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arXiv 0707.3142astro-ph
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射电有源星系中的吸积几何

The Accretion Geometry in Radio-Loud Active Galaxies

D. R. Ballantyne

摘要:

本文综述了确定射电强活动星系核(AGN)吸积几何的最新尝试。这些天体占活动星系核总数的10-20%,产生强大的准直射电喷流,可以从主星系中心延伸数千秒差距。最近的多波长观测表明,射电响度在低光度活动星系核中比在高光度的塞弗特星系或类星体中更常见。这些低光度活动星系核的吸积速率足够小,它们很可能是通过一个几何厚和辐射效率低的吸积流吸积。相比之下,对三个更高光度的宽线射电星系(3C 120、4C+74.26和PG 1425+267)的X射线光谱观测发现了一个未截断的薄盘延伸到非常接近黑洞的证据。这些试探性的探测表明,对于这类射电强活动星系核,其吸积几何与射电静活动星系核非常相似。这些观测结果表明,喷流的形成必须满足三个条件:一个快速旋转的黑洞的存在,一个大的H/r比的吸积流,以及一个有利的磁场几何形状。

英文摘要:

We review the latest attempts to determine the accretion geometry in radio-loud active galactic nuclei (AGN). These objects, which comprise ~10-20% of the AGN population, produce powerful collimated radio jets that can extend thousands of parsecs from the center of the host galaxy. Recent multiwavelength surveys have shown that radio-loudness is more common in low-luminosity AGN than in higher luminosity Seyfert galaxies or quasars. These low-luminosity AGN have small enough accretion rates that they are most likely accreting via a geometrically thick and radiatively inefficient accretion flow. In contrast, X-ray spectroscopic observations of three higher luminosity broad-line radio galaxies (3C 120, 4C+74.26 and PG 1425+267) have found evidence for an untruncated thin disk extending very close to the black hole. These tentative detections indicate that, for this class of radio-loud AGN, the accretion geometry is very similar to their radio-quiet counterparts. These observations suggest that there are three conditions to jet formation that must be satisfied: the presence of a rapidly spinning black hole, an accretion flow with a large H/r ratio, and a favorable magnetic field geometry.

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