In 1996 `Large Programmes' were introduced for the use of the VLT available observing time, following the recommendation of a working group nominated by the Observing Programmes Committee  (OPC). Since then, fifteen per cent of the entire science time available on ESO telescopes has been devoted to the execution of Large Programmes, with more than 150 such programmes scheduled for observations at the La Silla Paranal Observatory.

With the availability of dedicated survey telescopes, VISTA and VST, the ESO Public Surveys were added to the ESO landscape in order to enhance the legacy value of the data from the ESO facilities and serve broad communities. In 2010 and 2011, the public imaging surveys started on VISTA and VST, respectively, and were soon followed by the public spectroscopic surveys on the NTT and VLT.

In 2015, the public imaging surveys have reached five years of successful operation at VISTA and four years of successful operation at VST. At the same time the first two public spectroscopic surveys are more than half-way through. These are the Gaia-ESO survey of the dynamics and chemical evolution of the Milky Way, and the PESSTO survey, that investigates transient objects and in particular the physics of supernova explosions. The most recent additions to the suite of ESO Public Surveys are the two extragalactic projects with VIMOS: LEGA-C & VANDELS, which started in 2014. According to the current progress, some public surveys will require few more years to complete their planned data acquisition, but since several surveys are nearing completion, it is now the right time to learn about their results and impact, as well as to start planning possible new projects for the ESO survey telescopes.

ESO regularly organises workshops which provide an overview of the scientific advancements enabled by the use of its facilities. The assessment of the scientific return of Large Programmes was the goal of two workshops in 2003 and 2008, and the first results from the imaging Public Surveys were discussed in 2012. The thirteen ESO public surveys and a representative set of Large Programmes that were recently completed are now jointly the focus of the ESO workshop ``Rainbows on the Southern Sky: the legacy value of Public Surveys and Large Programmes''.

The aim of this workshop is to carry out an overview of the scientific results achieved through these large and coherent time allocations at the La Silla Paranal Observatory. The astronomers in charge of these Programmes will be invited to present their scientific results and the impact of their projects on their field of research. By bringing together these broad communities, new ways forward will be explored for a new phase of the use of the ESO facilities. Participants at this workshop will compare survey operations at different telescopes and discuss how observatories collect and publish reduced data from legacy programmes, like for example the HST Legacy & Treasury Programs. Furthermore it will provide a forum to discuss further needs and developments to support the community access to reduced data via the ESO Science Archive Facility.

The workshop will be hosted at ESO Headquarters in Garching in the new auditorium, which allows the extended participation of the community interested in the ESO Public Surveys and Large Programmes, beyond the PIs and Co-Is of these teams. The participation of archive users, who have tripled in number the community using data collected from these large coherent programmes, is very welcome.

Structure of the workshop

Workshop starts: Monday 05.10.2015 at 14:00. Workshop ends: Friday 09.10.2015 at 14:30

The Program is structured around these seven main topics:

• Stars and Planets - (GAIA ESO, PESSTO, VMC, VPHAS+ , VVV)
• Milky Way and Local Group -  (VVV, VPHAS+, GAIA ESO, VHS, VMC)
• Extragalactic Astronomy - (VIKING, KIDS, VHS, ATLAS)
• Galaxy Evolution -  (VIDEO, VANDELS, LEGA-C)
• Cosmology and High-redshift Universe - (VHS, ATLAS, ULTRAVISTA, VIDEO, VANDELS, LEGA-C)
• Legacy value of Public Surveys & Large Programmes

These topics will be introduced by key note speakers illustrating the latest results from surveys and large programmes and the open questions to be addressed.