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SPT First Data Release: Maps in Sanson-Flamsteed Projection

 

spt_imap_ra5h30dec-55_2008_150ghz_sfl_dr1.fits
spt_imap_ra5h30dec-55_2008_220ghz_sfl_dr1.fits

These files contain South Pole Telescope (SPT) temperature maps of the approximately 95-square-degree ra5h30dec-55 field observed during the 2008 season in the 150 GHz and 220 GHz bands, produced for the first SPT data release in December 2011. The 150 GHz map combines approximately 621 hours of observations with a median number of 304 individual bolometers contributing data during each observation. The 220 GHz map combines approximately 605 hours of observations with a median number of 166 detectors contributing data.

These maps use the Sanson-Flamsteed projection with 0.25 arcminute map pixels covering a 3120-pixel by 3120-pixel grid. The maps are stored in the primary image arrays of FITS files. The center of the ra5h30dec-55 field is at R.A. 82.70247 degrees and decl. -55.00076 degrees. The center of the coordinate system used for the Sanson-Flamsteed projection (as indicated by the CRVAL1 and CRVAL2 keywords) has a declination of 0 degrees.

The maps were constructed by a simple inverse-noise-weighted averaging of calibrated time-ordered-data from SPT bolometers over many observations of the field. The units of the maps are K-CMB, expressing deviations from the average measured intensity as equivalent fluctuations in the CMB in Kelvins. The combined weights computed for each map pixel are stored in associated FITS files.

Time-domain filtering of the raw data is used to deconvolve the detector time constants, remove noise on scales smaller than the pixel scale of the maps, and remove atmospheric noise. For the maps in the Sanson-Flamsteed projection, bright emissive sources in the field have been masked in the filtering to prevent "ringing." The sources masked in this release are those detected at greater than 5 sigma significance in either frequency band from the analysis presented in Vieira et al. 2010, ApJ, 719, 763. The brightest 9 sources in that list are masked to a radius of 5 arcminutes, and the rest are masked to a radius of 2 arcminutes.

Because of the filtering and mapmaking methods, these maps do not represent an unbiased estimate of sky signal. Correct interpretation of these maps requires understanding the noise properties of the maps as well as the effects of the filtering on signal. Fourier-domain noise power spectral density functions and filter transfer functions for these maps are provided in this release. In addition, two-dimensional beam profiles and measurements of the spectral bandpass functions for the 2008 season are provided in associated FITS and text files.

A complete description of the observations, data processing, calibration, instrument response, and mapmaking process for this data release is in Schaffer et al. 2011, ApJ, 743, 90.

 
 
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September 7, 2011