How accurately can suborbital experiments measure the CMB?

Great efforts are currently being channeled into ground- and balloon-based CMB experiments, mainly to explore polarization and anisotropy on small angular scales. To optimize instrumental design and assess experimental prospects, it is important to understand in detail the atmosphere-related systematic errors that limit the science achievable with new instruments. As a step in this direction, we spatially compare the 648 square degree ground- and balloon-based QMASK map with the atmosphere-free WMAP map, finding beautiful agreement on all angular scales where both are sensitive. Although much work remains on quantifying atmospheric effects on CMB experiments, this is a reassuring quantitative assessment of the power of the state-of-the-art fast-Fourier-transform- and matrix-based mapmaking techniques that have been used for QMASK and virtually all subsequent experiments.

Figure 1

Visual comparison of the QMASK (left panel) and WMAP (right panel) maps, both Wiener filtered with the same weighting (determined by the QMASK noise covariance matrix). The slightly larger fluctuation level seen in the left image gives a visual indication of the effect of QMASK noise.

Figure 2

Null-buster comparison of QMASK (left: $r=0$) and WMAP-Q (right: $r=\infty$). This figure shows the number of standard deviations (sigmas) at which the difference map $\mathbf{z}=\mathbf{x}-\mathrm{r}\mathbf{y}$ is inconsistent with pure noise.