Abstract
The thermal Sunyaev-Zeldovich effect contains information about the thermal history of the universe, observable in maps of the Compton $y$ parameter; however, it does not contain information about the redshift of the sources. Recent papers have utilized a tomographic approach, cross-correlating the Compton $y$ map with the locations of galaxies with known redshift, in order to deproject the signal along the line of sight. In this paper, we test the validity and accuracy of this tomographic approach to probe the thermal history of the universe. We use the state-of-the-art cosmological hydrodynamical simulation, Magneticum, for which the thermal history of the universe is a known quantity. The key ingredient is the Compton-$y$-weighted halo bias, $b_y$, computed from the halo model. We find that, at redshifts currently available, the method reproduces the correct mean thermal pressure (or the density-weighted mean temperature) to high accuracy, validating and confirming the results of previous papers. At higher redshifts ($z\gtrsim 2.5$), there is significant disagreement between $b_y$ from the halo model and the simulation.
Highlights
As cosmological structures form, the gravitational potential wells seeded by primordial density fluctuations become deeper [1]
0.0 0.5 1.0 1.5 2.0 2.5 3.0 Redshift z. The reason for this disagreement is not clear, but it is plausible that the assumption that pressure is dominated by the virialized structures and the contribution from supernova and active galactic nuclei (AGN) feedback are subdominant compared to the thermal pressure of virialized gas may be violated at such a high z
This study aimed to answer two principle questions: (1) The bias-weighted mean electron pressure hbPei is observable from cosmological surveys. Does this quantity measured from the Magneticum simulation agree with the data given in Ref. [10]? (2) In Ref. [10], the density-weighted mean electron temperature Te is derived by dividing hbPei by by, calculated from the halo model
Summary
As cosmological structures form, the gravitational potential wells seeded by primordial density fluctuations become deeper [1]. As the SZ signal is dominated by massive structure, the signal can be deprojected along the line of sight using clustering-based redshift inference [19,20,21] Following this method, an external sample of reference sources with known z is taken, and cross correlated with the Compton y parameter as a function of z. The halo bias-weighted mean electron pressure, hbPei, is the direct observable of the SZ-galaxy cross-correlation function on large scales [25]. To infer the mean electron pressure, hPei, we need to know the Compton y-weighted halo bias, by ≡ hbPei=hPei. In Refs. We use cross correlations of the density and pressure to calculate the density-weighted mean temperature of baryonic gas, which is a known quantity in the simulation.
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