The unusual host galaxy of the BL Lac object PKS 1413+135

The BL Lacertae object PKS 1413+135 is associated with a disc-dominated gal axy that heavily absorbs the BL Lac nucleus at optical and X-ray wavelength s. It has been argued whether this galaxy is actually the host galaxy of PK S 1413 + 135 or whether the BL Lac is a background QSO, gravitationally len sed by the apparent host galaxy. We have obtained deep high-resolution H-ba nd images of this unusual BL Lac object using the UKIRT IRCAM3. Our observa tions show that the BL Lac nucleus is centred within less than or equal to 0.05 arcsec of the galaxy. Based on this result, we assess the probability for the lensing scenario and come to the conclusion that the disc galaxy is indeed the host of PKS 1413+135. The galaxy shows peanut-shaped isophotes, suggesting the presence of a central bar, which is a common feature of AGN .