# A Comparison of Maps and Power Spectra Determined from South Pole Telescope and Planck Data

## TL;DR

This study compares the maps and power spectra from South Pole Telescope and Planck data over the same sky region, finding high consistency and improving calibration precision, with no significant systematic errors detected.

## Contribution

It provides a detailed comparison of SPT and Planck data, demonstrating their consistency and refining the SPT calibration accuracy.

## Key findings

- Cross-spectra are consistent with the null hypothesis of a shared sky map.
- Calibration of SPT data improved from 2.6% to 0.3%.
- Marginal differences in power spectra attributed to sample variance.

## Abstract

We study the consistency of 150 GHz data from the South Pole Telescope (SPT) and 143 GHz data from the Planck satellite over the patch of sky covered by the SPT-SZ survey. We first visually compare the maps and find that the residuals appear consistent with noise after accounting for differences in angular resolution and filtering. We then calculate (1) the cross-spectrum between two independent halves of SPT data, (2) the cross-spectrum between two independent halves of Planck data, and (3) the cross-spectrum between SPT and Planck data. We find the three cross-spectra are well-fit (PTE = 0.30) by the null hypothesis in which both experiments have measured the same sky map up to a single free calibration parameter---i.e., we find no evidence for systematic errors in either data set. As a by-product, we improve the precision of the SPT calibration by nearly an order of magnitude, from 2.6% to 0.3% in power. Finally, we compare all three cross-spectra to the full-sky Planck power spectrum and find marginal evidence for differences between the power spectra from the SPT-SZ footprint and the full sky. We model these differences as a power law in spherical harmonic multipole number. The best-fit value of this tilt is consistent among the three cross-spectra in the SPT-SZ footprint, implying that the source of this tilt is a sample variance fluctuation in the SPT-SZ region relative to the full sky. The consistency of cosmological parameters derived from these datasets is discussed in a companion paper.