Megamaser宇宙学计划：I. UGC 3789的VLBI观察结果
The Megamaser Cosmology Project: I. VLBI observations of UGC 3789
摘要：
巨脉泽宇宙学计划（MCP）旨在测量哈勃常数（Ho），以改善河外距离尺度和限制暗能量的性质。我们正在寻找来自活动星系核的水脉泽发射源，如在NGC 4258中的亚pc吸积盘，并通过甚长基线干涉测量（VLBI）成像和光谱监测跟踪这些发现。在这里，我们提出了一个VLBI地图的水脉泽对UGC 3789，一个星系的哈勃流。我们已经观测到脉泽以高达800 km/s的旋转速度运动，半径小至0.08 pc。我们的图显示了脉泽存在于一个以开普勒旋转方式围绕10^7 Msun的超大质量黑洞旋转的近边缘圆盘中。当结合向心加速度，通过观察脉泽特征的光谱漂移（将在论文II中介绍），UGC 3789脉泽可以提供一个精确的确定Ho，独立于光度和金属丰度和消光校正。
英文摘要：
The Megamaser Cosmology Project (MCP) seeks to measure the Hubble Constant (Ho) in order to improve the extragalactic distance scale and constrain the nature of dark energy. We are searching for sources of water maser emission from AGN with sub-pc accretion disks, as in NGC 4258, and following up these discoveries with Very Long Baseline Interferometric (VLBI) imaging and spectral monitoring. Here we present a VLBI map of the water masers toward UGC 3789, a galaxy well into the Hubble Flow. We have observed masers moving at rotational speeds up to 800 km/s at radii as small as 0.08 pc. Our map reveals masers in a nearly edge-on disk in Keplerian rotation about a 10^7 Msun supermassive black hole. When combined with centripetal accelerations, obtained by observing spectral drifts of maser features (to be presented in Paper II), the UGC 3789 masers may provide an accurate determination of Ho, independent of luminosities and metallicity and extinction corrections.
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