We report stellar velocity dispersion measurements for a sample of 28 AGN host galaxies including our previous work .
Using the mass-dispersion ( M _ { \bullet } - \sigma ) and the fundamental plane relations , we estimate the black hole mass for a sample of 66 BL Lac objects and investigate the role of black hole mass in the energetics of BL Lac objects .
The black hole mass range for different BL Lac spectral types is similar , 10 ^ { 7 } < M _ { \bullet } < 4 \times 10 ^ { 9 } .
Neither X-ray nor radio luminosity correlates with black hole mass .
Low-frequency-peaked BL Lac objects have higher Eddington ratios on average , because of either more beaming or higher intrinsic power .
For the black hole mass range 3 \times 10 ^ { 7 } < M _ { \bullet } < 10 ^ { 9 } , the radio luminosity of BL Lac objects and flat-spectrum radio quasars spans over 4 orders of magnitude , with BL Lac objects being low-power AGNs .
We also investigate the evolution of host galaxies for 39 AGNs out to z \approx 0.5 with measured stellar velocity dispersions .
Comparing the mass-to-light ratio evolution in the observed frame with population synthesis models , we find that single burst star formation models with z _ { form } = 1.4 ^ { +0.9 } _ { -0.2 } are consistent with the observations .
From our z _ { form } = 1.4 model , we estimated the intrinsic mass-to-light ratio evolution in the Cousins R band , \Delta log ( M / L ) / \Delta z = -0.502 \pm 0.08 , consistent with that of normal early type galaxies .