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Astronomy & Astrophysics

Near-IR Spectroscopy of the lens and source in the double quasar HE 1104-1805+

F. Courbin1, C. Lidman2, G. Meylan3, J.-P. Kneib4 and P. Magain5

1 Universidad Católica de Chile, Departamento de Astronomia y Astrofisica, Casilla 306, Santiago 22, Chile
2 European Southern Observatory, Casilla 19, Santiago, Chile
3 European Sourthern Observatory, Karl-Schwarzschild Strasse 2, D-85748 Garching bei München, Germany
4 Laboratoire d'Astrophysique, Observatoire Midi-Pyrénée, UMR5572, 14 Avenue Edouard Belin, F-31000, Toulouse, France
5 Institut d'Astrophysique et de Géophysique - Université de Liège, Avenue de Cointe 5, 4000 Liège, Belgium

+ Based on observations collected with the ESO New Technology Telescope (program 61.B-0413)


     A new technique for the spatial deconvolution of spectra is applied to near-IR (0.95 - 2.50µ) NTT/SOFI spectra of the lensed, radio-quiet quasar HE 1104-1805. The red continuum spectrum of the lensing galaxy is revealed between 1.5µ and 2.5µ. 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 estimate 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 QSO images and of a more extended component associated with a "dark" galaxy cluster with fairly low velocity dispersion (~ 575 km.s-1). Unless more constrains can be put on the mass distribution of the cluster (if detected at all), e.g., from deep X-ray observations, HE 1104-1805 will not be a good system to determine H0 based on its time delay measurement. The spectra of the two lensed images of the source remain 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 FeII feature, taking into account the underlying continuum over a wide wavelength range. HE 1104-1805 can be classified as a weak FeII 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 methods developed for source reconstruction from multiwavelengths photometric monitorings. 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. We also stress that multiply imaged QSOs with known time delays might prove more useful as tools for detecting dark mass in distant lenses than for determining cosmological parameters.

Key Words
gravitational lensing - cosmology - microlensing - infrared - quasars; individual: HE 1104-1805 - data processing

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