Emission at 3.3 µm and evidence for dust in 3C273

Abstract

The presence of dust grains in a variety of astronomical environments has been established from many IR observations1. Of particular interest is whether dust exists in the highly energetic quasars, and in the less energetic (but apparently similar) Seyfert 1 galaxies. Whilst both quasars and Seyfert 1 galaxies exhibit enhanced radiation over just the wavebands expected of thermal dust emission, the interpretation of this enhancement is a matter of controversy2. The origin of the non-thermal radiation that quasars emit at other wavebands is not understood; hence a non-thermal origin of their enhanced IR continua cannot be excluded. The existence of dust also has relevance to current discussions on the hydrogen emission-line ratios, for the weakness of the broad Lyα emission can possibly be explained by absorption on dust grains3,4. I present here circumstantial evidence that dust exists in the quasar 3C273, by demonstrating the existence of the 3.3 µm line in emission.