JWST spectroscopic insights into the diversity of galaxies in the first 500 Myr: Short-lived snapshots along a common evolutionary pathway Roberts-Borsani, Guido Oesch, Pascal A Ellis, Richard Weibel, Andrea Giovinazzo, Emma Bouwens, Rychard Dayal, Pratika Fontana, Adriano Heintz, Kasper E Matthee, Jorryt J ; https://orcid.org/0000-0003-2871-127X Meyer, Romain A Pentericci, Laura Shapley, Alice Tacchella, Sandro Treu, Tommaso Walter, Fabian Atek, Hakim Bose, Sownak Castellano, Marco Fudamoto, Yoshinobu Morishita, Takahiro Naidu, Rohan P Sanders, Ryan L van der Wel, Arjen ddc:520 We investigate the nature and spectroscopic diversity of early galaxies from a sample of 41 sources at $z\geqslant 10$ with James Webb Space Telescope (JWST)/NIRSpec prism observations. We compare the properties of strong ultraviolet (UV) line emitters, traced by intense C iv emission, with those of more ‘typical’ sources with weak or undetected C iv. The more typical (or ‘C iv-weak’) sources reveal significant scatter in their C iii] line strengths, UV continuum slopes, and physical sizes, spanning C iii] equivalent widths (EWs) of $\sim$1–51 Å, UV slopes of $\beta \sim -1.6$ to $-2.6$, and half-light radii of $\sim$50–1000 pc. In contrast, C iv-strong sources occupy the tail of these distributions, with C iii] EWs of 16–51 Å, UV slopes $\beta \lesssim -2.5$, compact morphologies ($r_{\rm 50} \lesssim 100$ pc), and elevated star formation surface densities ($\Sigma _{\rm SFR} \gtrsim 100\, M_\odot \, \mathrm{yr}^{-1}\, \mathrm{kpc}^{-2}$). These properties suggest concentrated starbursts that temporarily outshine the host galaxy. Comparing average properties from composite spectra, we find the diversity of the sample is primarily driven by bursty star formation on very short time-scales ($\le$3 Myr), with strong C iv emitters observed at the apex of the bursts and sources devoid of emission lines during relative inactivity. An apparent association between strong C iv and enhanced nitrogen abundance suggests both may be modulated by the same duty cycle, reflecting a generic mode of star formation. We show that active galactic nuclei are unlikely to contribute significantly to this duty cycle based on UV line diagnostics and photoionization models. Our results support a picture whereby brief bursts and lulls can explain the spectral diversity and early growth of bright galaxies in the first 500 Myr. Oxford University Press 2026 info:eu-repo/semantics/article doc-type:article text http://purl.org/coar/resource_type/c_2df8fbb1 https://research-explorer.ista.ac.at/record/21898 https://research-explorer.ista.ac.at/download/21898/21902 Roberts-Borsani G, Oesch PA, Ellis R, et al. JWST spectroscopic insights into the diversity of galaxies in the first 500 Myr: Short-lived snapshots along a common evolutionary pathway. <i>Monthly Notices of the Royal Astronomical Society</i>. 2026;548(3). doi:<a href="https://doi.org/10.1093/mnras/stag701">10.1093/mnras/stag701</a> eng info:eu-repo/semantics/altIdentifier/doi/10.1093/mnras/stag701 info:eu-repo/semantics/altIdentifier/issn/0035-8711 info:eu-repo/semantics/altIdentifier/e-issn/1365-2966 info:eu-repo/semantics/altIdentifier/arxiv/2508.21708 info:eu-repo/semantics/openAccess