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Astron. Astrophys. 360, 853-860 (2000)

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1. Introduction

HE 1104-1805 is one object in the growing list of gravitationally lensed quasars which might be used to constrain cosmological parameters. It was discovered in the framework of the Hamburg/ESO Quasar Survey and consists of 2 lensed images of a radio-quiet quasar (RQQ) at z= 2.319, separated by [FORMULA]3.15" (Wisotzki et al. 1993). The lensing galaxy was discovered from ground based near-IR (Courbin et al. 1998; hereafter C98) and HST optical observations (Remy et al. 1998; hereafter R98). The relatively wide angular separation between the quasar images makes this object suitable for photometric monitoring programs, as conducted at ESO by Wisotzki et al. (1998; hereafter W98). From light curves measured over a period of 6 years, they derived a time delay for HE 1104-1805 of [FORMULA] years, with a second possible value of 0.3 years. Although we show that the complex lensing potential involved in HE 1104-1805 makes it difficult to determine H0 from the time delay, we also show that HE 1104-1805 is probably much more of interest for microlensing studies, provided the lens redshift is better known. The present paper describes an attempt to measure the redshift of the main lensing galaxy from near-IR spectroscopy. Our near-IR observations where motivated by the very red colors measured for the lensing galaxy (C98, R98), and by the better contrast between the lens and the quasar in the near-IR. Although we were unsuccessful in measuring the lens redshift accurately, we did obtain high S/N spectra of the lensed quasar, between 0.95 and 2.5 microns.

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© European Southern Observatory (ESO) 2000

Online publication: August 23, 2000