Simulated JWST NIRCam point spread functions (PSFs) in each filter have predicted FWHM between 0.02" and 0.16" assuming nominal mirror wavefront errors.

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At wavelengths λ > 2 μm, JWST obtains diffraction-limited imaging with a Strehl ratio = 0.8 and point spread function (PSF) FWHM of ~λ/D radians (JWST's D = 6.5 m mirror). The NIRCam detectors achieve Nyquist sampling or better (FWHM > 2 pixels) above 2 µm in the short wavelength (SW) channel (0.6–2.3 µm) and above 4 µm in the long wavelength (LW) channel (2.4–5.0 µm). Below these wavelengths, the PSF is undersampled. PSF sampling may be improved by performing subpixel dithers between exposures.

NIRCam PSFs

JWST PSFs may be simulated with WebbPSF. Given a wavefront error budget for the mirror alignment, WebbPSF can create multiple realizations of the PSF in a given NIRCam filter. Each of these realizations assumes various contributions to the wavefront error from several optical components, which cause the PSF shape and orientation to vary slightly.

WebbPSF allows the user to select an optical path difference (OPD) map, which are measured regularly and made available through WebbPSF. The figures below show one realization for NIRCam imaging in each filter assuming a representative OPD map. This is the same OPD map used for the Cycle 2 ETC. It was found, during commissioning, that this provides a close match to the empirical PSF, with only small differences (Rigby et al. 2022).

FITS images of these simulated PSFs in each filter for LW and SW channels may be downloaded from the JWST PSF simulation library.

These are a single realization of NIRCam PSF FITS images for all filters simulated by WebbPSF using a representative OPD map. OPD maps are available through WebbPSF. SW PSFs are centered in the A1 detector, while LW PSFs are centered in the A5 detector. Each FITS file contains both an oversampled PSF (oversample = 4) and a version rebinned down onto the detector pixel scale (0.031" and 0.063" in the short and long wavelength channels, respectively). The source spectrum is a G0V star spectrum from the Castelli & Kurucz model library.

Note: Diffraction spikes are oriented relative to the telescope (V3 position angle), not to NIRCam (see Figure 2 in the NIRCam Field of View page).

Figures 1 and 2 show the PSF in each filter on a log scale. Figures 3 and 4 zoom in to the PSF cores.

NIRCam PSFs in each SW channel filter were simulated by WebbPSF using a representative OPD map. Each PSF image is 322 × 322 detector pixels (9.98" on a side). All are displayed with the same log scale. PSFs are shown in the detector pixel scale (0.031").

NIRCam PSF in each LW channel filter were simulated by WebbPSF using a representative OPD map. Each PSF image is 159 × 159 detector pixels (10.02" on a side), displayed with the same log scaling as Figure 1. PSFs are shown in the detector pixel scale (0.063").

These are zooms into the central 34 × 34 pixels (~1" on a side) of each simulated PSF shown in Figure 1. Each PSF is displayed with the same log scaling as Figure 1.

These are zooms into the central 35× 35 pixels (~2" on a side) of each simulated PSF shown in Figure 2. Each PSF is displayed with the same log scaling as Figure 1.

PSF FWHM

Figure 5 shows the PSF FWHM as a function of the filter pivot wavelength, for the simulated PSFs shown in Figures 1-4. Numerical values for each FWHM, in units of arcsec and pixel, are reported in Table 1. Table 1 also includes the FWHM of the empirical PSF, measured using observations of the standard star P330E from the Cycle 1 Absolute Flux Calibration program.

This figure shows the FWHM measured for each of the PSFs simulated by WebbPSF, shown in Figures 1–4. Each point, color-coded by wavelength, corresponds to one of the 29 NIRCam filters. The PSF is undersampled below 2 µm in the SW channel and below 4 µm in the LW channel. Note: for the extra-wide W2 filters (F150W2 and F322W2), the FWHM appears to be smaller then expected due to the choice of the star spectrum. Table 1 lists these simulated FWHM values and empirical PSF FWHM values measured from the Cycle 1 Absolute Flux calibration program.

Table 1. FWHM of both the simulated PSFs shown in Figures 1–4 and the empirical FWHM

