<i>JWST</i> spectroscopic insights into the diversity of galaxies in the first 500 Myr: short-lived snapshots along a common evolutionary pathway

ABSTRACT 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.

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Journal
Monthly Notices of the Royal Astronomical Society
Published
2026-04-14
DOI
https://doi.org/10.1093/mnras/stag701
Primary Topic
Galaxies: Formation, Evolution, Phenomena
Type
article
Field-Weighted Citation Impact
0.00

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article

JWST spectroscopic insights into the diversity of galaxies in the first 500 Myr: short-lived snapshots along a common evolutionary pathway

Pratika Dayal, Fabian Walter, Guido Roberts-Borsani, Jorryt Matthee et al.
Monthly Notices of the Royal Astronomical Society
Galaxies: Formation, Evolution, Phenomena
article

JWST spectroscopic insights into the diversity of galaxies in the first 500 Myr: short-lived snapshots along a common evolutionary pathway

Pratika Dayal, Fabian Walter, Guido Roberts-Borsani, Jorryt Matthee, R. Darin Ellis, L. Pentericci, Sownak Bose, Tommaso Treu, Rohan P. Naidu, Sandro Tacchella, R. A. Meyer, Takahiro Morishita, M. Castellano, Emma Giovinazzo, Hakim Atek, Rychard Bouwens, Pascal A. Oesch, Alice E. Shapley, Arjen van der Wel, A. Fontana, Andrea Weibel, K. E. Heintz, Yoshinobu Fudamoto
article en

Abstract

ABSTRACT 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.

Monthly Notices of the Royal Astronomical SocietyVol. 548(3)
University of Geneva (CH), Leiden University (NL), California Institute of Technology (US), University of Copenhagen (DK), Centre National de la Recherche Scientifique (FR), University of Kentucky (US), Institute of Science and Technology Austria (AT), Chiba University (JP), University of California, Los Angeles (US), University of Groningen (NL), Durham University (GB), Tohoku University (JP), University of Cambridge (GB), Astronomical Observatory of Rome (IT), Institut d'Astrophysique de Paris (FR), Ghent University (BE), Sorbonne Université (FR), Kavli Institute for Particle Astrophysics and Cosmology (US), Max Planck Institute for Astronomy (DE), DAWN Center for Independent Living (US), Canadian Institute for Theoretical Astrophysics (CA), Astronomical Institute of the Slovak Academy of Sciences (SK), University College London (GB)
National Science Foundation, National Aeronautics and Space Administration, Spine Education and Research Institute, Entomological Society of America, Gruber Foundation, Communal Studies Association, Space Telescope Science Institute, National Research Foundation, Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung, Danmarks Grundforskningsfond, Japan Society for the Promotion of Science, Staatssekretariat für Bildung, Forschung und Innovation
Openalex Percentile: Top 99%
Galaxies: Formation, Evolution, Phenomena
DOIOpen Access PDFOpenAlex
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