The JWST EXCELS Survey: A spectroscopic investigation of the ionizing properties of star-forming galaxies at 1<z<8
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| Natura: | Preprint |
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2025
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| author | Begley, R. McLure, R. J. Cullen, F. Carnall, A. C. Stanton, T. M. Scholte, D. McLeod, D. J. Dunlop, J. S. Arellano-Córdova, K. Z. Bondestam, C. Donnan, C. T. Hamadouch, M. L. Shapley, A. E. Stevenson, S. |
| author_facet | Begley, R. McLure, R. J. Cullen, F. Carnall, A. C. Stanton, T. M. Scholte, D. McLeod, D. J. Dunlop, J. S. Arellano-Córdova, K. Z. Bondestam, C. Donnan, C. T. Hamadouch, M. L. Shapley, A. E. Stevenson, S. |
| contents | Charting the Epoch of Reionization demands robust assessments of what drives the production of ionizing photons in high-redshift star-forming galaxies (SFGs), and requires better predictive capabilities from current observations. Using a sample of $N=159$ SFGs at $1<z<8$, observed with deep medium-resolution spectroscopy from the JWST/NIRSpec EXCELS survey, we perform a statistical analysis of their ionizing photon production efficiencies ($ξ_\rm{ion}$). We consider $ξ_\rm{ion}$, measured with Balmer line measurements, in relation to a number of key galaxy properties including; nebular emission line strengths ($W_λ(\rm{Hα})$ and $W_λ$( [OIII])), UV luminosity ($M_\rm{UV}$) and UV slope ($β_\rm{UV}$), as well as dust attenuation ($E(B-V)_\rm{neb}$) and redshift. Implementing a Bayesian linear regression methodology, we fit $ξ_\rm{ion}$ against the principal observables while fully marginalising over all measurement uncertainties, mitigating against the impact of outliers and determining the intrinsic scatter. Significant relations between $ξ_\rm{ion}$ and $ W_λ(\rm{Hα})$, $W_λ$([OIII]) and $β_\rm{UV}$ are recovered. Moreover, the weak trends with $M_\rm{UV}$ and redshift can be fully explained by the remaining property dependencies. Expanding our analysis to multivariate regression, we determine that $W_λ(\rm{Hα})$ or $W_λ$([OIII]), along with $β_\rm{UV}$ and $E(B-V)_\rm{neb}$, are the most important observables for accurately predicting $ξ_\rm{ion,0}$. The latter identifies the most common outliers as SFGs with relatively high $E(B-V)_\rm{neb}\gtrsim0.5$, possibly indicative of obscured star-formation or strong differential attenuation. Combining these properties enable $ξ_\rm{ion,0}$ to be inferred with an accuracy of $\sim0.15\,$dex, with a population intrinsic scatter of $σ_\rm{int}\sim0.035\,$dex. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2509_26591 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | The JWST EXCELS Survey: A spectroscopic investigation of the ionizing properties of star-forming galaxies at 1<z<8 Begley, R. McLure, R. J. Cullen, F. Carnall, A. C. Stanton, T. M. Scholte, D. McLeod, D. J. Dunlop, J. S. Arellano-Córdova, K. Z. Bondestam, C. Donnan, C. T. Hamadouch, M. L. Shapley, A. E. Stevenson, S. Astrophysics of Galaxies Charting the Epoch of Reionization demands robust assessments of what drives the production of ionizing photons in high-redshift star-forming galaxies (SFGs), and requires better predictive capabilities from current observations. Using a sample of $N=159$ SFGs at $1<z<8$, observed with deep medium-resolution spectroscopy from the JWST/NIRSpec EXCELS survey, we perform a statistical analysis of their ionizing photon production efficiencies ($ξ_\rm{ion}$). We consider $ξ_\rm{ion}$, measured with Balmer line measurements, in relation to a number of key galaxy properties including; nebular emission line strengths ($W_λ(\rm{Hα})$ and $W_λ$( [OIII])), UV luminosity ($M_\rm{UV}$) and UV slope ($β_\rm{UV}$), as well as dust attenuation ($E(B-V)_\rm{neb}$) and redshift. Implementing a Bayesian linear regression methodology, we fit $ξ_\rm{ion}$ against the principal observables while fully marginalising over all measurement uncertainties, mitigating against the impact of outliers and determining the intrinsic scatter. Significant relations between $ξ_\rm{ion}$ and $ W_λ(\rm{Hα})$, $W_λ$([OIII]) and $β_\rm{UV}$ are recovered. Moreover, the weak trends with $M_\rm{UV}$ and redshift can be fully explained by the remaining property dependencies. Expanding our analysis to multivariate regression, we determine that $W_λ(\rm{Hα})$ or $W_λ$([OIII]), along with $β_\rm{UV}$ and $E(B-V)_\rm{neb}$, are the most important observables for accurately predicting $ξ_\rm{ion,0}$. The latter identifies the most common outliers as SFGs with relatively high $E(B-V)_\rm{neb}\gtrsim0.5$, possibly indicative of obscured star-formation or strong differential attenuation. Combining these properties enable $ξ_\rm{ion,0}$ to be inferred with an accuracy of $\sim0.15\,$dex, with a population intrinsic scatter of $σ_\rm{int}\sim0.035\,$dex. |
| title | The JWST EXCELS Survey: A spectroscopic investigation of the ionizing properties of star-forming galaxies at 1<z<8 |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2509.26591 |