Does the Correlation between 2MRS Galaxies and the CMB Indicate an Unmodeled CMB Foreground?

Abstract

Abstract We revisit the claimed detection of a new cosmic microwave background (CMB) foreground based on the correlation between low-redshift Two Micron All Sky Survey Redshift Survey (2MRS) galaxies and CMB temperature maps from the Planck and Wilkinson Microwave Anisotropy Probe missions. We reproduce the reported measurements but argue that the original analysis significantly underestimated the uncertainties. We cross-correlate the 2MRS galaxy positions with simulated CMB maps and show that the correlation measured with the real data for late-type spiral galaxies at angular scales θ ≥ 0.°1 and redshift cz < 4500 km s−1 is consistent with zero at the 1.7σ level or less, depending on the exact CMB map and simulation construction. This was the sample that formed the basis for the original detection claim. For smaller angular separations the results are not robust to galaxy type or CMB cleaning method, and we are unable to draw firm conclusions. The original analysis did not propose a specific, falsifiable physical correlation mechanism, and it is impossible to rule out any contribution from an underlying physical effect. However, given our calculations, the lack of signal from expanding the redshift range, and the lack of corroboration from other galaxy surveys, we do not find the evidence for a new CMB foreground signal compelling.