Spatially Resolved Nebular-Stellar Reddening with JWST/NIRISS

Abstract

An accurate determination of the dust attenuation within galaxies is essential to derive key physical properties such as the star formation rate (SFR). We present an analysis using the JWST/NIRISS data from the GLASS-JWST ERS programme to investigate and characterise the stellar and nebular reddening of galaxies at 1.0<z<2.4, down to the sub-kpc scale. We use a multiregion fitting method to extract high-quality Hα and Hβ emission line maps for 99 individual galaxies across a stellar mass range 7.0<log₁₀(M_*/M_⊙)<10.5. We find no evidence for ratios of the Balmer decrement (Hα/Hβ) below the intrinsic limit for Case B recombination, beyond the expected variation from observational uncertainties. We reproduce the local correlation between the Balmer decrement and total stellar mass, and find no measurable difference when splitting the sample by redshift, with negligible attenuation below log₁₀(M_*/M_⊙)≲8.5. Similarly, the best-fit relation between the nebular and continuum reddening follows the same relation as in local starburst galaxies, E(B−V)_SED = (0.46±0.02)E(B−V)_neb, together indicating no significant evolution in the dust geometry within galaxies out to z≲2.4. We derive best-fit linear relations between the differential nebular-stellar reddening and the SED-derived star formation rate (SFR) and stellar mass, finding statistically significant relations for both quantities. We use our spatially-resolved measurements to derive an empirical calibration between the resolved differential reddening, and the SFR surface density. These will enable crucial dust attenuation corrections for spatially-resolved science at higher redshifts where the Balmer lines are inaccessible, such as with future Roman grism observations.

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BibTeX

@misc{watson2026spatially,
  title = {{Spatially Resolved Nebular-Stellar Reddening with JWST/NIRISS}},
  author = {Peter J. Watson and Benedetta Vulcani and Tommaso Treu and Ayan Acharyya and Marc Rafelski and Anahita Alavi and Matthew Hayes and Keunho Kim and Faezeh Manesh and Claudia Scarlata},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2606.12249},
  eprint = {2606.12249},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2606.12249},
}

RIS

TY  - UNPB
TI  - Spatially Resolved Nebular-Stellar Reddening with JWST/NIRISS
AU  - Peter J. Watson
AU  - Benedetta Vulcani
AU  - Tommaso Treu
AU  - Ayan Acharyya
AU  - Marc Rafelski
AU  - Anahita Alavi
AU  - Matthew Hayes
AU  - Keunho Kim
AU  - Faezeh Manesh
AU  - Claudia Scarlata
PY  - 2026
DA  - 2026/09/14
PB  - arXiv
DO  - 10.48550/arxiv.2606.12249
UR  - https://arxiv.org/abs/2606.12249
AB  - An accurate determination of the dust attenuation within galaxies is essential to derive key physical properties such as the star formation rate (SFR). We present an analysis using the JWST/NIRISS data from the GLASS-JWST ERS programme to investigate and characterise the stellar and nebular reddening of galaxies at 1.0<z<2.4, down to the sub-kpc scale. We use a multiregion fitting method to extract high-quality Hα and Hβ emission line maps for 99 individual galaxies across a stellar mass range 7.0<log_10(M_*/M_⊙)<10.5. We find no evidence for ratios of the Balmer decrement (Hα/Hβ) below the intrinsic limit for Case B recombination, beyond the expected variation from observational uncertainties. We reproduce the local correlation between the Balmer decrement and total stellar mass, and find no measurable difference when splitting the sample by redshift, with negligible attenuation below log_10(M_*/M_⊙)≲8.5. Similarly, the best-fit relation between the nebular and continuum reddening follows the same relation as in local starburst galaxies, E(B−V)_SED = (0.46±0.02)E(B−V)_neb, together indicating no significant evolution in the dust geometry within galaxies out to z≲2.4. We derive best-fit linear relations between the differential nebular-stellar reddening and the SED-derived star formation rate (SFR) and stellar mass, finding statistically significant relations for both quantities. We use our spatially-resolved measurements to derive an empirical calibration between the resolved differential reddening, and the SFR surface density. These will enable crucial dust attenuation corrections for spatially-resolved science at higher redshifts where the Balmer lines are inaccessible, such as with future Roman grism observations.
ER  -

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