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arXiv 2303.09374astro-ph.GAastro-ph.SR
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大麦哲伦云中R136星团的消光:从近红外到紫外的消光律

Extinction towards the cluster R136 in the Large Magellanic Cloud: An extinction law from the near-infrared to the ultraviolet

Sarah A. Brands, Alex de Koter, Joachim M. Bestenlehner, Paul A. Crowther, Lex Kaper, Saida M. Caballero-Nieves, Götz Gräfener

AI总结:

本研究采用“无标准星消光法”分析大麦哲伦云R136星团50颗恒星的近红外至紫外消光,发现其高$R_V$伴随异常强紫外消光,表明星暴区尘埃性质独特,导致紫外光子逃逸比例被高估三倍。

摘要:

大麦哲伦云(LMC)巨型恒星形成区30 Doradus中的R136星团为解析星暴环境中的恒星种群提供了独特机会。我们采用“无标准星消光法”获取了R136核心区50颗恒星从近红外到紫外的消光情况。为确保在全波长范围内获得良好的拟合,我们结合并修改了现有的消光律。我们在R136核心区的消光特性中探测到强烈的空间梯度,这与位于该星团东北部的一块分子云中冷气体的密度梯度相吻合。与先前对R136和30 Doradus区域的测量结果一致,我们获得了较高的总相对消光值($R_V = 4.38 \pm 0.87$)。然而,高$R_V$值伴随着相对较强的紫外消光,这与在银河系视线方向上观测到的情况相反。相对较强的紫外消光表明,R136方向的尘埃性质与银河系中的尘埃不同。对于$R_{V} \sim 4.4$,在相同$A_{V}$下,能从周围尘埃环境中逃逸的紫外光子数量比银河系典型值$R_{V} \sim 3.1$少约三倍。因此,如果R136星暴环境中的尘埃代表了宇宙学距离上的星暴区,那么相对于标准银河系总选择性消光假设,此类区域紫外光子的逃逸比例被高估了三倍。此外,与针对LMC其他区域量身定制的平均曲线进行比较表明,该星系内部在紫外消光上存在巨大差异。需要进一步研究以解读LMC中的$R_V$与紫外消光之间是否存在关联。

英文摘要:

The cluster R136 in the giant star-forming region 30 Doradus in the Large Magellanic Cloud (LMC) offers a unique opportunity to resolve a stellar population in a starburst-like environment. We obtain the near-infrared to ultraviolet extinction towards 50 stars in the core of R136, employing the `extinction without standards' method. To assure good fits over the full wavelength range, we combine and modify existing extinction laws. We detect a strong spatial gradient in the extinction properties across the core of R136, coinciding with a gradient in density of cold gas that is part of a molecular cloud lying northeast of the cluster. In line with previous measurements of R136 and the 30 Doradus region, we obtain a high total-to-relative extinction ($R_V = 4.38 \pm 0.87$). However, the high values of $R_V$ are accompanied by relatively strong extinction in the ultraviolet, contrary to what is observed for Galactic sightlines. The relatively strong ultraviolet extinction suggests that the properties of the dust towards R136 differ from those in the Milky Way. For $R_{V} \sim 4.4$, about three times fewer ultraviolet photons can escape from the ambient dust environment relative to the canonical Galactic value of $R_{V} \sim 3.1$ at the same $A_{V}$. Therefore, if dust in the R136 star-bursting environment is characteristic for cosmologically distant star-bursting regions, the escape fraction of ultraviolet photons from such regions is overestimated by a factor of three relative to the standard Milky Way assumption for the total-to-selective extinction. Furthermore, a comparison with average curves tailored to other regions of the LMC shows that large differences in ultraviolet extinction exist within this galaxy. Further investigation is required in order to decipher whether or not there is a relation between $R_V$ and ultraviolet extinction in the LMC.

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