JWST spectroscopic insights into the diversity of galaxies in the first 500 Myr

Authors

• Guido Roberts-Borsani, University College LondonFollow
• Pascal A. Oesch, University of Geneva
• Richard Ellis, University College London
• Andrea Weibel, University of Geneva
• Emma Giovinazzo, University of Geneva
• Rychard Bouwens, Leiden Observatory Research Institute
• Pratika Dayal, University of Groningen
• Adriano Fontana, Osservatorio Astronomico Roma
• Kasper E. Heintz, University of Geneva
• Jorryt Matthee, Institute of Science and Technology Austria
• Romain A. Meyer, University of Geneva
• Laura Pentericci, Osservatorio Astronomico Roma
• Alice Shapley, University of California, Los Angeles
• Sandro Tacchella, University of Cambridge
• Tommaso Treu, University of California, Los Angeles
• Fabian Walter, Max-Planck-Institut für Astronomie
• Hakim Atek, Sorbonne Universités
• Sownak Bose, Durham University
• Marco Castellano, Osservatorio Astronomico Roma
• Yoshinobu Fudamoto, Chiba University
• Takahiro Morishita, California Institute of Technology
• Rohan P. Naidu, MIT Kavli Institute for Astrophysics and Space Research
• Ryan L. Sanders, University of KentuckyFollow
• Arjen van der Wel, Ghent University

Abstract

We investigate the nature and spectroscopic diversity of early galaxies from a sample of 41 sources at (Formula presented) 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 (Formula presented) 1–51 Å, UV slopes of (Formula presented) to (Formula presented), and half-light radii of (Formula presented) 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 (Formula presented), compact morphologies ((Formula presented)  pc), and elevated star formation surface densities ((Formula presented) ). 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 ((Formula presented) 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.

Document Type

Article

Publication Date

5-1-2026

Notes/Citation Information

Publisher Copyright: © The Author(s) 2026. Published by Oxford University Press on behalf of Royal Astronomical Society.

Digital Object Identifier (DOI)

10.1093/mnras/stag701

Archival?

Archival

Repository Citation

Roberts-Borsani, Guido; Oesch, Pascal A.; Ellis, Richard; Weibel, Andrea; Giovinazzo, Emma; Bouwens, Rychard; Dayal, Pratika; Fontana, Adriano; Heintz, Kasper E.; Matthee, Jorryt; 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.; and van der Wel, Arjen, "JWST spectroscopic insights into the diversity of galaxies in the first 500 Myr" (2026). Physics and Astronomy Faculty Publications. 778.
https://uknowledge.uky.edu/physastron_facpub/778