Cosmology Seminar - Detecting Patchy Screening of the Cosmic Microwave Background

As cosmic microwave background (CMB) photons propagate through the Universe, their interactions with matter imprint various properties of the matter onto the CMB. These imprints can probe otherwise difficult to measure baryons such as the ionized gas around galaxies, which is too cool to emit X-rays and does not have optical/IR tracer light (i.e. stars). Patchy screening, the net effect of CMB photons Thomson scattering into and out of the line of sight, can directly probe the density profile of this gas. Measuring this effect does not require redshift information and thus is complementary to other gas probes like the thermal and kinematic Sunyaev-Zel'dovich effects. In this talk, I will introduce a new patchy screening estimator we have derived that is robust to biases from lensing and extragalactic foregrounds. I will then describe our analysis using this new estimator with data from the Atacama Cosmology Telescope and unWISE galaxy catalog to measure patchy screening at >7 sigma significance, the first detection of the effect. Our measurement of the average gas density profile around unWISE galaxies provides further evidence that the circumgalactic gas is more extended than the underlying dark matter distribution and, with further modeling, has the power to constrain baryonic feedback models, a major uncertainty in hydrodynamical simulations and optical weak lensing analyses. Finally, I will present detection forecasts for future CMB and large-scale structure surveys, including CMB-S4 and Rubin LSST, which show patchy screening will be a powerful probe of small-scale baryonic physics and cosmological parameters.