标题： 什么驱动了邻近椭圆和S0星系中的紧凑射电辐射? 显示英文标题

标题： What Powers the Compact Radio Emission in Nearby Elliptical and S0 Galaxies?

摘要： 许多附近的早型（椭圆星系和S0星系）在几百秒差距或更小的尺度上含有弱（毫焦耳级）核无线电源。然而，无线电辐射的起源仍然不清楚，尤其是在选择固有光度较低星系的体积受限样本中。活动星系核和核星形成都被认为是产生无线电辐射的可能机制。本文利用光学光谱信息来解决这个问题。Wrobel & Heeschen（1991）用甚大阵列调查的大量早型星系，在其核心中表现出可检测的光学发射线，即使在非常敏感的极限下也是如此。将观测到的无线电连续谱功率与由光学发射线所追踪的热气体预期的功率进行比较，表明大部分无线电辐射是非热的。光学线发射的出现和强度与无线电功率相关。在固定的线光度下，椭圆星系的核心无线电辐射比S0星系更强。本样本中观察到的无线电功率与线发射之间的关系与经典无线电星系和明亮塞弗特核中看到的类似关系的低光度延伸一致。这一结果的一个合理解释是，附近早型星系中的弱核源是更强大活动星系核的低光度对应物。光谱证据支持这一观点。大多数发射线天体在光学上被分类为塞弗特核或低电离核发射线区（LINERs），其中大部分很可能是吸积驱动的源。 显示英文摘要

摘要： Many nearby early-type (elliptical and S0) galaxies contain weak (milli-Jansky level) nuclear radio sources on scales a few hundred parsecs or less. The origin of the radio emission, however, has remained unclear, especially in volume-limited samples that select intrinsically less luminous galaxies. Both active galactic nuclei and nuclear star formation have been suggested as possible mechanisms for producing the radio emission. This paper utilizes optical spectroscopic information to address this issue. A substantial fraction of the early-type galaxies surveyed with the Very Large Array by Wrobel & Heeschen (1991) exhibits detectable optical emission lines in their nuclei down to very sensitive limits. Comparison of the observed radio continuum power with that expected from the thermal gas traced by the optical emission lines implies that the bulk of the radio emission is nonthermal. Both the incidence and the strength of optical line emission correlate with the radio power. At a fixed line luminosity, ellipticals have stronger radio cores than S0s. The relation between radio power and line emission observed in this sample is consistent with the low-luminosity extension of similar relations seen in classical radio galaxies and luminous Seyfert nuclei. A plausible interpretation of this result is that the weak nuclear sources in nearby early-type galaxies are the low-luminosity counterparts of more powerful AGNs. The spectroscopic evidence supports this picture. Most of the emission-line objects are optically classified as Seyfert nuclei or low-ionization nuclear emission-line regions (LINERs), the majority of which are likely to be accretion-powered sources.