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arXiv 2302.07378astro-ph.GA
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寻找缺失的尘埃:II —— 本星系群星系内解析出的尘埃-气体比跨越两个数量级的演化

The Quest for the Missing Dust: II -- Two Orders of Magnitude of Evolution in the Dust-to-Gas Ratio Resolved Within Local Group Galaxies

Christopher J. R. Clark, Julia C. Roman-Duval, Karl D. Gordon, Caroline Bot, Matthew W. L. Smith, Lea M. Z. Hagen

AI总结:

本研究利用Herschel新数据探究四个本星系群星系内尘埃-气体比随密度的演化,发现其变化最高达22.4倍,主因可能是致密区域的尘埃生长,并解决了麦哲伦云尘埃估算的分歧。

摘要:

我们利用新的Herschel地图,探究了四个解析良好的本星系群星系——LMC、SMC、M31和M33内部尘埃-气体比随密度的演化。这些新地图恢复了先前Herschel数据处理中遗漏的延展发射。这一改进的数据使我们能够探测跨越2.5个数量级的ISM表面密度范围内的尘埃-气体比。我们发现尘埃-气体比存在显著演化,在每个星系内部,尘埃-气体比随密度变化最高可达22.4倍。我们探讨了造成这一现象的几种可能原因,而我们最倾向的解释是ISM较致密区域中的尘埃颗粒生长。我们发现,尽管M31和M33在质量、金属丰度和恒星形成率上存在巨大差异,但两者的尘埃-气体比随ISM表面密度的演化非常相似;相反,我们发现M33和LMC尽管在这些性质上非常相似,但其尘埃-气体比的演化曲线却截然不同。我们的尘埃-气体比结果解决了先前基于紫外(UV)和远红外(FIR)对麦哲伦云尘埃-气体比估算之间的分歧,消除了LMC的分歧,并大幅减小了SMC的分歧——我们新的尘埃-气体比测量值分别是先前远红外估算值的2.4倍和2.0倍。我们还观察到,对于LMC、M31和M33,尘埃-气体比在最高密度下似乎出现下降;这不太可能是真实的物理现象,我们推测这可能是暗气体与变化的尘埃质量不透明度共同作用的结果。

英文摘要:

We explore evolution in the dust-to-gas ratio with density within four well-resolved Local Group galaxies - the LMC, SMC, M31, and M33. We do this using new ${\it Herschel}$ maps, which restore extended emission that was missed by previous ${\it Herschel}$ reductions. This improved data allows us to probe the dust-to-gas ratio across 2.5 orders of magnitude in ISM surface density. We find significant evolution in the dust-to-gas ratio, with dust-to-gas varying with density within each galaxy by up to a factor 22.4. We explore several possible reasons for this, and our favored explanation is dust grain growth in denser regions of ISM. We find that the evolution of the dust-to-gas ratio with ISM surface density is very similar between M31 and M33, despite their large differences in mass, metallicity, and star formation rate; conversely, we find M33 and the LMC to have very different dust-to-gas evolution profiles, despite their close similarity in those properties. Our dust-to-gas ratios address previous disagreement between UV- and FIR-based dust-to-gas estimates for the Magellanic Clouds, removing the disagreement for the LMC, and considerably reducing it for the SMC - with our new dust-to-gas measurements being factors of 2.4 and 2.0 greater than the previous far-infrared estimates, respectively. We also observe that the dust-to-gas ratio appears to fall at the highest densities for the LMC, M31, and M33; this is unlikely to be an actual physical phenomenon, and we posit that it may be due to a combined effect of dark gas, and changing dust mass opacity.

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