Kavli Affiliate: Joshua A. Frieman
| First 5 Authors: Anowar J. Shajib, Anowar J. Shajib, , ,
| Summary:
The spectral resolution ($R equiv lambda / Delta lambda$) of
spectroscopic data is crucial information for accurate kinematic measurements.
In this letter, we present a robust measurement of the spectral resolution of
the JWST’s Near Infrared Spectrograph (NIRSpec) in fixed slit (FS) and integral
field spectroscopy (IFS) modes. Due to the similarity of the utilized slit
dimension if the FS mode to that of the shutters in the multi-object
spectroscopy (MOS) mode, our resolution measurements in the FS mode can also be
used for the MOS mode in principle. We modeled H and He lines of the planetary
nebula SMP LMC 58 using a Gaussian line spread function (LSF) to estimate the
wavelength-dependent resolution for multiple disperser and filter combinations.
We corrected for the intrinsic width of the planetary nebula’s H and He lines
due to its expansion velocity by measuring it from a higher-resolution
X-shooter spectrum. We find that NIRSpec’s in-flight spectral resolutions
exceed the pre-launch estimates provided in the JWST User Documentation by
11-53% in the FS mode and by 1-24% in the IFS mode across the covered
wavelengths. We recover the expected trend that the resolution increases with
the wavelength within a configuration. The robust and accurate LSFs presented
in this letter will enable high-accuracy kinematic measurements using NIRSpec
for applications in cosmology and galaxy evolution.
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