Host galaxies of the optically violently variable quasars PKS 0736+017, OJ 287 and LB 2136

Abstract

Unified schemes for radio-loud active galaxies suggest that the different observed classes of active galactic nuclei (AGN) arise from the same basic phenomenon, with the luminosity and orientation of a relativistic jet determining the type of object seen. In the unification scheme for high-luminosity objects, optically violently variable (OVV) quasars are those systems seen end-on (i.e. down the jet), radio quasars are those seen at intermediate angles and Fanaroff-Riley type II (FRII) radio galaxies are those seen edge-on. However, the past lack of detailed information on the host galaxies of OVV quasars means that it has not been possible to confirm their place within the unified scheme. In order to provide such information, we have obtained deep optical and near-infrared images of three OVV quasars. We present both one- and two-dimensional numerical modelling which has been applied to derive the parameters of the underlying galaxies. We find that the host galaxy of PKS 0736+017 is reasonably well-represented by an elliptical morphology, with total absolute K-corrected galaxy magnitudes of Mv = −21.0 ± 0.1 and MR = −22.0 ± 0.2. Results from our two-dimensional modelling give an observed V — R colour of 0.8 ± 0.1 for the host, consistent with the underlying galaxy being elliptical. For LB 2136, the host galaxy is resolved in our near-infrared images, but the poor sampling of the frames prevents us from determining its morphological class. Assuming an elliptical morphology we derive an absolute K-corrected magnitude of 〈MK〉 = −27.3 ± 0.6 for the host. The situation for OJ 287 is less clear, with only one of our near-infrared images clearly showing the presence of a host galaxy, from which we are unable to determine a morphological class. From this image we derive an absolute K-corrected host galaxy magnitude of MK = −28.9 ± 0.6, assuming an elliptical model. Based on model fits to our optical data, we also estimate the upper limit on the host galaxy flux to be MR = −22.1 (assuming an elliptical model). The results for PKS 0736+017 and LB 2136 are consistent with the proposed unification schemes, as is the estimated optical magnitude of the host in OJ 287.