The Cosmic Thermal History Probed by Sunyaev-Zeldovich Effect Tomography (2006.14650v2)

Abstract: The cosmic thermal history, quantified by the evolution of the mean thermal energy density in the universe, is driven by the growth of structures as baryons get shock heated in collapsing dark matter halos. This process can be probed by redshift-dependent amplitudes of the thermal Sunyaev-Zeldovich (SZ) effect background. To do so, we cross-correlate eight sky intensity maps in the $\it{Planck}$ and Infrared Astronomical Satellite missions with two million spectroscopic redshift references in the Sloan Digital Sky Surveys. This delivers snapshot spectra for the far-infrared to microwave background light as a function of redshift up to $z\sim3$. We decompose them into the SZ and thermal dust components. Our SZ measurements directly constrain $\langle bP_{\rm e} \rangle$, the halo bias-weighted mean electron pressure, up to $z\sim 1$. This is the highest redshift achieved to date, with uncorrelated redshift bins thanks to the spectroscopic references. We detect a threefold increase in the density-weighted mean electron temperature $\bar{T}{\rm{e}}$ from $7\times 10^5~{\rm K}$ at $z=1$ to $2\times 10^6~{\rm K}$ today. Over $z=1$-$0$, we witness the build-up of nearly $70\%$ of the present-day mean thermal energy density $\rho{\rm{th}}$, with the corresponding density parameter $\Omega_{\rm th}$ reaching $1.5 \times10^{-8}$. We find the mass bias parameter of $\it{Planck}$'s universal pressure profile of $B=1.27$ (or $1-b=1/B=0.79$), consistent with the magnitude of non-thermal pressure in gas motion and turbulence from mass assembly. We estimate the redshift-integrated mean Compton parameter $y\sim1.2\times10^{-6}$, which will be tested by future spectral distortion experiments. More than half of which originates from the large-scale structure at $z<1$, which we detect directly.

• The paper employs redshift tomography of the thermal Sunyaev-Zeldovich effect with cross-correlated Planck, IRAS, and SDSS data to map cosmic thermal evolution.
• The paper finds a threefold increase in electron temperature from 7×10^5 K at z = 1 to 2×10^6 K today, with 70% of current thermal energy building up post z = 1.
• The paper estimates a mass bias parameter (B = 1.27) reflecting non-thermal pressures, offering key constraints for cosmological models on baryonic feedback.

The Cosmic Thermal History Probed by Sunyaev-Zeldovich Effect Tomography

The research conducted by Chiang et al. explores the cosmic thermal history by harnessing the redshift-dependent amplitudes of the thermal Sunyaev-Zeldovich effect (tSZ). This paper is a substantial step in understanding how baryons in collapsing dark matter halos drive the thermalization process on a cosmic scale. The authors employ a sophisticated approach, utilizing eight sky intensity maps from the Planck and Infrared Astronomical Satellite missions, and integrating this data with two million spectroscopic redshift references from the Sloan Digital Sky Surveys.

This work is centered around cross-correlating these datasets to construct snapshot spectra for the far-infrared to microwave background light, extending to redshifts as high as $z \sim 3$. The decomposition of these spectra into the tSZ and thermal dust components reveals key insights into the Universe's evolving structure.

Key Findings

• Redshift Tomography: The paper achieved tSZ measurements up to $z \sim 1$, marking a significant extension in the redshift domain for such analysis, made feasible by employing uncorrelated redshift bins due to the extensive spectroscopic references used.
• Thermal Energy Evolution: There is a noted threefold increase in the density-weighted mean electron temperature from $7 \times 10^5 \, \text{K}$ at $z = 1$ to $2 \times 10^6 \, \text{K}$ in the present epoch. This observation is indicative of sustained thermal activity and energy build-up through structure formation.
• Estimation of Present-Day Thermal Energy Density: Through rigorous analysis, it was determined that approximately 70% of the present-day mean thermal energy density built up between $z = 1$ and $z = 0$, with the corresponding density parameter $\Omega_{\text{th}}$ reaching $1.5 \times10^{-8}$.
• Mass Bias Parameter: The research provides a value for the mass bias parameter from Planck's universal pressure profile $B = 1.27$ (translating to $1 - b = \frac{1}{B} = 0.79$). This figure aligns with expectations of non-thermal pressure contributions due to gas motions and turbulence, underscoring the relevance of mass assembly processes.

Implications and Future Prospects

The implications of this research are multi-fold. By providing a detailed portrait of the cosmic thermal history, it enhances our understanding of baryonic processes across cosmic time. The numerically robust results pertaining to electron pressures and thermal energy density provide essential constraints for cosmological models and simulations aiming to depict the universe's evolution.

One noteworthy future prospect lies in the implications for spectral distortion experiments. The empirical estimate for the redshift-integrated mean Compton parameter ($y \sim 1.2 \times 10^{-6}$) is poised for validation through upcoming experiments targeting the CMB spectral distortions. Such advancements would not only refine our knowledge of baryonic thermalization but also help test the cosmological model's assumptions regarding energy transfer processes in large-scale structures.

This work stands as a testament to the potential of multi-frequency cross-correlation techniques. It paves the way for further exploration into astrophysical feedback mechanisms and their cosmic fingerprints, potentially unraveling more intricate aspects of large-scale structure formation.