NIRSpec IFU Wavelength Ranges and Gaps
There is a physical gap between the JWST NIRSpec detectors. This affects the IFU observations at high resolutions. The wavelengths that fall in the detector gap are not recoverable.
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JWST's NIRSpec supports integral field spectroscopy with an integral field unit (IFU). Light from the source of interest passes through a small (3" × 3") aperture in the MSA mounting frame and travels through the IFU image slicing mirror optics. Figure 1 shows the location of the IFU aperture on the MSA mounting frame between MSA quadrants 3 and 4. The light then is reflected by mirrors to form an image of the source on the image slicer, which consists of 30 stacked mirror surfaces. Figure 2 shows the layout of the slices, numbered from 0 to 29, within the IFU aperture in the plane of the detector. Figure 1 additionally shows the layout of the slices as positioned on the detector, also numbered 0 to 29.
There is a physical gap between the detectors that can be seen in Figure 1 which depicts the detector array boundaries in white. This gap affects NIRSpec high-resolution IFU observations, resulting in a gap in the wavelength coverage. Unlike other NIRSpec observing modes, wavelength losses due to the gap cannot be fully recovered by dithering within the IFU aperture. The IFU observing mode article provides the approximate spectral wavelengths lost in the detector gap, but the precise values differ for the individual IFU data slices. This article provides additional information on the exact wavelengths lost in the detector wavelength gap per IFU slice for high-resolution IFU observations.
Short wavelength cutoffs
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The range of nominal wavelengths for the G140H/F070LP configuration is shown. Slit #29 (top) and slit #0 (bottom) show the extrema of these differences. In the worst case, wavelengths below 0.96 μm are cut off (slice #0, bottom). At the top (slice #29) wavelengths below 0.92 μm are cut off. Spectra of the fixed slits appear in the middle of the figure. The detector cutoffs are less severe for spectra of the fixed slits over the same wavelength range, as seen in the figure.
Wavelength gaps
The presence of a physical gap between detectors affects high-resolution IFU observations because the spectra are long enough to span both NIRSpec detectors. Figure 4 presents an example using disperser G140H and filter F100LP. The limits of the detectors are shown with thick white lines. For clarity, the spectra from the 30 IFU slices are shown in the region around the detector gaps. Note that the wavelength range that falls within the detector gap is different for each slice.
Top: The complete range of nominal wavelengths for the G140H/F100LP configuration is shown. Spectra of the fixed slits also appear in the middle of the figure.
Bottom: A clipped portion of the nominal wavelength range near the gap is shown to more clearly show that the missing wavelengths differ for each slice, and to better differentiate the cutoff values using the color key. Slit #29 (top) and slit #0 (bottom) show the extrema of these differences. Spectra of the fixed slits over the same clipped wavelength range are shown, but in this case, the wavelengths land on the NRS2 detector and are recorded. Only a portion of the range from slit S200A2 falls off the right edge of NRS2.
SLIT_ID | G140H_MIN | G140H_MAX | G235H_MIN | G235H_MAX | G395H_MIN | G395H_MAX |
---|---|---|---|---|---|---|
0 | 1.44898 | 1.48580 | 2.42973 | 2.49153 | 4.09936 | 4.20323 |
1 | 1.44803 | 1.48484 | 2.42814 | 2.48993 | 4.09667 | 4.20053 |
2 | 1.44707 | 1.48388 | 2.42652 | 2.48831 | 4.09395 | 4.19779 |
3 | 1.44610 | 1.48290 | 2.42489 | 2.48668 | 4.09119 | 4.19503 |
4 | 1.44512 | 1.48192 | 2.42325 | 2.48503 | 4.08842 | 4.19226 |
5 | 1.44415 | 1.48095 | 2.42163 | 2.48340 | 4.08569 | 4.18951 |
6 | 1.44314 | 1.47994 | 2.41994 | 2.48170 | 4.08283 | 4.18663 |
7 | 1.44215 | 1.47894 | 2.41827 | 2.48003 | 4.08001 | 4.18381 |
8 | 1.44114 | 1.47793 | 2.41658 | 2.47833 | 4.07716 | 4.18094 |
9 | 1.44011 | 1.47689 | 2.41485 | 2.47659 | 4.07423 | 4.17801 |
10 | 1.43908 | 1.47585 | 2.41312 | 2.47486 | 4.07131 | 4.17507 |
11 | 1.43803 | 1.47480 | 2.41136 | 2.47309 | 4.06835 | 4.17210 |
12 | 1.43698 | 1.47375 | 2.40960 | 2.47132 | 4.06537 | 4.16911 |
13 | 1.43589 | 1.47265 | 2.40777 | 2.46949 | 4.06228 | 4.16601 |
14 | 1.43480 | 1.47156 | 2.40595 | 2.46766 | 4.05921 | 4.16292 |
15 | 1.42518 | 1.46189 | 2.38981 | 2.45144 | 4.03196 | 4.13555 |
16 | 1.42402 | 1.46073 | 2.38787 | 2.44949 | 4.02868 | 4.13225 |
17 | 1.42286 | 1.45956 | 2.38592 | 2.44753 | 4.02539 | 4.12894 |
18 | 1.42167 | 1.45837 | 2.38393 | 2.44553 | 4.02203 | 4.12557 |
19 | 1.42047 | 1.45716 | 2.38190 | 2.44350 | 4.01862 | 4.12213 |
20 | 1.41925 | 1.45593 | 2.37987 | 2.44145 | 4.01517 | 4.11867 |
21 | 1.41804 | 1.45471 | 2.37783 | 2.43941 | 4.01174 | 4.11522 |
22 | 1.41681 | 1.45348 | 2.37577 | 2.43734 | 4.00827 | 4.11173 |
23 | 1.41553 | 1.45219 | 2.37362 | 2.43517 | 4.00463 | 4.10807 |
24 | 1.41428 | 1.45094 | 2.37154 | 2.43307 | 4.00111 | 4.10453 |
25 | 1.41302 | 1.44967 | 2.36942 | 2.43094 | 3.99753 | 4.10094 |
26 | 1.41174 | 1.44839 | 2.36728 | 2.42879 | 3.99392 | 4.09730 |
27 | 1.41045 | 1.44708 | 2.36510 | 2.42660 | 3.99025 | 4.09361 |
28 | 1.40914 | 1.44577 | 2.36291 | 2.42440 | 3.98655 | 4.08989 |
29 | 1.40780 | 1.44442 | 2.36067 | 2.42214 | 3.98276 | 4.08608 |
Table note: Values are in microns.