		Simulated FWHM		Empirical FWHM
Filter	Pivot wavelength (µm)	PSF FWHM (arcsec)	PSF FWHM (pixel)	PSF FWHM (arcsec)	PSF FWHM (pixel)
F070W	0.704	0.023	0.742	0.029	0.935
F090W	0.901	0.030	0.968	0.033	1.065
F115W	1.154	0.037	1.194	0.040	1.290
F140M	1.404	0.046	1.484	0.048	1.548
F150W	1.501	0.049	1.581	0.050	1.613
F162M	1.626	0.053	1.710	0.055	1.774
F164N	1.644	0.054	1.742	0.056	1.806
F150W2	1.671	0.045	1.452
F182M	1.845	0.060	1.935	0.062	2.000
F187N	1.874	0.061	1.968	0.064	2.065
F200W	1.990	0.064	2.065	0.066	2.129
F210M	2.093	0.068	2.194	0.071	2.290
F212N	2.120	0.069	2.226	0.072	2.323
F250M	2.503	0.082	1.302	0.085	1.349
F277W	2.786	0.088	1.397	0.092	1.460
F300M	2.996	0.097	1.540	0.100	1.587
F322W2	3.247	0.096	1.524
F323N	3.237	0.106	1.683	0.108	1.714
F335M	3.365	0.109	1.730	0.111	1.762
F356W	3.563	0.114	1.810	0.116	1.841
F360M	3.621	0.118	1.873	0.120	1.905
F405N	4.055	0.132	2.095	0.136	2.159
F410M	4.092	0.133	2.111	0.137	2.175
F430M	4.280	0.139	2.206	0.144	2.286
F444W	4.421	0.140	2.222	0.145	2.302
F460M	4.624	0.151	2.397	0.157	2.492
F466N	4.654	0.152	2.413	0.158	2.508
F470N	4.707	0.154	2.444	0.160	2.540
F480M	4.834	0.157	2.492	0.164	2.603

Radial profiles

Figures 6 and 7 show the radial profiles for each of the simulated PSFs shown in Figures 1-4. The radial profiles have been normalized to the value of the peak pixels.

In these plots of the radial profiles for each simulated LW PSF, the pixel size (0.063") is reported in each panel as a dotted line.

Encircled energy

Figures 8 and 9 show the encircled energy curves (the fraction of light contained in a circular aperture) for each simulated PSF in red, and the empirical PSF in blue. Table 2 lists the 50% and 80% EE values for both. Numerical values for the encircled energy as a function of radius for each simulated PSF are provided in the ASCII tables below.

Download the encircled energy measured from the simulated PSFs here:
SW Encircled Energy (.txt)
LW Encircled Energy (.txt)

In these encircled energy curves for each SW PSF, the radius (in arcsec) at which the encircled energy is 50% and 80% is reported in Table 2. The blue dots show the empirical encircled energy measured with data from the Cycle 1 Absolute Flux calibration program, and the red line is the simulated PSF shown in Figures 1–4. These plots show an average of the encircled energy for PSFs on detectors A1 and B1. The annotated EE values are measured from the simulated (red) curve.

In these encircled energy curves for each LW PSF, the radius (in arcsec) at which the encircled energy is 50% and 80% is reported in Table 2. The blue dots show the empirical encircled energy measured with data from the Cycle 1 Absolute Flux calibration program, and the red line is the simulated PSF shown in Figures 1–4. These plots show an average of the encircled energy for PSFs on detectors A5 and B5. The annotated EE values are measured from the simulated (red) curve.

Table 2. Radius (in arcsec) at which the encircled energy (EE) is 50% and 80%, measured using the curves in Figures 8 and 9 for both the simulated PSF and the empirical PSF.

	Simulated PSF		Empirical PSF
Filter	radius (EE = 50%) (arcsec)	radius (EE = 80%) (arcsec)	radius (EE = 50%) (arcsec)	radius (EE = 80%) (arcsec)
F070W	0.032	0.165	0.038	0.173
F090W	0.024	0.140	0.034	0.157
F115W	0.025	0.136	0.029	0.148
F140M	0.030	0.123	0.031	0.149
F150W	0.032	0.121
F150W2	0.034	0.135	0.033	0.146
F162M	0.035	0.121	0.033	0.141
F164N	0.035	0.121	0.034	0.140
F182M	0.039	0.129	0.037	0.138
F187N	0.040	0.130	0.038	0.138
F200W	0.042	0.138	0.040	0.144
F210M	0.044	0.143	0.042	0.146
F212N	0.045	0.145	0.043	0.147
F250M	0.049	0.164	0.049	0.176
F277W	0.055	0.179	0.054	0.192
F300M	0.061	0.194	0.059	0.200
F322W2	0.062	0.204
F323N	0.069	0.214	0.064	0.213
F335M	0.070	0.216	0.066	0.221
F356W	0.073	0.228	0.069	0.230
F360M	0.075	0.232	0.071	0.234
F405N	0.084	0.256	0.078	0.253
F410M	0.084	0.258	0.079	0.258
F430M	0.088	0.270	0.083	0.269
F444W	0.090	0.276	0.085	0.276
F460M	0.095	0.291	0.090	0.290
F466N	0.095	0.292	0.090	0.292
F470N	0.097	0.296	0.091	0.294
F480M	0.099	0.303	0.094	0.301

References

WebbPSF

Perrin, M., et al. 2014, Proc SPIE, 9143
Updated point spread function simulations for JWST with WebbPSF

Rigby, J., et al. 2022, arXiv:2207.05632
Characterization of JWST science performance from commissioning

Latest updates	27 Nov 2022 Updated all figures and tables with the simulated PSF used in the Cycle 2 ETC Included FWHM and EE measurements from the Cycle 1 Absolute Flux Calibration Program
Originally published	27 Sep 2017

JWST User Documentation

NIRCam Point Spread Functions

NIRCam PSFs

PSF FWHM

Radial profiles

Encircled energy

References