A Measurement of the Galaxy Group-Thermal Sunyaev-Zel'dovich Effect Cross-Correlation Function

Abstract

Stacking cosmic microwave background maps around known galaxy clusters and groups provides a powerful probe of the distribution of hot gas in these systems via the Sunyaev-Zel'dovich (SZ) effect. A stacking analysis allows one to detect the average SZ signal around low-mass haloes, to extend measurements out to large scales and measure the redshift dependence of the SZ background. Motivated by these exciting prospects, we measure the two-point cross-correlation function between ∼380 000 galaxy groups (at z = 0.01-0.2) from the Sloan Digital Sky Survey and Compton-y parameter maps constructed by the Planck collaboration. We find statistically significant correlations in each of six separate mass bins, with halo masses ranging from 10^11.5 to 10^15.5 M_⊙ h^-1. We compare with halo models of the SZ signal, which describe the stacked measurement in terms of one-halo and two-halo contributions. The one-halo term quantifies the average pressure profile around the groups in a mass bin, while the two-halo term describes the contribution of correlated neighbouring haloes. For the massive groups, we find clear evidence for the one- and two-halo regimes, while groups with mass below 10¹³ M_⊙ h^-1 are dominated by the two-halo term, given the resolution of Planck data. We use the signal in the two-halo regime to determine the bias-weighted electron pressure of the Universe: <bP_e> = 1.50 ± 0.226 × 10^-7 keV cm^-3 (1σ) at z ≈ 0.15.