标题： 低光度活动星系核中的射电核：是ADAFs还是喷流？ 显示英文标题

标题： Radio Cores in Low-Luminosity AGN: ADAFs or Jets?

摘要： 我们用甚大天线阵（VLA）对两个附近的低光度活动星系核（AGN）的大样本进行了观测，以寻找银河系中心类似Sgr A*的平坦光谱射电核。 大约三分之一的星系被探测到（如果从样本中排除HII过渡天体，则约为二分之一），其中许多具有紧凑的射电核。 后续使用甚长基线干涉阵列（VLBA）的观测确认了这些核是非热起源的，亮度温度下限约为10^8 K。其中最亮的核被解析为线性结构。 核的射电谱指数相当平缓（α~0），没有发现ADAF模型预测的高度反转的射电核的证据。 紧凑射电发射的能谱和形态与在更亮AGN中看到的射电喷流典型特征一致。 发射线的光度似乎与射电核通量相关。 结合甚长基线干涉测量（VLBI）观测表明，在至少一半的低光度赛弗特星系和LINER中，光学和射电辐射可能是由黑洞供能的。 我们发现星系核球光度与射电通量之间只有微弱的相关性，并且在给定的光学光度下，椭圆星系和螺旋星系产生射电辐射的效率似乎不同。 显示英文摘要

摘要： We have surveyed two large samples of nearby low-luminosity AGN with the VLA to search for flat-spectrum radio cores, similar to Sgr A* in the Galactic Center. Roughly one third of all galaxies are detected (roughly one half if HII transition objects are excluded from the sample), many of which have compact radio cores. Follow-up observations with the VLBA have confirmed that these cores are non-thermal in origin, with lower limits for the brightness temperatures around ~10^8 K. The brightest of these are resolved into linear structures. The radio spectral indices of the cores are quite flat (alpha~0), with no evidence for the highly inverted radio cores predicted in the ADAF model. Spectrum and morphology of the compact radio emission is typical for radio jets seen also in more luminous AGN. The emission-line luminosity seems to be correlated with the radio core flux. Together with the VLBI observations this suggests that optical and radio emission in at least half the low-luminosity Seyferts and LINERs are black hole powered. We find only a weak correlation between bulge luminosity and radio flux and an apparently different efficiency between elliptical and spiral galaxies for producing radio emission at a given optical luminosity.