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arXiv · 2605.30427

The AURORA Survey: Multiple Balmer and Paschen Emission Lines for Individual Star-forming Galaxies at z=1.5-4.4. II. Implications for Nebular Dust Corrections, Nebular SFRs, and Differential Reddening

Naveen A. Reddy·Alice E. Shapley·Ryan L. Sanders·Michael W. Topping·Max Pettini·Natascha M. Forster Schreiber·Charles C. Steidel·Leonardo Clarke·Richard S. Ellis·Anthony J. Pahl·Garth D. Illingworth·Mariska Kriek·Desika Narayanan
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Abstract

We discuss the implications of the nebular dust attenuation curves derived for 24 galaxies at z=1.5-4.4 with multiple detections of HI Balmer and Paschen recombination emission lines from the JWST/AURORA survey. The total attenuation of Ha is ~0.20 dex larger on average than the values obtained with the commonly adopted combination of the Balmer decrement and the Galactic extinction curve. Nebular-line SFRs and SED-based SFRs are consistent on average when using the MOSDEF attenuation or SMC extinction curves for the latter. The relation between nebular and stellar reddening is consistent with a scenario where the Paschen lines are sensitive to heavily reddened OB associations, while relatively unreddened OB associations contribute significantly to the Balmer line and UV continuum emission. There is a stark contrast between the low Rv (or steepness) of stellar dust attenuation curves and the high Rv (or flatness) of nebular dust attenuation curves. We suggest that the latter could be reflective of a more porous medium established by strong feedback from massive stars. For the youngest galaxy in the sample, the stellar reddening curve is identical to the nebular attenuation curve, in accordance with our expectation that OB associations dominate the stellar continuum emission at all wavelengths for this very young galaxy. Larger samples will be needed to determine whether this conclusion holds for young galaxies in general, and provide further insights into the dust and metals mixing timescale on the scale of HII regions.

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Naveen A. Reddy, Alice E. Shapley, Ryan L. Sanders, Michael W. Topping, Max Pettini, Natascha M. Forster Schreiber, Charles C. Steidel, Leonardo Clarke, Richard S. Ellis, Anthony J. Pahl, Garth D. Illingworth, Mariska Kriek, Desika Narayanan. 2026-05-28. The AURORA Survey: Multiple Balmer and Paschen Emission Lines for Individual Star-forming Galaxies at z=1.5-4.4. II. Implications for Nebular Dust Corrections, Nebular SFRs, and Differential Reddening. https://arxiv.org/abs/2605.30427

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