Radio Sources in Low-Luminosity Active Galactic Nuclei. I. VLA Detections of Compact, Flat-Spectrum Cores
Radio Sources in Low-Luminosity Active Galactic Nuclei. I. VLA Detections of Compact, Flat-Spectrum Cores
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DOI：
10.1086/309524
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发表时间：
2000-05
期刊：
影响因子：
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通讯作者：
N. Nagar;H. Falcke;A. Wilson;L. Ho
中科院分区：
文献类型：
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作者：
N. Nagar;H. Falcke;A. Wilson;L. Ho
我们报告了使用甚大阵列对 48 个低光度活动星系核样本进行的高分辨率 (0.″2)、15 GHz 调查。在 57%（30 个中的 17 个）低电离核发射线区域 (LINER) 核和低光度 Seyfert 星系中检测到通量密度高于 1.1 mJy 的致密射电发射。 2 cm 无线电功率与发射线 ([O I] λ6300) 光度显着相关。使用文献中其他频率的无线电通量，我们发现 18 个检测到的无线电核心中至少有 15 个具有平坦到倒置的频谱（α ≥ -0.3，Sν ∝ να）。虽然目前的观测结果与源自恒星形成区域的射电发射一致（亮度温度≥102.5-4.5 K），但在随附的论文中报告的对 10 个检测到的源的更高分辨率射电观测表明，核心非常紧凑（≲1 pc），具有高亮度温度（Tb ≳ 108 K），并且可能是同步加速器自吸收，排除了星暴起源。因此，我们的结果表明，样本中至少 50% 的低光度 Seyfert 星系和 LINER 是吸积动力的，无线电发射可能来自喷流或平流主导的吸积流。我们仅检测到观察到的 18 个“跃迁”（即 LINER + H II）核中的 1 个，表明它们的射电核明显弱于“纯”LINER。紧凑的 2 cm 射电核存在于 1 型（即具有宽 Hα）和 2 型（无宽 Hα）核中。有微弱的证据表明，具有紧凑射电核心的低光度活动星系核表现出射电喷射物优先沿星系盘的旋转轴排列，但数量有限，其重要性有限。如果这个结果被更大的样本所证实，它将支持以下观点：在更明亮的塞弗特星系中，吸积盘与星系恒星盘的错位是由辐射压力引起的吸积盘扭曲的结果。
We report a high-resolution (0.″2), 15 GHz survey of a sample of 48 low-luminosity active galactic nuclei with the Very Large Array. Compact radio emission has been detected above a flux density of 1.1 mJy in 57% (17 of 30) of low-ionization nuclear emission-line region (LINER) nuclei and low-luminosity Seyfert galaxies. The 2 cm radio power is significantly correlated with the emission-line ([O I] λ6300) luminosity. Using radio fluxes at other frequencies from the literature, we find that at least 15 of the 18 detected radio cores have a flat to inverted spectrum (α ≥ -0.3, Sν ∝ να). While the present observations are consistent with the radio emission originating in star-forming regions (the brightness temperatures are ≥102.5-4.5 K), higher resolution radio observations of 10 of the detected sources, reported in an accompanying paper, show that the cores are very compact (≲1 pc), of high brightness temperature (Tb ≳ 108 K), and probably synchrotron self-absorbed, ruling out a starburst origin. Thus, our results suggest that at least 50% of low-luminosity Seyfert galaxies and LINERs in the sample are accretion powered, with the radio emission presumably coming from jets or advection-dominated accretion flows. We have detected only 1 of 18 "transition" (i.e., LINER + H II) nuclei observed, indicating that their radio cores are significantly weaker than those of "pure" LINERs. Compact 2 cm radio cores are found in both type 1 (i.e., with broad Hα) and type 2 (without broad Hα) nuclei. There is weak evidence, limited in significance by small numbers, that low-luminosity active galactic nuclei with compact radio cores exhibit radio ejecta preferentially aligned along the rotation axis of the galaxy disk. If this result were confirmed by a larger sample, it would lend support to the idea that the misalignment of accretion disks with the galaxy stellar disk in more luminous Seyfert galaxies is a result of radiation-pressure-induced warping of their accretion disks.