  We explore the potential of the kinetic Sunyaev-Zel'dovich (kSZ) effect as
the cornerstone of a future observational probe for halo spin bias, the
secondary dependence of halo clustering on halo spin at fixed halo mass. Using
the IllustrisTNG magneto-hydrodynamical cosmological simulation, we measure
both the kSZ and the thermal SZ (tSZ) effects produced by the baryonic content
of more than 50,000 haloes within the halo mass range $11 < \log_{10} ({\rm
M_{vir}}/ h^{-1} {\rm M_{\odot}}) \lesssim 14.5$. First, we confirm that the
magnitude of both effects depends strongly on the total gas and virial mass of
the haloes, and that the integrated kSZ signal displays a significant
correlation with the angular momentum of the intra-halo gas, particularly for
massive haloes. Second, we show that both the integrated kSZ signal and the
ratio of the integrated kSZ and tSZ signals trace total halo spin, even though
significant scatter exists. Finally, we demonstrate that, in the absence of
observational and instrumental uncertainties, these SZ-related statistics can
be used to recover most of the underlying IllustrisTNG halo spin bias signal.
Our analysis represents the first attempt to develop a future observational
probe for halo spin bias, bringing forward alternative routes for measuring the
secondary bias effects.
