z=6.42类星体宿主星系中原子和高激发分子气体的成像：宇宙再电离结束时Eddington极限星暴的丰富燃料
Imaging Atomic and Highly Excited Molecular Gas in a z=6.42 Quasar Host Galaxy: Copious Fuel for an Eddington-Limited Starburst at the End of Cosmic Reionization
摘要：
我们利用Plateau de Bure干涉仪对z=6.42的类星体SDSS J114816.64+525150.3（以下简称J1148+5251）的宿主星系进行了CO（J=7-6）和CI（3 P2 - 3 P1）辐射的观测。CO（J=7-6）发射的区域是空间分辨的，其大小为5 kpc，与早期的CO（J=3-2）观测结果一致。结合这个源中碰撞线激发的修正模型，这表明CO J=7-6线追踪的高激发分子气体是亚热激发的（仅显示CO J=3-2光度的58+/-8%），但不是更集中的。我们还在主星系J1148+5251中检测到CI（3 P2 - 3 P1）发射，但该线太暗，无法进行可靠的尺寸测量。根据CI（3 P2 - 3 P1）线通量，我们得出总碳原子质量为M_CI= 1.1 × 10 ^7 M_sun，相当于总分子气体质量的约5 × 10 ^-4倍。我们还搜索了H_2O（J_KaKc=2_12-1_01）的发射，得到了一个灵敏的谱线发光极限：L ′_H_2O <4.4 × 10^9 K kms pc ^2，即<CO（J=3-2）光度的15%。在宇宙再电离结束时，这个类星体宿主中温暖的、高度激发的分子气体、原子气体和尘埃维持着一个强烈的星暴，其表面密度达到了爱丁顿（Eddington）在千秒差距尺度上限制恒星形成所预测的那样高。
英文摘要：
We have imaged CO(J=7-6) and CI(3P2-3P1) emission in the host galaxy of the z=6.42 quasar SDSS J114816.64+525150.3 (hereafter: J1148+5251) through observations with the Plateau de Bure Interferometer. The region showing CO(J=7-6) emission is spatially resolved, and its size of 5 kpc is in good agreement with earlier CO(J=3-2) observations. In combination with a revised model of the collisional line excitation in this source, this indicates that the highly excited molecular gas traced by the CO J=7-6 line is subthermally excited (showing only 58+/-8% of the CO J=3-2 luminosity), but not more centrally concentrated. We also detect CI(3P2-3P1) emission in the host galaxy of J1148+5251, but the line is too faint to enable a reliable size measurement. From the CI(3P2-3P1) line flux, we derive a total atomic carbon mass of M_CI=1.1x10^7 M_sun, which corresponds to ~5x10^-4 times the total molecular gas mass. We also searched for H2O(J_KaKc=2_12-1_01) emission, and obtained a sensitive line luminosity limit of L'_H2O<4.4x10^9 K kms pc^2, i.e., <15% of the CO(J=3-2) luminosity. The warm, highly excited molecular gas, atomic gas and dust in this quasar host at the end of cosmic reionization maintain an intense starburst that reaches surface densities as high as predicted by (dust opacity) Eddington limited star formation over kiloparsec scales.
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