C II* Absorption in Damped Lyα Systems. I. Star Formation Rates in a Two-Phase Medium
C II* Absorption in Damped Lyα Systems. I. Star Formation Rates in a Two-Phase Medium
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阻尼 Lyα 系统中的 C II* 吸收。 I. 两相介质中的恒星形成速率。
DOI：
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发表时间：
2003
期刊：
影响因子：
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通讯作者：
E. Gawiser
中科院分区：
文献类型：
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作者：
A. Wolfe;J. Prochaska;E. Gawiser
我们描述了一种技术，首次直接测量阻尼Lyα系统（DLAs）中的恒星形成速率（SFRs）。我们假设大质量恒星在DLAs中形成，它们发射的远紫外辐射通过颗粒光电机制加热气体。我们通过将升温速率等同于由C II* λ1335.7吸收强度测量的冷却速率来推断升温速率。由于加热速率与尘气比、颗粒光电加热效率和单位面积SFR的乘积成正比，对于测量了冷却速率和尘气比的DLAs，我们可以推断。我们考虑由碳质颗粒和硅酸盐颗粒组成的尘埃模型。我们提出了冷中性介质（CNM）和热中性介质（WNM）处于压力平衡的两相模型。在CNM模型中，视线穿过CNM和WNM气体，而在WNM模型中，视线只穿过WNM气体。由于纳米碳纳米管的晶粒光电加热效率比纳米碳纳米管至少高出一个数量级，因此在纳米碳纳米管模型中，大部分的碳II*吸收都发生在纳米碳纳米管中。我们使用测量的C II*吸收谱线推导出约30个DLAs样品，其中κ是从元素耗尽模式推断出来的。我们表明，推断对应于DLA的恒星形成体积的平均值，而不是沿着视线的局部恒星形成。我们得到了平均值，并表明CNM溶液= 10-2.2 M☉y -1 kpc-2， WNM溶液= 10-1.3 M☉y -1 kpc-2。有趣的是，CNM溶液中单位面积的SFR与银河系星际介质中测量的SFR相似。
We describe a technique that for the first time measures star formation rates (SFRs) in damped Lyα systems (DLAs) directly. We assume that massive stars form in DLAs and that the far-ultraviolet (FUV) radiation they emit heats the gas by the grain photoelectric mechanism. We infer the heating rate by equating it to the cooling rate measured by the strength of C II* λ1335.7 absorption. Since the heating rate is proportional to the product of the dust-to-gas ratio, the grain photoelectric heating efficiency, and the SFR per unit area, , we can deduce for DLAs in which the cooling rate and dust-to-gas ratio have been measured. We consider models in which the dust consists of carbonaceous grains and silicate grains. We present two-phase models in which the cold neutral medium (CNM) and warm neutral medium (WNM) are in pressure equilibrium. In the CNM model the line of sight passes through CNM and WNM gas, while in the WNM model the line of sight passes only through WNM gas. Since the grain photoelectric heating efficiency is at least an order of magnitude higher in the CNM than in the WNM, most of the C II* absorption arises in the CNM in the CNM model. We use the measured C II* absorption lines to derive for a sample of ≈30 DLAs in which κ has been inferred from element depletion patterns. We show that the inferred corresponds to an average over the star-forming volume of the DLA rather than to local star formation along the line of sight. We obtain the average and show that = 10-2.2 M☉ yr-1 kpc-2 for the CNM solution and = 10-1.3 M☉ yr-1 kpc-2 for the WNM solution. Interestingly, the SFR per unit area in the CNM solution is similar to that measured in the Milky Way interstellar medium.