Super-Eddington growth of black holes in the early universe: effects of disc radiation spectra
Super-Eddington growth of black holes in the early universe: effects of disc radiation spectra
复制标题
DOI：
10.1093/mnras/stz1899
复制
发表时间：
2019-01
影响因子：
4.8
通讯作者：
Eishun Takeo;K. Inayoshi;K. Ohsuga;H. R. Takahashi;S. Mineshige
中科院分区：
文献类型：
--
作者：
Eishun Takeo;K. Inayoshi;K. Ohsuga;H. R. Takahashi;S. Mineshige
我们研究了黑洞 (BH) 吸积流的特性，其中质量为 MBH 的物质嵌入密度为 n∞ 的初始均匀气体云中，以便研究早期宇宙中 BH 的快速增长。在之前的工作中，通过假设中央 BH 附近产生的辐射在 $h\nu \ge 13.6\, {\rm eV}$ (α ∼ 1.5) 处具有单一幂律谱 ν−α ，研究了邦迪半径外部超爱丁顿吸积所需的条件。然而，辐射光谱肯定取决于 BH 质量和吸积率，并决定辐射反馈的效率。在这里，我们进行二维多频辐射流体动力学模拟，考虑到与核吸积盘特性相关的更真实的辐射光谱。我们发现，对于大范围质量的种子 BH (10 ≲ MBH/M⊙ ≲ 106)，BH 周围气体的临界密度（高于该临界密度会发生向超爱丁顿吸积）的减轻，因为吸积盘光谱的光电离效率低于 1 ≲ α ≲ 3 的单一幂律光谱。对于吸积盘光谱，向超爱丁顿吸积的转变更有可能对于较低 BH 质量会发生这种情况，因为辐射光谱变得太难电离气体。即使当吸积流暴露于各向异性辐射时，辐射光谱的效应也会缩小电离区域，并可能导致过渡到完全中性的吸积相。最后，通过推广我们的模拟结果，我们构建了超爱丁顿吸积所需的新分析标准； $(M_{\rm BH}/10^5\, {\rm M}_\odot) (n_{\infty }/10^4\, {\rm cm}^{-3}) \gtrsim 2.4 (\langle \epsilon \rangle /100\, {\rm eV})^{-5/9}$，其中 <ϵ> 是来自中心 BH 的电离辐射的平均能量。
We investigate the properties of accretion flows on to a black hole (BH) with a mass of MBH embedded in an initially uniform gas cloud with a density of n∞ in order to study rapid growth of BHs in the early Universe. In previous work, the conditions required for super-Eddington accretion from outside the Bondi radius were studied by assuming that radiation produced at the vicinity of the central BH has a single power-law spectrum ν−α at $h\nu \ge 13.6\, {\rm eV}$ (α ∼ 1.5). However, radiation spectra surely depend on the BH mass and accretion rate, and determine the efficiency of radiative feedback. Here, we perform two-dimensional multifrequency radiation hydrodynamical simulations taking into account more realistic radiation spectra associated with the properties of nuclear accretion discs. We find that the critical density of gas surrounding the BH, above which transitions to super-Eddington accretion occur, is alleviated for a wide range of masses of seed BHs (10 ≲ MBH/M⊙ ≲ 106) because photoionization for accretion disc spectra are less efficient than those for single power-law spectra with 1 ≲ α ≲ 3. For disc spectra, the transition to super-Eddington is more likely to occur for lower BH masses because the radiation spectra become too hard to ionize the gas. Even when accretion flows are exposed to anisotropic radiation, the effect due to radiation spectra shrinks the ionized region and likely leads to the transition to a wholly neutral accretion phase. Finally, by generalizing our simulation results, we construct a new analytical criterion required for super-Eddington accretion; $(M_{\rm BH}/10^5\, {\rm M}_\odot) (n_{\infty }/10^4\, {\rm cm}^{-3}) \gtrsim 2.4 (\langle \epsilon \rangle /100\, {\rm eV})^{-5/9}$, where 〈ϵ〉 is the mean energy of ionizing radiation from the central BH.