APM 08279+5255: Keck Near- and Mid-Infrared High-Resolution Imaging

We present Keck high-resolution near-IR (2.2 μm FWHM~0.15") and mid-IR (12.5 μm FWHM~0.4") images of APM 08279+5255, a z=3.91 IR-luminous broad absorption line quasi-stellar object with a prodigious apparent bolometric luminosity of 5×10¹⁵ L_solar, the largest known in the universe. The K-band image shows that this system consists of three components, all of which are likely to be the gravitationally lensed images of the same background object, and the 12.5 μm image shows a morphology consistent with such an image configuration. Our lens model suggests that the magnification factor is ~100 from the rest-frame UV to mid-IR, where most of the luminosity is released. The intrinsic bolometric luminosity and IR luminosity of APM 08279+5255 are estimated to be 5×10¹³ L_solar and 1×10¹³ L_solar, respectively. This indicates that APM 08279+5255 is intrinsically luminous, but it is not the most luminous object known. As for its dust contents, little can be determined with the currently available data because of the uncertainties associated with the dust emissivity and the possible effect of differential magnification. We also suggest that the lensing galaxy is likely to be a massive galaxy at z~3. Based on observations obtained at the W. M. Keck Observatory, which is operated jointly by the California Institute of Technology, the University of California, and NASA.