[论文解读] Atacama Large Aperture Submillimeter Telescope (AtLAST) Science: The hidden circumgalactic medium

Minju Lee, Alice Schimek+30 more|arXiv (Cornell University)|Mar 1, 2024

Radio Astronomy Observations and Technology被引用 6

一句话总结

本文认为通过 AtLAST 对隐藏的寒冷环绕星系介质（CGM）进行成像，可以揭示 galaxy evolution 的关键方面，并概述追求这一科学所需的望远镜与仪器要求。

ABSTRACT

Our knowledge of galaxy formation and evolution has incredibly progressed through multi-wavelength observational constraints of the interstellar medium (ISM) of galaxies at all cosmic epochs. However, little is known about the physical properties of the more diffuse and lower surface brightness reservoir of gas and dust that extends beyond ISM scales and fills dark matter haloes of galaxies up to their virial radii, the circumgalactic medium (CGM). New theoretical studies increasingly stress the relevance of the latter for understanding the feedback and feeding mechanisms that shape galaxies across cosmic times, whose cumulative effects leave clear imprints into the CGM. Recent studies are showing that a -- so far unconstrained -- fraction of the CGM mass may reside in the cold (T < 1e4 K) molecular and atomic phase, especially in high-redshift dense environments. These gas phases, together with the warmer ionised phase, can be studied in galaxies from z ~ 0 to z ~ 10 through bright far-infrared and sub-millimeter emission lines such as [C II] 158$μ$m, [O III] 88 $μ$m, [C I] 609$μ$m, [C I] 370$μ$m, and the rotational transitions of CO. Imaging such hidden cold CGM can lead to a breakthrough in galaxy evolution studies but requires a new facility with the specifications of the proposed Atacama Large Aperture Submillimeter Telescope (AtLAST). In this paper, we use theoretical and empirical arguments to motivate future ambitious CGM observations with AtLAST and describe the technical requirements needed for the telescope and its instrumentation to perform such science.

研究动机与目标

• 推动将寒冷 CGM 研究作为星系演化的关键组成部分及其与吸积与反馈的联系。
• 强调现有设施无法填补的观测空缺，强调需要一台 50 米单口亚毫米望远镜。
• 描述以高灵敏度绘制延展且低表观亮度 CGM 发射所需的望远镜规格与仪器。
• 讨论与现有及未来设施的协同作用，以实现多波段 CGM 研究。

提出的方法

• 利用理论与经验性论据为将来在 AtLAST 进行的 CGM 观测提供辩护。
• 概述在亚毫米波段进行 CGM 成像所需的技术要求与仪器能力。
• 确定用于冷 CGM 表征的关键分子与原子示踪物（如 [C II]、CO、[CI]）。
• 讨论覆盖热、暖、冷气相的多相 CGM 方法以解释观测结果。
• 描述与当前及未来设施在互补数据方面的预期协同作用。

Figure 1: Cartoon illustrating different scenarios for the CGM composition, inspired by Figure 1 in Tumlinson et al. ( 2017 ) . The galaxy is illustrated as a star-forming (yellow dots) disc partially shrouded by dust (black) and a central bulge (red) surrounded by loosely defined CGM components as

实验结果

研究问题

• RQ1 推动星系吸积的宇宙物质的性质与相态是什么，以及它如何填充 CGM？
• RQ2 缺失的重子中有多少驻留在 CGM/IGM，以及这些贮藏中冷气体的分布如何？
• RQ3 星形成和活动性星系核（AGN）反馈对 CGM 的影响与历史在宇宙时间上的变化是什么？
• RQ4 AtLAST 的观测如何约束不同星系环境中 CGM 的多相结构与动力学？

主要发现

• 在多种环境中存在寒冷、致密的 CGM 成分的证据，表明星系盘外存在大量延展的分子和原子气体。
• 当前的亚毫米观测设施在表观亮度灵敏度和视场方面不足以绘制大尺度 CGM 结构，因此需要 AtLAST 的能力。
• 一个灵敏、宽视场、大口径的亚毫米望远镜，配备多路多束仪器，对在不同红移下成像隐藏的寒冷 CGM 至关重要。
• 用 AtLAST 对 CGM 进行成像将有助于区分寒冷气体吸积、喷流、潮汐与在晕内凝结等情景，推进对星系演化的理解。
• 观测 CGM 研究需要多线、多相的示踪物（分子、原子、中性、带电离子）并与其他波段的观测协同。

Figure 2: The inferred baryon fraction in the CGM and IGM of star-forming main sequence galaxies as a function of stellar mass and halo mass, based on the observational constraints of the following: (i) a baryon fraction of 16% ( Planck Collaboration et al. , 2020 ) , (ii) the stellar-to-halo mass r