JWST Imaging Roadmap

A roadmap to guide users, step-by-step, through the process of designing a JWST imaging observing program using NIRCamNIRISS or MIRI, is provided in this article.

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Each step listed below is followed by a list of articles with additional details. 

Preliminary considerations

  1. Choose the instrument(s) suitable for your science based on needed wavelength coverage and science goals. 

    NIRCam is the primary near-infrared imager for JWST. However, there are science cases in which a user may prefer to use NIRISS imaging:

    1. NIRISS is more sensitive to low surface brightness features between 0.8–2.5 μm than NIRCam, which is applicable to science goals like studying galactic tidal tails at "cosmic noon" (~ 2), due to the larger pixel scale of 0.066"/pixel compared with the pixel scale of NIRCam short wavelength channel (0.031"/pixel).

    2. NIRISS offers a "simple" field of view of 2.2' × 2.2' while NIRCam offers 2 modules each covering 2.2' × 2.2' with a 44" gap between modules, and 4"–5" gaps between detectors within each module in the short-wavelength channel. For cases where the position of a target is not known to great accuracy (e.g., tens of arc seconds), such as target of opportunity requests to identify electromagnetic counterparts to gravitational wave sources, NIRISS may be preferable to optimize observation planning. Without precise astrometry, observations with NIRCam run the risk of the target of interest falling in a detector or module gap.

    3. For science programs using the NIRISS WFSS mode, a direct image is taken before and after each set of grism exposures in a filter. Some observers may choose to take additional imaging exposures in filters in which they do not take grism exposures. NIRISS imaging in this case would optimize both the science return, by using the same instrument set-up as the WFSS observations, and observing efficiency, by saving on observatory overheads associated with switching to another instrument.

    NIRCam Imaging (0.6–5.0 μm), NIRCam Imaging Recommended Strategies
    NIRISS Imaging (0.8–5.0 μm), NIRISS Imaging Recommended Strategies
    MIRI Imaging (5.6–25.5 μm), MIRI Imaging Recommended Strategies

  2. Decide on whether you will observe with multiple instruments simultaneously.
    Coordinated Parallel Observations

  3. Consider using the quick-look JWST Interactive Sensitivity Tool (JIST) to obtain a sense of the signal-to-noise and exposure time parameter space you may require for your target(s).

Work through the steps below for the primary imaging instrument before adding the coordinated parallel observations, which may be imaging or some other allowed mode.

For each instrument you will use for standard imaging, proceed through the steps below.

Standard imaging

  1. Check the feasibility of your observations to achieve your science goals.
    NIRCam Imaging Sensitivity
    NIRISS Imaging Sensitivity
    MIRI Sensitivity

  2. Select your wavelength coverage and filters.
    NIRCam Filters
    NIRISS Filters
    MIRI Filters and Dispersers

  3. Consider the areal coverage needed and whether mosaicking of the instrument field of view will be needed.
    NIRCam Mosaics
    NIRISS Mosaics

    MIRI Imaging Mosaics
    APT Simple Mosaic Example
    Use the Aladin viewer in APT to view instrument fields of view on sky images.

  4. Based on the brightness of your target, determine whether a subarray is needed to avoid saturation. (Subarrays are not offered for the NIRISS imaging mode.)
    NIRCam Bright Source LimitsNIRCam Detector Subarrays
    MIRI Bright Source LimitsMIRI Detector Subarrays

  5. Select a dithering strategy.

    NIRCam Dithers and Mosaics
    NIRISS Imaging Dithers
    MIRI Dithering
    If proposing coordinated parallel observations, consider: 
    JWST Coordinated Parallels Custom Dithers

  6. For selected instrument(s), calculate the required exposure times using the JWST Exposure Time Calculator (ETC).

    JWST ETC Imaging Aperture Photometry Strategy

  7. Fill out the Astronomers Proposal Tool (APT) for your observations.
    NIRCam Imaging APT Template
    NIRISS Imaging APT Template
    MIRI Imaging APT Template

  8. If adding coordinated parallel observations, now is the time to do that.  See the separate Roadmap for coordinated parallels

Go to the Getting Started with JWST Proposing to complete the steps for proposal submission.

Notable updates

    Updated to support NIRISS imaging as a prime observing mode starting in Cycle 2

    Reviewed and updated for Cycle 1 release.

Originally published