Cosmic web dependence of galaxy clustering and quenching in SDSS

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 delta(8) and tidal anisotropy alpha(5) centred on each galaxy. We find that galaxy clustering is a strong function of either delta(8) or alpha(5), and the large-scale galaxy bias shows complex and rich behaviour on the delta(8) versus alpha(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 delta(8), with some subtle yet non-trivial dependence on alpha(5) at fixed delta(8). We compare these observed cosmic web dependences of galaxy clustering and quenching with a mock galaxy catalogue constructed from the i HOD 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 delta(8) and alpha(5) dependences of i HOD 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 i HOD model. Thus, any additional direct effect of the large-scale (>5 h(-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.