# Probing gaseous galactic halos through the rotational kSZ effect

Authors
Publication Date
Sep 10, 2019
Source
INSPIRE-HEP
Keywords
The rotational kinematic Sunyaev-Zeldovich (rkSZ) signal, imprinted on the cosmic microwave background (CMB) by the gaseous halos of foreground galaxies, would be a novel probe of galaxy formation. Although the signal is too weak to detect in individual galaxies, we analyze the feasibility of its statistical detection via stacking CMB data on many galaxies for which the spin orientation can be estimated spectroscopically. We use an "optimistic" model, in which fully ionized atmospheres contain the cosmic baryon fraction and spin at the halo's circular velocity $v_{\rm circ}$, and a more realistic model, with multi-phase atmospheres spinning at a fraction of $v_{\rm circ}$. We incorporate realistic noise estimates into our analysis. Using low-redshift galaxy properties from the MaNGA spectroscopic survey (with median halo mass of $6.6\times10^{11}\,M_{\odot}$), and CMB data quality from Planck, we find that a $3\sigma$ detection would require $\gtrsim 10^6$ galaxies. This is too high for current surveys, but higher-angular resolution future CMB experiments will significantly reduce the requirements: stacking CMB data on galaxy spins in a few$\times10$ deg$^2$ can rule out the optimistic models, and $\approx$1,300 deg$^2$ will suffice for a $3\sigma$ detection with CMB-S4 experiments. As a proof-of-concept, we stacked Planck data on the position of $\approx2,000$ MaNGA galaxies. We rule out average temperature dipoles larger than $\approx5.7 \mu$K. Restricted to spiral galaxies outside clusters, we find a hint of a temperature dipole of 2.3$\mu$K (at $\approx2\sigma$). This value is two orders of magnitude larger than the expected rkSZ signal, but if the detection is confirmed in future data to be real, it could be explained by Doppler-shifted emission from dust that is kinematically coupled to the gas.