With the advent of very large telescopes, such as the VLT, a largely unexplored domain of the universe becomes accessible to observations which may dramatically enhance our understanding of different physical phenomena, in particular the origin and evolution of galaxies and large scale structures. In the next few years a wide array of 8-m telescopes will become available world-wide. Among these, the European VLT project is particularly striking because of its four 8-m telescopes and an impressive array of complementary instrumentation. Viewed as a unit, the VLT provides great flexibility by combining complementarity for certain programs with multiplexing capabilities for others. First-light for the VLT is scheduled for May 1998, with regular science operation starting in April 1999.
In order to take full-advantage of the VLT from the start of its operation, ESO and its Observing Programmes Committee (OPC) decided to coordinate an imaging survey to provide candidate targets well-suited to the first set of VLT instruments. The ESO Imaging Survey (EIS) has been conceived as a collaborative effort between ESO and astronomers in its member states. Following the recommendation of the OPC, the survey has been overseen by a Working Group (WG). The EIS WG is composed of leading experts in different fields and has the responsibility of defining the survey science goals and strategy, and monitor its progress. In order to carry out the survey a dedicated team was assembled, starting March 1997. To stimulate cooperation between ESO and the astronomical community of the member states, EIS has sponsored the participation of experts as well as students and post-docs from the community in the development of software, observations and data reduction.
As described by Renzini & da Costa (1997) (see also "http://www.eso.org/eis''), EIS consists of two parts: EIS-wide to search for rare objects (e.g., distant clusters and quasars) and EIS-deep to define samples of high-redshift galaxies. These science goals were chosen to match as well as possible the capabilities of the first VLT instruments, FORS, ISAAC and UVES. EIS is also an essential first step in the long-term effort, currently underway at ESO, to provide adequate imaging capabilities in support of VLT science (Renzini 1998). The investment made in EIS will be carried over to a Pilot Survey utilizing the ESO/MPIA 2.2 m telescope at La Silla, with its new wide-field camera. This Pilot Survey, which will follow the model of EIS, has been recommended by the EIS WG and is being submitted to the OPC.
The goal of this paper is to describe the characteristics of I-band observations carried out in the fall of 1997 over a region of 3.2 square degrees (EIS patch A, da Costa et al. 1998a) and of the corresponding data products, in the form of calibrated images and single frame catalogs. These products have been made publicly available through the ESO Science Archive, as a first step towards the full distribution of the EIS data. The purpose of the present release is also to provide potential users with a preview of the data, which may help them in the preparation of VLT proposals, and to encourage the community to provide constructive comments for the final release. It is important to emphasize that due to time limitations the results presented here should be viewed as preliminary and improvements are expected to be made before the final release of the EIS data later this year.
In Sect. 2, a brief description is presented of the criteria adopted in the field selection, the strategy of observations and the characteristics of the data in patch A already completed. It also describes the filters used, the definition of the EIS magnitude system and its relation to other systems, and the data used for the photometric calibration of the survey. In Sect. 3, a brief description of the data reduction pipeline is presented, followed in Sect. 4 by a description of the data products made publicly available in this preliminary data release. In Sect. 5, the algorithms used to detect and classify objects, and the information available in the catalogs being distributed are described. Preliminary results from a scientific evaluation of the data is presented in Sect. 6. In Sect. 7, future plans are presented, followed in Sect. 8 by a brief summary.
Copyright The European Southern Observatory (ESO)