恒星形成星系尘埃消光标度关系中弥散的物理起源：恒星—尘埃几何
The Physical Origins of Scatter in the Dust Attenuation Scaling Relation of Star-Forming Galaxies: Star--Dust Geometry
- Purple Mountain Observatory, Chinese Academy of Sciences（中国科学院紫金山天文台）
- School of Astronomy and Space Science, University of Science and Technology of China（中国科学技术大学天文与空间科学学院）
- State Key Laboratory of Dark Matter Physics, Tsung-Dao Lee Institute, Shanghai Jiao Tong University（上海交通大学李政道研究所暗物质物理全国重点实验室）
- School of Physics and Astronomy, Sun Yat-sen University（中山大学物理学院）
- Department of Physics, University of Bath（巴斯大学物理系）
- School of Physics and Astronomy, Shanghai Key Laboratory for Particle Physics and Cosmology, Shanghai Jiao Tong University（上海交通大学粒子物理与宇宙学上海市重点实验室物理与天文学院）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
本研究利用约3.2万个本地恒星形成星系，发现IRX标度关系的弥散主要由恒星—尘埃三维几何差异导致，紫外光度可有效示踪这些几何与物理差异。
AI中文摘要：
表征恒星形成星系（SFGs）中尘埃消光的物理驱动因素，对于解释其光谱能量分布和恒星形成历史至关重要。红外超（IRX≡L_IR/L_UV）与金属丰度、恒星形成率、星系大小和倾角遵循一个普适的标度关系。然而，该关系周围弥散的起源仍知之甚少。我们利用来自SDSS、GALEX和WISE的约32,000个本地SFGs重新审视这一关系，并探究为何一些星系系统性地偏离最佳拟合关系。我们发现这些偏离与紫外光度系统性相关。紫外暗弱的SFGs（log(L_UV/L_☉)≤9）相对于由占主导的紫外中等亮度星系群（占样本的86.38%）所定义的关系，表现出中位IRX超出+0.23 dex；而紫外明亮的SFGs（log(L_UV/L_☉)≥10）则表现出中位不足−0.20 dex。这些偏移并非由金属丰度、总红外光度或比恒星形成率所驱动。相反，这些偏离与恒星—尘埃几何的系统性差异密切相关。紫外暗弱的SFGs结构致密（中位R_e=2.90 kpc），且倾向于侧向观测（中位b/a=0.41），导致沿视线方向的有效尘埃柱密度较高。紫外明亮的SFGs结构延展（中位R_e=5.99 kpc），且倾向于正面观测（中位b/a=0.74），使得紫外光子能够有效逃逸。具有显著核球成分（B/T>0.4）的星系位于该关系的包络上，表现出更大的弥散。我们得出结论：IRX关系中的弥散在很大程度上可由三维恒星—尘埃几何的变化来解释，而紫外光度可作为这些几何和物理差异的有效示踪器。
英文摘要：
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$\equiv$$L_{\rm IR}/L_{\rm 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 $\sim$32,000 local SFGs from SDSS, GALEX, and WISE, and investigate why some galaxies deviate systematically from the best-fit relation. We find that the deviations are systematically linked to UV luminosity. UV-faint SFGs ($\log(L_{\rm UV}/{\rm L}_\odot)\le 9$) exhibit a median IRX excess of +0.23 dex, while UV-bright SFGs ($\log(L_{\rm UV}/{\rm L}_\odot)\ge 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 $R_{\rm e} = 2.90$ 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 $R_{\rm e} = 5.99$ 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.
