Detection of intercluster gas in superclusters using the thermal Sunyaev-Zel'dovich effect
Using a thermal Sunyaev-Zel'dovich (tSZ) signal, we search for the hot gas in superclusters identified in the Sloan Digital Sky Survey Data Release 7 (SDSS/DR7). We stack the Comptonization y map produced by the Planck Collaboration around the superclusters and detect the tSZ signal at a significance of 5.9 sigma. We further search for an intercluster component of gas in the superclusters. We thus remove the intracluster gas in the superclusters by masking all the galaxy groups/clusters detected by the Planck tSZ, ROSAT X-ray and SDSS optical surveys down to the total mass of 10^13 Msun. We report the first detection of intercluster gas in the superclusters at a significance of 2.1 sigma. Assuming a simple, isothermal and flat density distribution of the intercluster gas over the superclusters, we estimate the product of over-density and temperature to be (delta_e)(Te/8*10^6 K) = 1.5 +- 0.1 (sys) +- 0.7 (stat). This can be translated as a baryon (gas) density of (Omega_gas/Omega_b)(Te/8*10^6 K) = 0.11 +- 0.01 +- 0.05. Our measurement of the intercluster gas in the superclusters may account for up to 10% of the missing baryons at low resdhifts. However, a better understanding of the physical state of the gas, especially its temperature, is required to properly estimate this contribution.
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Astronomy & Astrophysics