We introduce a new estimator for the mean pairwise velocities of galaxy clusters , which is based on the measurement of the clusters ’ transverse velocity components .
The Rees-Sciama ( RS ) effect offers an opportunity to measure transverse peculiar velocities through its distinct dipolar signature around the halo centers in the Cosmic Microwave Background ( CMB ) temperature map .
We exploit this dipolar structure to extract the magnitude and direction of the transverse velocity vectors from CMB maps simulated with the expected characteristics of future surveys like CMB-S4 .
Although in the presence of lensed CMB and instrumental noise individual velocities are not reliably reconstructed , we demonstrate that the mean pairwise velocity measurement obtained using the estimator yields a signal-to-noise ratio of 5.2 for \sim 21 , 000 halos with M > 7 \times 10 ^ { 13 } M _ { \odot } in a 40 \times 40 [ deg ^ { 2 } ] patch at z = 0.5 .
While the proposed estimator carries promising prospects for measuring pairwise velocities through the RS effect in CMB stage IV experiments , its applications extend to any other potential probe of transverse velocities .