Atacama Cosmology Telescope (ACT)
These files contain the Atacama Cosmology Telescope (ACT) temperature maps of the southern and equatorial fields, observed during the 2008-2010 seasons, in the 148 GHz and 217 GHz bands, and produced for the ACT data release in February 2014.
These maps are stored in the primary image arrays of FITS files. The units of the maps are uK-CMB, expressing deviations from the average measured intensity as equivalent fluctuations in the CMB in microkelvins.
The maps were computed by solving the maximum likelihood problem (inverse-noise-weighted average) for approximately 1012 calibrated data samples in the time domain.
The map-making process can be summarized as follows: The median level of each detector was removed together with a single array-wide slope across the 15-minute file; a pre-calculated data selection, calibration and pointing solution were applied (67% of the total raw data were left after data selection); 7 pre-computed dark modes were de-projected from each detector time stream; and the expected signal from the bright point sources using the ACT beam were also subtracted from them. Then the maps were solved for by minimizing chi-square over a noise model, which included correlated modes, cut data, with detector noises described by bins in the frequency domain. For maps with "src_free" in the title the flux from point sources has been removed, while maps with "summed" in the title have had the point source flux re-added to the maps. The resulting maps are expected to be unbiased at the scales of interest, and have shown to be consistent with WMAP at multipoles l > 300.
The 4way maps are used for the power spectrum analysis, where the data have been split into 4 subsets by TOD to enable cross correlation. The 1way maps are made from the entire subset together.