ALMA2040：高红移星系际介质——早期宇宙中星系的燃料供给与反馈成像
ALMA2040: The High-Redshift Circumgalactic Medium. Imaging the fueling and feedback of galaxies in the early universe
AI总结：
该研究提出 ALMA2040 望远镜，旨在通过提升光谱线灵敏度，实现对早期宇宙高红移星系 CGM 的成像与探测，为理解星系的燃料供给与反馈机制提供关键观测手段。
摘要：
星系并非孤立形成，而是作为更广阔互联网络的一部分，在其界面处由延伸的气态大气（即星系际介质（Circum-Galactic Medium，CGM））介导。这一动态多相区域由来自星系际介质的气体流入与并合，以及中心星系的反馈驱动外流和辐射所供给并塑造。CGM 承载着其中心星系及环境过去、现在和未来演化的印记。冷原子与分子相尤为受关注，因为它们在外流质量预算中占主导地位，并为星系吸积提供直接的恒星形成燃料库。在吸积率、并合及反馈过程达到峰值的早期宇宙中，气体通过 CGM 的循环最为活跃。亚毫米观测已探测到高红移星系周围延伸晕中的冷气体及气体流，但目前仅局限于质量最大、极端或受引力透镜放大的源，且仅使用少数最强的发射线和吸收线。与当前 ALMA 相比，光谱线灵敏度需显著提升（5-10 倍），才能将物理尺度、密度和特性推向新的研究领域。我们提出 ALMA2040 望远镜的三个关键科学目标：(i) 直接成像 z=4-8 处银河系原星系周围由 [CII] 示踪的延伸 CGM 晕；(ii) 在约 100 pc 尺度上分辨探测与单个恒星形成团块相关的冷团块状外流；(iii) 多物种/跃迁发射与吸收诊断，以联合约束冷 CGM 及其多相气体流中的密度、化学组成和辐射场。
英文摘要：
Galaxies do not form in isolation, but rather as part of a wider interconnected web mediated at their interface by an extended gaseous atmosphere - the Circum-Galactic Medium (CGM). This dynamic and multiphase region is fed and shaped by gas inflows and mergers from the intergalactic medium and by feedback-driven outflows and radiation from the central galaxy. The CGM is imprinted by the past, present and future evolution of its central galaxy and environment. The cool atomic and molecular phases are of particular interest as they dominate the mass budget of outflows and provide a reservoir of direct star forming fuel for the galaxy to accrete. In the early universe where accretion rates, mergers, and feedback processes peak, the cycle of gas through the CGM is most vigorous. Sub-mm observations have detected cold gas in extended halos and gas flows around high redshift galaxies but are thus far limited to the most massive, extreme or gravitationally lensed sources, using just a handful of the strongest emission and absorption lines. A significant increase ($5-10\times$) in spectral line sensitivity compared with the current ALMA is needed to push physical scales, densities and properties to a new regime. We present three key scientific cases for an ALMA2040 telescope: (i) direct imaging of extended [CII]-traced CGM halos around Milky-Way-progenitor galaxies at $z=4$-8; (ii) resolved detection of cold, clumpy outflows on $\sim$100 pc scales tied to individual star-forming clumps; and (iii) multi-species/-transition emission and absorption diagnostics that jointly constrain the density, chemistry, and radiation fields permeating the cool CGM and its multiphase gas flows.
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