NIRCam Imaging Sensitivity
The exposure times vs. flux estimates at signal-to-noise ratio = 10 in NIRCam images presented here have been obtained using the Pandeia JWST Exposure Time Calculator (ETC) Python engine.
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The Pandeia Exposure Time Calculator should be used for all observation planning. This article provides ETC results determined using the Python engine to loop through many calculations of signal-to-noise ratio (SNR) for various readout patterns and exposure times, given the assumptions detailed below. These calculations are then interpolated to determine depth (SNR = 10) vs. exposure time.
Depth vs. exposure time
The NIRCam Imaging and NIRCam Sensitivity articles show SNR = 10 sensitivity estimates for imaging in all NIRCam filters given a total exposure time of 10 ks (166.7 minutes = 2.78 hours). Figure 1 shows similar estimates for a range of exposure times in 7 wide filters and one medium filter.
Sensitivity estimates can vary significantly depending on the background and the assumed photometric aperture sizes as discussed below. Please use the Exposure Time Calculator to plan your observations.
Exposure time
Words in bold are GUI menus/
panels or data software packages;
bold italics are buttons in GUI
tools or package parameters.
Note we do not generally recommend integration times greater than 1,000 s. After 1,000 s, the majority of pixels would likely be affected by cosmic rays. See discussion in MIRI Cross-Mode Recommended Strategies.
Table 1. Recommended readout specifications for maximal depth in a given exposure time
Readout pattern | NGROUPS | NINT | Exposure time (s) | NEXP | Total exposure time (s) |
---|---|---|---|---|---|
RAPID | 2 | 1 | 21.5 | 4 | 86.0 |
BRIGHT2 | 2 | 1 | 42.9 | 4 | 171.8 |
BRIGHT2 | 3 | 1 | 64.4 | 4 | 257.6 |
BRIGHT2 | 4 | 1 | 85.9 | 4 | 343.6 |
BRIGHT1 | 5 | 1 | 96.6 | 4 | 386.4 |
BRIGHT1 | 6 | 1 | 118.1 | 4 | 472.4 |
BRIGHT1 | 7 | 1 | 139.6 | 4 | 558.4 |
BRIGHT1 | 8 | 1 | 161.1 | 4 | 644.4 |
BRIGHT1 | 9 | 1 | 182.5 | 4 | 730.0 |
BRIGHT1 | 10 | 1 | 204.0 | 4 | 816.0 |
SHALLOW4 | 5 | 1 | 257.7 | 4 | 1030.8 |
SHALLOW4 | 6 | 1 | 311.4 | 4 | 1245.6 |
SHALLOW4 | 7 | 1 | 365.1 | 4 | 1460.4 |
SHALLOW4 | 8 | 1 | 418.7 | 4 | 1674.8 |
SHALLOW4 | 9 | 1 | 472.4 | 4 | 1889.6 |
SHALLOW4 | 10 | 1 | 526.1 | 4 | 2104.4 |
MEDIUM8 | 6 | 1 | 622.7 | 4 | 2490.8 |
MEDIUM8 | 7 | 1 | 730.1 | 4 | 2920.4 |
MEDIUM8 | 8 | 1 | 837.5 | 4 | 3350.0 |
MEDIUM8 | 9 | 1 | 944.8 | 4 | 3779.2 |
MEDIUM8 | 10 | 1 | 1052.2 | 4 | 4208.8 |