JWST Imaging

Several JWST instruments have imaging capabilities, covering different fields of view and wavelengths.

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Standard imaging overview

Main articles: MIRI Imaging, NIRCam Imaging, NIRISS Imaging
See also: JWST Mosaic OverviewJWST Dithering Overview
See also: Imaging Roadmap

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.

In addition, an Imaging Roadmap article is available for planning imaging observations.  If you plan to use imaging in coordinated parallel mode, see the Coordinated Parallels Roadmap.

Figure 1. Imager fields of view in the JWST focal plane

The 3 imaging instruments (NIRCam, NIRISS, and MIRI) are highlighted here in the JWST focal plane. FGS indicates the Fine Guidance Sensor fields of view, used for guiding.


Table 1. Summary of JWST's standard imaging capabilities

InstrumentWavelength rangeMode of use
NIRCam0.6 μm < λ < 5 μm Primary or parallel
MIRI5.6 μm < λ < 25.5 μm Primary or parallel
NIRISS0.8 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.


Figure 2. Summary of JWST's imaging capabilitities

Wavelength coverage of each instrument, highlighting different imaging capabilities. Note that standard imaging with NIRISS is allowed in parallel mode only.

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.

All the standard imaging modes offer a mosaicking capability for observing larger areas.  Dithering is also recommended for imaging to improve data quality.

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:


Table 2. Information on imaging spatial resolution


PSF FWHM

(pix)

Plate scaleNyquist sampled
NIRCam

0.987–2.341 (SW)

1.340–2.574 (LW)

0.031 (SW)

0.063 (LW)

>2 μm (SW)

>4 μm (LW)

NIRISS2 pix @ 3.4 μm0.066>3.4 μm 
MIRI1.00–7.450.11>6 μm 

Imaging sensitivities

Main articles: NIRCam Imaging Sensitivity, NIRISS Sensitivity, MIRI Sensitivity
See also: NIRCam Detector Readout PatternsMIRI Detector Readout OverviewNIRISS Detector Readout PatternsJWST ETC

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.

Figure 3. JWST imaging sensitivity

The S/N = 10 detection limits of JWST's imaging instruments in 10 ks, shown for every available filter. The horizontal error bars represent the width of the filter. Sources are assumed to have a flat spectrum in nJy and a benchmark background, as described on the JWST Background Model article. Please use the JWST Exposure Time Calculator (ETC) to calculate sensitivity estimates for your specific proposed observations.





Published

 

Latest updates
  •  
    Revised and streamlined information for support of Cycle 1.

  • Updated links, including to the new imaging Roadmap article. Simplified and clarified text.