The Hamburg/ESO Survey for Bright QSOs — Slitless Spectroscopy at High Resolution

Abstract

The digital revolution in the evaluation of photographic plates and the introduction of automated quasar search techniques have drastically increased the number of known QSOs over the past decade. However, most of these QSOs are so faint that their use is limited to statistical studies. The bright end of the quasar population is still dominated by objects selected in other wavebands, such as radio, X-rays, or even infrared. We have started in 1990 a wide-angle objective-prism survey (the Hamburg/ESO Survey, HES) using the 1 m ESO Schmidt telescope (Reimers 1990). The survey is intended to cover 5000 deg2, of which about a third has been acquired up to now. The prime goal is to compile a large sample of bright (B < 17.5) QSOs suited for detailed follow-up studies, in particular for high-resolution spectroscopy. Other objectives are to search for gravitational lens candidates and to directly measure the local luminosity function of quasars. In each Schmidt field, a spectral and a direct plate are scanned with the PDS 1010G microdensitometer at Hamburg, followed by an automated candidate selection and subsequent follow-up spectroscopy with the ESO 1.52 m and 3.6 m telescopes. A novel feature in our survey is the use of an objective-prism with a dispersion of 450 å/mm at Hγ, yielding a seeing-limited spectral resolution of 10–20 å FWHM. A full documentation of the survey techniques is in preparation. First results include the discoveries of the second-brightest QSO in the south (Wisotzki et al. 1991), and of a bright double QSO at high redshift, probably a gravitational lens (Wisotzki et al. 1993). In this contribution I want to show how a wide-angle quasar survey like the HES can benefit from the high resolution of the survey spectra.