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First Look Survey (FLS): Community Workshop Report


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The FLS extragalactic component
C. Description of Survey

The recommended shallow survey consists of near the minimum coverage one would allow while maintaining reliability and robustness. This conservative approach is best suited for the very early stages of the mission. The MIPS survey consists of freeze-frame scan mapping at the fast speed with 3 seconds of integration time per frame, repeated 5 times. This results in 75 seconds of integration over 15 sightings of each sky pixel at 24 and 70 microns, and 15 seconds of integration during 5 partial sightings at 160 microns. Adding approximate overheads of 30% yields a mapping rate of about 4 hours per square degree. The IRAC shallow survey consists similarly of 5 sightings of the sky at 12 seconds of integration each time, adding up to 60 seconds total integration time. This works out to a mapping rate of about 5 hours per square degree.

The confirmation surveys should cover 3 to 4% of the area covered by the shallow survey, and assuming similar efficiency, i.e. same observing strategy, should require one third as much observing time for 8 to 10 times more integration time. However, these confirming observations may be more effective if the time were spent on fewer sightings with longer integration time in each. The SSC should look into optimizing this choice as part of detailed observation planning for the FLS.

The estimated total time required, depth of integration, and approximate expected source counts are given in the table below. The "nominal sensitivity" correponds to the limits achievable if all the data were co-added, and sources extracted at the resulting optimal noise levels. Similarly, the confirmation survey would reach an ultimate sensitivity roughly three times deeper (except at 160um where confusion is the limit), assuming all data are co-added optimally, and in quadrature. This ultimate sensitivity will be achieved only after considerable experience with instrument and data characteristics, at least several months into the mission.

The total time required should therefore come up to 45 hours for the shallow survey, and about 15 hours for the confirmation survey, for a grand total of 60 hours.

The proposed shallow survey
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SHALLOW SURVEY, 5 sq.deg:

           Survey            Nominal Estimated
Instrument  Time  Wavelength  5*rms  Number of
            (hr)  (microns)   (mJy)   sources

MIPS         20        24      1.3      400
                       70      4.5     1500
                      160      27      2500     Nearly confusion limited

IRAC         25   3.6, 4.5     0.04
                      5.8      0.04
                      8.0      0.06    ~750
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This file was last modified on Fri Jan 9 09:42:46 2009.
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