标题： 亚毫米波 H$_2$O 巨型脉泽在 NGC 4945 和圆盘星系中的情况 显示英文标题

标题： Submillimeter H$_2$O megamasers in NGC 4945 and the Circinus galaxy

摘要： 我们展示了对五种活动星系核（AGN）的321 GHz观测结果，数据来自ALMA第一轮档案：NGC 5793、NGC 1068、NGC 1386、NGC 4945和圆盘星系。首次在NGC 4945方向检测到亚毫米波脉泽发射，并且我们对圆盘星系中的亚毫米波脉泽系统进行了新的分析。其他三个星系没有检测到脉泽发射，尽管我们已经检测并成像了每个星系的连续谱。NGC 4945和圆盘星系已知拥有强（$\gtrsim 10$Jy）22 GHz巨脉泽发射，VLBI观测表明这些脉泽位于星系最内部的$\sim 1$秒差距内。这两个系统的321 GHz脉泽峰值通量密度明显较弱（比22 GHz观测值低一个数量级$\sim$100），尽管两种跃迁之间的各向同性光度更为接近（相差不超过一个数量级$\sim$10）。我们将此处展示的亚毫米波谱与两个星系中已知的22 GHz谱进行了比较，并认为虽然两种跃迁都起源于活动星系核附近的气体环境，但并非所有区域都一定相同。在圆盘星系中，321 GHz脉泽的光谱结构表明它们可能追踪着22 GHz脉泽以内半径的吸积盘。NGC 4945和NGC 5793的连续谱发射显示出与星系盘起源相关的空间分布（可能是热尘埃辐射），而对于其他三个星系，辐射则集中在中心，很可能起源于核心。 显示英文摘要

摘要： We present 321 GHz observations of five AGN from ALMA Cycle 0 archival data: NGC 5793, NGC 1068, NGC 1386, NGC 4945, and the Circinus galaxy. Submillimeter maser emission is detected for the first time towards NGC 4945, and we present a new analysis of the submillimeter maser system in Circinus. None of the other three galaxies show maser emission, though we have detected and imaged the continuum from every galaxy. Both NGC 4945 and Circinus are known to host strong ($\gtrsim 10$ Jy) 22 GHz megamaser emission, and VLBI observations have shown that the masers reside in the innermost $\sim 1$ parsec of the galaxies. The peak flux densities of the 321 GHz masers in both systems are substantially weaker (by a factor of $\sim$100) than what is observed at 22 GHz, though the corresponding isotropic luminosities are more closely matched (within a factor of $\sim$10) between the two transitions. We compare the submillimeter spectra presented here to the known 22 GHz spectra in both galaxies, and we argue that while both transitions originate from the gaseous environment near the AGN, not all sites are necessarily in common. In Circinus, the spectral structure of the 321 GHz masers indicates that they may trace the accretion disk at radii interior to the 22 GHz masers. The continuum emission in NGC 4945 and NGC 5793 shows a spatial distribution indicative of an origin in the galactic disks (likely thermal dust emission), while for the other three galaxies the emission is centrally concentrated and likely originates from the nucleus.