Halo Spin Depends on The Distance to Large-scale Filament

TL;DR

The paper addresses whether dark matter halo spin correlates with proximity to cosmic filaments by applying a semi-analytical halo-spin estimator to ~3{,}300 HI-rich galaxies from ALFALFA. Halo spin is inferred from HI-disk properties under an isothermal-halo assumption, with distances to filaments sourced from the Tempel catalog and mass-distribution matched across environmental bins via a mass-weighting scheme. The main finding is a statistically significant trend: halos nearer to filaments exhibit higher spin, quantified by medians in $\log\lambda_{\rm h}$ shifting from about $-2.20$ (far from filaments) to $-2.16$ (within $d_{gf}\le 1.0$ Mpc/$h$), with a $\sim4\sigma$ separation between inner and outer bins. This supports the notion that tidal torques from large-scale filaments impact halo angular momentum, consistent with simulation expectations, while acknowledging systematic uncertainties from inclination misalignment that do not erase the detected trend.

Abstract

We employ a semi-analytical methodology to estimate the dark matter halo spin of HI gas-rich galaxies in the Arecibo Legacy Fast Alfa Survey and investigate the relationship between halo spin and the proximity of galaxies to large-scale filaments. We exclude galaxies with low HI signal-to-noise ratios, those potentially influenced by velocity dispersions, and those affiliated with galaxy clusters/groups. Additionally, we apply a mass-weighting technique to ensure consistent mass distribution across galaxy samples at varying distances from filaments. Our analysis reveals, for the first time, a subtle yet statistically significant correlation between halo spin and filament distance in observational data, indicating higher spins closer to filaments. This suggests that the tidal forces exerted by filaments may impact the spin of dark matter halos.

Figures (2)

• Figure 1: The distributions of stellar masses of the galaxy subsamples with $d_{\rm{gf}}\leq 1.0$ Mpc$/h$ (red), $1.0<d_{\rm{gf}}\leq 3.0$ Mpc$/h$ (cyan), and $d_{\rm{gf}}> 3.0$ Mpc$/h$ (blue). Panels a and b correspond to the original galaxy samples and samples after mass-weighting method, respectively.
• Figure 2: The comparison between the halo spin distributions of subsamples with $d_{\rm{gf}}\leq 1.0$ Mpc$/h$ (red), $1.0<d_{\rm{gf}}\leq 3.0$ Mpc$/h$ (cyan), and $d_{\rm{gf}}> 3.0$ Mpc$/h$ (blue). Panels a and b correspond to the results of using optical inclinations and Monte-Carlo-sampled inclinations, respectively. The small $p$-values from K-S tests of comparing the halo spin distributions indicate significant spin distribution differences.