The near-IR and milliarcsec radio structure of PKS 1345 + 125

Abstract

We present near-IR (2.2 μm) photometry at high spatial resolution (0.62 arcsec |$\text {pixel}^{-1}$|⁠) and 6-cm radio observations (beamwidth ∼ 10 mas) of the central regions of the Seyfert galaxy PKS 1345 + 125, which is a radio-loud and an ultraluminous IRAS system. The near-IR data confirm the presence of two nuclei within an asymmetric outer envelope. We find little evidence for extinction within the central regions, thus supporting a previous hypothesis in which the interstellar medium of the Seyfert galaxy has been stripped during a recent merger. The radio structure is resolved into a linear feature misaligned by |$\sim 49^\circ$| with respect to the position angle defining the two near-IR nuclei. This suggests that the previously observed optical line emission within the western (Seyfert) nucleus is not due to any narrow-line region or extended narrow-line region associated with the radio elliptical, thus distinguishing PKS 1345 + 125 from archetypal double-nucleus Seyferts such as Mkn 78 and NGC 5929. PKS 1345 + 125 is therefore likely to be the result of the recent merger of radio elliptical and Seyfert spiral galaxies. In spite of the asymmetric nature of the isophotes, the averaged near-IR luminosity distribution can be well described by an |$r^{1/4}$| law for radii |$\lt 10$| arcsec, with evidence for a diffuse envelope of low surface brightness beyond this point. The stellar component within this complex is hence developing the appearance of a cD galaxy.