Several JWST instruments have imaging capabilities, covering different fields of view and wavelengths.
Standard imaging overview
MIRI, NIRCam, and NIRISS are the imaging instruments on JWST. The wavelength ranges and available modes of use are summarized in Table 1. The "main article" links above connect you to the details for each instrument. Note that NIRISS imaging is only offered as a parallel observing mode. Figure 1 shows the relative positions of these imaging fields of view in the JWST focal plane.
Table 1. Summary of JWST's standard imaging capabilities
|Instrument||Wavelength range||Mode of use|
|NIRCam||0.6 μm < λ < 5 μm||Primary or parallel|
|MIRI||5.6 μm < λ < 25.5 μm||Primary or parallel|
|NIRISS||0.8 μm < λ < 5 μm||Parallel only|
For convenience, Figure 2 provides a visual representation of the relative wavelength coverage. JWST time-series observations (TSO) and high-contrast imaging (HCI) also use the imagers and are shown for completeness. However, they involve specialized operations that are described elsewhere in JDox.
NIRCam provides imaging in 2 wavelength ranges simultaneously over the same 9.7 arcmin² field of view (via a dichroic): 0.6–2.3 μm (0.031"/pix) and 2.4–5.0 μm (0.063"/pix). It uses 2 near-identical side-by-side modules, separated by a 44" gap. NIRCam's short wavelength channel also has small 4"–5" gaps between detectors.
MIRI offers imaging at a complementary wavelength range, from 5.6 to 25.5 μm over a 3.1 arcmin² field of view, and has a detector plate scale of 0.11"/pixel.
NIRISS offers 0.8–5.0 μm (0.065"/pix) imaging in a 4.84 arcmin² field of view and many of its filters are essentially identical counterparts to the NIRCam filters. Consequently, NIRCam and NIRISS can be used in parallel to increase the sky coverage at a particular wavelength. NIRISS imaging is not offered as a primary mode.
Imaging spatial resolution
Details about the point spread function (PSF) FWHMs for each instrument are summarized in Table 2. More information is available in these articles:
- NIRCam Point Spread Functions
- Near Infrared Imager and Slitless Spectrograph (Table 1)
- MIRI Point Spread Functions
Table 2. Information on imaging spatial resolution
|Plate scale||Nyquist sampled|
>2 μm (SW)
>4 μm (LW)
|NIRISS||2 pix @ 3.4 μm||0.066||>3.4 μm|
The sensitivity of each JWST imaging filter is summarized in Figure 3. The JWST Exposure Time Calculator (ETC) was used to estimate the signal to noise (S/N), with readout patterns chosen to reach approximately 10 ks in each instrument and using a benchmark background, as described in the JWST Background Model article. Also, consider using the JWST Interactive Sensitivity Tool to explore the relevant parameter space for the various imagers.