The Atacama Cosmology Telescope: Data Characterization and Mapmaking
Abstract
We present a description of the data reduction and mapmaking pipeline used for the 2008 observing season of the Atacama Cosmology Telescope (ACT). The data presented here at 148 GHz represent 12% of the 90 TB collected by ACT from 2007 to 2010. In 2008 we observed for 136 days, producing a total of 1423 hr of data (11 TB for the 148 GHz band only), with a daily average of 10.5 hr of observation. From these, 1085 hr were devoted to an 850 deg^{2} stripe (11.2 hr by 9.°1) centered on a declination of 52.°7, while 175 hr were devoted to a 280 deg^{2} stripe (4.5 hr by 4.°8) centered at the celestial equator. The remaining 163 hr correspond to calibration runs. We discuss sources of statistical and systematic noise, calibration, telescope pointing, and data selection. For the 148 GHz band, out of 1260 survey hours and 1024 detectors in the array, 816 hr and 593 effective detectors remain after data selection, yielding a 38% survey efficiency. The total sensitivity in 2008, determined from the noise level between 5 Hz and 20 Hz in the timeordered data stream (TOD), is 32 μ {K}√{{s}} in cosmic microwave background units. Atmospheric brightness fluctuations constitute the main contaminant in the data and dominate the detector noise covariance at low frequencies in the TOD. The maps were made by solving the leastsquares problem using the Preconditioned Conjugate Gradient method, incorporating the details of the detector and noise correlations. Simulations, as well as crosscorrelations with Wilkinson Microwave Anisotropy Probe sky maps on large angular scales, reveal that our maps are unbiased at multipoles l > 300. This paper accompanies the public release of the 148 GHz southern stripe maps from 2008. The techniques described here will be applied to future maps and data releases.
 Publication:

The Astrophysical Journal
 Pub Date:
 January 2013
 DOI:
 10.1088/0004637X/762/1/10
 arXiv:
 arXiv:1208.0050
 Bibcode:
 2013ApJ...762...10D
 Keywords:

 cosmic background radiation;
 cosmology: observations;
 instrumentation: miscellaneous;
 Astrophysics  Instrumentation and Methods for Astrophysics;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 20 pages, 18 figures, 6 tables, an ACT Collaboration paper