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arXiv 1006.5484astro-ph.COastro-ph.HE
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显微镜下的反馈：M87中的热力学结构和AGN驱动的冲击

Feedback under the microscope: thermodynamic structure and AGN driven shocks in M87

E. T. Million, N. Werner, A. Simionescu, S. W. Allen, P. E. J. Nulsen, A. C. Fabian, H. Bohringer, J. S. Sanders

备注：
18 pages, 16 figures. Accepted to MNRAS
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摘要：

使用深度钱德拉曝光（574 k），我们呈现了从$\sim$ 16，000个独立区域的光谱创建的高分辨率热力学图，每个区域具有$\sim$ 1，000个净计数。热力学图出色的空间分辨率揭示了系统的温度、压力、熵和金属丰度结构的戏剧性和复杂性。排除“X射线臂”，在给定半径的扩散团簇气体是惊人的等温。这表明，要么周围的集群气体，超出了武器，保持相对不受干扰的活动星系核隆起，或在集群内介质（ICM）的传导是有效的沿方位角方向。我们证实了在距活动星系核中心半径为$\sim$ 180弧秒（$\sim$ 14 kpc）处存在一个厚的（$\sim$ 40弧秒或$\sim$ 3 kpc）高压气体环。我们验证了这一特征与经典激波阵面有关，平均马赫数M = 1.25。在活动星系核中心周围半径为$\sim$ 40弧秒（$\sim$ 3千秒差距）的地方，观测到了另一个较年轻的类似激波的特征，估计马赫数M > 1.2。如前所述，如果像这些观测所表明的那样，每隔$\sim$ 1000万年发生一次重复的冲击，那么活动星系核驱动的弱冲击就可以产生足够的能量来抵消ICM的辐射冷却。在半径350 - 400弧秒（27 - 31千秒差距）处观察到Fe丰度的显著增加。这个脊可能是在充满无线电发射等离子体的气泡上升后形成的，这些气泡将冷的富含金属的气体拖出中央星系。我们估计，至少有$\sim1.0\times10^6$太阳质量的Fe被抬升并沉积在半径为350-400弧秒的地方;在X射线亮臂中测量到的Fe质量大致相同，这表明在350 - 400弧秒处观测到的Fe过量可能是由单代浮力射电泡造成的。

英文摘要：

(abridged) Using a deep Chandra exposure (574 ks), we present high-resolution thermodynamic maps created from the spectra of $\sim$16,000 independent regions, each with $\sim$1,000 net counts. The excellent spatial resolution of the thermodynamic maps reveals the dramatic and complex temperature, pressure, entropy and metallicity structure of the system. Excluding the 'X-ray arms', the diffuse cluster gas at a given radius is strikingly isothermal. This suggests either that the ambient cluster gas, beyond the arms, remains relatively undisturbed by AGN uplift, or that conduction in the intracluster medium (ICM) is efficient along azimuthal directions. We confirm the presence of a thick ($\sim$40 arcsec or $\sim$3 kpc) ring of high pressure gas at a radius of $\sim$180 arcsec ($\sim$14 kpc) from the central AGN. We verify that this feature is associated with a classical shock front, with an average Mach number M = 1.25. Another, younger shock-like feature is observed at a radius of $\sim$40 arcsec ($\sim$3 kpc) surrounding the central AGN, with an estimated Mach number M > 1.2. As shown previously, if repeated shocks occur every $\sim$10 Myrs, as suggested by these observations, then AGN driven weak shocks could produce enough energy to offset radiative cooling of the ICM. A high significance enhancement of Fe abundance is observed at radii 350 - 400 arcsec (27 - 31 kpc). This ridge is likely formed in the wake of the rising bubbles filled with radio-emitting plasma that drag cool, metal-rich gas out of the central galaxy. We estimate that at least $\sim1.0\times10^6$ solar masses of Fe has been lifted and deposited at a radius of 350-400 arcsec; approximately the same mass of Fe is measured in the X-ray bright arms, suggesting that a single generation of buoyant radio bubbles may be responsible for the observed Fe excess at 350 - 400 arcsec.

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