标题： 宁静超大质量黑洞的核区介质 显示英文标题

标题： Circumnuclear Media of Quiescent Supermassive Black Holes

摘要： 我们计算了处于缓慢吸积（“宁静”）星系核中热气体的稳态、一维流体力学剖面，涉及中心黑洞质量为$M_{\bullet}$的范围、参数化的气体加热率以及观测启发的恒星密度分布。 物质通过恒星风供应到核区介质中，而能量主要通过恒星风、超新星爆发和黑洞反馈注入。 我们推导了停滞半径（气流径向速度通过零点处）和大尺度气体流入速率$\dot{M}$的解析估计值，作为函数$M_{\bullet}$和气体加热效率的函数，后者与恒星形成历史相关。 我们评估了在停滞半径附近的静力区域内，辐射不稳定性发展的条件，包括单次恒星形成爆发的情况以及宇宙学模拟预测的平均恒星形成历史情况。 通过结合附近宁静星系核的核X射线亮度样本$L_x$和我们的$\dot{M}(M_{\bullet})$结果，我们探讨这些核是否以稳态、热稳定的方式吸积，符合辐射效率低效吸积流所预测的效率。 我们发现热稳定的吸积无法解释本地宇宙中低质量黑洞的短平均增长时间，这必须归因于气体从大半径处被供给，可能是由于气体流入或更大尺度上的热不稳定性。 我们的结果对利用平均$L_x-M_{\bullet}$关系约束低质量星系中小质量黑洞（SMBH）的占位分数尝试具有影响，同时也对潮汐瓦解事件的相对论喷流遇到的核区密度多样性预测有影响。 显示英文摘要

摘要： We calculate steady-state, one-dimensional hydrodynamic profiles of hot gas in slowly accreting ("quiescent") galactic nuclei for a range of central black hole masses $M_{\bullet}$, parametrized gas heating rates, and observationally-motivated stellar density profiles. Mass is supplied to the circumnuclear medium by stellar winds, while energy is injected primarily by stellar winds, supernovae, and black hole feedback. Analytic estimates are derived for the stagnation radius (where the radial velocity of the gas passes through zero) and the large scale gas inflow rate, $\dot{M}$, as a function of $M_{\bullet}$ and the gas heating efficiency, the latter being related to the star-formation history. We assess the conditions under which radiative instabilities develop in the hydrostatic region near the stagnation radius, both in the case of a single burst of star formation and for the average star formation history predicted by cosmological simulations. By combining a sample of measured nuclear X-ray luminosities, $L_x$, of nearby quiescent galactic nuclei with our results for $\dot{M}(M_{\bullet})$ we address whether the nuclei are consistent with accreting in a steady-state, thermally-stable manner for radiative efficiencies predicted for radiatively inefficiency accretion flows. We find thermally-stable accretion cannot explain the short average growth times of low mass black holes in the local Universe, which must instead result from gas being fed in from large radii, due either to gas inflows or thermal instabilities acting on larger, galactic scales. Our results have implications for attempts to constrain the occupation fraction of SMBHs in low mass galaxies using the mean $L_x-M_{\bullet}$ correlation, as well as the predicted diversity of the circumnuclear densities encountered by relativistic outflows from tidal disruption events.