The JWST NIRISS enables imaging in 12 filters (seven wide-band and five medium-band). Estimated sensitivities for point sources are presented in this article.
NIRISS imaging is not available as a primary observing mode but is offered as a coordinated parallel mode when another JWST instrument is the primary science instrument. Currently, NIRISS imaging in parallel is only offered when NIRCam imaging is the primary science mode. Other prime+parallel combinations involving NIRISS imaging in parallel will be considered for implementation in Cycle 2. Images are obtained through filters in the pupil wheel, spanning wavelengths 0.8 μm–2.2 μm, and in the filter wheel, covering wavelengths 2.5 μm–5.0 μm. Five medium-band filters (F140M, F158M, F380M, F430M, F480M) and 7 wide-band filters (F090W, F115W, F150W, F200W, F277W, F356W, F444W) are available.
NIRISS imaging is also used to take direct images before and after grism exposures in wide field slitless spectroscopy mode. Direct images allow identification of objects in the grism exposures and absolute wavelength calibration. Direct images are only available through the short wavelength filters in the Pupil Wheel: F090W, F115W, F140M, F150W, F158M, F200W.
Table 1 lists the broad-band filter sensitivities corresponding to a S/N=10 for a 10 ks observation of a point source. The sensitivities in the F140M and F158M filters are expected to be about a factor of 1.4 higher than the sensitivity for the F150W filter. The long wavelength medium-band filters are expected to have sensitivities that are a factor of about 3 higher than the F356W filter (for F380M) or the F444W filter (for F430M and F480M). Vega magnitudes (i.e. for which the colors of an average A0V star are 0.0) are also given in Table 1.
Table 1: Wide-Band Filter Point-Source Imaging Sensitivity for S/N=10 in 10ks