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.
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. The script is available on Github.
Depth vs. exposure time
The NIRCam Imaging overview 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 seven 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 Pandeia Exposure Time Calculator to plan your observations.
JWST's background model varies with the target coordinates (RA, Dec) and time of year. These calculations assume the fiducial "1.2 × MinZodi" (1.2 times the minimum zodiacal light) background at RA = 17:26:44, Dec = -73:19:56 on June 19, 2019, as used in the NIRCam Imaging article. The background model for these observations must be generated using the online ETC GUI and then imported into the Python ETC engine.
Words in bold italics are buttons
or parameters in GUI tools. Bold
style represents GUI menus/
panels & data software packages.
Note we do not generally recommend integration times greater than 1000 seconds. After 1000 seconds, 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)|