Variation in the dust emissivity index across M 33 with Herschel and Spitzer (HerM 33es)
Variation in the dust emissivity index across M 33 with Herschel and Spitzer (HerM 33es)
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DOI：
10.1051/0004-6361/201321441
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发表时间：
2013-10
影响因子：
6.5
通讯作者：
F. Tabatabaei;J. Braine;E. Xilouris;C. Kramer;M. Boquien;F. Combes;Christian Henkel;Christian Henkel;M. Relaño;S. Verley;P. Gratier;F. Israel;M. Wiedner;M. Röllig;K. Schuster;P. V. D. Werf
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文献类型：
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作者：
F. Tabatabaei;J. Braine;E. Xilouris;C. Kramer;M. Boquien;F. Combes;Christian Henkel;Christian Henkel;M. Relaño;S. Verley;P. Gratier;F. Israel;M. Wiedner;M. Röllig;K. Schuster;P. V. D. Werf
我们研究的尘埃排放的波长依赖性作为一个功能的位置和环境的整个磁盘的M33使用斯皮策和赫歇尔测光数据。M 33是一个本星系群的螺旋星系，其金属丰度略低于太阳，这使它成为一个理想的垫脚石，可以用来寻找不太规则和金属丰度较低的天体，如矮星系，甚至可能是双宇宙天体。将尘埃的发射率表示为幂律，幂律指数（β）由两种独立的方法估计，这两种方法被设计成适当地处理β和尘埃温度（T）之间的简并。内盘的β和T都比外盘高，这与其他来源中发现的β − T反相关相反。在冷+暖尘埃模型中，暖成分和电离气体（Hα）在整个星系中的分布非常相似，表明该模型以适当的方式分离了成分。在恒星形成区，冷尘埃柱和暖尘埃柱的密度都很高，并且在巨大的恒星形成复合体NGC 604和NGC 595附近达到最大值。β从中心的接近2下降到外盘的约1.3。β与星星的形成和分子气柱正相关，这可以通过Hα和CO的发射来追踪。M33外部较低的尘埃发射率指数很可能与金属含量降低（不同的颗粒成分）以及可能与不同的粒度分布有关。这不是简单地由于恒星辐射场或温度的降低，因为外盘的远红外亮区也具有低β。像大多数螺旋星系一样，M 33在星星的形成和分子-原子气体比率方面有一个（逐渐减小的）径向梯度，这样Hα或CO的明亮区域往往会跟踪内部的盘，这使得很难区分它们对尘埃的影响。发射率指数β恒定的假设显然是不合适的。
We study the wavelength dependence of the dust emission as a function of position and environment across the disk of M 33 using Spitzer and Herschel photometric data. M 33 is a Local Group spiral with slightly subsolar metallicity, which makes it an ideal stepping-stone to less regular and lower-metallicity objects such as dwarf galaxies and, probably, young-universe objects. Expressing the emissivity of the dust as a power law, the power-law exponent (β) was estimated from two independent approaches designed to properly treat the degeneracy between β and the dust temperature (T ). Both β and T are higher in the inner than in the outer disk, contrary to reported β − T anti-correlations found in other sources. In the cold + warm dust model, the warm component and the ionized gas (Hα) have a very similar distribution across the galaxy, demonstrating that the model separates the components in an appropriate way. Both cold- and warm-dust column densities are high in star-forming regions and reach their maxima toward the giant star-forming complexes NGC 604 and NGC 595. β declines from close to 2 in the center to about 1.3 in the outer disk. β is positively correlated with star formation and with the molecular gas column, as traced by the Hα and CO emission. The lower dust-emissivity index in the outer parts of M 33 is most likely related to the reduced metallicity (different grain composition) and possibly to a different size distribution. It is not due to the decrease in stellar radiation field or temperature in a simple way because the far-infrared-bright regions in the outer disk also have a low β. Like most spirals, M 33 has a (decreasing) radial gradient in star formation and molecular-to-atomic gas ratio such that the regions bright in Hα or CO tend to trace the inner disk, which makes it difficult to distinguish between their effects on the dust. The assumption of a constant emissivity index β is obviously not appropriate.