The effects of galaxy assembly bias on the inference of growth rate from redshift-space distortions

The large-scale redshift-space distortion (RSD) in galaxy clustering can probe fσ₈, a combination of cosmic structure growth rate and matter fluctuation amplitude, which can constrain dark energy models and test theories of gravity. While the RSD on small scales (e.g. a few to tens of h^{-1} {Mpc}) can further tighten the fσ₈ constraints, galaxy assembly bias, if not correctly modelled, may introduce systematic uncertainties. Using a mock galaxy catalogue with built-in assembly bias, we perform a preliminary study on how assembly bias may affect the fσ₈ inference. We find good agreement on scales down to 8-9 h^{-1} {Mpc} between a fσ₈ metric from the redshift-space two-point correlation function with the central-only mock catalogue and that with the shuffled catalogue free of assembly bias, implying that fσ₈ information can be extracted on such scales even with assembly bias. We then apply the halo occupation distribution (HOD) and three subhalo clustering and abundance matching (SCAM) models to model the redshift-space clustering with the mock. Only the SCAM model based on V_peak (used to create the mock) can reproduce the fσ₈ metric, and the other three could not. However, the fσ₈ metrics determined from central galaxies from all the models are able to match the expected one down to 8 h^{-1} {Mpc}. Our results suggest that halo models with no or an incorrect assembly bias prescription could still be used to model the RSD down to scales of 8 h^{-1} {Mpc} to tighten the fσ₈ constraint, with a sample of central galaxies or with a flexible satellite occupation prescription.