Observing Plan

General Considerations

The WG reviewed the implications of the necessity to carry out the WIDE part of the survey in ``shift-and-stare'' mode, requiring an increase of the overhead (mainly due to readout time) to about 100 seconds per science exposure. The proposal of the EIS Team was aiming at keeping the surveyed area the same as originally proposed (i.e., about 30 square degrees) by observing two fields in the spring to provide targets for the initial period of regular VLT observations in the first semester of 1999. The WG revised this proposal based on the considerations that it would have led to an imbalance in the distribution of observing hours strongly peaking in Period 60, and that it would have significantly increased the total observing time. In an effort to address these points, matching at the same time the scientific goals of the project, the WG is proposing the following solution:

EIS WIDE

- The goal of finding a useful sample of distant cluster is preserved even by slightly reducing the surveyed area to 24 square degrees, distributed in 4 fields of six square degrees each (see map below), one of which is in the northern galactic cap to allow for FORS and ISAAC follow up in the early period of regular VLT observations (Q1, Q2 1999). These 4 fields will have to be observed in Vwide and Iwide, with total integration time of 300 seconds per filter. This results in a total observing time of 42 hours per field per filter. In this way this part of the EIS WIDE survey will be completed by March 1998.

- The WG felt the particular importance of one aspect of the ``Quasar Part'' of the project, namely, to provide the targets for a study of the three-dimensional large-scale structure of quasar-absorption systems through VLT spectroscopy. The main goal of obtaining a relevant set of high-redshift quasars in a compact field will therefore be achieved by observing one EIS-WIDE field also in the B band with a longer integration time than originally proposed. The total integration time of 300 seconds in B thus results in a total observing time of 42 hours. One third of this field (about 1.9 square degrees) will also be observed in the U' band using SUSI2 (which will have a higher efficiency than EMMI blue and approximately the same field of view). This will allow to identify also quasars with redshift lower than 3 over 1.9 square degrees and at the same time give an adequate number (about 100) of z>3 quasars. It was also decided to eliminate the Gunn-z observations as envisaged in the EIS proposal for Period 59. Based on extensive simulations presented to the WG, the use of this band will be effective for finding very high-redshift QSOs only with appreciably longer integration times or over a wider area than initially envisaged.

- General agreement was reached on the choice of the EIS WIDE fields, to be observed during Period 59/60.

EIS DEEP

Given the current schedule of the VLT regular operations, the WG recommends that EIS DEEP be revised, by splitting it into two parts.

- In order to provide targets for the first semester of 1999, a single SUSI2/SOFI field is planned to be observed in 4 optical (U', Gunn-g, Gunn-r, I) and 2 infrared passbands (J and K'). The primary goal is to obtain galaxies in the redshift range 1< z< 4 for spectroscopic follow-up with ISAAC and FORS. This part of the survey will also be useful to provide a benchmark of the performance of SUSI2 and SOFI. It may be possible that some of the data will be collected during the commissioning of these two instruments in the period January/March 1998, in which case the OPC will be informed and the time required in Period 61 correspondingly decreased.

- The WG proposes the original 0.07 square degrees EIS DEEP field to be postponed to the Periods 61 and 62, which would avoid an overlap with EIS WIDE. It also suggests that it should be centered on the HDF South, the exact location of which is to be decided within the next three months. Recent communications from STScI indicate that the HST observations will be carried out either in 1998 or 1999. This choice was based on the fact that several surveys in other wavelengths are being considered to cover the same region. The observations are currently planned to be carried out in U', Gunn-g, Gunn-r, I and K'.

Figure caption: The red shading is from the Burstein & Heiles reddening map (no values are available for low galactic latitude). The hatched regions show various radio surveys: blue = NVSS, wide-spaced green = future WENSS region, orange= MOST, narrow-spaced green = AT-ESP survey. The solid blue curve is the ecliptic with +/- 10 degrees plotted in dashed lines. Because of reselection of patch D, note that its position is different from the new coordinates listed below. The new figure will be provided soon.

Field Centers (J2000) for EIS-WIDE

Field		RA		DEC
A		22 42 54		-39 28 00
B (SGP)		00 51 00		-28 54 00
C		05 38 24		-23 51 00
D		09 51 36		-21 00 00

Exposure times (in hours) per field on EIS-WIDE

Field		U		B		V		I		Total
A		----		----		42		42		84
B		32		42		42		42		158
C		----		----		42		42		84
D		----		----		42		42		84
Total		----		----		----		----		410

More information on the observing plan and related issues can be found on the EIS progress report from the WG meeting that took place on April 25, 1997