Quasar Surveys in Hamburg

Scientific Goals

Survey Requirements:

Survey Technique

Technical data:

Digitisation and extraction of spectra

For each survey field at least two photographic plates are required: A direct plate where objects can be accurately located, and a spectral plate, obtained with objective prism to disperse each object into a slitless spectrum on the plate. Upon arrival in Hamburg, plates taken with the Calar Alto and ESO Schmidt telescopes are digitised with the Hamburg PDS machine. The details of the digitisation mode (scanning speed, aperture and step size etc.) depend on the particular application.


Small section from the Digitized Sky Survey:

In this image there are several starlike objects in the magnitude range B = 12-20, and a small group of galaxies on the left. The section covers 8???? x 3???? mm on the Schmidt plate, or ???? x ???? arcmin in the sky.

The same sky area in the corresponding spectral image:

Each object brighter than B=18 has produced a spectrum on the plate, ranging from 5400 Å (left end) to 3200 Å at the right end, respectively. Most of the galaxies have very fuzzy images and so make only fuzzy and short spectra, implying that they are very red. However, one bright galaxy shows a sharp and exceptionally blue spectrum, typical for a low-redshift Seyfert 1 galaxy.

By establishing a precise astrometric transformation from direct to spectral plate it is possible to extract one-dimensional spectra for all detected objects. The above located Seyfert galaxy looks now like this:

The ordinate gives photographic density above diffuse sky background in integer units (800 units correspond to one density step). The wavelength scale is nonlinear because of the objective prism which has a nonlinear dispersion relation. There are several emission lines in the spectrum, allowing to estimate the redshift of the galaxy: z = 0.032. Further examples of digital objective prism spectra: ...

Survey Projects

Hamburg Quasar Survey (HQS):

Hamburg/ESO survey (HES):

QSO Selection Strategy

(based on database of digitised spectra)

1. Search for

2. Separate stellar contamination from absorption lines

3. Snapshot slit spectroscopy of high-grade candidates

Calar Alto 2.2 m
ESO 1.52 m and 1.54 m Danish

4. For bright high-redshift QSOs: follow-up with IUE

Basic Properties

More Properties

Current status

Last modified 21.01.1999 by L. Wisotzki