ASTRID模拟中游荡中等质量黑洞的轨道与辐射性质
Orbital and Radiative Properties of Wandering Intermediate-Mass Black Holes in the ASTRID Simulation
AI总结：
本研究利用ASTRID模拟分析了z~3大质量星系中游荡中等质量黑洞的轨道与辐射特性，发现其轨道偏心率高且多在近心点吸积，仅极少数达到超亮X射线源光度，需专门巡天探测这类暗弱群体。
摘要：
质量为 $10^3-10^6 \\, M_\odot$ 的中等质量黑洞（IMBHs）通常位于矮星系的中心。模拟和观测令人信服地表明，大量IMBH群体可能在星系中偏离中心游荡。我们使用宇宙学模拟 ASTRID 来研究 $z\sim3$ 时大质量星系中游荡 IMBHs 的轨道和辐射特性。我们发现，这群黑洞相对于宿主主平面具有较大的轨道倾角（$60^\circ\pm22^\circ$）。其轨道偏心率也较为显著（$0.6\pm0.2$）且随时间推移而减小。游荡 IMBHs 在其轨道近心点附近经历吸积活动的峰值，吸积率为 Eddington rate 的 $10^{-3}-10^{-5}$ 倍，中位吸积占空比约为 $12\\%$。它们的典型光谱能量分布在红外波段的静止系 $\sim 11 \\, μ\rm m$ 处达到峰值。假设物质到能量的辐射效率为 $10\\%$ 的标准值，IMBHs 有约 $10\\%$ 的时间达到 $>10^{37} \\, \mathrm{erg\\,s^{-1}}$ 的 2-10 keV X射线光度。该光度对应于 10 Mpc 内 $>10^{-15} \\, \mathrm{erg \\, s^{-1} \\, cm^{-2}}$ 的流量。由于受到 X射线双星和星际介质的竞争性发射干扰，它们可能难以被探测到。约 $7\\%$ 的 IMBHs 达到了 $> 10^{41} \\, \mathrm{erg \\, s^{-1}}$ 的 X射线光度，进入超亮 X射线源（HLXs）状态。这些发现表明，HLXs 只是游荡 IMBH 群体的一小部分，该群体的特征光度要暗 $10^3-10^4$ 倍。需要专门的巡天来评估这一缺失黑洞群体的统计学特征。
英文摘要：
Intermediate-Mass Black Holes (IMBHs) of $10^3-10^6 \, M_\odot$ are commonly found at the center of dwarf galaxies. Simulations and observations convincingly show that a sizable population of IMBHs could wander off-center in galaxies. We use the cosmological simulation ASTRID to study the orbital and radiative properties of wandering IMBHs in massive galaxies at $z\sim3$. We find that this population of black holes has large orbital inclinations ($60^\circ\pm22^\circ$) with respect to the principal plane of the host. The eccentricity of their orbits is also significant ($0.6\pm0.2$) and decreases with time. Wandering IMBHs undergo spikes of accretion activity around the pericenter of their orbits, with rates $10^{-3}-10^{-5}$ times the Eddington rate and a median accretion duty cycle of $\sim 12\%$. Their typical spectral energy distribution peaks in the infrared at $\sim 11 \, μ\rm m$ rest-frame. Assuming a standard value of $10\%$ for the matter-to-energy radiative efficiency, IMBHs reach $2-10$ keV X-ray luminosities $>10^{37} \, \mathrm{erg\,s^{-1}}$ for $\sim10\%$ of the time. This luminosity corresponds to fluxes $>10^{-15} \, \mathrm{erg \, s^{-1} \, cm^{-2}}$ within $10$ Mpc. They could be challenging to detect because of competing emissions from X-ray binaries and the interstellar medium. X-ray luminosities $> 10^{41} \, \mathrm{erg \, s^{-1}}$, in the hyper-luminous X-ray sources (HLXs) regime, are reached by $\sim 7\%$ of the IMBHs. These findings suggest that HLXs are a small subset of the wandering IMBH population, which is characterized by luminosities $10^3-10^4$ times fainter. Dedicated surveys are needed to assess the demographics of this missing population of black holes.
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