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arXiv 1106.1676astro-ph.CO
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中红移超红外群中的分子气

Molecular Gas in Intermediate Redshift ULIRGs

Robert Braun, Attila Popping, Kate Brooks, Francoise Combes

摘要:

本文报道了用Mopra 22米望远镜对南半球中等红移(z = 0.2 - 0.5)的超亮红-红银河系完整样品的CO(1-0)跃迁的观测结果。在Dec = -12 deg以南观测到11个L_FIR > 10^12.5 L_Sun的ULIRG,积分时间在5到24小时之间变化。样品中的单个靶标获得了四个边缘检测。整个样品的“堆叠”光谱在z = 0.38的平均红移处产生CO(1-0)跃迁的高显著性1 - 0 σ检测。对已发表的低红移ULIRG样品(z < 0.2)的L_FIR和L_CO进行归一化处理后,得到了它们之间最紧密的相关关系。通过这种归一化,关系是线性的。尘埃-分子氢气体质量的分布显示了系统的增加,尘埃-气体质量与星系光度的低红移样品,但这一比例下降显着的中间红移ULIRGs的值相媲美的小麦哲伦云。ULIRG分子质量分布的上包络线作为回顾时间的函数,表明从当前时代到5 Gyr几乎有一个数量级的急剧上升。这种最大ULIRG气体质量随回望时间的增加甚至比恒星形成率密度的增加更快。

英文摘要:

We report on the results of observations in the CO(1-0) transition of a complete sample of Southern, intermediate redshift (z = 0.2 - 0.5) Ultra-Luminous Infra-Red Galaxies using the Mopra 22m telescope. The eleven ULIRGs with L_FIR > 10^12.5 L_Sun south of Dec = -12 deg were observed with integration times that varied between 5 and 24 hours. Four marginal detections were obtained for individual targets in the sample. The "stacked" spectrum of the entire sample yields a high significance, 10σ detection of the CO(1-0) transition at an average redshift of z = 0.38. The tightest correlation of L_FIR and L_CO for published low redshift ULIRG samples (z < 0.2) is obtained after normalisation of both these measures to a fixed dust temperature. With this normalisation the relationship is linear. The distribution of dust-to-molecular hydrogen gas mass displays a systematic increase in dust-to-gas mass with galaxy luminosity for low redshift samples but this ratio declines dramatically for intermediate redshift ULIRGs down to values comparable to that of the Small Magellanic Cloud. The upper envelope to the distribution of ULIRG molecular mass as function of look-back time demonstrates a dramatic rise by almost an order of magnitude from the current epoch out to 5 Gyr. This increase in maximum ULIRG gas mass with look-back time is even more rapid than that of the star formation rate density.

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