Asymmetry in Galaxy Spin Directions—Analysis of Data from DES and Comparison to Four Other Sky Surveys

Shamir, Lior

doi:10.3390/universe8080397

Cited by 9 publications

(35 citation statements)

References 266 publications

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“…As a model-driven method, it is not based on any kind of machine learning, and therefore it is not subjected to possible biases in the training data. The simple "mechanical" nature of Ganalyzer allows it to be fully symmetric (Shamir, 2021b(Shamir, , 2022c.…”

Section: Datamentioning

confidence: 99%

“…Previous work using different telescopes showed that the spin directions of spiral galaxies form a statistically significant large-scale axis (Shamir, 2022b). That was done by fitting the spin directions to the cosine of the angle between the galaxies and every possible integer (α, δ) combination in the sky (Shamir, 2022c), as shown by Equation 1χ…”

Section: Identification Of a Possible Dipole Axis Alignmentmentioning

confidence: 99%

“…If more counterclockwise galaxies are selected as spiral galaxies compared to clockwise galaxies, that will result in a dataset that has a higher number of counterclockwise galaxies. In previous work the bias was addressed by comparing the distribution in two opposite hemispheres (Shamir, 2020c(Shamir, , 2021b(Shamir, ,a, 2022c. In these experiments, the galaxies were separated into two hemispheres such that one hemisphere showed a higher number of galaxies spinning clockwise, and the opposite hemisphere showed a higher number of galaxies spinning counterclockwise.…”

Section: Analysis Of Possible Algorithm Biasmentioning

confidence: 99%

“…In the SDSS galaxies with spectra used in Galaxy Zoo 1, the vast majority of the galaxies are concentrated in one hemisphere, with very few galaxies in the opposite hemisphere as shown in Figure 1. The absence of galaxies in two opposite hemispheres makes it difficult to apply the same analysis as done in (Shamir, 2020c(Shamir, , 2021b(Shamir, ,a, 2022c, and the example shown in Table 4.…”

Section: Analysis Of Possible Algorithm Biasmentioning

confidence: 99%

“…In addition to SDSS, other telescopes also showed parity violation in the distribution of the spin direction of spiral galaxies. These include Pan-STARRS (Shamir, 2020c), DECam (Shamir, 2021b), Hubble Space Telescope (Shamir, 2020b), the Dark Energy Survey (Shamir, 2022c), and the DESI Legacy Survey (Shamir, 2022b). These telescopes cover both the Northern and Southern hemispheres, and the Hubble Space Telescope provides analysis that is not subjected to a possible effect of the atmosphere.…”

Section: Introductionmentioning

confidence: 99%

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Reanalysis of the spin direction distribution of Galaxy Zoo SDSS spiral galaxies

McAdam¹,

Shamir²

2023

Preprint

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The distribution of the spin directions of spiral galaxies in the Sloan Digital Sky Survey has been a topic of debate in the past two decades, with conflicting conclusions reported even in cases where the same data was used. Here we follow one of the previous experiments by applying the SpArcFiRe algorithm to annotate the spin directions in original dataset of Galaxy Zoo 1. The annotation of the galaxy spin directions is done after a first step of selecting the spiral galaxies in three different manners: manual analysis by Galaxy Zoo classifications, by a model-driven computer analysis, and with no selection of spiral galaxies. The results show that when spiral galaxies are selected by Galaxy Zoo volunteers, the distribution of their spin directions as determined by SpArcFiRe is not random, which agrees with previous reports. When selecting the spiral galaxies using a model-driven computer analysis or without selecting the spiral galaxies at all, the distribution is also not random. Simple binomial distribution analysis shows that the probability of the parity violation to occur by chance is lower than 0.01. Fitting the spin directions as observed from Earth to cosine dependence exhibits a dipole axis with statistical strength of 2.33σ to 3.97σ. These experiments show that regardless of the selection mechanism and the analysis method, all experiments show similar conclusions. These results are aligned with previous reports using other methods and telescopes, suggesting that the spin directions of spiral galaxies as observed from Earth exhibit a dipole axis formed by their spin directions. Possible explanations can be related to the large-scale structure of the Universe, or to internal structure of galaxies. The catalogs of annotated galaxies generated as part of this study are available.

