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arXiv · 2512.23958

Variation of the 2175 {\AA} extinction feature in Andromeda galaxy

Bing Yan·Shu Wang·Jian Gao·Yuxi Wang·Bingqiu Chen
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Abstract

Extinction curves contain key information on interstellar dust composition and size distribution, with the 2175 {\AA} bump being the most prominent feature. We analyze 20 sightlines toward M31 using HST/STIS UV spectroscopy combined with multi-band photometry to characterize this feature. The extinction curves show substantial diversity, from MW-like shapes to flatter profiles with $R_V$ reaching up to $\sim5.8$. The strength of the 2175 {\AA} feature varies widely, including two sightlines where the bump is essentially absent. The bump central wavelength spans a broader range than previously reported, while its width remains consistent with earlier studies. A moderate positive correlation is found between bump strength ($c_3$) and width ($\gamma$). We derive an average UV extinction curve toward M31 with $R_V \approx 3.53$. These results provide new constraints on dust properties and their spatial variations in this galaxy.

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Bing Yan, Shu Wang, Jian Gao, Yuxi Wang, Bingqiu Chen. 2025-12-30. Variation of the 2175 {\AA} extinction feature in Andromeda galaxy. https://arxiv.org/abs/2512.23958

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