MIRI Bright Source Limits

Bright source limits of JWST's Mid-Infrared Instrument (MIRI) are derived from in-flight measurements.

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The performance of MIRI has been measured directly at both the component and system level using the fully assembled MIRI flight model in a flight-like radiative environment with a well characterized radiometric source (Glasse et al. 2015).  Results of these JWST throughput measurements have been integrated into a sensitivity model, which includes the following components: (1) background, (2) photon conversion efficiency (PCD), (3) encircled energy, and (4) detector performance  (Pontoppidan 2016).

The values in the tables and plot below were obtained from ETC 4.0.


All modes

Figure 1. MIRI bright source limits for point sources (for Ngroups = 5)

MIRI bright source limits for point sources for all modes based on ETC 4.0. The plotted values represent the flux densities at which the signal will reach 70% of full well in Ngroups of 5. All calculations assume FULL frame, except the LRS slitless mode, which exclusively operated in the SLITLESSPRISM subarray. Spectroscopic values are calculated per spectral pixel.

Imager

Table 1.MIRI imager bright source limits (for Ngroups = 5)

FilterFull Frame (mJy)SUB64 subarray (mJy)
F560W3.95128.85
F770W3.22105.65
F1000W5.83192.11
F1130W22.32731.18
F1280W11.07366.78
F1500W12.33415.84
F1800W21.74753.07
F2100W25.44974.83
F2550W57.632686.02


Table 2.MIRI imager subarray bright source limits (for Ngroups = 5)

SubarrayBrightness limit
in F560W (mJy)		Brightness limit
in F2550W (mJy)

FULL

3.9557.63

BRIGHTSKY

12.67241.21

SUB256

36.61745.05

SUB128

92.131913.37

SUB64

128.852686.02


References

Glasse, A., et al. 2015, PASP, 127, 686
The Mid-Infrared Instrument for the James Webb Space Telescope, IX: Predicted Sensitivity


Pontoppidan, K. 2016, Proc of SPIE, 9910, 16
Pandeia: a multi-mission exposure time calculator for JWST and WFIRST 


Notable updates
  •  
    Tables and plot updated for Cycle 4 based on ETC 4.0

  •  
    Updated for Cycle 3 based on in-flight measurements and ETC 3.0

  •  
    Updated plots and values for ETC v1.5.1
Originally published