Abstract
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 Comptonizationymap produced by thePlanckCollaboration around the superclusters and detect the tSZ signal at a significance of 6.4σ. 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 thePlancktSZ, ROSAT X-ray, and SDSS optical surveys down to a total mass of 1013 M⊙. We report the first detection of intercluster gas in superclusters withy = (3.5 ± 1.4) × 10−8at a significance of 2.5σ. Assuming a simple isothermal and flat density distribution of intercluster gas over superclusters, the estimated baryon density is (Ωgas/Ωb)×(Te/8 × 106 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.
Highlights
The formation of cosmic web structure composed of voids, filaments, and clusters of galaxies is expected in the standard cosmological model of structure formation (e.g., Zeldovich et al 1982)
We report the first detection of intercluster gas in superclusters with y = (3.5 ± 1.4) × 10−8 at a significance of 2.5σ
We draw a random sampling of 669 superclusters (790 before masking galaxy clusters) with replacement and re-calculate the average y value for the new set of 669 superclusters. We repeat this process 1000 times and the bootstrapped data produce 1000 average y values. Their average and rms fluctuation are y = (3.5 ± 1.4) × 10−8 at a significance of 2.5σ, which is consistent with the error estimate from the null test
Summary
The formation of cosmic web structure composed of voids, filaments, and clusters of galaxies is expected in the standard cosmological model of structure formation (e.g., Zeldovich et al 1982). Some detections of the tSZ signal from filamentary structures are reported in Planck Collaboration VIII (2013) and Bonjean et al (2018) and statistically by stacking methods in de Graaff et al (2019) and Tanimura et al (2019), but the results may be affected by the fact that properties of filaments (shape, density, temperature, etc.) are not well understood. A cross-correlation with SDSS-DR7 luminous red galaxies (LRG) and SDSS-DR7 superclusters (Liivamägi et al 2012) suggested that this triple system is encompassed in a very-large-scale structure located at z ∼ 0.45 (Planck Collaboration VI 2013), as part of supercluster structure These multi-frequency studies shows that only ∼68% of the total tSZ signal can be explained by the predictions from the X-ray signal. Masses are quoted in solar mass and M∆ is the mass enclosed within a sphere of radius R∆ such that the enclosed density is ∆ times the critical density at redshift z
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