DETECTION OF THE LENSING GALAXY FOR THE DOUBLE QSO HE-1104-1805

High angular resolution ground-based direct imaging (V, R, I-c) of the double QSO HE 1104-1805 has been obtained with the NOT and NTT telesc opes. Analysis of these data led to the first detection of the lensing galaxy. Direct imaging of HE 1104-1805 has subsequently been carried out with the Planetary Camera (WFPC2) through the F555W (nearly Johnso n V) and F814W (nearly Kron-Cousins I-c) filters onboard HST. These im ages confirm the presence of the deflector between the two lensed quas ar components (A & B). Direct imaging of this system in the near infra red (IR) at 2.2 mu m (K'), with IRAC-2b at the Cassegrain focus of the ESO/MPI 2.2 m telescope, indicates that the additional component is i ndeed a very red extended object with magnitude K approximate to 16.5. We present deconvolutions of the HST and IR images using the 2-channe l PLUCY method. From the HST observations, we also report very accurat e relative positions and brightnesses of the QSO components. By compar ison between the ground-based and the HST observations, from February- March 1994 to November 1995, we possibly detect the fading of componen t A by similar to 0.3 magnitudes in the optical and a corresponding fa ding of B by about half this value. The observed monotonic decrease of the magnitude difference between B and A as a function of wavelength is consistent with a partial amplification of the A component by micro lensing. Evolutionary models for galaxies show that, in order to produ ce the observed colour indices V - I-c > 2 and 4 < I-c - K < 4.5, the galaxy is likely to be of elliptical type with a redshift 0.95 < z < 1 .4. This range is consistent with the redshift z = 1.32 measured from the absorption lines of metallic species in the spectra of the quasar components. However, other values for the redshift of the lens inside this range cannot be excluded. This galaxy would presently be among th e most distant known gravitational lenses. Several theoretical models are found to fit the observations. The simplest one is a singular isot hermal sphere (SIS) lens immersed in an external shear with gamma = 0. 123. The derived mass-to-light ratio (11 h(50) M./L.) for the galaxy i s large but does not imply an excess of dark matter with respect to ot her well known lensing galaxies. (C) 1998 Elsevier Science B. V.