The Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission (ARCADE 2) measures the absolute temperature of the cosmic microwave background and astrophysical foregrounds at frequencies from 3 to 90 GHz. Differential radiometers compare the sky intensity to a full-aperture blackbody calibrator maintained within a few mK of the sky temperature. Careful control of the instrumental signature establishes the zero level of the sky maps to an accuracy of several mK (see Table 3 of Fixsen et al. 2011).
The delivered files contain sky maps from the 2006 flight of the ARCADE 2 instrument. Each FITS file 'arc2_fffff_v19.fits' consists of a sky map in Galactic coordinates with units K thermodynamic temperature. The string "fffff" denotes thecenter frequency in MHz, so for example file arc2_9720_v19.fits contains the sky map from the 9720 MHz channel. There are two channels at 29500 MHz with different beam widths. File arc2_29500s_v19.fits has a 4 deg FWHM beam width while file arc2_29500_v19.fits has the same 11.6 deg beam width as all of the other maps.
Each file contains a map in a binary FITS extension; this extension contains two fields: