Spin Parity of Spiral Galaxies VI -- A Search for Dynamical Memory in the Spin Distribution of Galaxies in HSC WIDE Survey Regions

TL;DR

This study investigates the distribution of spiral galaxy spin parity in the HSC WIDE survey, finding it consistent with randomness and supporting the standard cosmological model.

Contribution

It provides the first large-scale statistical analysis of spiral galaxy spin parity distribution, testing for dynamical memory in galaxy spins.

Findings

The distribution of S/Z spiral parity matches random expectations.

No significant evidence for non-random spin alignment was found.

Results support the standard cosmological model of structure formation.

Abstract

We analyzed the distribution of spin parity in spiral galaxies using the HSC DR2 data. The spiral winding parity of disk galaxies, observed as S-spiral or Z-spiral projected onto the sky plane, provides robust information on the sign of the line-of-sight component of their spin vectors, specifically whether the spin vector points toward or away from us. The distribution of 49,494 S/Z annotated spirals with spectroscopic redshift (0.05 $\le z$) was analyzed for 46,247 fiducial cubic search volumes of various sizes, 20--200 Mpc, deployed in the 3D supergalactic coordinates. We counted the number of S-spirals and Z-spirals in each cube, evaluated the binomial probability of the observed S/Z imbalance, and identified statistically anomalous cube candidates. The observed cumulative distribution functions for the 256 sets of cubes are in good agreement with the theoretical binomial distribution and with those obtained from 1000 Monte Carlo realizations assuming random S/Z spin assignments. The number of statistically anomalous cubes is also comparable to that expected from the random assignments. These results indicate that the spin-vector distribution of spiral galaxies is consistent with statistical randomness expected from the standard cosmological model of structure formation.