NIRCam will provide imaging in the wavelength range 0.6 ^m to 5 ^m and addresses the core astronomical science goals of JWST including: (1) detection of the early phases of star and galaxy formation; (2) morphology and color of galaxies at very high redshift; (3) detection and study of distant supernovae; (4) mapping dark matter via gravitational lensing; and (5) the study of stellar populations in nearby galaxies.
The current design of NIRCam consists of four modules: two broadband and intermediate-band imaging modules and two tunable filter-imaging modules, each with a FOV of 140 x 140". The imaging modules will have a short wavelength and a long wavelength channel, taking images simultaneously with light split by a dichroic at about 2.35 ^m. The short wavelength channels will be sampled by a 4,096 x 4,096 detecting array (giving a pixel size of 0.03"), and the long wavelength channels by a 2,048 x 2,048 detector array (giving a pixel size of 0.06"). The tunable filter-imaging modules will have a resolving power of about 100 with one filter module optimized for wavelengths from about 1.2 ^m to 2.5 ^m, and the other from 2.5 ^m to 4.5 ^m. It is planned to incorporate coronagraphs into all modules, which allow for the observation of faint targets lying very close to bright targets by blocking the light from the central object (see Section 8.7.3). The detectors will most likely be either InSb or HgCdTe.
The position of the segmented optical elements of JWST must be measured and re-aligned on a regular basis to reach the required optical performance, and NIRCam will provide this wavefront-sensing function. To maintain the optimum configuration will probably require dedicated observations of bright stars by NIRCam on a weekly or perhaps more frequent basis.
Near Infrared Spectrograph (NIRSpec)
NIRSpec, to be provided by ESA, will provide spectroscopy in the wavelength range 0.6 ^m to 5 ^m with a spectral resolving power of between ~100 and 1,000. NIRSpec is planned to be able to obtain simultaneous spectra of more than 100 objects in a 9 arcmin2 FOV. To improve sensitivity, the pixel size will be larger than for NIRCam and the detectors will again be either InSb or HgCdTe, although the design is yet to be finalized.
While NIRSpec will again be designed to primarily address astronomical studies such as galaxy formation, clustering, chemical abundances, star formation, etc., its great sensitivity and wavelength range would make it a useful tool for studies of the giant planets, particularly Uranus and Neptune, whose near-IR reflection spectra are not well-known and whose 5 ^m spectra may provide clues to these planets' deep composition.
Was this article helpful?