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The cold molecular gas in z ≳ 6 quasar host galaxies
Astronomy & Astrophysics ( IF 6.5 ) Pub Date : 2024-03-29 , DOI: 10.1051/0004-6361/202348463 Melanie Kaasinen , Bram Venemans , Kevin C. Harrington , Leindert A. Boogaard , Romain A. Meyer , Eduardo Bañados , Roberto Decarli , Fabian Walter , Marcel Neeleman , Gabriela Calistro Rivera , Elisabete da Cunha
Astronomy & Astrophysics ( IF 6.5 ) Pub Date : 2024-03-29 , DOI: 10.1051/0004-6361/202348463 Melanie Kaasinen , Bram Venemans , Kevin C. Harrington , Leindert A. Boogaard , Romain A. Meyer , Eduardo Bañados , Roberto Decarli , Fabian Walter , Marcel Neeleman , Gabriela Calistro Rivera , Elisabete da Cunha
Context. Probing the molecular gas reservoirs of z ≳ 6 quasar (QSO) host galaxies is fundamental to understanding the coevolution of star formation and black hole growth in these extreme systems. Yet, there is still an inhomogeneous coverage of molecular gas tracers for z ≳ 6 QSO hosts.Aims. To measure the average excitation and mass of the molecular gas reservoirs in the brightest z > 6.5 QSO hosts, we combined new observations of CO(2–1) emission with existing observations of CO(6–5), CO(7–6), [C I] (2–1), [C II] 158 μm, and dust-continuum emission.Methods. We reduced and analysed observations of CO(2–1), taken with the Karl G. Jansky Very Large Array, in three z = 6.5 − 6.9 QSO hosts – the highest redshift observations of CO(2–1) to date. By combining these with the nine z = 5.7 − 6.4 QSO hosts for which CO(2–1) emission has already been observed, we studied the spread in molecular gas masses and CO excitation of z ≳ 6 QSOs.Results. Two of our three QSOs, P036+03 and J0305–3150, were not detected in CO(2–1), implying more highly excited CO than in the well-studied z = 6.4 QSO J1148+5251. However, we detected CO(2–1) emission at 5.1σ for our highest-redshift target, J2348–3054, yielding a molecular gas mass of (1.2 ± 0.2)×1010 M⊙, assuming αCO = 0.8 (K km s−1 pc2)−1 and r2, 1 = 1. This molecular gas mass is equivalent to the lower limit on the dynamical mass measured previously from resolved [C II] 158 μm observations, implying that there is little mass in stars or neutral gas within the [C II]-emitting region and that a low CO-to-H2 conversion factor is applicable. On average, these z ≳ 6 QSO hosts have far higher CO(6–5)-, CO(7–6)-, and [C II] 158 μm versus CO(2–1) line ratios than the local gas-rich and IR-luminous galaxies that host active galactic nuclei, but with a large range of values, implying some variation in their interstellar medium conditions. We derived a mean CO(6–5)-to-CO(1–0) line luminosity ratio of r6, 1 = 0.9 ± 0.2.Conclusions. Our new CO(2–1) observations show that even at 780 Myr after the Big Bang, QSO host galaxies can already have molecular gas masses of 1010 M⊙, consistent with a picture in which these z ≳ 6 QSOs reside in massive starbursts that are coevolving with the accreting supermassive black holes. Their high gas versus dynamical masses and extremely high line excitation imply the presence of extremely dense and warm molecular gas reservoirs illuminated by strong interstellar radiation fields.
