The NIRSpec instrument is the workhorse near-infrared spectrograph on board the James Webb Space Telescope and is provided by ESA.

NIRSpec can make spectroscopic observations of complex targets in space, such as galaxies, nebulae, or crowded fields of stars or galaxies, in one single shot.

One technology it uses is that of the ‘integral field unit’ (IFU). Here, an optical image-slicing technique is used to reorganise the signal from a two-dimensional image of the sky into a set of slices.

These slices are fed to a spectrograph that generates a spectrum for each pixel, where the light is split into its different wavelengths. The slices are then arranged into a data cube. This cube is a stack of many images of the same target object in space, each at a different wavelength, and provides a comprehensive overview of the whole object under study.

Spaxel: Spatial Element (as opposed to a pixel which is a picture element). Is one 3D element of the IFU cube (x, y, wavelength). It is a spectrum at a certain point of the IFU image.

Counts: The count of photons that were received by the detector for this specific wavelength.

NIRSpec will allow scientists to study objects embedded in shrouds of gas and dust, to find out more about how galaxies formed and evolved, and to characterise the atmospheres of extrasolar planets to determine if water is present.

NIRSpec is built by European industry to ESA’s specifications and managed by the ESA Webb Project at ESTEC, the Netherlands. The prime contractor is Airbus Defence and Space in Ottobrunn, Germany. The NIRSpec detector and Micro-Shutter Array subsystems are provided by NASA’s Goddard Space Flight Center (GSFC).

Learn more about spectroscopy with the Webb telescope here.