Observational Cosmology Seminar

The bulk motion of ionized gas in galaxy clusters imprints a small Doppler shift on the cosmic microwave background (CMB), known as the kinematic Sunyaev–Zel'dovich (kSZ) effect. This signal is proportional to both the peculiar velocity of the cluster and the amount of gas it contains. An effective way to extract this signal is through the pairwise kSZ effect, which leverages the fact that pairs of clusters tend to fall towards each other under gravity. The resulting measurement probes the mean pairwise velocity, which is sensitive to the growth of cosmic structure, while simultaneously constraining the gas distribution, which is sensitive to baryonic feedback physics.
Optically selected galaxy clusters trace the massive end of the halo mass function, which dominates the feedback suppression on cosmological observables such as weak lensing. However, previous pairwise kSZ measurements on these samples were substantially limited by uncertainties of photometric redshifts, especially at small scales (<50 Mpc). With spectroscopic data from large surveys such as the Dark Energy Spectroscopic Instrument (DESI), this limitation can now be overcome. In this talk, I will present a pairwise kSZ measurement using optical clusters with spectroscopic redshifts, combining data from the Legacy Survey, DESI, and the Atacama Cosmology Telescope. We detect the signal with a significance above 6 sigma, and measure the average optical depth profile of clusters out to 4 arcmin. Finally, I will compare these measurements to mock clusters constructed from the Magneticum hydrodynamical simulations, showing that the observed gas profile is consistent with the simulation predictions, and discuss the implications for baryonic feedback in massive halos.