Detection of intercluster gas in superclusters using the thermal
  Sunyaev-Zel'dovich effect
  Using a thermal Sunyaev-Zel'dovich (tSZ) signal, we search for hot gas in
superclusters identified using the Sloan Digital Sky Survey Data Release 7
(SDSS/DR7) galaxies. We stack a Comptonization y map produced by the Planck
Collaboration around the superclusters and detect the tSZ signal at a
significance of 6.4 sigma. We further search for an intercluster component of
gas in the superclusters. For this, we remove the intracluster gas in the
superclusters by masking all galaxy groups/clusters detected by the Planck tSZ,
ROSAT X-ray, and SDSS optical surveys down to a total mass of 10^13 Msun. We
report the first detection of intercluster gas in superclusters with y = (3.5
+- 1.4) * 10^(-8) at a significance of 2.5 sigma. Assuming a simple isothermal
and flat density distribution of intercluster gas over superclusters, the
estimated baryon density is (Omega_gas / Omega_b) * (T_e/(8*10^6 K)) = 0.067 +-
0.006 +- 0.025. This quantity is inversely proportional to the temperature,
therefore taking values from simulations and observations, we find that the gas
density in superclusters may account for 17 - 52 % of missing baryons at low
redshifts. A better understanding of the physical state of gas in the
superclusters is required to accurately estimate the contribution of our
measurements to missing baryons.
