Cosmic web dependence of galaxy clustering and quenching in SDSS

Abstract

Galaxies exhibit different clustering and quenching properties in clusters, filaments, and the field, but it is still uncertain whether such differences are imprints of the tidal environment on galaxy formation, or if they reflect the variation of the underlying halo mass function across the cosmic web. We measure the dependence of galaxy clustering and quenching on the cosmic web in the SDSS, characterized by the combination of overdensity δ8 and tidal anisotropy α 5 centred on each galaxy. We find that galaxy clustering is a strong function of either δ8 or α 5, and the large-scale galaxy bias shows complex and rich behaviour on the δ8 versus α 5 plane. Using the mean galaxy colour as a proxy for the average quenched level of galaxies, we find that galaxy quenching is primarily a function of δ8, with some subtle yet non-trivial dependence on α 5 at fixed δ8. We compare these observed cosmic web dependences of galaxy clustering and quenching with a mock galaxy catalogue constructed from the iHOD model, which places quenched and star-forming galaxies inside dark matter haloes based on the stellar-to-halo mass relation and the halo quenching model - the δ8 and α 5 dependences of iHOD galaxies are thus solely derived from the cosmic web modulation of the halo mass function. The main observed trends are accounted for extremely well by the iHOD model. Thus, any additional direct effect of the large-scale (>5h-1,Mpc) tidal field on galaxy formation must be extremely weak in comparison with the dominant indirect effects that arise from the environmental modulation of the halo mass function.