What is PACS?

 

PACS is an imaging photometer and integral field line spectrometer for wavelengths up to ~210 µm. It has recently been redesigned to employ in total four detector arrays, two bolometer arrays for photometry, and two Ge:Ga detector arrays for spectroscopy.

PACS has three photometric bands with R~2. The short wavelength `blue' array covers the 60-90 and 90-130 µm bands, while the `red' array covers the 130-210 µm band. In photometric mode one of the `blue' bands and the `red' band are observed simultaneously. The bolometer arrays fully sample a field of view of 1.75x3.5 arcmin, and provide a point source detection limit of ~3 mJy (5 sigma, 1 hour). An internal He3 sorption cooler will provide the 300 mK environment needed by the bolometers.

For spectroscopy PACS covers 57-210 µm in three contiguous bands, providing a velocity resolution in the range 150-200 km/s and an instantaneous coverage of ~1500 km/s. The two Ge:Ga arrays are appropriately stressed and operated at slightly different temperatures - cooled by being `strapped' to the liquid helium - in order to optimise sensitivity for their respective wavelength coverage. The point source detection limit is ~3x10^-18 W/m^2.