Keck Mid‐Infrared Imaging of QSO 2237+0305

Abstract

Using the Long Wavelength Spectrometer on Keck, we have imaged the gravitationally lensed radio-quiet quasi-stellar object QSO 2237+0305 at 8.9 and 11.7 μm for the first time. The mid-IR flux ratios are inconsistent with the optical flux ratios but agree with the radio flux ratios and with some published gravitational lens models. These flux ratios indicate that the IR emission is not affected by microlensing, which rules out the synchrotron emission model. The IR emission is likely produced by hot dust extended on a length scale of more than 0.03 pc. The spectral energy distribution further implies a narrow range of dust temperatures, suggesting that the dust may be located in a shell extending between ~1 and 3 pc from the nucleus and intercepting about half of the QSO luminosity.