The maximum accretion rate of hot gas in dark matter haloes
The maximum accretion rate of hot gas in dark matter haloes
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DOI：
10.1093/mnras/staa198
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发表时间：
2019-09
影响因子：
4.8
通讯作者：
J. Stern;D. Fielding;C. Faucher-Giguère;E. Quataert
中科院分区：
文献类型：
--
作者：
J. Stern;D. Fielding;C. Faucher-Giguère;E. Quataert
我们使用稳态冷却流解决方案和理想的3D流体动力学模拟重新审视星系的“热模式”与“冷模式”吸积问题。我们证明了热吸积模式的存在，需要冷却时间长于气体旋转支撑半径附近的自由落体时间Rcirc，即热模式的存在取决于星系尺度的物理条件而不是晕尺度的物理条件。当考虑到晕重子分数相对于宇宙平均值的损耗时，较长的冷却时间意味着，在晕质量低于$\sim 10^{12}\, {\rm M_{\odot }}$的重子完全晕的阈值时，可能会形成一个被激活的气体晕。我们表明，对于任何光晕质量，都有一个最大吸积率，使气体在整个光晕中被活化，并可以通过${\dot{M}}_{\rm crit}\approx 0.7(v_{\rm c}/100\, \rm km\ s^{-1})^{5.4}(R_{\rm circ}/10\, {\rm kpc})(Z/\, {\rm Z_{\odot }})^{-0.9}\, {\rm M_{\odot }}\, {\rm yr}^{-1}$的热模式吸积，其中Z和vc是在Rcirc测量的金属丰度和圆速度。对于吸积速率$\gtrsim {\dot{M}}_{\rm crit}$来说，充满体积的气相原则上可以是“跨音速”的——在外层晕中被激活，但在星系附近冷却并自由落体。我们将${\dot{M}}_{\rm crit}$与恒星-质量-光晕-质量关系所暗示的0 < z < 10时光晕中的平均恒星形成速率（SFR）进行了比较。对于金属丰度随红移的合理演化，我们发现在大多数质量和红移处都存在${\rm SFR}\lesssim {\dot{M}}_{\rm crit}$，这表明星系的SFR可能主要由远低于$\sim 10^{12}\, {\rm M_{\odot }}$经典阈值的光晕质量中的热模式维持。
We revisit the question of ‘hot mode’ versus ‘cold mode’ accretion on to galaxies using steady-state cooling flow solutions and idealized 3D hydrodynamic simulations. We demonstrate that for the hot accretion mode to exist, the cooling time is required to be longer than the free-fall time near the radius where the gas is rotationally supported, Rcirc, i.e. the existence of the hot mode depends on physical conditions at the galaxy scale rather than on physical conditions at the halo scale. When allowing for the depletion of the halo baryon fraction relative to the cosmic mean, the longer cooling times imply that a virialized gaseous halo may form in halo masses below the threshold of $\sim 10^{12}\, {\rm M_{\odot }}$ derived for baryon-complete haloes. We show that for any halo mass there is a maximum accretion rate for which the gas is virialized throughout the halo and can accrete via the hot mode of ${\dot{M}}_{\rm crit}\approx 0.7(v_{\rm c}/100\, \rm km\ s^{-1})^{5.4}(R_{\rm circ}/10\, {\rm kpc})(Z/\, {\rm Z_{\odot }})^{-0.9}\, {\rm M_{\odot }}\, {\rm yr}^{-1}$, where Z and vc are the metallicity and circular velocity measured at Rcirc. For accretion rates $\gtrsim {\dot{M}}_{\rm crit}$ the volume-filling gas phase can in principle be ‘transonic’ – virialized in the outer halo but cool and free-falling near the galaxy. We compare ${\dot{M}}_{\rm crit}$ to the average star formation rate (SFR) in haloes at 0 < z < 10 implied by the stellar-mass–halo-mass relation. For a plausible metallicity evolution with redshift, we find that ${\rm SFR}\lesssim {\dot{M}}_{\rm crit}$ at most masses and redshifts, suggesting that the SFR of galaxies could be primarily sustained by the hot mode in halo masses well below the classic threshold of $\sim 10^{12}\, {\rm M_{\odot }}$.