ABOUT LAMBDA

Atacama Cosmology Telescope (ACT)

Product Name
CMB Temperature Maps 2008 Data
Mission
ACT

Description

These files contain the Atacama Cosmology Telescope (ACT) temperature maps of the southern stripe field, observed during the 2008 season, in the 148 GHz band, and produced for the first ACT data release in March 2012. The maps cover an area of approximately 780 square degrees and combines 848 hours of observations with an average of 611 bolometer detectors. They have an angular resolution of 1.37 arcminutes and a noise level that ranges between 25 and 50 uK-arcmin.

The maps are stripe like, elongated in R.A. (21h27m to 7h52m) and thin in declination (-57.15 degrees to -48.1 degrees). They are provided in a cylindrical equal-area projection with a standard latitude of -53.5 degrees and 0.25 square arcminute pixels, containing 18787 by 1177 pixels. 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. Finally, for maps not marked "ptsrc removed" the flux from point sources previously removed was 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.

This release is composed of 10 maps plus auxiliary material as described:

    - One full map produced with all the data available.
    - One map produced with all the data available but without the sources re-added, as described above.
    - Four maps produced with a quarter of the data each and with the sources re-added (full).
    - Four maps produced with a quarter of the data each (independent maps), without the sources re-added.
    - The hit-count maps computed for each map pixel are stored and provided as auxiliary FITS files also available on LAMBDA.

A complete description of the observations, data processing, calibration, instrument response, and mapmaking process for this data release is in Dunner et al. 2012, arXiv:e-print.

Back to Product Page

A service of the HEASARC and of the Astrophysics Science Division at NASA/GSFC
Goddard Space Flight Center, National Aeronautics and Space Administration
HEASARC Director: Dr. Alan P. Smale
LAMBDA Director: Dr. Eric R. Switzer
NASA Official: Dr. Eric R. Switzer
Web Curator: Mr. Michael R. Greason