# NIRCam Point Spread Functions

Simulated JWST NIRCam point spread functions (PSFs) in each filter have predicted FWHM between 0.03" and 0.16" assuming nominal mirror wavefront errors.

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.

# Simulated NIRCam PSFs

Expected 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 between a "predicted" optical path difference (OPD) map and a "requirements" OPD map. The figures below show one realization for NIRCam imaging in each filter assuming the (slightly more conservative) "requirements" OPD map. 

FITS images of simulated PSFs in each filter for LW and SW channels may be downloaded: PSFs_SW_filters and PSFs_LW_filters

These are a single realization of NIRCam PSF FITS images for all filters simulated by WebbPSF using the "requirements" OPD map. SW (LW) PSFs are centered in the A1 (A5) detector. Each PSF is assumed to be centered within a pixel. 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). Source spectrum is a G5V star spectrum from the PHOENIX model library.

NOTE: Diffraction spikes are oriented relative to the telescope (V3 Position Angle), not 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.

**Figure 1. One realization of simulated NIRCam PSFs predicted in the SW channel (0.6–2.3 µm)**

NIRCam PSFs in each SW channel filter were simulated by WebbPSF. Each PSF image is 299 × 299 detector pixels (9.27" on a side). All are displayed with the same log scale. PSFs are shown in the detector pixel scale (0.031").

**Figure 2. One realization of simulated NIRCam PSFs predicted in the LW channel (2.4–5.0 µm)**

NIRCam PSF in each LW channel filter were simulated by WebbPSF. Each PSF image is 299 × 299 detector pixels (18.84" on a side), displayed with the same log scaling as Figure 1. PSFs are shown in the detector pixel scale (0.063").

**Figure 3. One realization of simulated NIRCam PSF cores predicted in the SW channel (0.6–2.3 µm)**

These are zooms into the central 32 × 32 pixels (~1" on a side) of each simulated PSF shown in Figure 1. Each PSF is centered within a pixel, displayed with the same log scaling as Figure 1.

**Figure 4. One realization of simulated NIRCam PSF cores predicted in the LW channel (2.4–5.0 µm)**

These are zooms into the central 32 × 32 pixels (~2" on a side) of each simulated PSF shown in Figure 2. Each PSF is centered within a pixel. Displayed with the same log scaling as Figure 1.

# PSF FWHM

Figure 5 shows the FWHM as a function of the filter pivot wavelength for each simulated PSF. Numerical values for each FWHM, in units of arcsec and pixel, are reported in Table 1. Note: due to severe undersampling below 2 µm (4 µm) in the SW (LW) channel, the oversampled PSFs were used to calculate the FWHM.

**Figure 5. PSF FWHM in each filter, as measured in one realization of simulated PSFs**

This figure shows the FWHM measured for each of the PSF simulated by WebbPSF, shown in Figures 1–4. Each point, color-coded by wavelength, corresponds to one of the 29 filters in Table 1. 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. FWHM values for each PSF, from Figure 5**

Filter| Wavelength  
(µm)| PSF FWHM   
(arcsec) | **PSF FWHM (pixel)**  
---|---|---|---  
F070W| 0.704| 0.030| 0.987  
F090W| 0.902| 0.034| 1.103  
F115W| 1.154| 0.040| 1.298  
F140M| 1.405| 0.048| 1.553  
F150W| 1.501| 0.050| 1.628  
F162M| 1.627| 0.055| 1.770  
F164N| 1.645| 0.056| 1.801  
F150W2| 1.659| 0.046| 1.494  
F182M| 1.845| 0.062| 1.990  
F187N| 1.874| 0.064| 2.060  
F200W| 1.989| 0.066| 2.141  
F210M| 2.095| 0.071| 2.304  
F212N| 2.121| 0.072| 2.341  
F250M| 2.503| 0.084| 1.340  
F277W| 2.762| 0.091| 1.444  
F300M| 2.989| 0.100| 1.585  
F322W2| 3.232| 0.097| 1.547  
F323N| 3.237| 0.108| 1.711  
F335M| 3.362| 0.111| 1.760  
F356W| 3.568| 0.115| 1.830  
F360M| 3.624| 0.120| 1.901  
F405N| 4.052| 0.136| 2.165  
F410M| 4.082| 0.137| 2.179  
F430M| 4.281| 0.145| 2.300  
F444W| 4.408| 0.145| 2.302  
F460M| 4.630| 0.155| 2.459  
F466N| 4.654| 0.158| 2.507  
F470N| 4.708| 0.160| 2.535  
F480M| 4.874| 0.162| 2.574  
  
# Radial profiles

Figures 6 and 7 show the radial profiles for each simulated PSF. The radial profiles have been normalized to the value of the peak pixels. 

**Figure 6. SW PSF radial profiles**

In these plots of the radial profiles for each SW simulated PSF, the pixel size (0.031") is reported in each panel as a dotted line.

**Figure 7. LW PSF radial profiles**

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 and ensquared energy

Figures 8 and 9 show the encircled energy curves for each simulated PSF. Numerical values for the encircled energy (the fraction of light contained in a circular aperture) and ensquared energy (the fraction of energy falling within a certain number of pixels) for each simulated PSF are provided inn these ACII tables:

Encircled_Energy_SW.txt

Encircled_Energy_LW.txt

Ensquared_Energy_SW.txt

Ensquared_Energy_LW.txt

**FIgure 8. SW PSF encircled energy curves**

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 the figure and in Table 2.

**Figure 9. LW PSF encircled energy curves**

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 the figure and in Table 2.

**Table 2. Radius (in arcsec) at which the encircled energy (EE) is 50% and 80%**

Filter| radius (EE = 50%)(arcsec)| radius (EE = 80%)(arcsec)  
---|---|---  
F070W| 0.068| 0.266  
F090W| 0.060| 0.232  
F115W| 0.055| 0.213  
F140M| 0.043| 0.187  
F150W| 0.043| 0.189  
F162M| 0.044| 0.191  
F164N| 0.044| 0.192  
F150W2| 0.047| 0.197  
F182M| 0.046| 0.178  
F187N| 0.047| 0.175  
F200W| 0.049| 0.176  
F210M| 0.051| 0.177  
F212N| 0.051| 0.177  
F250M| 0.057| 0.181  
F277W| 0.061| 0.195  
F300M| 0.066| 0.205  
F322W2| 0.067| 0.218  
F323N| 0.071| 0.220  
F335M| 0.073| 0.225  
F356W| 0.076| 0.235  
F360M| 0.077| 0.238  
F405N| 0.086| 0.263  
F410M| 0.086| 0.266  
F430M| 0.090| 0.277  
F444W| 0.092| 0.283  
F460M| 0.096| 0.295  
F466N| 0.098| 0.299  
F470N| 0.099| 0.302  
F480M| 0.101| 0.308  
  
# References

WebbPSF

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