Percent-level constraints on baryonic feedback with spectral distortion measurements

Abstract

High-significance measurements of the monopole thermal Sunyaev-Zel'dovich CMB spectral distortions have the potential to tightly constrain poorly understood baryonic feedback processes. The sky-averaged Compton-y distortion and its relativistic correction are measures of the total thermal energy in electrons in the observable universe and their mean temperature.We use the CAMELS suite of hydrodynamic simulations to explore possible constraints on parameters describing the subgrid implementation of feedback from active galactic nuclei and supernovae, assuming a PIXIE-like measurement.The small 25 h −1 Mpc CAMELS boxes present challenges due to the significant cosmic variance. We utilize machine learning to construct interpolators through the noisy simulation data. Using the halo model, we translate the simulation halo mass functions into correction factors to reduce cosmic variance where required.Our results depend on the subgrid model. In the case of IllustrisTNG, we find that the bestdetermined parameter combination can be measured to 2 % and corresponds to a product of AGN and SN feedback. In the case of SIMBA, the tightest constraint is 0.2 % on a ratio between AGN and SN feedback. A second orthogonal parameter combination can be measured to 8 %. Our results demonstrate the significant constraining power a measurement of the late-time spectral distortion monopoles would have for baryonic feedback models.

Inverse-Compton Scattering of the Cosmic Infrared Background

“…Additionally, we note that our results depend on the electron pressure profile used in the model of the Compton-y field, which is not currently fully constrained (see, e.g., Fig. 1 in Thiele et al (2022) for the range of Compton-y monopole predictions from hydrodynamical simulations and Chiang et al (2020) for a range of measurements of the Compton-y monopole redshift kernel). Other than the Battaglia et al (2012) pressure profile that we used here (assuming the original fiducial parameter values reported in Table 3), another common choice in the literature is the Arnaud et al (2010) pressure profile, whose normalization depends on the hydrostatic equilibrium (HSE) mass bias.…”

“…Using the Kompaneets equation, we then compute the inverse-Compton-induced distortion that arises from CIB photons obeying this SED scattering off free electrons in a cluster at z = 0. Multiplying the resulting distortion template by the total Compton-y value expected in our Hubble volume, y ≈ 1 − 2 × 10 −6 (Hill et al 2015;Dolag et al 2016;Chiang et al 2020;Thiele et al 2022), then gives a rough estimate of the observable CIB distortion signal. (Our fiducial model, described in the next subsection, yields y = 1.59 × 10 −6 ).…”

“…com/simonsobs/hmvec/blob/master/data/alpha consistency.txt. 3 Note that this value includes only the Compton-y signal from the ICM, neglecting the intergalactic medium and reionization contributions, each of which contributes roughly y ≈ 10 −7 (Hill et al 2015;Thiele et al 2022). 4 https://github.com/borisbolliet/class sz, commit number 336ae0986bd2657287860192b9a445842d6fad2d.…”

“…A detection of the monopole signal considered here would yield new information about the redshift kernel of the CIB, as well as the SED properties of the CIB sources. This signal is also potentially a new "foreground" for CMB spectral distortions, such as the all-sky relativistic tSZ distortion (Hill et al 2015;Abitbol et al 2017;Thiele et al 2022). As we show below, the impact on forecasts for CMB spectral distortions' signal-to-noise is fortunately small.…”

Inverse-Compton scattering of the cosmic infrared background

“…Like the CMB, the photons in the radio and infrared backgrounds are at much lower energies than typical electrons in the ICM (T γ T e ∼ keV), and thus Comptonization leads to the photons being upscattered to higher energies. However, the exact shape of the inverse-Compton-induced distortion a new "foreground" for CMB spectral distortions, such as the all-sky relativistic tSZ distortion [54][55][56]. As we show below, the impact on forecasts for CMB spectral distortions' signal-to-noise is fortunately small.…”