JWST Sensitivity

During the JWST feasibility studies, we estimated sensitivities for the major instruments using the JWST Mission Simulator (JMS). We currently recommend the use of sensitivity estimates provided by the four instrument teams. In general, these estimates are based upon a 10 sigma detection after a 10,000s exposure. For both spectrographs and cameras, the teams have chosen specific apertures rather than PSF fitting for estimating sensitivities. Hence they are slightly conservative. Otherwise, the estimates are based upon the expected performance (procurement specifications) for the optical components and detectors. Note that these estimated sensitivities are generally better than the requirements for the instruments (~15-20%) in order to provide management margin both in verification testing and as-built performance.

In the NIR, these sensitivities assume a relatively low zodiacal background (~ 20% higher than the lowest possible) and a low scattered light component. The scattered light component is conservatively estimated to be:

lambda(micron)	Scattered Light (MJy/sr)
1.0	0.112
2.0	0.088
3.0	0.070
3.5	0.074
5.0	0.40/0.47 (NIRCam/NIRSpec)

Instruments

Near Infrared Camera (NIRCam)

All NIRCam Sensitivities

All NIRCam filter sensitivities on one plot. Dots are wide filters, squares are medium filters, and triangles are narrow filters. Horizontal lines indicate filter bandpasses when they are larger than the symbols.

The next three plots show wide, medium and narrow filters separately.
Wide NIRCam Filter Sensitivities
Medium NIRCam Filter Sensitivities
Narrow NIRCam Filter Sensitivities

Table of NIRCam Sensitivities

Near Infrared Spectrograph (NIRSpec)

All data refer to unresolved point sources observed with a canonical three shutter long MSA slit. Extended galaxies will experience significantly higher slit-losses with respect to their integrated magnitudes than do point sources, so the point source numbers should be used with caution.

The equivalent NIRSpec IFU and NIRSpec Fixed Slit sensitivities should be comparable.

In the plots, we indicate the two top-level NIRSpec sensitivity requirements:

• R=100 mode shall reach a limiting continuum flux of 132 nJy at 3.0 micron at S/N=10 in t=10.000 s.
  
• R=1000 mode shall reach a limiting line flux of 5.72E-19 erg/s/cm2 at 2.0 micron at S/N=10 in t=100.000 s (note the increased exposure time for all R=1000 sensitivities).
  

The effective aperture size assumes that the signal is summed in the spatial direction along the slit and across 2 pixels in the dispersion direction. Since the resolution changes with wavelength for all modes (and particularly the R = 100 CaF2 prism), we list the 2 pixel spectral resolution for each mode.

R100 Continuum	R100 Line
R1000 Continuum	R1000 Line
R2700 Continuum	R2700 Line

The following text files provide these data in tabular form.

NIRSpec R100 Sensitivities

NIRSpec R1000 Sensitivities

NIRSpec R2700 Sensitivities

Mid Infrared Instrument (MIRI)

Tunable Filter Imager (TFI)

While the TFI wavelength range requirement is 1.6-2.5; 3.2-4.9 um, they provide sensitivity estimates from 1.5-2.6 and 3.1-5.0 (the goal).

These data are also provided in tabular form.

TFI Sensitivity Table