MUFASA: The strength and evolution of galaxy conformity in various tracers

Abstract

We investigate galaxy conformity using the Mufasa cosmological hydrodynamical simulation. We show a bimodal distribution in galaxy colour with radius, albeit with too many low-mass quenched satellite galaxies compared to observations. Mufasa produces conformity in observed properties such as colour, sSFR, and Hi content; i.e neighbouring galaxies have similar properties. We see analogous trends in other properties such as in environment, stellar age, H2 content, and metallicity. We intro- duce quantifying conformity using S(R), measuring the relative difference in upper and lower quartile properties of the neighbours.We show that low-mass and non-quenched haloes have weak conformity (S(R) < 0.5) extending to large projected radii R in all properties, while high-mass and quenched haloes have strong conformity (S(R) ~ 1) that diminishes rapidly with R and disappears at R & 1 Mpc. S(R) is strongest for environment in low-mass haloes, and sSFR (or colour) in high-mass haloes, and is dominated by one-halo conformity with the exception of Hi in small haloes. Metal- licity shows a curious anti-conformity in massive haloes. Tracking the evolution of conformity for z = 0 galaxies back in time shows that conformity broadly emerges as a late-time (z < 1) phenomenon. However, for fixed halo mass bins, conformity is fairly constant with redshift out to z > 2. These trends are consistent with the idea that strong conformity only emerges once haloes grow above Mufasa’s quenching mass scale of ~ 1012M⊙. A quantitative measure of conformity in various properties, along with its evolution, thus represents a new and stringent test of the impact of quenching on environment within current galaxy formation models.