P16	March 1998

¹ Institut d'Astrophysique et de Géophysique - Université de Liège, Avenue de Cointe 5, 4000 Liège, Belgium
² Nordic Institute for Theoretical Physics, Blegdamsvej 17, DK-2100 Copenhagen Ø, Denmark
³ Hamburg Observatory, Gojenbergsweg 112, D-21029 Hamburg, Germany
⁴Copenhagen University Observatory, Niels Bohr Institute for Astronomy, Physics and Geophysics, Juliane Maries Vej 30, DK-2100 Copenhagen Ø, Denmark
⁵Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, National Research Council of Canada, 5071 W. Saanich Road, Victoria, BC. V8X 4M6, Canada

^* Aspirant FNRS, Belgium
^** Directeur de Recherches FNRS, Belgium

⁺ Based on observations made with the NASA/ESA Hubble Space Telescope (HST), obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555, with the Nordic Optical Telescope (NOT), operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, with the European Southern Observatory/Max Planck Institute (ESO/MPI) 2.2m telescope and with the ESO 3.5m New Technology Telescope (NTT) in La Silla, Chile.

Abstract

     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 telescopes. 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 Johnson V) and F814W (nearly Kron-Cousins I_c) filters onboard HST. These images confirm the presence of the deflector between the two lensed quasar components (A & B). Direct imaging of this system in the near infrared (IR) at 2.2 µm (K'), with IRAC-2b at the Cassegrain focus of the ESO/MPI 2.2 m telescope, indicates that the additional component is indeed a very red extended object with magnitude K 16.5. We present deconvolutions of the HST and IR images using the 2-channel PLUCY method. From the HST observations, we also report very accurate relative positions and brightnesses of the QSO components. By comparison between the ground-based and the HST observations, from February-March 1994 to November 1995, we possibly detect the fading of component A by ~ 0.3 magnitudes in the optical and a corresponding fading 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 microlensing. Evolutionary models for galaxies show that, in order to produce 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 the most distant known gravitational lenses. Several theoretical models are found to fit the observations. The simplest one is a singular isothermal sphere (SIS) lens immersed in an external shear with = 0.123. The derived mass-to-light ratio (11 h₅₀ M/L) for the galaxy is large but does not imply an excess of dark matter with respect to other well known lensing galaxies.