Bidirectional Relativistic Jets of the Radio Galaxy 1946+708: Constraints on the Hubble Constant

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Abstract
We present measurements of bidirectional motions in the jets of the radio galaxy 1946+708 at z = 0.101. This is a compact symmetric object with striking S-symmetry. Sensitive 15 GHz observations reveal a compact component at the center of symmetry with a strongly inverted spectrum, which we identify as the core. From five 4.9 GHz observations spread over 4 yr we have determined the velocities of four compact jet components. If simple kinematic models can be applied, then the inclination of the source and the bulk jet velocity can be directly determined for any assumed value of the Hubble constant. Conversely, the measurements already place constraints on the Hubble constant, and we show how further observations of 1946+708 can yield an increasingly accurate determination of H0.
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