MOS Data and Example JWST Science Use Cases

JWST multi-object spectroscopy (MOS) is used for simultaneous spectroscopy of multiple sources in a single exposure. It is offered using the NIRSpec micro-shutter assembly (MSA), and the WFSS modes in NIRCam and NIRISS using the Grisms. Science cases introduced below present some concrete examples that may help to understand the rationale behind observational strategies and observing parameter choices.

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Working with MOS data

Main article: NIRSpec Multi-Object Spectroscopy

Tools are available on the public github repository to help with the inspection and analysis of post-pipeline MOS data. Most are written in Python and require the installation of Astroconda. More information can be found in the JWST Analysis Tools article. Primarily intended for NIRSpec MOS data analysis are SpecViz and MOSViz. SpecViz is a tool for visualization and quick-look analysis of 1D astronomical spectra. MOSViz is a quick-look analysis and visualization tool for multi-object spectroscopy (MOS). It is designed to work with pipeline output: spectra and associated images, or just with spectra. MOSViz is created to work with data from any telescope/instrument, but is built with the Micro-Shutter Assembly (MSA) on the JWST/NIRSpec spectrograph in mind. As such, MOSViz has some features specific to NIRSpec data. User training workshops are offered periodically to help users become more expert at the use of the tools. See NIRSpec Training Webinars and Webcasts.

Example JWST science cases

 Multi-object spectroscopy is particularly well suited to a number of different science goals in the NIR. Some science use case examples include:

  • measuring redshifts of distant galaxies for wide-area cosmological surveys
  • measuring emission lines from galaxies, to obtain constraints on their physical conditions
  • deep continuum spectroscopy of distant galaxies, covering feedback-sensitive outflow diagnostics in the rest-frame UV.
  • Galactic star formation chemical abundances and stellar radial velocities

The science cases referenced below present some concrete examples that may help to understand the rationale behind observing strategies with the NIRSpec MSA. They include a rationale for different parameter choices in the MSA Planning Tool (MPT) in APT for the particular observing strategies used and other important observing considerations.

NIRSpec MOS Observations of NGC 346

NIRSpec MOS Deep Extragalactic Survey

NIRISS WFSS with NIRCam Parallel Imaging of Galaxies in Lensing Clusters

NIRCam WFSS Deep Galaxy Observations


Wikipedia article on near-infrared spectroscopy



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