VIMOS – a Cosmology Machine for the VLT

Successful Test Observations With Powerful New Instrument at Paranal

One of the most fundamental tasks of modern astrophysics is the study of the evolution of the Universe. This is a daunting undertaking that requires extensive observations of large samples of objects in order to produce reasonably detailed maps of the distribution of galaxies in the Universe and to perform statistical analysis.

Much effort is now being put into mapping the relatively nearby space and thereby to learn how the Universe looks today. But to study its evolution, we must compare this with how it looked when it still was young. This is possible, because astronomers can “look back in time” by studying remote objects – the larger their distance, the longer the light we now observe has been underway to us, and the longer is thus the corresponding “look-back time”.

This may sound easy, but it is not. Very distant objects are very dim and can only be observed with large telescopes. Looking at one object at a time would make such a study extremely time-consuming and, in practical terms, impossible. To do it anyhow, we need the largest possible telescope with a highly specialised, exceedingly sensitive instrument that is able to observe a very large number of (faint) objects in the remote universe simultaneously.

The VLT VIsible Multi-Object Spectrograph (VIMOS) is such an instrument. It can obtain many hundreds of spectra of individual galaxies in the shortest possible time; in fact, in one special observing mode, up to 6400 spectra of the galaxies in a remote cluster during a single exposure, augmenting the data gathering power of the telescope by the same proportion. This marvellous science machine has just been installed at the 8.2-m MELIPAL telescope, the third unit of the Very Large Telescope (VLT) at the ESO Paranal Observatory. A main task will be to carry out 3-dimensional mapping of the distant Universe from which we can learn its large-scale structure.

“First light” was achieved on February 26, 2002, and a first series of test observations has successfully demonstrated the huge potential of this amazing facility. Much work on VIMOS is still ahead during the coming months in order to put into full operation and fine-tune the most efficient “galaxy cruncher” in the world.

VIMOS is the outcome of a fruitful collaboration between ESO and several research institutes in France and Italy, under the responsibility of the Laboratoire d`Astrophysique de Marseille (CNRS, France). The other partners in the “VIRMOS Consortium” are the Laboratoire d`Astrophysique de Toulouse, Observatoire Midi-Pyrenees, and Observatoire de Haute-Provence in France, and Istituto di Radioastronomia (Bologna), Istituto di Fisica Cosmica e Tecnologie Relative (Milano), Osservatorio Astronomico di Bologna, Osservatorio Astronomico di Brera (Milano) and Osservatorio Astronomico di Capodimonte (Naples) in Italy.