快速旋转椭圆星系中的X射线等射线：流入气体的证据
X-ray Isophotes in a Rapidly Rotating Elliptical Galaxy: Evidence of Inflowing Gas
摘要：
我们描述了二维气体动力学计算的X射线发射气体在旋转的椭圆星系NGC 4649，表明流入约一个太阳质量，每年在每个半径。如此大的瞬时流入不可能持续超过哈勃时间。最近在最内层150秒差距观测到的中央恒熵温度峰值可以用气体流向中央大质量黑洞时的压缩加热来解释。由于这种气体的冷却时间只有几百万年，NGC 4649提供了已知的冷却流问题最集中的例子，其中流入银河系核心的时间积分表观质量超过了那里观测到的总质量。这个悖论可以通过黑洞附近释放的吸积能量驱动的能量或质量的间歇性外流来解决。流入的气体也需要在中间kpc半径，以解释椭圆率的X射线等照度线由于自旋的质量喷射的恒星旋转的星系，并解释当地的密度和温度分布。我们提供的证据表明，许多明亮的椭圆星系经历类似的流入自旋。在NGC 4649中需要小的湍流粘度，以避免形成无法观察到的大X射线发光盘，但湍流压力很小，不会干扰假设流体静力平衡的质量测定。
英文摘要：
We describe two-dimensional gasdynamical computations of the X-ray emitting gas in the rotating elliptical galaxy NGC 4649 that indicate an inflow of about one solar mass per year at every radius. Such a large instantaneous inflow cannot have persisted over a Hubble time. The central constant-entropy temperature peak recently observed in the innermost 150 parsecs is explained by compressive heating as gas flows toward the central massive black hole. Since the cooling time of this gas is only a few million years, NGC 4649 provides the most acutely concentrated known example of the cooling flow problem in which the time-integrated apparent mass that has flowed into the galactic core exceeds the total mass observed there. This paradox can be resolved by intermittent outflows of energy or mass driven by accretion energy released near the black hole. Inflowing gas is also required at intermediate kpc radii to explain the ellipticity of X-ray isophotes due to spin-up by mass ejected by stars that rotate with the galaxy and to explain local density and temperature profiles. We provide evidence that many luminous elliptical galaxies undergo similar inflow spin-up. A small turbulent viscosity is required in NGC 4649 to avoid forming large X-ray luminous disks that are not observed, but the turbulent pressure is small and does not interfere with mass determinations that assume hydrostatic equilibrium.
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