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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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