Abstract:

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–Zeldovich (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. At the same time, the pairwise kSZ
measures the distribution of cluster gas, providing constraints on
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 in 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.