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 for
the JWST’s Near Infrared Spectrograph (NIRSpec) in all its modes: fixed slit
(FS), integral field spectroscopy (IFS), and multi-object spectroscopy (MOS).
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 5-45% across all the configurations
and 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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