Spin Parity of Spiral Galaxies. III. Dipole Analysis of the Distribution of SDSS Spirals with 3D Random Walk Simulations

Abstract

Observation has not yet determined whether the distribution of spin vectors of galaxies is truly random. It is unclear whether is there any large-scale symmetry-breaking in the distribution of the vorticity field in the universe. Here, we present a formulation to evaluate the dipole component D max of the observed spin distribution, whose statistical significance σ D can be calibrated by the expected amplitude for 3D random walk (random flight) simulations. We apply this formulation to evaluate the dipole component in the distribution of Sloan Digital Sky Survey (SDSS) spirals. Shamir published a catalog of spiral galaxies from the SDSS DR8, classifying them with his pattern recognition tool into clockwise and counterclockwise (Z-spiral and S-spiral, respectively). He found significant photometric asymmetry in their distribution. We have confirmed that this sample provides dipole asymmetry up to a level of σ D = 4.00. However, we also found that the catalog contains a significant number of multiple entries of the same galaxies. After removing the duplicated entries, the number of samples shrunk considerably to 45%. The actual dipole asymmetry observed for the “cleaned” catalog is quite modest, σ D = 0.29. We conclude that SDSS data alone do not support the presence of a large-scale symmetry-breaking in the spin vector distribution of galaxies in the local universe. The data are compatible with a random distribution.

Large-scale asymmetry in galaxy spin directions: evidence from the Southern hemisphere

“…Another difference between the study of Iye et al (2021) and the work done in previous papers (Shamir 2012, 2020a,b) is that Iye et al (2021) reported on random distribution in a subset of the data, limited to . As shown in Shamir (2020b), no statistically significant asymmetry is expected in that redshift range, and in fact all previous attempts to limit the redshift to any value below 0.15 showed random distribution (Shamir 2020b).…”

“…As mentioned in Section 2, in some cases, photometric objects can be part of the same galaxy, and therefore any object that has another object within less than 0.01 was removed from the dataset to ensure that no galaxy is represented more than once. Previously, Iye, Yagi, & Fukumotoi (2021) reported on photometric objects that are part of the same galaxies in the dataset of Shamir (2017b). If that dataset was used for the purpose of profiling asymmetry in the population of clockwise and counterclockwise galaxies, photometric objects that are part of the same galaxy become duplicate objects.…”

“…It is important to mention that unlike the analysis applied here, in which the location of each galaxy is identified by its RA and Dec, Iye et al (2021) applied a 3D analysis, which required each galaxy to have its RA, Dec, and redshift. Because the vast majority of the galaxies used in Shamir (2017b) do not have spectra, Iye et al (2021) used the photometric redshifts taken from the photometric redshift catalogue of Paul, Virag, & Shamir (2018). The error of the photometric redshift in that catalogue is , which is far greater than the expected asymmetry.…”

Large-scale asymmetry in galaxy spin directions: evidence from the Southern hemisphere

“…As mentioned in Section 2, in some cases photometric objects can be part of the same galaxy, and therefore any object that has another object within less than 0.01 o was removed from the dataset to ensure that no galaxy is represented more than once. Previously, Iye et al (2020) reported on photometric objects that are part of the same galaxies in the dataset of (Shamir, 2017c). If that dataset was used for the purpose of profiling asymme-try in the population of clockwise and counterclockwise galaxies, photometric objects that are part of the same galaxy become duplicate objects.…”

“…It is important to mention that unlike the analysis applied here, in which the location of each galaxy is determined by its RA and Dec, Iye et al ( 2020) applied a 3D analysis, which required each galaxy to have its RA, Dec, and redshift. Because the vast majority of the galaxies used in (Shamir, 2017c) do not have spectra, Iye et al (2020) used the photometric redshifts taken from the photometric redshift catalog of (?). The error of the photometric redshift in that catalog is ∼18.5%, which is far greater than the expected asymmetry.…”