NICMOS images of JVAS/CLASS gravitational lens systems

We present Hubble Space Telescope (HST) infrared images of four gravitation al lens systems from the JVAS/CLASS gravitational lens survey and compare t he new infrared HST pictures with previously published WFPC2 HST optical im ages and radio maps. Apart from the wealth of information that we get from the flux ratios and accurate positions and separations of the components of the lens systems, which we can use as inputs for better constraints on the lens models, we are able to discriminate between reddening and optical/rad io microlensing as the possible cause of differences observed in the flux r atios of the components across the three wavelength bands. Substantial redd ening has been known to be present in the lens system B1600+434 and has bee n further confirmed by the present infrared data. In the two systems B0712472 and B1030+074 microlensing has been pinpointed as the main cause of the flux ratio discrepancy both in the optical/infrared and in the radio, the radio possibly caused by the substructure revealed in the lensing galaxies. In B0218+357, however, the results are still not conclusive. If we are act ually seeing the two 'true' components of the lens system then the flux rat io differences are attributed to a combination of microlensing and reddenin g or are alternatively the result of some variability in at least one of th e images. Otherwise the second 'true' component of B0218+357 may be complet ely absorbed by a molecular cloud and the anomalous flux density ratios and large difference in separation between the optical/infrared and radio that we see can be explained by emission either from a foreground object or fro m part of the lensing galaxy.