3D Map of Distant Galaxies Completed
VLT survey shows distribution in space of 90 000 galaxies
2016. december 15.
For nearly eight years, the VIsible MultiObject Spectrograph (VIMOS) on ESO’s Very Large Telescope (VLT) in Chile has been piecing together a three-dimensional map of galaxies in two patches of the southern sky. A total of 440 hours of observing time has gone into measuring the spectra of more than 90 000 distant galaxies, producing a map of a 24-square-degree region on the sky, out to a distance corresponding to when the Universe was around half its current age .
In 2013, ESO reported that the international team of astronomers behind the VIMOS Public Extragalactic Survey (VIPERS) had collected data for around 60% of their target galaxies. With the full set of observations now completed, this is the largest redshift survey ever undertaken with ESO telescopes  and it provides a view of structures in the younger Universe with an unprecedented combination of detail and spatial extent. By surveying how galaxies were distributed in space several billion years ago, astronomers are able to learn more about the distribution of matter on the largest scales in the cosmos, as well as to further probe the effect that the mysterious dark energy had on the young Universe, when it acquired some of the properties we see today.
Using these unique data, astronomers are already obtaining exciting new results concerning how galaxies have evolved since the Universe was much younger, and how this connects to the details of large-scale structures, such as filaments, clusters and voids. The full set of data from the survey was released to the public in November 2016 and is now available in standard form on the ESO archive.
 Light has a finite speed limit, so the more distant an object, the more time it has taken for the light from it to reach us. This means that we see distant objects as they were long in the past.
 The light from each galaxy is spread out into its component colours within the VIMOS instrument. Careful analysis allows astronomers to work out how fast the galaxy is moving away from us — usually expressed as its redshift. This in turn reveals its distance from us and, when combined with its position on the sky, its location in the Universe.
The team is composed of astronomers in Italy, France, Poland and the UK. Full details are available on the VIPERS website.
Dipartimento di Fisica, Università Statale di Milano
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