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The tidal field as a mediator between dark matter halo spin and its large-scale bias

Grant number: 20/10520-5
Support type:Scholarships in Brazil - Master
Effective date (Start): November 01, 2020
Effective date (End): October 31, 2022
Field of knowledge:Physical Sciences and Mathematics - Astronomy - Extragalactic Astrophysics
Principal researcher:Luis Raul Weber Abramo
Grantee:Beatriz Tucci Schiewaldt
Home Institution: Instituto de Física (IF). Universidade de São Paulo (USP). São Paulo , SP, Brazil


The dependence of dark matter halo bias on spin at fixed mass is known as spin bias. However, although at the high-mass end the higher-spin halos have a higher bias than their lower-spin counterparts, this trend inverts for low-mass halos. This complex scenario was recently clarified by the student, who found that this inversion of the mass dependence of spin bias can be completely explained by the population of splashback halos -- i.e., halos that at some point in the past fell inside the virial radius of another halo (typically, a larger-mass halo), but then exited that parent halo. This dependence of spin bias on splashback halos was first explained by the student during her undergraduate research project (Iniciação Científica with FAPESP fellowship, Proc. 2018/17688-9), and has recently become a paper (Tucci et al, 2020, submitted to MNRAS). What the student found is that, when this specific population is excluded from the sample, only the intrinsic spin bias signal remains, i.e., a higher bias for higher-spin halos. The goal of this project is to shed light onto the physical origins of the intrinsic spin bias, by using the tidal field (one of the properties of the halo environment) as the mediator between halo spin and halo bias. In order to connect halo spin to its bias in a single analytical framework, we will investigate the role of the tidal field in determining halo angular momentum, as well as the connection of the tidal field with the large-scale bias. We will also explore how this mechanism, which is more readily studied via halos in N-body simulations, can be extended to galaxies in the context of the halo-galaxy connection framework and galaxy formation. Finally, we will study possible consequences for observational cosmology. (AU)

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