A Novel kinetic Sunyaev-Zel'dovich Estimator for Electron-Electron Correlations

Abstract

Recent advancements in small-scale observations of the cosmic microwave background (CMB) 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 (kSZ) 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 work, we present a novel kSZ$\times$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 $\sim 8$ ($\sim 31$) for a configuration corresponding to Atacama Cosmology Telescope DR6 (Simons Observatory) CMB data combined with spectroscopic galaxy samples from DESI. This approach will enable the first tomographic measurements of the electron auto-power spectrum, providing new constraints on feedback-driven redistribution of baryons and its role in shaping cosmic structure.

12 pages, 4 figures. Comments are welcome!

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