Percent-level constraints on baryonic feedback with spectral distortion
  measurements
  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 Mpc/h 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
best-determined 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.
