rest-frame UV spectrum of GNz11, providing the first direct view of its massive stars (Chen et al. 2026b).
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.
SPURS: The SPectroscopic Ultra-deep Reionization-era Survey (GO-9214) is obtaining 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 is providing the community with a vital legacy dataset for understanding the properties of the first galaxies and AGN, and what drove the reionization process.
