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arXiv 2402.17837astro-ph.GA
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揭示一个 z ~ 3.4 透镜恒星形成星系中的 [CII] 团块

Unveiling [CII] clumps in a lensed star-forming galaxy at z ~ 3.4

A. Zanella, E. Iani, M. Dessauges-Zavadsky, J. Richard, C. De Breuck, J. Vernet, M. Kohandel, F. Arrigoni Battaia, A. Bolamperti, F. Calura, C. -C. Chen, T. Dev… 展开作者

A. Zanella, E. Iani, M. Dessauges-Zavadsky, J. Richard, C. De Breuck, J. Vernet, M. Kohandel, F. Arrigoni Battaia, A. Bolamperti, F. Calura, C. -C. Chen, T. Devereaux, A. Ferrara, V. Mainieri, A. Pallottini, G. Rodighiero, L. Vallini, E. Vanzella

备注：
Accepted for publication in A&A
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AI总结：

本文利用 ALMA 在 z~3.4 透镜星系中分辨单个恒星形成团块的 [CII] 发射，估算分子气体质量与耗竭时间，证明 [CII] 可揭示紫外不可见的早期形成团块。

摘要：

紫外和光学波段观测表明，z~1–4 的星系拥有被称为“团块”的恒星形成区，这些团块被认为是由引力不稳定、富含气体的盘碎裂形成的。然而，目前仍只能在少数星系中探测到孕育这些团块的母分子云，而且大多位于 z~1。我们研究了一个 z~3.4 的透镜星系的 [CII] 和尘埃形态，该星系拥有4个在紫外连续谱中探测到的团块。我们的目标是观测单个团块的 [CII] 发射；与紫外不同，这种发射不受尘埃消光影响，可用于探究团块的性质及其冷气体含量。我们开展了 ALMA 观测，可探测尺度小至约300 pc，并发现了3个 [CII] 团块。其中一个（称为“NE”）与最亮的紫外团块重合，而另外两个（“SW”和“C”）未在紫外连续谱中被探测到。我们没有探测到尘埃连续谱。我们将单个团块的 [CII] 光度转换为分子气体质量，得到 Mmol~10^8 Msun。结合由紫外连续谱估算的恒星形成率（SFR），我们估算了团块的气体耗竭时间（tdep），并研究了它们在 Schmidt–Kennicutt 平面上的位置。NE 团块的 tdep=0.16 Gyr 较短，可与高红移星暴相比；而 SW 和 C 团块则具有更长的 tdep>0.65 Gyr，可能反映恒星形成的初始阶段。未探测到尘埃连续谱与该星系估计的蓝色紫外连续谱斜率（beta~-2.5）一致，表明尘埃非均匀性并未显著影响该目标中紫外团块的探测。我们将单个团块冷气体含量的观测推进到 z~3.4，并证明 [C II] 线发射是高红移分子云的一种有前景的示踪剂，能够探测具有很宽耗竭时间范围的团块。

英文摘要：

Observations at UV and optical wavelengths have revealed that galaxies at z~1-4 host star-forming regions, dubbed "clumps", which are believed to form due to the fragmentation of gravitationally unstable, gas-rich disks. However, the detection of the parent molecular clouds that give birth to such clumps is still possible only in a minority of galaxies, mostly at z~1. We investigated the [CII] and dust morphology of a z~3.4 lensed galaxy hosting four clumps detected in the UV continuum. We aimed to observe the [CII] emission of individual clumps that, unlike the UV, is not affected by dust extinction, to probe their nature and cold gas content. We conducted ALMA observations probing scales down to ~300 pc and detected three [CII] clumps. One (dubbed "NE") coincides with the brightest UV clump, while the other two ("SW" and "C") are not detected in the UV continuum. We do not detect the dust continuum. We converted the [CII] luminosity of individual clumps into molecular gas mass and found Mmol~10^8 Msun. By complementing it with the star formation rate (SFR) estimate from the UV continuum, we estimated the gas depletion time (tdep) of clumps and investigated their location in the Schmidt-Kennicutt plane. While the NE clump has a short tdep=0.16 Gyr, comparable with high-redshift starbursts, the SW and C clumps instead have longer tdep>0.65 Gyr and are likely probing the initial phases of star formation. The lack of dust continuum detection is consistent with the blue UV continuum slope estimated for this galaxy (beta~-2.5) and it indicates that dust inhomogeneities do not significantly affect the detection of UV clumps in this target. We pushed the observation of the cold gas content of individual clumps up to z~3.4 and showed that the [C II] line emission is a promising tracer of molecular clouds at high redshift, allowing the detection of clumps with a large range of depletion times.

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