NIRCam Mosaics

JWST NIRCam mosaics are used primarily to cover areas larger than the 5.1' × 2.2' NIRCam field of view. 

See also: NIRCam Deep Field Imaging with MIRI Imaging Parallels

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JWST mosaics may be used in NIRCam imaging and wide field slitless spectroscopy observations — its primary purpose is to cover areas larger than the 5.1' × 2.2' NIRCam field of view. This spacing may be decreased (to make the pointings overlap, as is the default) or increased (to widen the gaps between pointings).  By default, spacing is defined along NIRCam's ALL aperture axis, which is approximately aligned with the JWST (V2, V3) coordinate system and the NIRCam detector rows and columns.

Optionally, shifts may be added between rows and/or columns to skew the pattern; these "shifts" are specified as rotation angles in the APT observation form's Mosaic Properties tab.

All dithers and filter changes are performed at each pointing (or tile) in the mosaic before proceeding to the next tile.

To obtain approximately even observing depth over large areas, consider using the NIRCam FULL primary dither patterns in conjunction with mosaics with tile spacings of 5.8' × 2.25'.

Figure 1. Sky coverage of nominal NIRCam 2 × 2 mosaic with zero overlap

This figure shows a nominal tile spacing of a NIRCam mosaic composed of 2 rows and 2 columns, with 0% overlap and zero shifts between rows or columns. The mosaic may be adjusted to have smaller or larger spacing, as well as shifts between columns or rows. Short and long wavelength detectors are shown as blue filled squares and red outlines, respectively. Each X marks the reference target spot for one pointing when observing with both modules. Note that when observing with both modules, the target reference position falls in the gap between modules.

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