Clumpy turbulent structures in HII regions leave the slope of the internal nebular attenuation curve unchanged because dust obscuration in dense clumps is offset by higher local emission-line production.
The JWST/AURORA Survey: Multiple Balmer and Paschen Emission Lines for Individual Star-forming Galaxies at z=1.5-4.4. I. A Diversity of Nebular Attenuation Curves and Evidence for Non-Unity Dust Covering Fractions
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abstract
We present the nebular attenuation curves and dust covering fractions for 24 redshift z=1.5-4.4 star-forming galaxies using multiple Balmer and Paschen lines from the JWST/AURORA survey. Nebular reddening derived from Paschen lines exceeds that from Balmer lines for at least half the galaxies in the sample when assuming the commonly-adopted Galactic extinction curve, implying the presence of heavily reddened star formation. The nebular attenuation curves exhibit a broad range of normalizations (Rv ~ 3.2-16.4). Motivated by the offsets in reddening deduced from the Balmer and Paschen lines, and the high Rv values for the individual nebular attenuation curves, both of which suggest variations in the dust-stars geometry, we propose a model with a subunity dust covering fraction (fcov). Fitting such a model to the HI recombination line ratios indicates fcov ~ 0.6-1.0. The normalizations of the nebular attenuation curves, Rv, are driven primarily by fcov and the mix of reddened and unreddened OB associations. Thus, the diversity of nebular attenuation curves can be accommodated by assuming dust grain properties similar to that of Milky Way sightlines but with a subunity covering fraction of dust. Integrated measurements of multiple Balmer and Paschen lines can be used to place novel constraints on the dust covering fraction towards OB associations. These, in turn, provide new avenues for exploring the role of dust and gas covering fraction in a number of relevant aspects of high-redshift galaxies, including the impact of stellar feedback on ISM porosity and the escape of Ly-alpha and Lyman continuum radiation.
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astro-ph.GA 5representative citing papers
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The Internal Nebular Attenuation Curve of Three-Dimensional Turbulent HII regions
Clumpy turbulent structures in HII regions leave the slope of the internal nebular attenuation curve unchanged because dust obscuration in dense clumps is offset by higher local emission-line production.
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New empirical calibrations between 19 emission-line ratios and oxygen abundance are derived from direct electron-temperature measurements in 139 star-forming galaxies at z=1.4-10.6.
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Little Red Dots at z~2 in EIGER reveal a gentle decline with respect to their peak number density at z~5
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Star-formation variability on the star-forming main sequence during the Epoch of Reionization
PSD modeling of SFR scatter at six timescales shows dominant variability on 10-30 Myr scales, stronger in lower-mass galaxies at z=3-8.
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Calibrating Photometric Mid-Infrared Star Formation Rates for JWST
Rest-frame 6-8um MIRI luminosity provides broken power-law SFR calibrations with 0.2-0.3 dex scatter and UV+IR composites at 0.15 dex, supporting robust use above log M* ~9 up to z~3.