SPIRE (Spectral and Photometric Imaging Receiver) is one of three cryogenic focal plane instruments to fly on Herschel. Its main scientific goals are the investigation of the statistics and physics of galaxy and structure formation in the early universe and the study of the earliest stages of star formation, when the protostar is still coupled to the interstellar medium (Figure 5). These studies require the capabilities to carry out large-area (many tens of square degrees), photometric imaging surveys at far-infrared and submillimetre wavelengths, and to follow up these systematic survey observations with spectroscopy of selected sources. SPIRE will exploit the advantages of Herschel: its large-aperture, cold, low-emissivity telescope, the complete lack of atmospheric emission and attenuation giving access to the poorly explored 200 to 700-μm range, and the large amount of high quality observing time. Because of these advantages, SPIRE will have unmatched sensitivity for deep imaging photometry and moderate-resolution spectroscopy.
SPIRE will provide the astronomical community with a powerful tool for many other astrophysical studies: giant planets, comets, the galactic interstellar medium, nearby galaxies, ultraluminous infrared galaxies, and active galactic nuclei. Its capabilities will remain unchallenged by the ground-based and airborne observatories, which are planned to come into operation over the next decade.
The design of the SPIRE instrument has been dictated by two particular scientific programs for which Herschel is particularly well suited:
Galaxies emit a large amount (from 30% to nearly 100%) of their energy in the far infrared due to re-processing of stellar UV radiation by interstellar dust grains. The far infrared peak is shifted into the SPIRE wavelength range for very distant galaxies with redshift, z, greater than ~ 1. The total luminosity of a galaxy cannot be determined without an accurate measurement of its Spectral Energy Distribution (SED). The study of the early stages of galaxy evolution thus requires an instrument that can detect emission from distant galaxies in the submillimetre, enabling their SEDs and luminosities to be derived.
Stars form through the fragmentation and collapse of dense cloud cores in the interstellar medium (ISM), and the very first stages of this process are not well known. A good understanding of this early evolution is crucial, as it governs the origin of the stellar initial mass function (IMF). Sensitive far infrared and submillimetre observations with high spatial resolution are necessary to make complete surveys of protostellar clumps to determine their bolometric luminosities and mass functions. SPIRE will also, for the first time, enable astronomers to observe at high spatial resolution the physical and chemical conditions prevailing in the cold phases of the ISM and to study the behaviour of the interstellar gas and dust before and during star formation. SPIRE's unique, high sensitivity to very cold dust emission also makes it the ideal instrument to study the material that is ejected in copious quantities from evolved stars, enriching the ISM with heavy elements. Large amounts of matter - as yet undetected - are ejected from stars before the white dwarf stage. Theories of stellar evolution, and of the enrichment of galaxies in heavy elements and dust, will be incomplete until these earlier mass loss phases are characterized and understood. Studies of star formation and of the interaction of forming and evolved stars with the ISM are also, of course, intimately related to the investigation of galaxy formation and evolution, which occur through just these processes. These high priority programs for Herschel require sensitive continuum imaging in several bands to carry out surveys, and a low-resolution spectroscopic mode to obtain detailed SEDs of selected objects and measure key spectral lines.
For more information please visit the following sites:
- Technical website on the Canadian contribution to Herschel/SPIRE
- Public Outreach on the Canadian contribution to Herschel/SPIRE
- ESA's Herschel website
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