Novel Kinetic Sunyaev-Zel'dovich Estimator for Electron-Electron Correlations

Recent advancements in small-scale observations of the cosmic microwave background have provided a unique opportunity to characterize the distribution of baryons in the outskirts of galaxies via stacking-based analyses of the kinetic Sunyaev-Zel'dovich effect. Such measurements, mathematically equivalent to probing the galaxy-electron cross-correlation, have revealed that gas is more extended than dark matter and that the strength of baryonic feedback may vary with halo mass and redshift. However, because these analyses are conditioned on galaxy positions, deriving a host-independent description of the baryon distribution depends on uncertain galaxy-halo modeling on small scales. In this Letter, we present a novel kinetic Sunyaev-Zel'dovich × galaxy four-point estimator that directly probes the full ionized electron field, extending beyond the gas traced by luminous galaxies. This method exploits large-scale velocity reconstruction from galaxy surveys to characterize the electron distribution unbiased by small-scale galaxy clustering. We forecast that the proposed signal can be measured with a signal-to-noise ratio of ∼8 (∼31) for a configuration corresponding to Atacama Cosmology Telescope DR6 (Simons Observatory) cosmic microwave background data combined with spectroscopic galaxy samples from the Dark Energy Spectroscopic Instrument. This approach will enable the first tomographic measurements of the electron autopower spectrum, providing new constraints on feedback-driven redistribution of baryons and its role in shaping cosmic structure.