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arXiv 1401.0773astro-ph.GAastro-ph.CO
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背光螺旋半导体中紫外线的衰减规律

The Ultraviolet Attenuation Law in Backlit Spiral Galaxies

William C. Keel, Anna M. Manning, Benne W. Holwerda, Chris J. Lintott, Kevin Schawinski

摘要:

星系在发出的紫外线中的有效消光定律(衰减行为)仅对活跃的恒星形成物体是众所周知的,并结合了颗粒特性,尘埃分布中的精细结构以及恒星和尘埃的相对分布的影响。我们使用GALEX,XMM光学监视器和HST数据来探索由其他UV明亮星系背光的螺旋盘外部的UV衰减,从银河动物园参与者提供的候选人开始。我们的分析采用了星系对称性,使用每个星系的非重叠区域来获得衰减测量的误差估计。整个样本的衰减规律接近于Calzetti等人(1994)的形式;整个样本的紫外线斜率比Wild等人(2011)发现的要小得多,这与我们样本中更遥远的星系相匹配,但与包括NGC 2207在内的加权组合不匹配。附近明亮的螺旋星系NGC 2207的精度几乎与我们样本的其他部分相同,它的外臂具有非常低的前景星光水平。这个“灰色”定律可以单独从尘埃的分布中产生,而不需要恒星从稠密云层中的差异逃逸的贡献。外推需要比较中等红移的背光星系和SDSS数据的本地系统之间的衰减,是温和的,足以允许使用星系重叠来追踪宇宙历史的尘埃。对于NGC 2207,具有小光学衰减的云的覆盖因子成为更远紫外线的主导因素,这打开了广泛扩散的尘埃在深入紫外线的恒星形成区域中占主导地位的可能性。与已发表的辐射传输模型的比较表明,在这种空间分辨率的作用,灰尘结块占主导地位的粮食人口的差异。

英文摘要:

(Abridged) The effective extinction law (attenuation behavior) in galaxies in the emitted ultraviolet is well known only for actively star-forming objects and combines effects of the grain properties, fine structure in the dust distribution, and relative distributions of stars and dust. We use GALEX, XMM Optical Monitor, and HST data to explore the UV attenuation in the outer parts of spiral disks which are backlit by other UV-bright galaxies, starting with candidates provided by Galaxy Zoo participants. Our analysis incorporates galaxy symmetry, using non-overlapping regions of each galaxy to derive error estimates on the attenuation measurements. The entire sample has an attenuation law close to the Calzetti et al. (1994) form; the UV slope for the overall sample is substantially shallower than found by Wild et al. (2011), a reasonable match to the more distant galaxies in our sample but not to the weighted combination including NGC 2207. The nearby, bright spiral NGC 2207 alone gives accuracy almost equal to the rest of our sample, and its outer arms have a very low level of foreground starlight. This "grey" law can be produced from the distribution of dust alone, without a necessary contribution from differential escape of stars from dense clouds. The extrapolation needed to compare attenution between backlit galaxies at moderate redshifts, and local systems from SDSS data, is mild enough to allow use of galaxy overlaps to trace the cosmic history of dust. For NGC 2207, the covering factor of clouds with small optical attenuation becomes a dominant factor farther into the ultraviolet, which opens the possibility that widespread diffuse dust dominates over dust in star-forming regions deep into the ultraviolet. Comparison with published radiative-transfer models indicates that the role of dust clumping dominates over differences in grain populations, at this spatial resolution.

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