The accretion mechanism in low-power radio galaxies.
The accretion mechanism in low-power radio galaxies.
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DOI：
10.1051/0004-6361:200809810
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发表时间：
2008-05
影响因子：
6.5
通讯作者：
B. B. A. C. A. M. G. Torino-B.-B.-A.-C.-A.-M.-G.-Torino-2000604574;I. Torino;Torino;Italy
中科院分区：
文献类型：
--
作者：
B. B. A. C. A. M. G. Torino-B.-B.-A.-C.-A.-M.-G.-Torino-2000604574;I. Torino;Torino;Italy
我们研究了44个低光度射电噪活动星系核的样本，这些样本代表了核射电功率跨越5个数量级的范围，以揭示这些星系的吸积机制。我们通过分析Chandra档案数据来估计与热日冕相关的气体吸积速率，以推导出球面近似下的密度和温度分布。从核射电光度测量喷流功率，我们发现吸积功率与喷流功率线性相关，从静止质量到喷流功率的转换效率为1.012。这些结果加强和扩展了艾伦及其合作者对9个射电星系的研究结果的有效性，表明在FR I射电星系的整个射电光度范围内，热气吸积是主要的过程。我们发现，不同水平的核活动是由银河系热日冕结构的全球差异所驱动的。一个线性关系链接的喷射功率与主机X射线表面亮度。这意味着喷气动力的实质性变化必须伴随着其ISM属性的全球变化，例如由重大合并驱动。这种相关性提供了一种简单而广泛适用的方法，通过观察其宿主X射线发射的强度来估计给定物体的喷射功率。为了维持喷流中的质量流，穿过邦迪半径到达吸积盘的气体的分数必须是0.002。这意味着吸积盘的辐射效率必须是η 0.005，这表明这些物体中的吸积不仅以较低的速率发生，而且比标准吸积盘的效率更低。
We study a sample of 44 low-luminosity radio-loud AGN, which represent a range of nuclear radio-power spanning 5 orders of magnitude, to unveil the accretion mechanism in these galaxies. We estimate the accretion rate of gas associated with their hot coronae by analyzing archival Chandra data, to derive the deprojected density and temperature profiles in a spherical approximation. Measuring the jet power from the nuclear radio-luminosity, we find that the accretion power correlates linearly with the jet power, with an efficiency of conversion from rest mass into jet power of ∼0.012. These results strengthen and extend the validity of the results obtained by Allen and collaborators for 9 radio galaxies, indicating that hot gas accretion is the dominant process in FR I radio galaxies across their full range of radio-luminosity. We find that the different levels of nuclear activity are driven by global differences in the structure of the galactic hot coronae. A linear relation links the jet power with the host X-ray surface brightness. This implies that a substantial change in the jet power must be accompanied by a global change in its ISM properties, driven for example by a major merger. This correlation provides a simple widely applicable method to estimate the jet-power of a given object by observing the intensity of its host X-ray emission. To maintain the mass flow in the jet, the fraction of gas that crosses the Bondi radius reaching the accretion disk must be 0.002. This implies that the radiative efficiency of the disk must be η 0.005, an indication that accretion in these objects occurs not only at a lower rate, but also at lower efficiency than in standard accretion disks.