Keck Mid-Infrared Imaging of the QSO 2237+0305

Using the Long Wavelength Spectrometer on Keck I, we have imaged the gravitationally lensed radio quiet quasi-stellar object (QSO) 2237+0305 at 8.9 and 11.7 microns for the first time. The mid-infrared 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 infrared emission is not affected by microlensing, which rules out the synchrotron emission model. The infrared emission is likely produced by hot dust extended on a length scale of more than 0.03 parsecs. 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 to 3 parsecs from the nucleus, and intercepting about half of the QSO luminosity.