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 Sloan Digital Sky Survey, characterized by the combination of spherical overdensity $δ_8$ and tidal anisotropy $α_5$ centred on each galaxy. We find that galaxy clustering is a strong function of either $δ_8$ or $α_5$, and the large-scale galaxy bias shows complex and rich behaviour on the $δ_8$ vs. $α_5$ 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 $δ_8$, with some subtle yet non-trivial dependence on $α_5$ at fixed $δ_8$. The quenched galaxies generally show stronger small-scale clustering than the star-forming ones at fixed $δ_8$ or $α_5$, while the characteristic scale at which the amplitude of clustering becomes comparable for both galaxy populations varies with $δ_8$ and $α_5$. 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 $δ_8$ 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~(${>}5\,h^{-1}{\rm Mpc}$) tidal field on galaxy formation must be extremely weak. [Abridged]