Cosmic Tunnels and the Integrated Sachs-Wolfe effect

TL;DR

Cosmic Tunnels introduce a new 2D void-like tracer defined by underdense lines of sight identified from galaxy cluster catalogs via the tunnel algorithm. Their void-like nature is validated through strong cross-correlations with galaxy and CMB weak-lensing maps and with galaxy density maps, with lensing profiles well described by the universal HSW void profile. The ISW signal obtained by cross-correlating with Planck CMB data reaches $3.6\sigma$ for the ACT-based tunnels, representing one of the highest significances from a single tracer catalog; a low-redshift sign flip is tentatively detected, though with modest significance. These results establish Cosmic Tunnels as a robust, complementary void probe with potential for cosmological constraints and synergy with existing 2D and 3D void analyses.

Abstract

Cosmic voids, vast underdensities in the large-scale structure, offer unique sensitivity to cosmological parameters. However, traditional 3D galaxy-based void finding is limited by many factors, including uncertainties in the galaxy-halo connection and distortions from redshift errors. Using alternative tracers and new 2D void definitions can alleviate these limitations and be tailored to maximise the signal for specific observables. Here, we introduce Cosmic Tunnels, a new class of 2D void-like objects traced by galaxy clusters, corresponding to large underdense lines of sight. We identify Cosmic Tunnels by applying the tunnel algorithm to the RASS-MCMF and ACT-MCMF cluster catalogues. We validate their void-like nature by measuring the cross-correlation of Cosmic Tunnels with galaxy density contrast maps from the DESI Legacy Survey (measured at 63$σ$ significance), galaxy weak-lensing maps from DES Y3 (31$σ$), and CMB weak-lensing maps from ACT DR6 (15$σ$), all of which show underdense interiors enclosed by compensation ridges, consistent with 3D galaxy voids, measured at high statistical significance. We also show that the lensing profiles fit the universal HSW void profile, further validating their void-like nature. We cross-correlate the Cosmic Tunnels with Planck CMB temperature maps to measure the ISW signal. Using the ACT-MCMF Cosmic Tunnels, we achieve a 3.6$σ$ ISW detection, one of the highest significances ever reported from a single tracer catalogue. These results confirm that Cosmic Tunnels are robust underdense structures and demonstrate their potential as a new tool for cosmological analyses. Finally, we report a tentative detection of a sign flip in the ISW signal at very low redshift (z<0.03), consistent with previous studies, challenging the standard $Λ\rm{CDM}$ paradigm.

Figures (7)

• Figure 1: The observational used in this analysis, the shaded grey regions indicate the survey mask associated with the data in each panel. Colour bars indicate the continuous variable with its range and units used in each panel. The top two panels show the Cosmic Tunnels (black) identified in RASS-MCMF (left) and ACT-MCMF (right), using all clusters in the catalogues, which are shown by the red points. The second row shows the Planck CMB temperature anisotropy map (right), and the Legacy Survey projected galaxy overdensity field for $z\in[0,0.5]$(left). The bottom row shows the ACT CMB WL convergence map (left) and the DES-Y3 galaxy WL convergence map (right).
• Figure 2: The redshift distribution of the galaxy cluster catalogues used in this analysis. The blue and orange curves show the data for the RASS and ACT MCMF catalogues respectively. The orange curve shows the combination of the two catalogues, where duplicate clusters present in both catalogues have been removed.
• Figure 3: The cosmic tunnel abundance plotted as a function of the cosmic tunnel size $R_v$. The blue, orange, and green curves correspond to the cosmic tunnels identified in the RASS, ACT, and RASS+ACT MCMF galaxy cluster catalogues respectively.
• Figure 4: The radial WL profiles of cosmic tunnels, measured with the DES Y3 mass map (top) and the ACT DR6 mass map (bottom). The WL profiles show the WL convergence $\kappa$ as a function of the distance from the tunnel centre. The data points correspond to the stack of the entire cosmic tunnel population, weighted by void size, for a given cluster catalogue. The blue, orange, and green curves correspond to the Cosmic Tunnels WL profiles measured with the RASS, ACT, and RASS+ACT MCMF cluster catalogues respectively. The error bars indicate the $1\sigma$ standard errors. The solid lines show the HSW fit to the data points, with colours matching the data as shown in the legend. The sub panels show the residuals between the data and the HSW fit.
• Figure 5: The radial profiles of Cosmic Tunnels in the galaxy field. The profiles are measured in terms of the galaxy overdensity $\delta_g$, and plotted as a function of distance from the tunnel centre normalised by the tunnel radius. The curves shown here correspond to the stack of the entire cosmic tunnel population, weighted by tunnel size, for a given cluster catalogue. Blue, orange, and green show the Cosmic Tunnel galaxy profiles for the RASS, ACT, and RASS+ACT MCMF galaxy cluster catalogues respectively. The shaded regions indicate the $1\sigma$ standard errors.