We have obtained 1 µm - 2.5 µm spectra of the gravitational lens HE 1104-1805. Although we were not successful in measuring a precise redshift for the lens, the lens is probably an early type galaxy with a plausible redshift of . This is slightly larger than estimates based on the measured time delay and estimates based from the position of the lens on the fundamental plane. We show however, that we can reconcile time delay and lens redshift by adding a shallower mass component to the mass model that may be related to the presence of a cluster/group along the line of sight.
We find that the continuum in the A component is harder than the continuum in the B component. The most probable explanation is that the A component is microlensed by compact objects in the lens galaxy.
The ratio of the emission lines between the two components is . This is consistent with that measured at optical wavelengths. The constancy of this ratio over a large wavelength range limits strongly the amount of differential extinction between the two components. We find that the differential extinction is magnitudes.
We find that broad and narrow emission lines can be removed very well by subtracting a scaled version of the spectrum of component B from the spectrum of component A. The residual near the line is less than of the original line flux. It may be possible to use this near perfect subtraction to limit models of the BLR. This possibility should be investigated further.
Finally, we note that the time delay measured in HE 1104-1805 allows us to demonstrate that the lensing potential is composed of a main lensing galaxy and a more extended "cluster" component. Without the time delay a single galaxy lens would also have been a viable model. With the rapidly increasing number of lenses with known time delay, we can therefore expect to constrain the content in dark matter of lens galaxies and it may be found that intervening clusters are a lot more frequent than first thought.
© European Southern Observatory (ESO) 2000
Online publication: August 23, 2000