On the Capability of High Redshift Ksz Measurement with Galaxy Surveys

The kSZ effect has been detected at z<1 using various techniques and datasets. The ongoing and upcoming spectroscopic galaxy surveys such as DESI andPFS will push the detection beyond z = 1, and therefore map the baryondistribution at high redshifts. Such detection can be achieved by both the kSZstacking and tomography methods. While the two methods are theoreticallyequivalent, they differ significantly in the probed physics and scales, andrequired data sets. Taking the combination of PFS and ACT as an example, webuild mocks of kSZ and galaxies, quantify the kSZ detection S/N, and comparebetween the two methods. We segment the PFS galaxies into three redshift bins:0.6 < z < 1.0, 1.0 < z < 1.6, and 1.6 < z < 2.4. For tomography method, ouranalysis reveals that the two higher redshift bins exhibit higher S/N, withvalues of 32 and 28, respectively, compared to the first redshift bin (S/N =8). This is attributed to not only the increasing of electron density withredshifts, but also the larger survey volume and the reduced non-linearity,facilitating velocity reconstruction at higher redshifts. Therefore, thecapability of the PFS survey to measure high redshift kSZ effect stands as asubstantial advantage over other spectroscopic surveys at lower redshift. TheS/N of kSZ stacking largely depends on the number of clusters/groups availablefrom another photometric survey. But in general, its S/N is lower than that ofkSZ tomography. Incorporating next-generation CMB surveys like CMB-S4,characterized by significantly reduced instrument noise and improved angularresolution, is expected to enhance tomographic detection by a factor of ten andstacking detection by five. This future high S/N detection holds the promise ofnot only providing precise constraints on the overall baryon abundance but alsoinitiating a new insight into baryon distribution.