The AGN Hubble Diagram and Its Implications for Cosmology
  We use a recently proposed luminosity distance measure for relatively nearby
active galactic nuclei (AGNs) to test the predicted expansion of the Universe
in the R_h=ct and LCDM cosmologies. This comparative study is particularly
relevant to the question of whether or not the Universe underwent a transition
from decelerated to accelerated expansion, which is believed to have
occurred---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 AGN
Hubble Diagram constructed from currently available sources does not support
the existence of such a transition. While the scatter in the AGN data is still
too large for any firm conclusions to be drawn, the results reported here
nonetheless somewhat strengthen similar results of comparative analyses using
other types of source. We show that the Akaike, Kullback, and Bayes Information
Criteria all consistently yield a likelihood of ~84-96% that R_h=ct is closer
to the "true" cosmology than LCDM is, though neither model adequately accounts
for the data, suggesting an unnaccounted-for source of scatter.
