How does the cosmic web impact assembly bias?

Abstract

The mass, accretion rate and formation time of dark matter haloes near\nproto-filaments (identified as saddle points of the potential) are analytically\npredicted using a conditional version of the excursion set approach in its\nso-called "upcrossing" approximation. The model predicts that at fixed mass,\nmass accretion rate and formation time vary with orientation and distance from\nthe saddle, demonstrating that assembly bias is indeed influenced by the tides\nimposed by the cosmic web. Starved, early forming haloes of smaller mass lie\npreferentially along the main axis of filaments, while more massive and younger\nhaloes are found closer to the nodes. Distinct gradients for distinct tracers\nsuch as typical mass and accretion rate occur because the saddle condition is\nanisotropic, and because the statistics of these observables depend on both the\nconditional means and their covariances. The theory is extended to other\ncritical points of the potential field. The response of the mass function to\nvariations of the matter density field (the so-called large scale bias) is\ncomputed, and its trend with accretion rate is shown to invert along the\nfilament. The signature of this model should correspond at low redshift to an\nexcess of reddened galactic hosts at fixed mass along preferred directions, as\nrecently reported in spectroscopic and photometric surveys and in\nhydrodynamical simulations. The anisotropy of the cosmic web emerges therefore\nas a significant ingredient to describe jointly the dynamics and physics of\ngalaxies, e.g. in the context of intrinsic alignments or morphological\ndiversity.\n