Evidence of the Missing Baryons from the Kinematic Sunyaev-Zeldovich Effect in Planck Data

We estimate the amount of the missing baryons detected by the Planck measurements of the cosmic microwave background in the direction of central galaxies (CGs) identified in the Sloan galaxy survey. The peculiar motion of the gas inside and around the CGs unveils values of the Thomson optical depth ${\tau }_T$ in the range $0.2–2\times 10^{-4}$, indicating that the regions probed around CGs contain roughly half of the total amount of baryons in the Universe at the epoch where the CGs are found. If baryons follow dark matter, the measured ${\tau }_T$’s are compatible with the detection of all of the baryons existing inside and around the CGs.

Figure 1

(Left panel) Measured pairwise peculiar momenta under different aperture sizes for the sevem map. (Right panel) Measured $w^{\delta T{v}^{\text{rec}}}(r)$ correlation function under different aperture radii (${\theta }_{\mathrm{AP}}$) for the sevem clean map. In both panels the green solid lines provide the expectation from the galaxy mock catalogue, while the dash-dotted lines correspond to expectations found after averaging over 100 Gaussian simulations. In both cases, we assume ${\tau }_T=5\times 10^{-5}$.

Figure 2

(Left panel) Probability distribution for the optical depth ${\tau }_T$ inferred from the $w^{\delta T{v}^{\text{rec}}}(r)$ correlation function (the solid lines) and the kSZ peculiar momenta (the dashed lines), under different apertures, for the sevem map. These estimates of ${\tau }_T$ are obtained after fitting the data to the prediction inferred from the average of the Gaussian simulations. (Right panel) Same as the left panel, but using the galaxy $N$-body prediction as a reference, rather than the Gaussian simulations.

Figure 3

(Top panel) Baryon fraction versus aperture angle, as inferred from $w^{\delta T{v}^{\text{rec}}}(r)$ (the filled circles and squares) and $p_{\mathrm{kSZ}}(r)$ (the filled and empty triangles) measurements. Red (green) denotes positive (negative) values. (Bottom panel) Recovered profile of gas overdensity from $w^{\delta T{v}^{\text{rec}}}(r)$ measurements and for $L_{\text{corr}}=38h^{-1}\mathrm{Mpc}$ (the filled symbols). In both panels, we compare our data to the predictions for dark matter (as provided by Ref. [20]), which are given by the blue lines.