中文翻译：
z ≳ 6 类星体宿主星系中的冷分子气体
语境。探测z ≳ 6 类星体 (QSO) 宿主星系的分子气藏 对于理解这些极端系统中恒星形成和黑洞生长的协同演化至关重要。然而，对于z ≳ 6 QSO 宿主，分子气体示踪剂的覆盖范围仍然不均匀 。目标。为了测量最亮z > 6.5 QSO 宿主中分子气藏的平均激发和质量 ，我们将 CO(2–1) 排放的新观测结果与 CO(6–5)、CO(7–6) 的现有观测结果结合起来，[C I] (2–1)，[C II] 158 μm，以及粉尘连续发射。方法。我们减少并分析了使用 Karl G. Jansky 甚大阵列在三个z = 6.5 − 6.9 QSO 宿主中对 CO(2–1) 的观测结果——迄今为止 CO(2–1) 的最高红移观测结果。通过将这些与已经观察到 CO(2-1) 发射的九个z = 5.7 − 6.4 QSO 宿主相结合，我们研究了z ≳ 6 QSO 的气体分子质量扩散和 CO 激发 。结果。我们的三个 QSO 中的两个 P036+03 和 J0305–3150 在 CO(2–1) 中未检测到，这意味着比经过充分研究的z = 6.4 QSO J1148+5251 中存在更多高度激发的 CO。然而，我们在 5.1 σ处检测到我们最高红移目标 J2348–3054 的 CO(2–1) 发射，产生 (1.2 ± 0.2)×10 10 M ⊙的气体分子质量，假设α CO = 0.8 (K km s −1 pc 2 ) −1和r 2, 1 = 1。该分子气体质量相当于先前从解析的 [C II] 158 μm 观测中测得的动态质量的下限，这意味着恒星中的质量很小或[C II]发射区域内的中性气体，并且低CO到H 2转换因子是适用的。平均而言，这些z ≳ 6 QSO 宿主的 CO(6–5)-、CO(7–6)- 和 [C II] 158 μm 与 CO(2–1) 线比远高于当地富含天然气的区域以及拥有活跃星系核的红外发光星系，但其值范围很大，这意味着它们的星际介质条件存在一些变化。我们得出平均 CO(6–5) 与 CO(1–0) 线光度比r 6, 1 = 0.9 ± 0.2。结论。我们新的 CO(2–1) 观测表明，即使在大爆炸后 780 Myr，QSO 宿主星系也已经具有 10 10 M ⊙的分子气体质量，这与这些z的图片一致。 ≳ 6 个 QSO 存在于与吸积的超大质量黑洞共同演化的大质量星暴中。它们的高气体与动力质量和极高的线激发意味着存在被强星际辐射场照亮的极其致密和温暖的分子气藏。
更新日期：2024-03-29
中文翻译：
z ≳ 6 类星体宿主星系中的冷分子气体
语境。探测z ≳ 6 类星体 (QSO) 宿主星系的分子气藏 对于理解这些极端系统中恒星形成和黑洞生长的协同演化至关重要。然而，对于z ≳ 6 QSO 宿主，分子气体示踪剂的覆盖范围仍然不均匀 。目标。为了测量最亮z > 6.5 QSO 宿主中分子气藏的平均激发和质量 ，我们将 CO(2–1) 排放的新观测结果与 CO(6–5)、CO(7–6) 的现有观测结果结合起来，[C I] (2–1)，[C II] 158 μm，以及粉尘连续发射。方法。我们减少并分析了使用 Karl G. Jansky 甚大阵列在三个z = 6.5 − 6.9 QSO 宿主中对 CO(2–1) 的观测结果——迄今为止 CO(2–1) 的最高红移观测结果。通过将这些与已经观察到 CO(2-1) 发射的九个z = 5.7 − 6.4 QSO 宿主相结合，我们研究了z ≳ 6 QSO 的气体分子质量扩散和 CO 激发 。结果。我们的三个 QSO 中的两个 P036+03 和 J0305–3150 在 CO(2–1) 中未检测到，这意味着比经过充分研究的z = 6.4 QSO J1148+5251 中存在更多高度激发的 CO。然而，我们在 5.1 σ处检测到我们最高红移目标 J2348–3054 的 CO(2–1) 发射，产生 (1.2 ± 0.2)×10 10 M ⊙的气体分子质量，假设α CO = 0.8 (K km s −1 pc 2 ) −1和r 2, 1 = 1。该分子气体质量相当于先前从解析的 [C II] 158 μm 观测中测得的动态质量的下限，这意味着恒星中的质量很小或[C II]发射区域内的中性气体，并且低CO到H 2转换因子是适用的。平均而言，这些z ≳ 6 QSO 宿主的 CO(6–5)-、CO(7–6)- 和 [C II] 158 μm 与 CO(2–1) 线比远高于当地富含天然气的区域以及拥有活跃星系核的红外发光星系，但其值范围很大，这意味着它们的星际介质条件存在一些变化。我们得出平均 CO(6–5) 与 CO(1–0) 线光度比r 6, 1 = 0.9 ± 0.2。结论。我们新的 CO(2–1) 观测表明，即使在大爆炸后 780 Myr，QSO 宿主星系也已经具有 10 10 M ⊙的分子气体质量，这与这些z的图片一致。 ≳ 6 个 QSO 存在于与吸积的超大质量黑洞共同演化的大质量星暴中。它们的高气体与动力质量和极高的线激发意味着存在被强星际辐射场照亮的极其致密和温暖的分子气藏。
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