The IRAC cycle data
166 hours of observations with the IRAC camera have been dedicated to cover the entire 2 sq.deg. COSMOS field. The field has been observed simultaneously in the 4 IRAC chanels - 3.6, 4.5, 5.6 and 8.0 micron. These observations (Cycle 2) have just recently been obtained (Dec'05-Jan'06), and the data reduction is on-going.
Observing strategy
The entire COSMOS field has been covered using a tiling procedure. 48 AORs were used to cover the full 2 sq.deg. Each AOR is the combination of typically more than 100 exposures, each with a field-of-view of 5.2'x5.2', and an exposure time of 100s. The exposures are dithered to allow an efficient removal of spurious objects. The spatial coverage is shown below. [Note: The reduced sampling rate apparent in the lower right corner of the field is due to a spacecraft down link malfunction involving 9 AORs. These missing data will be reobtained in the near future.]
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Data reduction
The S-COSMOS survey inherits the data reduction methodology and analysis softwares developed for the GOODS, SWIRE, and xFLS surveys. Our team is in the process of optimizing these analysis tools for use in reducing the S-COSMOS data.
First step: the BCDThe Spitzer Science Center produced the basic calibrated data (BCD) from the raw data. The BCD images are flux calibrated and the well-understood instrumental signatures are removed. The BCDs are dark subtracted, corrected for non-linearity, divided by the flat field. Effects like latent images, muxbleed, column pull-down are masked. Work is in progress to improve the correction of "jail bars", "stray light", the background computation and the detection of asteroids present in the field.
Second step: the mosaic
The BCDs are coadded and combined using MOPEX software. The BCDs are corrected for array distortions and projected onto a sky grid with square pixels 0.6''x0.6''. Using the redundancy of the IRAC data, spurious data are masked and rejected from the coaddition.
Below, we show the RGB image of the S-COSMOS IRAC data using the three
bands- 3.6, 4.5 and 8.0 micron.
(save the full resolution image)
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A zoom in region containing a massive structure at z=0.73
(full resolution image)
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