We present Very Large Array (VLA) observations of 21 cm H I absorption in the high-velocity (HV) system toward the external galaxy NGC 1275 (Per A). The primary motivation for our observations is to examine whether the only existing (single-dish) detection of the magnetic field in an external galaxy will stand up to independent scrutiny with an interferometer. The H I absorption profile in the HV system toward NGC 1275 has a number of velocity components. In this paper, we focus on the prominent narrow component at 8114 km s-1, in which we have detected the Zeeman effect. The measured line-of-sight magnetic field is Blos = -21.5 ± 6.5 μG. Within the errors, this is consistent with the single-dish detection. A weighted average of the single-dish and VLA detections gives a value for the line-of-sight magnetic field of Blos = -10.7 ± 3.2 μG. The derived ratio of total internal kinetic energy to gravitational energy suggests that the clouds responsible for H I absorption are likely not gravitationally bound. The ratio of magnetic energy to total internal kinetic energy indicates that magnetic effects are likely dominant in these clouds. Finally, the measured ratio of mass to magnetic flux is found to be much lower than the critical value, indicating that the observed H I absorbing clouds are significantly subcritical. This agrees with a recent study of H I absorbing clouds in the cold neutral medium of our Galaxy, thereby extending an important result for Galactic clouds to an extragalactic case.
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机译：我们目前在高速（HV）系统中朝向外部星系NGC 1275的21 cm H I吸收的超大阵列（VLA）观测结果（每A）。我们进行观测的主要动机是检查外部星系中唯一存在的磁场检测（单皿）是否能经受干涉仪的独立检查。 HV系统中朝向NGC 1275的H I吸收曲线具有许多速度分量。在本文中，我们将重点放在8114 km s -1的突出窄分量上，在该分量中我们检测到了塞曼效应。测得的视线磁场为Blos = -21.5±6.5μG。在误差范围内，这与单盘检测是一致的。单碟和VLA检测的加权平均值给出Blos的视线磁场值= -10.7±3.2μG。得出的内部总动能与重力的比值表明负责H I吸收的云可能不受重力约束。磁能与总内部动能之比表明，在这些云中磁效应可能占主导地位。最后，测得的质量与磁通之比远低于临界值，表明观察到的吸收H I的云明显低于临界。这与最近关于H I在银河系的寒冷中性介质中吸收云的研究相吻合，从而将银河云的重要结果扩展到了银河外情况。
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