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arXiv 0809.3977astro-ph
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低红移宽线活动星系核的射电性质

Radio Properties of Low Redshift Broad Line Active Galactic Nuclei

Stephen E. Rafter, D. Michael Crenshaw, Paul J. Wiita

备注：
28 pages, 14 figures, accepted to AJ
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摘要：

关于活动星系核（AGN）的射电响度分布是否为双峰分布的问题，文献中已经进行了广泛的讨论。然而，有人声称射电响度取决于黑洞质量和爱丁顿比。我们使用Greene & Ho（2007）的低红移宽线AGN样本来研究这些说法，该样本由斯隆数字巡天第四次数据发布（SDSS DR 4）中z < 0.35的8434个天体组成。我们从SDSS AGN的甚大阵20厘米射电天空微弱图像（FIRST）巡天中获得了射电通量。在8434个SDSS AGN中，有821个在FIRST巡天中观测到了相应的射电通量。我们计算了高于第一检测限（1 mJy）的所有物体的无线电响度参数（R），以及未检测到的物体的R上限。使用这些数据，无线电双峰的问题进行了研究，为不同的子集的总样本。我们发现在无线电大声（RL，R > 10）和无线电安静（RQ，R < 10）对象之间没有明确的界限，而是以连续的方式为所有子样本填充更多的无线电中间群体。我们发现，4.7%的活动星系核的通量有限的子样本是RL的基础上，核心的无线电发射单独。我们计算无线电响亮的分数（RLF）作为黑洞质量和爱丁顿比的函数。当爱丁顿比增加超过2.5个数量级时，RLF减小（从13%到2%）。在黑洞质量的40年中，RLF几乎是恒定的（~5%），除了质量大于10^8太阳质量时会增加。我们发现，对于第一个探测到的子样本，367个RL活动星系核的黑洞质量小于10^8太阳质量，这一数量足以表明RL活动星系核不仅仅是本宇宙中质量最大的黑洞的产物。

英文摘要：

The question as to whether the distribution of radio-loudness in active galactic nuclei (AGN) is actually bimodal has been discussed extensively in the literature. Futhermore, there have been claims that radio-loudness depends on black hole mass and Eddington ratio. We investigate these claims using the low redshift broad line AGN sample of Greene & Ho (2007), which consists of 8434 objects at z < 0.35 from the Sloan Digital Sky Survey Fourth Data Release (SDSS DR4). We obtained radio fluxes from the Very Large Array Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) survey for the SDSS AGN. Out of the 8434 SDSS AGN, 821 have corresponding observed radio fluxes in the FIRST survey. We calculated the radio-loudness parameter (R) for all objects above the FIRST detection limit (1 mJy), and an upper limit to R for the undetected objects. Using these data, the question of radio bimodality is investigated for different subsets of the total sample. We find no clear demarcation between the radio-loud (RL, R > 10) and radio-quiet (RQ, R < 10) objects, but instead fill in a more radio-intermediate population in a continuous fashion for all subsamples. We find that 4.7% of the AGN in the flux-limited subsample are RL based on core radio emission alone. We calculate the radio-loud fraction (RLF) as both a function of black hole mass and Eddington ratio. The RLF decreases (from 13% to 2%) as Eddington ratio increases over 2.5 order of magnitude. The RLF is nearly constant (~5%) over 4 decades in black hole mass, except for an increase at masses greater than 10^8 solar masses. We find for the FIRST detected subsample that 367 of the RL AGN have black hole masses less than 10^8 solar masses, a large enough number to indicate that RL AGN are not a product of only the most massive black holes in the local universe.

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