Tracing Missing Baryons in the Cosmic Filaments with tSZ and CMB-Lensing Stacking

TL;DR

This study detects and characterizes the warm-hot intergalactic medium in cosmic filaments using stacking of Planck tSZ and CMB lensing data, revealing significant baryon content.

Contribution

It provides the first joint analysis of tSZ and CMB lensing signals in filaments, constraining their gas density and temperature, and quantifying their contribution to missing baryons.

Findings

Detected tSZ signal at 7.82σ significance.

Measured filament electron temperature around 2.7 million K.

Estimated filament baryon fraction as approximately 13% of cosmic baryons.

Abstract

We investigate the distribution of missing baryons in the cosmic filaments by stacking $\sim 30,700$ filaments across the northern and southern SDSS sky regions using Planck Compton-$y$ and CMB lensing maps. Filaments are identified using the DisPerSE algorithm applied to the SDSS LOWZ-CMASS galaxy samples, selecting structures with lengths between 30-100 cMpc and redshifts in the range $0.2 < z < 0.6$. Radial profiles are extracted out to 25 cMpc from the filament spines, and galaxy clusters with halo masses above $\sim 3 \times 10^{13} M_\odot$ are masked to reduce contamination. We detect the thermal Sunyaev-Zeldovich (tSZ) signal at $7.82\sigma$ and the CMB lensing signal at $7.78\sigma$. The stacked profiles are corrected by a geometric bias correction based on filament inclination with respect to the line-of-sight, and they are portrayed assuming isothermal, cylindrically symmetric models. We explore different gas and matter density distributions, focusing on the $\beta$-models with $(\alpha,\beta) = (2,2/3)$ or $(1,1)$. By jointly fitting the Compton-$y$ and $\kappa$ profiles, we constrain the central electron overdensity and temperature to be $\delta = 4.18^{+2.01}_{-1.06}$ and $T_e = 2.74^{+0.65}_{-0.53}\times 10^6 \mathrm{K}$ for the standard $\beta$-model. These results suggest that filamentary WHIM in our selected long filaments contributes a significant baryon fraction of $0.127^{+0.019}_{-0.021}\times \Omega_b$ to the cosmic baryon budget.