Cosmic filaments confirm unexplained cooling of CMB photons in two independent redshift ranges

TL;DR

The study extends evidence for a CMB temperature decrement along large-scale cosmic filaments from $z<0.02$ to the higher range $0.004<z<0.040$, by analyzing mean transversal CMB temperature profiles around filaments identified in the 2MRS survey. Using Planck PR3 SMICA maps and a robust multipole filtering scheme, the authors show a $3-4\sigma$ decrement toward filament spines, with the signal strengthening for the densest filaments and those oriented radially along the line of sight. The decrement remains when masking galaxy halos and cannot be explained by the thermal SZ effect, being frequency-independent across SMICA and SEVEM maps, and strongest for radially oriented filaments, suggesting a connection to the 3-D density field or non-standard ISW-like processes. Overall, the work provides strong evidence for extragalactic CMB cooling linked to massive filamentary structures in the nearby universe, inviting further theoretical interpretation and cross-checks with additional data.

Abstract

Recent papers have reported an unexplained cooling of CMB photons passing through galaxies in nearby cosmic filaments $z<0.02$ at the $>5σ$ level. Here we show for the first time that this effect is also present at higher redshifts $0.02<z<0.04$. Instead of calculating the CMB temperature around individual galaxies as in previous works, we analyze mean CMB temperature profiles associated to cosmic filaments in three dimensions. We have considered different thresholds in the linear K-band luminosity density of the filaments as a proxy to mass density. Furthermore, we have analyzed the dependence of the results on the average orientation of filaments with respect to the line of sight. These studies were implemented to test the expected dependence on mass density as well as on photon trajectory length within the cosmic filaments. We find a $3-4σ$ detection of a temperature decrement trend towards the spine of the filaments, the larger the mass and the more radially oriented the filament, the stronger the temperature decrement. This trend is seen independently in both redshift ranges $0.004<z<0.02$ and $0.02<z<0.04$. We therefore conclude that our results provide strong evidence for a lower CMB temperature along massive cosmic filaments in the nearby universe $z<0.04$.

Figures (9)

• Figure 1: Projection of 3D filamentary structure on the plane of the sky in the redshift range $0.004 < z < 0.020$ (upper panel, 278 total filaments identified) and $0.020<z<0.040$ (lower panel, 908 total filaments identified). Grey lines correspond to the sky-projection of all filaments, red lines to the densest hexile and purple to the densest decile in their corresponding redshift interval. The gray mask corresponds to the PR3 CMB common mask, which leaves $\sim 78\%$ of available sky.
• Figure 2: The red curved line is a close-up of one of the projected filaments from Figure \ref{['fig:filament_projection']}. The rectangles along the filament show an example of how the filament is divided into segments, one rectangle for each segment. Each segment has a different length, but the width which is orthogonal to the filament, is always $12$Mpc. In the top of the figure, we show a close-up of the first segment rectangle where we show the 24 distance bins, each of $0.5$Mpc. The mean temperature is taken within each of these bins. The two orange rectangles represent the area $C_{bks}$ of equation \ref{['eq:deltat']}: the CMB temperature of all the pixels inside the orange rectangles is the contribution of this segment to the given distance bin from the centre of the spine.
• Figure 3: Mean CMB temperature profiles in perpendicular distances to the filament spine for the redshift range $0.004<z<0.020$, with $\ell>5$. The solid line is the data, vertical solid lines are the standard deviation of the data and the shadowed regions are the variance in synthetic simulations. In the upper panel the analysis is done for the filaments in the densest and least dense tertile of luminosity density. In the lower panel the analysis is done for the filaments in the densest and least dense hexile of luminosity density.
• Figure 4: Analysis of filaments in the redshift range $0.020<z<0.040$. Upper panel: densest and least dense (luminosity per unit length) hexile filaments. Middle panel: densest and least dense decile filaments. In both panels, the solid line is the data, vertical solid lines are the standard deviation of the data and the shadowed regions are the variance in CMB synthetic simulations. Lower panel: mean CMB temperature of a bin ($0-1.0\,$Mpc) of densest filaments decile, for different ranges of low multipoles removed. The solid vertical lines correspond to the standard deviation of the data, while the shadowed boxes correspond to the variance from CMB synthetic simulations with the same ranges of multipoles removed.
• Figure 5: CMB temperature profile for the full redshift range $0.004<z<0.04$ as variance weighted combination of the individual ranges based on the densest hexile with $\ell>5$ for the lowest redshift range and densest decile with $\ell>32$ for the highest redshift range. The solid line is the data, the vertical solid line is the standard deviation of this data and the shadowed regions are the variance in simulations.