The Photoconductor Array Camera and Spectrometer (PACS) is a
photometer and medium resolution spectrometer that is being
developed and built by a consortium led by Albrecht Poglitsch
of the Max Planck Institute for Extraterrestrial Physics, Garching,
Germany. NASA is not one of the contributors to this instrument.
It has two bolometer arrays for imaging photometry, and two
stressed/unstressed germanium galium bolometer arrays for imaging
PACS observes wavelengths from 60 to 210 microns, a range in
which the spectral energy distributions from forming planetary systems,
stars, and galaxies reach their maximum. This range is optimal for
studying young, distant, dusty, star-forming galaxies, since their
line and continuum emissions are red-shifted into the middle of PACS'
In photometry mode, PACS simultaneously images its 130-210 micron
band with a choice of either the 60-90 or 90-130 micron band.
PACS performs deep broadband surveys to measure the redshifted
radiation from interstellar dust, and the emission from nonthermal
sources in forming galaxies and quasars. It has investigated nearby
AGNs and interacting galaxies.
PACS' grating spectrometer observes the range from 55-210 microns.
PACS employs a reflection grating, in which numerous grooves at regular
intervals on a reflective surface diffract light like a prism.
The spectrometer measures the redshift of intermediate to very distant
objects through bright ionic fine structure lines, performs detailed
spectroscopy of AGNs to determine what produces their copious amounts of
energy (thought to be starbursts or black hole accretion), and observes
atomic and molecular transitions in very distant objects to study star
formation and heavy element production in the early Universe.
PACS combines the photometric sensitivity needed to survey over a large
dynamic range with the spectroscopic sensitivity and resolution needed to
identify and characterize the discovered objects, and to interpret the
mechanisms that drive star and galaxy formation and the high-energy phenomena
that occur in active galaxies and outflows from young stellar objects.
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