4MOST is conceived as a survey facility that comprises the instrument as well as associated operations and data management services. The VISTA telescope will spend 100% of its observing time on Public Surveys with 4MOST for a minimum of 5 years. The largest fraction of the observing time on 4MOST will be allocated to a unique operations concept in which 5-year Public Surveys from both the 4MOST Consortium and the ESO community will be combined and executed in parallel, with multiple surveys sharing the available fibres in any given observation. These surveys are jointly called Participating Surveys.
However, it will also be possible to operate 4MOST efficiently in the more traditional single survey mode, provided a sufficiently high target density is available, and this mode will also be available to Community Surveys. Community Surveys using 4MOST in single survey mode are called Non-Participating Surveys.
Note that all surveys executed by 4MOST (irrespective of whether they are Participating or Non-Participating, Consortium or Community Surveys) will be ESO Public Surveys. That means that all raw data will become public immediately (through ESO’s Science Archive Facility), and that all surveys will have to deliver a set of data products back to ESO for publication (Phase 3), where both the contents of the data set and the schedule of the delivery will have been previously agreed upon by ESO and the surveys.
Participating Surveys will be executed in parallel, not sequentially. They will pool their targets such that in any given observation 4MOST will typically obtain spectra for many different science cases simultaneously. Parallel observing enables efficient use of 4MOST for surveys that have compatible observing conditions requirements and/or a target density lower than the 4MOST multiplexing capability. Note that in this mode, each Participating Survey will only be “charged” the observing time for the fibres actually used by that survey (including fractional overheads and any residual inefficiencies). This mode does imply, however, that all Participating Surveys will have to agree on a common survey strategy and prepare Observation Blocks (OBs) jointly. As a consequence, all Participating Surveys will have to fully share the raw data as well as the calibrated spectra in order to be able to assess selection functions and mitigate the impact of any cross-talk effect on their science.
4MOST operations have been designed to work within ESO’s La Silla-Paranal Observatory framework, with as few changes to infrastructure and processes as possible. Still, two main differences to the standard ESO science operations model are necessary: (1) although each Participating Survey will have submitted its own proposal, from the operations perspective there will only be a single science “customer”: the joint 4MOST Science Team, which will comprise all members of all 4MOST Consortium Surveys and of all Participating Community Surveys; (2) common tasks in observation preparation and data management will be centralized and provided by the 4MOST Consortium as a service.
Joint Operations Group
4MOST is unique in that its operations will be the joint responsibility of ESO and the 4MOST Consortium. The coordination of the various stakeholders in 4MOST operations will be ensured by the Joint Operations Group. The Joint Operations Group will implement the scientific and operational guidance given by ESO, the Survey PIs, and the 4MOST PI. It will include representatives from the various work packages in operations. Its main task will be to ensure that observations for the Participating Surveys progress with the best possible quality over the entire survey duration.
Infrastructure Working Groups (IWGs) perform tasks common to all surveys. Their members are also members of the Science Team and are delegated to operations. Every Participating Survey is requested to provide resources to the IWGs. The current working groups are: “Survey Strategy”, “Selection Functions”, “Galactic Pipeline”, “Extragalactic Pipeline”, and “Classification Pipeline”.
Science Data Flow for Participating Surveys
The data flow through the 4MOST facility (see figure below) will follow concepts that are familiar to most astronomers working with either ESO or large survey projects. In a nutshell, the following steps in the data and work flow are foreseen:
- Preparation of target catalogues with relevant associated data (e.g. Figure-of-Merit) by Surveys
- Submission of target catalogues to the Operations System run by the 4MOST Consortium
- Merging of catalogues and preparation of OBs by the Operations System
- Submission of OBs to ESO
- Execution of OBs at the VISTA telescope by ESO
- Transfer of raw data from telescope to the Data Management System run by the 4MOST Consortium
- Data reduction from raw (Level 0) data to calibrated spectra (Level 1 data) by the data reduction pipeline of the Data Management System
- Transfer of reduced (Level 1) data to the advanced pipelines
- Data analysis and creation of advanced (Level 2) data products by advanced pipelines run by the IWGs
- Transfer of all data to archives
- Science exploitation by Surveys and (after a delay) the world-wide community
Note that for Participating Surveys most of the data flow, including the delivery of data products to ESO (Phase 3), is handled centrally by the Operations and Data Management Systems. Surveys will typically only interact with the data flow by providing their target catalogues and through their participation in the IWGs (who will be responsible for the advanced pipelines).
Community Surveys wishing to use 4MOST in single survey mode are called Non-Participating Surveys. These will not pool their targets with any other survey, and their observing time will be allocated in named nights or half nights (for accurate planning) during which they will be the only survey using the facility. Accordingly, these surveys will be “charged” the full equivalent in fibre-hours, regardless of how many fibres they actually used. Although these surveys will not join the 4MOST Science Team, the Consortium’s Operations System will nevertheless provide these surveys with the software necessary to produce OBs, which, however, they will need to run themselves. In addition, the Consortium’s Data Management System will reduce the data of Non-Participating Surveys and provide them with calibrated, science-ready spectra (i.e. Level 1 data). However, Non-Participating Surveys will not have access to the advanced data analysis pipelines developed by the IWGs, i.e. the 4MOST Science Team. Non-Participating Surveys will have to produce their own advanced data products and deliver them to ESO.