Gamma-Ray Emissions of AGN and Cosmological Standard Candles

In this work,we compile a sample which contains 71 Gev Gamma-ray-loud Active Galactic Nuclei(AGNs)(14 BL Lacs and 57 FSRQs),53 FR Ⅰ radio galaxies and 63 FR Ⅱ radio galaxies.We make a nonlinear least-square fit to this sample,and find that the best fit value of the Hubble constant is H₀=71.5±3.8km s^-1 Mpc^-1 with a reduced χ²≈2.46 by assuming M_v=-23.0 and accepting q₀=1.0,and the corresponding regression line has a correlation index R≈0.78.The best fit value of H₀=71.5±3.8 km s^-1 Mpc^-1 is in well agreement with H₀=72±8 km s^-1 obtained by the Hubble Space Telescope Key Project.Our results show that the Gev Gamma-ray emissions of AGNs can be used as cosmological standard candles indeed.