Spatially Resolved Near-Infrared Imaging of a Gravitationally Lensed Quasar, APM 08279+5255, with Adaptive Optics on the Subaru Telescope

We present a spatially resolved imaging analysis of a three-component gravitationally lensed quasar at z = 3.91, APM 08279+5255, in the L'- and M'-bands, and a narrow band centered at 3.05 μm using the 188-element adaptive optics system on the Subaru Telescope. The third, faintest quasar image, component C, has been clearly resolved in all of these bands for the first time. All of the three components are point sources in all three bands. No new component, neither a fourth quasar image nor a lens galaxy, was discovered. The observed bands correspond to the long-wavelength end of the optical power-law continuum of the source quasar in its rest frame, and are little contaminated by strong emission lines like Hα. The measured flux ratio of components C to B is shown to be constant in all of the observed bands, and its achromatic nature agrees well with preceding work done at short near-infrared wavelengths one decade ago. On the other hand, the flux ratio of components A to B shows an increase from that of past measurements. This could be ascribed to a microlensing event.