arXiv 0909.24592009-09-14astro-ph.CO

阻尼Lyman- $α$系统中的金属度-自旋温度关系

A metallicity-spin temperature relation in damped Lyman-$α$ systems

Nissim Kanekar, Alain Smette, Frank H. Briggs, Jayaram N. Chengalur

备注：: 5 pages, 2 figures; accepted for publication in Astrophysical Journal Letters
发表信息：: Astrophys.J.705:L40-L44,2009
DOI：: 10.1088/0004-637X/705/1/L40

摘要：

我们报告了自旋温度$T_s$和金属度[Z/H]之间的反相关性的证据，在26个阻尼莱曼- $α$吸收体（DLAs）的样品中检测到$3.6 σ$显著性，红移为$0.09 < z < 3.45$。在具有测量覆盖因子的20个DLAs的子样本中，在$3 σ$显著性下检测到反相关性，这意味着它并不源于低覆盖因子。我们从线性回归分析获得$T_s = (-0.68 \pm 0.17) \times {\rm [Z/H]} + (2.13 \pm 0.21)$。我们的研究结果表明，在DLAs中发现的高$T_s$值并不是由光学和无线电视线之间的差异引起的，而是可能反映了底层的气体温度分布。$T_s$和[Z/H]之间的趋势可以解释为，在具有高金属丰度的星系中，用于气体冷却的辐射路径的数量更大，导致了高的冷气体分数，因此，低的自旋温度。相反，低金属量星系的冷却路径较少，产生较大的暖气体部分和较高的$T_s$。大多数在$z>1.7$的DLA具有低金属丰度[Z/H] $< -1$，这意味着高$z$ DLA中的HI主要是温暖的. $T_s$和[Z/H]之间的反相关性与DLA中存在的质量-金属丰度关系一致，这是由DLA金属丰度和金属线的运动学宽度之间的紧密相关性所暗示的。大多数高$z$的DLA可能产生于低质量（$M_{\rm vir} < 10^{10.5} M_\odot$）、低金属丰度（[Z/H] $< -1$）和低冷气分数的星系中。

英文摘要：

We report evidence for an anti-correlation between spin temperature $T_s$ and metallicity [Z/H], detected at $3.6 σ$ significance in a sample of 26 damped Lyman-$α$ absorbers (DLAs) at redshifts $0.09 < z < 3.45$. The anti-correlation is detected at $3 σ$ significance in a sub-sample of 20 DLAs with measured covering factors, implying that it does not stem from low covering factors. We obtain $T_s = (-0.68 \pm 0.17) \times {\rm [Z/H]} + (2.13 \pm 0.21)$ from a linear regression analysis. Our results indicate that the high $T_s$ values found in DLAs do not arise from differences between the optical and radio sightlines, but are likely to reflect the underlying gas temperature distribution. The trend between $T_s$ and [Z/H] can be explained by the larger number of radiation pathways for gas cooling in galaxies with high metal abundances, resulting in a high cold gas fraction, and hence, a low spin temperature. Conversely, low-metallicity galaxies have fewer cooling routes, yielding a larger warm gas fraction and a high $T_s$. Most DLAs at $z>1.7$ have low metallicities, [Z/H] $< -1$, implying that the HI in high-$z$ DLAs is predominantly warm. The anti-correlation between $T_s$ and [Z/H] is consistent with the presence of a mass-metallicity relation in DLAs, suggested by the tight correlation between DLA metallicity and the kinematic widths of metal lines. Most high-$z$ DLAs are likely to arise in galaxies with low masses ($M_{\rm vir} < 10^{10.5} M_\odot$), low metallicities ([Z/H]$< -1$, and low cold gas fractions.

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