Letter to the Editor

A possible common explanation for several cosmic microwave background (CMB) anomalies: A strong impact of nearby galaxies on observed large-scale CMB fluctuations

¹ Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029 Blindern, 0315 Oslo, Norway
e-mail: frodekh@astro.uio.no
² Instituto de Astronomía Teórica y Experimental, CONICET-UNC, Córdoba, Argentina
³ Observatorio Astronómico de Córdoba, UNC, Córdoba, Argentina

Received: 29 April 2023
Accepted: 24 June 2023

Abstract

Context. A new and hitherto unknown cosmic microwave background (CMB) foreground has recently been detected. A systematic decrease in CMB temperatures around nearby large spiral galaxies points to an unknown interaction with CMB photons in a sphere up to several projected megaparsecs around these galaxies.

Aims. We investigate to what extent this foreground may impact the CMB fluctuation map and create the so-called CMB anomalies.

Methods. Using the observed temperature decrements around the galaxies, and making some general assumptions about the unknown interaction, we propose a common radial temperature profile. By assigning this profile to nearby galaxies in the redshift range z = [0.004, 0.02], we created a foreground map model.

Results. We find a remarkable resemblance between this temperature model map, based on nearby galaxies, and the Planck CMB map. Compared to 1000 simulated maps, we find that none of them show such a strong correlation with the foreground map over both large and small angular scales. In particular, the quadrupole, octopole, and ℓ = 4 and ℓ = 5 modes correlate with the foreground map to a high significance. Furthermore, one of the most prominent temperature decrements in the foreground map coincides with the position of the CMB cold spot.

Conclusions. The largest scales of the CMB, and thereby the cosmological parameters, may change significantly after this foreground component is properly corrected. However, a reliable corrected CMB map can only be derived when suitable physical mechanisms are proposed and tested.