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Section: Datamentioning

confidence: 99%

Section: Identification Of a Possible Dipole Axis Alignmentmentioning

confidence: 99%

Section: Analysis Of Possible Algorithm Biasmentioning

confidence: 99%

Section: Analysis Of Possible Algorithm Biasmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Reanalysis of the spin direction distribution of Galaxy Zoo SDSS spiral galaxies

McAdam¹,

Shamir²

2023

Preprint

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Galaxy spin direction asymmetry in JWST deep fields

Shamir

2024

Publ. Astron. Soc. Aust.

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The unprecedented imaging power of JWST provides new abilities to observe the shapes of objects in the early Universe in a way that has not been possible before. Recently, JWST acquired a deep field image inside the same field imaged in the past as the HST Ultra Deep Field. Computer-based quantitative analysis of spiral galaxies in that field shows that among 34 galaxies for which their rotation of direction can be determined by the shapes of the arms, 24 rotate clockwise, and just 10 rotate counterclockwise. The one-tailed binomial distribution probability to have asymmetry equal or stronger than the observed asymmetry by chance is ∼0.012. While the analysis is limited by the small size of the data, the observed asymmetry is aligned with all relevant previous large-scale analyses from all premier digital sky surveys, all show a higher number of galaxies rotating clockwise in that part of the sky, and the magnitude of the asymmetry increases as the redshift gets higher. This paper also provides data and analysis to reproduce previous experiments suggesting that the distribution of galaxy rotation in the Universe is random, to show that the exact same data used in these studies in fact show non-random distribution, and in excellent agreement with the results shown here. These findings reinforce consideration of the possibility that the directions of rotation of spiral galaxies as observed from Earth are not necessarily randomly distributed. The explanation can be related to the large-scale structure of the Universe, but can also be related to a possible anomaly in the physics of galaxy rotation.

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Using 3D and 2D analysis for analyzing large-scale asymmetry in galaxy spin directions

Shamir

2022

Publications of the Astronomical Society of Japan

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The nature of galaxy spin is still not fully known. Iye, Yagi, and Fukumoto (2021, AJ, 907, 123) applied a 3D analysis to a dataset of bright SDSS galaxies that was used in the past for photometric analysis. They showed that the distribution of spin directions of spiral galaxies is random, providing a dipole axis with low statistical significance of 0.29σ. However, to show random distribution, two decisions were made, each of which can lead to random distribution regardless of the real distribution of the spin direction of galaxies. The first decision was to limit the dataset arbitrarily to z < 0.1, which is a redshift range in which previous literature already showed that random distribution is expected. More importantly, while the 3D analysis requires the redshift of each galaxy, the analysis was done with the photometric redshift. If the asymmetry existed, its signal is expected to be an order of magnitude weaker than the error of the photometric redshift, and therefore a low statistical signal under these conditions is expected. When using the exact same data without limiting to zphot < 0.1 and without using the photometric redshift, the distribution of the spin directions in that dataset shows a statistical signal of >2σ. Code and data for reproducing the analysis are publicly available. These results are in agreement with other experiments with SDSS, Pan-STARRS, HST, and the DESI Legacy Survey. The paper also examines other previous studies that showed random distribution in galaxy spin directions. While further research will be required, the current evidence suggests that large-scale asymmetry between the number of clockwise and counterclockwise galaxies cannot be ruled out.

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Asymmetry in Galaxy Spin Directions—Analysis of Data from DES and Comparison to Four Other Sky Surveys

Cited by 9 publications

References 266 publications

Reanalysis of the spin direction distribution of Galaxy Zoo SDSS spiral galaxies

Reanalysis of the spin direction distribution of Galaxy Zoo SDSS spiral galaxies

Galaxy spin direction asymmetry in JWST deep fields

Using 3D and 2D analysis for analyzing large-scale asymmetry in galaxy spin directions

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