arXiv astro-ph/00112372000-11-13astro-ph

星系中尘埃的发射：金属丰度依赖性

Emission from Dust in Galaxies: Metallicity Dependence

H. Hirashita, A. K. Inoue, H. Kamaya, H. Shibai

备注：: 8 pages LaTeX, to appear in A&A
DOI：: 10.1051/0004-6361:20000008

摘要：

来自星系的红外尘埃辐射经常被用作恒星形成率（SFR）的指标。然而，尘气比的影响（即，尘埃量）对红外光度到SFR转换规律的影响至今尚未被考虑。然后，在本文中，我们提出了一个方便的分析公式，包括这种影响。为了得到与尘气比的关系，我们推广了前人的公式，导出了红外光度转换为SFR的理论公式。该公式表示为${\rm SFR}/(M_\odot~{\rm yr}^{-1})=\{3.3\times 10^{-10}(1- η)/(0.4-0.2f+0.6ε)\} (L_{\rm IR}/L_\odot)$，其中f是氢吸收的电离光子的分数，$ε$是尘埃吸收非电离光子的效率，$η$是观测到的尘埃光度的卷云分数，$L_{\rm IR}$是观测到的尘埃发射在8-1000- $μ$ m范围内的光度。我们的公式解释了银河系和大麦云云的红外过剩。在本文中，特别是，我们提出的SFR和$L_{\rm IR}$之间的转换律的金属丰度依赖。这是可能的，因为f和$ε$都可以通过与金属丰度有关的尘气比来估计。我们已经证实，金属丰度和尘埃与气体比之间的关系适用于巨星系和矮星系。最后，我们将结果应用于宇宙恒星形成历史。我们发现，从以前的经验公式计算的z=3的同向SFR被低估了4-5倍。

英文摘要：

Infrared (IR) dust emission from galaxies is frequently used as an indicator of star formation rate (SFR). However, the effect of the dust-to-gas ratio (i.e., amount of the dust) on the conversion law from IR luminosity to SFR has not so far been considered. Then, in this paper, we present a convenient analytical formula including this effect. In order to obtain the dependence on the dust-to-gas ratio, we extend the formula derived in our previous paper, in which a theoretical formula converting IR luminosity to SFR was derived. That formula was expressed as ${\rm SFR}/(M_\odot~{\rm yr}^{-1})=\{3.3\times 10^{-10}(1- η)/(0.4-0.2f+0.6ε)\} (L_{\rm IR}/L_\odot)$, where f is the fraction of ionizing photons absorbed by hydrogen, $ε$ is the efficiency of dust absorption for nonionizing photons, $η$ is the cirrus fraction of observed dust luminosity, and $L_{\rm IR}$ is the observed luminosity of dust emission in the 8-1000-$μ$m range. Our formula explains the IR excess of the Galaxy and the Large Magellanic Cloud. In the current paper, especially, we present the metallicity dependence of our conversion law between SFR and $L_{\rm IR}$. This is possible since both f and $ε$ can be estimated via the dust-to-gas ratio, which is related to metallicity. We have confirmed that the relation between the metallicity and the dust-to-gas ratio is applied to both giant and dwarf galaxies. Finally, we apply the result to the cosmic star formation history. We find that the comoving SFR at z=3 calculated from previous empirical formulae is underestimated by a factor of 4-5.

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英文摘要：

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