ALMA reveals a chemically evolved submillimeter galaxy at z = 4.76
ALMA reveals a chemically evolved submillimeter galaxy at z = 4.76
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DOI：
10.1051/0004-6361/201219518
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发表时间：
2012-05
影响因子：
6.5
通讯作者：
T. Nagao;R. Maiolino;C. Breuck;P. Caselli;B. Hatsukade;K. Saigo
中科院分区：
文献类型：
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作者：
T. Nagao;R. Maiolino;C. Breuck;P. Caselli;B. Hatsukade;K. Saigo
高z星系的化学性质为约束星系演化情景提供了重要信息。然而，广泛使用的基于静止框架光学发射线的金属丰度诊断不适用于重度尘埃覆盖的星系（例如亚毫米星系；SMG），特别是在 z > 3 时。这里我们重点关注远红外精细结构发射线 [N ii]205 μ 和 [Cii]158 μm 的通量比来评估高 z SMG 的金属丰度。通过 ALMA 循环 0 观测，我们在 z = 4.76 处检测到强 [C ii] 发射 SMG LESS J033229.4-275619 中的 [N ii]205 μm 发射。速度积分 [N ii]/[C ii] 通量比为 0.043 ± 0.008。这是对高 z 星系中 [N ii]/[C ii] 通量比的首次测量，推断的通量比与在附近宇宙中观测到的通量比 (∼0.02−0.07) 相似。速度积分通量比和光电离模型表明，该 SMG 中的金属丰度与太阳一致，这意味着该系统在 z = 4.76 时的化学演化进展非常迅速。我们还获得了 CO(12−11) 跃迁的严格上限，即 CO(12−11)/CO(2−1) < 3. 8( 3σ)。这表明 LESS J033229.4-275619 中的分子气体云并未受到该系统中活动星系核发出的辐射场的显着影响。
The chemical properties of high-z galaxies provide important information for constraining galaxy evolutionary scenarios. However, widely used metallicity diagnostics based on rest-frame optical emission lines are unusable for heavily dust-enshrouded galaxies (such as submillimeter galaxies; SMGs), especially at z > 3. Here we focus on the flux ratio of the far-infrared fine-structure emission lines [N ii]205 μ ma nd [Cii]158 μm to assess the metallicity of high-z SMGs. Through ALMA cycle 0 observations, we have detected the [N ii]205 μm emission in a strongly [C ii]-emitting SMG, LESS J033229.4‐275619 at z = 4.76. The velocityintegrated [N ii]/[C ii] flux ratio is 0.043 ± 0.008. This is the first measurement of the [N ii]/[C ii] flux ratio in high-z galaxies, and the inferred flux ratio is similar to the ratio observed in the nearby universe (∼0.02−0.07). The velocity-integrated flux ratio and photoionization models suggest that the metallicity in this SMG is consistent with solar, implying that the chemical evolution has progressed very rapidly in this system at z = 4.76. We also obtain a tight upper limit on the CO(12−11) transition, which translates into CO(12−11)/CO(2−1) < 3. 8( 3σ). This suggests that the molecular gas clouds in LESS J033229.4‐275619 are not significantly affected by the radiation field emitted by the AGN in this system.