Galactic Plane image sharpness as a check on cosmic microwave background mapmaking

TL;DR

This paper investigates whether a timing offset in WMAP data calibration affected the accuracy of the CMB quadrupole measurement, concluding that calibration errors led to overestimation of the quadrupole signal.

Contribution

It demonstrates that the calibration process, not mapmaking, introduced significant errors in the WMAP CMB quadrupole estimates.

Findings

Calibration errors caused overestimation of the quadrupole by 15-60%.

Optimal focusing of Galactic Plane objects confirms mapmaking was correct.

Timing offset did not significantly affect the mapmaking process.

Abstract

The largest uncollapsed inhomogeneity in the observable Universe is statistically represented in the quadrupole signal of the cosmic microwave background (CMB) sky maps as observed by the Wilkinson Microwave Anisotropy Probe (WMAP). The constant temporal offset of -25.6 ms between the timestamps of the spacecraft attitude and observational data records in the time-ordered data (TOD) of the WMAP observations was suspected to imply that previously derived all-sky CMB maps are erroneous, and that the quadrupole is in large part an artefact. The optimal focussing of bright objects in the Galactic Plane plays a key role in showing that no error occurred at the step of mapmaking from the calibrated TOD. Instead, the error had an effect when the uncalibrated TOD were calibrated. Estimates of the high-latitude quadrupole based on the wrongly calibrated WMAP maps are overestimated by about 15-60%.