Exploring the gravitationally lensed system HE 1104-1805: near-IR spectroscopy

A new technique for the spatial deconvolution of spectra is applied to near-IR (0.95-2.50 mum) NTT/SOFI spectra of the lensed, radio-quiet quasar HE 1104-1805. The continuum of the lensing galaxy is revealed between 1.5 mum and 2.5 mum. Although the spectrum does not show strong emission features, it is used in combination with previous optical and IR photometry to infer a plausible redshift in the range 0.8 < z < 1.2. Modeling of the system shows that the lens is complex, probably composed of the red galaxy seen between the quasar images and a more extended component associated with a galaxy cluster with fairly low velocity dispersion (~ 575 km s[SUP]-1[/SUP]). Unless more constrains can be put on the mass distribution of the cluster, e.g. from deep X-ray observations, HE 1104-1805 will not be a good system to determine H[SUB]0[/SUB]. We stress that multiply imaged quasars with known time delays may prove more useful as tools for detecting dark mass in distant lenses than for determining cosmological parameters. The spectra of the two lensed images of the source are of great interest. They show no trace of reddening at the redshift of the lens nor at the redshift of the source. This supports the hypothesis of an elliptical lens. Additionally, the difference between the spectrum of the brightest component and that of a scaled version of the faintest component is a featureless continuum. Broad and narrow emission lines, including the FeII features, are perfectly subtracted. The very good quality of our spectrum makes it possible to fit precisely the optical Fe II feature, taking into account the underlying continuum over a wide wavelength range. HE 1104-1805 can be classified as a weak Fe II emitter. Finally, the slope of the continuum in the brightest image is steeper than the continuum in the faintest image and supports the finding by Wisotzki et al. (1993) that the brightest image is microlensed. This is particularly interesting in view of the new source reconstruction methods from multiwavelength photometric monitoring. While HE 1104- 1805 does not seem the best target for determining cosmological parameters, it is probably the second most interesting object after Q 2237+0305 (the Einstein cross), in terms of microlensing. Based on observations collected with the ESO New Technology Telescope (program 61.B-0413)