Galaxy spin direction distribution in HST and SDSS show similar large-scale asymmetry

TL;DR

This study compares galaxy spin direction asymmetries in HST and SDSS datasets, revealing a consistent large-scale dipole asymmetry in galaxy orientations across different surveys and redshift ranges.

Contribution

It demonstrates a similar large-scale asymmetry in galaxy spin directions in both HST and SDSS datasets, suggesting a potential universal cosmic anisotropy.

Findings

Both datasets show a significant dipole asymmetry in galaxy spin directions.

The most likely dipole axes are within 10 degrees of each other.

Asymmetry is consistent across different redshift ranges and observation methods.

Abstract

Several recent observations using large datasets of galaxies showed non-random distribution of the spin directions of spiral galaxies, even when the galaxies are too far from each other to have gravitational interaction. Here, a dataset of $\sim8.7\cdot10^3$ spiral galaxies imaged by Hubble Space Telescope is used to test and profile a possible asymmetry between galaxy spin directions. The asymmetry between galaxies with opposite spin directions is compared to the asymmetry of galaxies from the Sloan Digital Sky Survey. The two datasets contain different galaxies at different redshift ranges, and each dataset was annotated using a different annotation method. The results show that both datasets show a similar asymmetry in the COSMOS field, which is covered by both telescopes. Fitting the asymmetry of the galaxies to cosine dependence shows a dipole axis with probabilities of $\sim2.8\sigma$ and $\sim7.38\sigma$ in HST and SDSS, respectively. The most likely dipole axis identified in the HST galaxies is at $(\alpha=78^o,\delta=47^o)$, and is well within the $1\sigma$ error range compared to the location of the most likely dipole axis in the SDSS galaxies with $z>0.15$, identified at $(\alpha=71^o,\delta=61^o)$.