The Physical Conditions of Low-Mass Galaxies at z=3.5-7.0 from JWST Spectroscopy: The Behaviour of Spectral Line Ratios with Burstiness
Abstract
We present a study of the physical conditions of galaxies at redshifts z=3.5−7.0, based on emission-line diagnostics of JWST NIRSpec spectra for 1889 star-forming sources spanning more than 4~dex in stellar mass. We find that the median Hα/Hβ and [OIII]/Hβ are constant throughout these redshifts, indicating a slow evolution of the interstellar medium conditions from the Epoch of Reionization to Cosmic Noon. The stellar-mass evolution of these line ratios follow the expected trend for chemical enrichment and dust build-up, with \ohb~being maximum for galaxies with M⋆ ≈ 109 M⊙, and the medians of Hα/Hβ and [OII]/Hβ monotonically increasing from M⋆ ≈ 107 through $ \approx 10^{10}\, \rm M_\odot$. Focusing on the 1552 low stellar-mass (<109 M⊙) galaxies, we particularly investigate the behaviour of the main spectral-line ratios with burstiness. We find a significantly higher degree of scatter in [OIII]/Hβ and [OII]/Hβ for high-burstiness than for low-burstiness galaxies. Values of log([OIII]/Hβ)~≳ 0.8 are almost exclusively seen amongst those with high burstiness. Meanwhile, log([OIII]/Hβ)~≲ 0.3 are virtually not found amongst high-burstiness galaxies, except at the lowest stellar masses log(M⋆/M⊙)<7.5. Our results are consistent with a scenario in which star-formation bursts produce temporary chemical enrichment that is quickly lost via stellar winds. They also suggest that metallicity measures in bursting galaxies are unstable, and that the search for the most metal-poor objects should optimally be conducted amongst low-burstiness or very low-stellar mass sources.
Related
- The Delegate Survey: KOALA/AAOmega-IFU spectroscopy of three nearby dwarf galaxies
- Precise C-N-O Abundances of Individual Galaxies in the First Billion Years from Ultra-Deep, Rest-UV-to-Optical JWST Spectroscopy
- An Archival Calibration of JWST/MIRI Prism Wide-Field Slitless Spectroscopy: Methodology, Performance, and a Mid-Infrared Spectral Atlas of Galaxies at z=0−4 in the GOODS-N/S Fields
- Quiescent Galaxies at z > 2 from CAPERS spectroscopy and their Number densities
- Cosmic Noon Galaxies in the Hubble Ultra Deep Field with MIRI Wide-Field Slitless Spectroscopy
BibTeX
@misc{cooper2026physical,
title = {{The Physical Conditions of Low-Mass Galaxies at z=3.5-7.0 from JWST Spectroscopy: The Behaviour of Spectral Line Ratios with Burstiness}},
author = {Ryan A. Cooper and Karina I. Caputi and Alessandro Marconi and Anna Feltre and Edoardo Iani and Pierluigi Rinaldi and Guillaume Desprez and Harley Katz},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.01205},
eprint = {2609.01205},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.01205},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - The Physical Conditions of Low-Mass Galaxies at z=3.5-7.0 from JWST Spectroscopy: The Behaviour of Spectral Line Ratios with Burstiness
AU - Ryan A. Cooper
AU - Karina I. Caputi
AU - Alessandro Marconi
AU - Anna Feltre
AU - Edoardo Iani
AU - Pierluigi Rinaldi
AU - Guillaume Desprez
AU - Harley Katz
PY - 2026
DA - 2026/09/02
PB - arXiv
DO - 10.48550/arxiv.2609.01205
UR - https://arxiv.org/abs/2609.01205
AB - We present a study of the physical conditions of galaxies at redshifts z=3.5−7.0, based on emission-line diagnostics of JWST NIRSpec spectra for 1889 star-forming sources spanning more than 4~dex in stellar mass. We find that the median Hα/Hβ and [OIII]/Hβ are constant throughout these redshifts, indicating a slow evolution of the interstellar medium conditions from the Epoch of Reionization to Cosmic Noon. The stellar-mass evolution of these line ratios follow the expected trend for chemical enrichment and dust build-up, with \ohb~being maximum for galaxies with M_⋆ ≈ 10^9 M_⊙, and the medians of Hα/Hβ and [OII]/Hβ monotonically increasing from M_⋆ ≈ 10^7 through $ \approx 10^{10}\, \rm M_\odot$. Focusing on the 1552 low stellar-mass (<10^9 M_⊙) galaxies, we particularly investigate the behaviour of the main spectral-line ratios with burstiness. We find a significantly higher degree of scatter in [OIII]/Hβ and [OII]/Hβ for high-burstiness than for low-burstiness galaxies. Values of log([OIII]/Hβ)~≳ 0.8 are almost exclusively seen amongst those with high burstiness. Meanwhile, log([OIII]/Hβ)~≲ 0.3 are virtually not found amongst high-burstiness galaxies, except at the lowest stellar masses log(M_⋆/M_⊙)<7.5. Our results are consistent with a scenario in which star-formation bursts produce temporary chemical enrichment that is quickly lost via stellar winds. They also suggest that metallicity measures in bursting galaxies are unstable, and that the search for the most metal-poor objects should optimally be conducted amongst low-burstiness or very low-stellar mass sources.
ER -