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The kinematic Sunyaev-Zel'dovich (kSZ) effect --- the Doppler boosting ofcosmic microwave background (CMB) photons due to Compton-scattering off freeelectrons with non-zero bulk velocity --- probes the abundance and distributionof baryons in the Universe. All kSZ measurements to date have explicitlyrequired spectroscopic redshifts. Here, we implement a novel estimator for thekSZ -- large-scale structure cross-correlation based on projected fields: itdoes not require redshift estimates for individual objects, allowing kSZmeasurements from large-scale imaging surveys. We apply this estimator tocleaned CMB temperature maps constructed from Planck and Wilkinson MicrowaveAnisotropy Probe data and a galaxy sample from the Wide-field Infrared SurveyExplorer (WISE). We measure the kSZ effect at 3.8-4.5$\sigma$ significance,depending on the use of additional WISE galaxy bias constraints. We verify thatour measurements are robust to possible dust emission from the WISE galaxies.Assuming the standard $\Lambda$CDM cosmology, we directly constrain $({f_{b}}/{0.158} ) ( {f_{\rm free}}/{1.0} ) = 1.48 \pm 0.19$ (statistical erroronly) at redshift $z \approx 0.4$, where $f_{b}$ is the fraction of matter inbaryonic form and $f_{\rm free}$ is the free electron fraction. This is thetightest kSZ-derived constraint reported to date on these parameters. Theconsistency between the $f_{b}$ value found here and the values inferred fromanalyses of the primordial CMB and Big Bang nucleosynthesis verifies thatbaryons approximately trace the dark matter distribution down to $\sim$Mpcscales. While our projected-field estimator is already competitive with otherkSZ approaches when applied to current datasets (because we are able to use thefull-sky WISE photometric survey), it will yield enormous signal-to-noise whenapplied to upcoming high-resolution, multi-frequency CMB surveys.

The Kinematic Sunyaev-Zel'dovich Effect with Projected Fields: A Novel Probe of the Baryon Distribution with Planck, WMAP, and WISE Data