A measurement of gas rotation in galaxy groups via the kinetic Sunyaev-Zeldovich effect

TL;DR

This study measures the rotation of ionised gas in galaxy groups using the kinetic Sunyaev-Zeldovich effect, revealing a coherent rotational signal consistent with simulations and estimating typical rotational velocities around 100-200 km/s.

Contribution

First detection of the rotational kinetic Sunyaev-Zeldovich effect in galaxy groups using SDSS and Planck data, providing new insights into gas dynamics within galaxy clusters.

Findings

Detected a 2.3σ rotational kSZ signal in SDSS galaxy groups.

Estimated average rotational velocities of 100-200 km/s.

Results align with predictions from cosmological simulations.

Abstract

We utilise the kinetic Sunyaev-Zeldovich effect (kSZ) to measure the rotation of ionised gas within galaxy groups defined in the SDSS-DR7 galaxy sample, via their dipolar imprint on the cosmic microwave background (CMB). We estimate the direction of the projected angular momentum for each group by measuring the redshift dipole of satellite galaxies around their group centre. We find a clear redshift dipole in the stacked data for the SDSS groups. We then perform oriented stacking of the Planck CMB temperature map using the group centres and directions of angular momenta. We report a $2.3\sigma$ measurement of the coherent rotational kSZ effect (rkSZ) within the virial radii of SDSS groups with an average mass of $10^{14}h^{-1} \rm M_{\odot}$. We estimate the averaged rotational velocity of the sample to be $\sim 100-200 ~\rm km ~s^{-1}$, peaking at approximately half the virial radius. Our results are consistent within the errors with predictions based on the ELUCID constrained realisation simulation, with the predicted amplitude of the rkSZ signal being slightly lower near the centre. We also identify a systematic bias when estimating rotational velocities using the observed redshifts of galaxies, but find it to be subdominant for our analysis.