Halo Spin Dependence on Environment for HI-bearing galaxies

TL;DR

This study investigates how the spin of dark matter halos hosting HI-rich galaxies varies with environment, revealing a subtle decrease in halo spin in denser regions, contrasting with prior simulation results.

Contribution

It introduces a semi-analytic approach to measure halo spins for HI galaxies and highlights environmental effects on halo spin, challenging previous simulation-based assumptions.

Findings

Halo spin decreases in denser environments.

Discrepancy with N-body simulation results.

Environmental gas stripping affects halo spin measurements.

Abstract

Leveraging the semi-analytic method, we compute halo spins for a substantial sample of HI-bearing galaxies observed in the Arecibo Legacy Fast Alfa Survey. Our statistical analysis reveals a correlation between halo spin and environment, although the trend is subtle. On average, galaxies exhibit a decreasing halo spin tendency in denser environments. This observation contrasts with previous results from $N$-body simulations in the Lambda cold dark matter framework. The discrepancy may be attributed to environmental gas stripping, leading to an underestimation of halo spins in galaxies in denser environments, or to baryonic processes that significantly alter the original dark matter halo spins, deviating from previous $N$-body simulation findings.