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We use a recently proposed luminosity distance measure for relatively nearbyactive galactic nuclei (AGNs) to test the predicted expansion of the Universein the R_h=ct and LCDM cosmologies. This comparative study is particularlyrelevant to the question of whether or not the Universe underwent a transitionfrom decelerated to accelerated expansion, which is believed to haveoccurred---on the basis of Type Ia SN studies---within the redshift range (0 <z < 1.3) that will eventually be sampled by these objects. We find that the AGNHubble Diagram constructed from currently available sources does not supportthe existence of such a transition. While the scatter in the AGN data is stilltoo large for any firm conclusions to be drawn, the results reported herenonetheless somewhat strengthen similar results of comparative analyses usingother types of source. We show that the Akaike, Kullback, and Bayes InformationCriteria all consistently yield a likelihood of ~84-96% that R_h=ct is closerto the "true" cosmology than LCDM is, though neither model adequately accountsfor the data, suggesting an unnaccounted-for source of scatter.

The AGN Hubble Diagram and Its Implications for Cosmology