The Physical Origins of Scatter in the Dust Attenuation Scaling Relation of Star-Forming Galaxies: Star--Dust Geometry

@misc{lyu2026physical,
  title = {{The Physical Origins of Scatter in the Dust Attenuation Scaling Relation of Star-Forming Galaxies: Star--Dust Geometry}},
  author = {Zongfei Lyu and Xian Zhong Zheng and Zhizheng Pan and Antonios Katsianis and Stijn Wuyts and Haiguang Xu and Pedro Cataldi and Wenhao Liu and Man Qiao and Dong Dong Shi and Yuheng Zhang and Shuang Liu and Run Wen and Chao Yang},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.32284},
  eprint = {2609.32284},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.32284},
}

TY  - UNPB
TI  - The Physical Origins of Scatter in the Dust Attenuation Scaling Relation of Star-Forming Galaxies: Star--Dust Geometry
AU  - Zongfei Lyu
AU  - Xian Zhong Zheng
AU  - Zhizheng Pan
AU  - Antonios Katsianis
AU  - Stijn Wuyts
AU  - Haiguang Xu
AU  - Pedro Cataldi
AU  - Wenhao Liu
AU  - Man Qiao
AU  - Dong Dong Shi
AU  - Yuheng Zhang
AU  - Shuang Liu
AU  - Run Wen
AU  - Chao Yang
PY  - 2026
DA  - 2026/09/26
PB  - arXiv
DO  - 10.48550/arxiv.2609.32284
UR  - https://arxiv.org/abs/2609.32284
AB  - Characterising the physical drivers of dust attenuation in star-forming galaxies (SFGs) is essential for interpreting their spectral energy distributions and star formation histories. The infrared excess (IRX≡L_IR/L_UV) follows a universal scaling relation with metallicity, star formation rate, galaxy size, and inclination. However, the origin of the scatter around this relation remains poorly understood. We revisit this relation using ∼32,000 local SFGs from SDSS, GALEX, and WISE, and investigate why some galaxies deviate systematically from the best-fit relation. We find that the deviations are systematically linked to UV luminosity. UV-faint SFGs (log(L_UV/L_⊙)≤ 9) exhibit a median IRX excess of +0.23 dex, while UV-bright SFGs (log(L_UV/L_⊙)≥ 10) show a median deficit of −0.20 dex relative to the relation defined by the dominant UV-intermediate population (86.38 percent of the sample). These offsets are not driven by metallicity, total infrared luminosity, or specific star formation rate. Instead, the deviations are closely linked to systematic differences in star--dust geometry. UV-faint SFGs are compact (median R_e = 2.90 kpc) and preferentially viewed edge-on (median b/a = 0.41), leading to high effective dust column densities along the line of sight. UV-bright SFGs are extended (median R_e = 5.99 kpc) and preferentially viewed face-on (median b/a = 0.74), allowing UV photons to escape efficiently. Galaxies with significant bulge components (B/T > 0.4) populate the envelope of the relation, exhibiting larger scatter. We conclude that the scatter in the IRX relation can be largely explained by variations in the three-dimensional star--dust geometry, with UV luminosity acting as an effective tracer of these geometric and physical differences.
ER  -