DEEP HE ii AND C iv SPECTROSCOPY OF A GIANT LYα NEBULA: DENSE COMPACT GAS CLUMPS IN THE CIRCUMGALACTIC MEDIUM OF A z ∼ 2 QUASAR
DEEP HE ii AND C iv SPECTROSCOPY OF A GIANT LYα NEBULA: DENSE COMPACT GAS CLUMPS IN THE CIRCUMGALACTIC MEDIUM OF A z ∼ 2 QUASAR
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DOI：
10.1088/0004-637x/809/2/163
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发表时间：
2015-04
期刊：
影响因子：
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通讯作者：
F. A. Battaia;J. Hennawi;J. Prochaska;S. C. M. F. Astronomie;UCOLick Observatory;U. Cruz;Eth
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文献类型：
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作者：
F. A. Battaia;J. Hennawi;J. Prochaska;S. C. M. F. Astronomie;UCOLick Observatory;U. Cruz;Eth
Cantalupo等人最近发现了与类星体UM 287（z = 2.279）有关的最大（1500 kpc）发光（L = 1.43 × 1045 erg s−1）Lyα星云，这对我们目前对大质量z ≥ 2星系晕的天体物理学理解提出了巨大挑战。要么需要一个巨大的冷气体库M <$1012 M <$，超过预期的重子质量，要么必须调用高分辨率宇宙学模拟中不存在的极端气体聚集因子。然而，仅观测Lyα发射并不能区分这两种情况。我们已经在He ii λ1640和C iv λ1549发射线上获得了有史以来最深的光谱积分，目的是探测扩展线发射，但没有探测到3σ极限SB 10−18 erg s−1 cm−2 arcsec−2的线。我们构建了简单的模型，预期的发射光谱在很可能的情况下，星云是由中央超亮类星体的光电离供电。没有探测到He ii意味着星云的辐射来自于质量为Mc = 6.4 × 1010 M的冷气体，其尺度为200 kpc，分布在一群非常致密（nH = 3 cm−3）和紧凑（R = 20 pc）的云中，这显然是目前的宇宙学模拟无法解决的。考虑到Lyα线（v = 500 km s−1）所暗示的大气体运动，我们还不清楚这些云是如何在不被流体动力学不稳定性破坏的情况下生存下来的。我们的工作是未来与当前和计划中的宽视场IFU光谱仪（如MUSE、KCWI和KMOS）深度集成的基准。我们的观测和模型表明，10小时的曝光可能会检测到10个静止帧的紫外线/光发射线，开辟了进行详细的光电离建模的可能性，以推断环星系介质中气体的物理状态。
The recent discovery by Cantalupo et al. of the largest (∼500 kpc) luminous (L ≃ 1.43 × 1045 erg s−1) Lyα nebula associated with the quasar UM287 (z = 2.279) poses a great challenge to our current understanding of the astrophysics of the halos hosting massive z ∼ 2 galaxies. Either an enormous reservoir of cool gas is required M ≃ 1012 M⊙, exceeding the expected baryonic mass available, or one must invoke extreme gas clumping factors not present in high-resolution cosmological simulations. However, observations of Lyα emission alone cannot distinguish between these two scenarios. We have obtained the deepest ever spectroscopic integrations in the He ii λ1640 and C iv λ1549 emission lines with the goal of detecting extended line emission, but detect neither line to a 3σ limiting SB ≃ 10−18 erg s−1 cm−2 arcsec−2. We construct simple models of the expected emission spectrum in the highly probable scenario that the nebula is powered by photoionization from the central hyper-luminous quasar. The non-detection of He ii implies that the nebular emission arises from a mass Mc ≲ 6.4 × 1010 M⊙ of cool gas on ∼200 kpc scales, distributed in a population of remarkably dense (nH ≳ 3 cm−3) and compact (R ≲ 20 pc) clouds, which would clearly be unresolved by current cosmological simulations. Given the large gas motions suggested by the Lyα line (v ≃ 500 km s−1), it is unclear how these clouds survive without being disrupted by hydrodynamic instabilities. Our work serves as a benchmark for future deep integrations with current and planned wide-field IFU spectrographs such as MUSE, KCWI, and KMOS. Our observations and models suggest that a ≃10 hr exposure would likely detect ∼10 rest-frame UV/optical emission lines, opening up the possibility of conducting detailed photoionization modeling to infer the physical state of gas in the circumgalactic medium.