We present the results of deep I-band imaging of two BL Lacerate objects , RGB 0136+391 and PKS 0735+178 , during an epoch when the optical nucleus was in a faint state in both targets .
In PKS 0735+178 we find a significant excess over a point source , which , if fitted by the de Vaucouleurs model , corresponds to a galaxy with I = 18.64 \pm 0.11 and r _ { eff } = 1.8 \pm 0.4 arcsec .
Interpreting this galaxy as the host galaxy of PKS 0735+178 we derive z = 0.45 \pm 0.06 using the host galaxy as a “ standard candle ” .
We also discuss the immediate optical environment of PKS 0735+178 and the identity of the MgII absorber at z = 0.424 .
Despite of the optimally chosen epoch and deep imaging we find the surface brightness profile of RGB 0136+391 to be consistent with a point source .
By determining a lower limit for the host galaxy brightness by simulations , we derive z > 0.40 for this target .