Frode K. Hansen

We find a significant cosmic microwave background (CMB) temperature excess in the direction of local underdensities within z5σ$ cooling of CMB photons in galactic filaments in the same redshift range, we now may have possible evidence for a negative integrated Sachs-Wolfe (ISW) effect in the very recent Universe. In addition to having the opposite sign, the observed amplitude is an order of magnitude larger than the predicted Rees-Sciama and ISW effects, pointing to an unknown physical process, possibly related with a non-standard model of dark energy. We discuss the results in light of the latest Data Release 2 results of the Dark Energy Spectroscopic Instrument (DESI) showing hints of dynamical dark energy. Removing the quadrupole, we find the CMB temperatures measured in nearby voids to a large degree uncorrelated with the temperature measured around nearby galaxies, and the observed mean difference between these temperatures is almost 6.5σ larger than what is found in simulations.

The origin of small deviations from statistical isotropy in the Cosmic Microwave Background (CMB) — the so-called CMB anomalies — remains an open question in modern cosmology. In this work, we test statistical isotropy in Planck Data Release 4 (PR4) by estimating the temperature and E -mode power spectra across independent sky regions. We find that the directions with higher local bandpower amplitudes in intensity are clustered for multipoles between 200 and 2000 with clustering probabilities consistently below 1% for all these scales when compared to end-to-end (E2E) Planck simulations; notably, this range extends beyond that reported in Planck Data Release 3 (PR3). On the other hand, no significant clustering is observed in the polarisation E -modes. In a complementary analysis, we search for dipolar variations in cosmological parameters fitted using the previously computed power spectra. When combining temperature and polarisation power spectra, we identify a potential anomaly in the amplitude of the primordial power spectrum, A _s , with only 5 out of 600 simulations exhibiting a dipole amplitude as large as that observed in the data. Interestingly, the dipole direction aligns closely with the known hemispherical power asymmetry, suggesting a potential link between these anomalies. All other cosmological parameters remain consistent with ΛCDM expectations. Our findings highlight the need to further investigate these anomalies and understand their nature and potential implications for better understanding of the early Universe.

The Cosmic Microwave Background (CMB) reaches homogeneity at relatively modest angular scales compared to the expectation of the standard ΛCDM model revealing an important challenge to the theoretical predictions. We analyze this inconsistency through the homogeneity scale H and the slope of the homogeneity index at θ = 90°. We find that the removal of low multipoles, in particular the quadrupole, from both the data and the ΛCDM synthetic CMB maps, significantly improve the consistency between models and observations. This adds to indications of the relevant contribution of the low value of the CMB quadrupole to the observed anomalies in the homogeneity scale. Due to the presence of a new extragalactic foreground in the CMB maps, we have performed statistical analyses with different masking taking into account the regions mostly affected. In particular we consider galaxies in the local neighborhood which are expected to affect more significantly the large angular scales. We find that by masking these regions, the analysis cannot solve the discrepancy between the observations and the ΛCDM model in spite of a small improvement of their mutual consistency. The studies with both foreground masking and low-ℓ removed CMB maps show similar results than those of the full CMB map indicating that the main discrepancy between theory and observations is associated to the quadrupole anomaly and may require more exhaustive analysis.

We confirm, at the 5.7σ level, previous studies reporting cosmic microwave background (CMB) temperatures being significantly lower around nearby spiral galaxies than expected from the ΛCDM model. Results from our earlier work were disputed in a recent paper, however, that analysis included areas far beyond the galactic halos, while disregarding the neighbourhood of the galaxies where the main signal is seen. Here, we limit the present study to pixels that are well within the galactic halos, focussing on galaxies in dense cosmic filaments and improving the signal-to-noise ratio (S/N), as compared to previous studies. The average CMB temperature in discs around these galaxies is always much lower in Planck data than in any of the 10 000 Planck-like CMB simulations. Even when correcting for the look-elsewhere effect, the detection is still at the 3 − 4σ level. We further show that the largest scales (ℓ < 16) of the Planck CMB fluctuations are more correlated with the distribution of nearby galaxies than 99.99% of simulated CMB maps. We argue that the existence of a new CMB foreground cannot be ignored and a physical interaction mechanism should be sought, which could possibly involve dark matter and could also be linked to intergalactic magnetic fields.

We perform cosmological parameters estimation on Planck Cosmic Microwave Background (CMB) maps masking the recently discovered foreground related to nearby spiral galaxies. In addition, we also analyse the association between these foreground regions and recent claims of cosmological causal horizons in localized CMB parameter estimates. Our analysis shows consistent cosmological parameter values regardless of the masking approach, though reduced sky areas introduce larger uncertainties. By modelling the new extragalactic foreground, we identify a resemblance with local parameter variation maps with a statistical significance at the 3 sigma level, suggesting that a simplified foreground model partially accounts, (40-50)% correlation with 15% uncertainty, for the observed causal horizons. These findings add new evidence to the existence of the new foreground associated with large spiral galaxies and show that estimates of cosmological parameters on smaller patches on the sky can be largely affected by these foregrounds, but that the parameters taken over the full sky are unaltered.

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.