Spin Parity of Spiral Galaxies. I. Corroborative Evidence for Trailing Spirals

Iye, Masanori; Tadaki, Ken-ichi; Fukumoto, Hideya

doi:10.3847/1538-4357/ab4a18

Cited by 23 publications

(15 citation statements)

References 194 publications

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“…Let galaxy C be a face-on spiral galaxy rotating in the same direction as galaxy A, but located in the opposite hemisphere to A relative to the Milky Way. The spin patterns of a galaxy is normally expected to agree with its actual direction of rotation (Iye et al 2019). While galaxies A and C rotate in the same direction, their spin pattern will seem opposite to an Earth-based observer.…”

Section: Bandmentioning

confidence: 99%

Asymmetry between galaxies with different spin patterns: A comparison between COSMOS, SDSS, and Pan-STARRS

Shamir

2020

Open Astronomy

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Previous observations of a large number of galaxies show differences between the photometry of spiral galaxies with clockwise spin patterns and spiral galaxies with counterclockwise spin patterns. In this study the mean magnitude of a large number of clockwise galaxies is compared to the mean magnitude of a large number of counterclockwise galaxies. The observed difference between clockwise and counterclockwise spiral galaxies imaged by the space-based COSMOS survey is compared to the differences between clockwise and counterclockwise galaxies imaged by the Earth-based SDSS and Pan-STARRS around the same field. The annotation of clockwise and counterclockwise galaxies is a fully automatic process that does not involve human intervention, and in all experiments both clockwise and counterclockwise galaxies are separated from the same fields. The comparison shows that the same asymmetry was identified by all three telescopes, providing strong evidence that the rotation direction of a spiral galaxy is linked to its luminosity as measured from Earth. Analysis of the luminosity difference using a large number of galaxies from different parts of the sky shows that the difference between clockwise and counterclockwise galaxies changes with the direction of observation, and oriented around an axis.

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Section: Bandmentioning

confidence: 99%

Asymmetry between galaxies with different spin patterns: A comparison between COSMOS, SDSS, and Pan-STARRS

Shamir

2020

Open Astronomy

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“…The winding direction of spiral arms with respect to the galaxy rotation direction has also been a classic subject of controversial debates in observational and theoretical studies of spiral galaxies until around the decade of the 1960s. Iye et al (2019) demonstrate a corroborative evidence that ⋆ E-mail: tadaki.ken@nao.ac.jp all galaxies are trailing spirals provided that the dark lane dominant side is the side of the disk near to us. Once the winding direction of spiral arms is identified, we can infer the spin vector of galaxies, which is one of important physical properties in the process of galaxy formation.…”

Section: Introductionmentioning

confidence: 55%

Spin Parity of Spiral Galaxies II: A catalogue of 80k spiral galaxies using big data from the Subaru Hyper Suprime-Cam Survey and deep learning

Tadaki,

Iye,

Fukumoto

et al. 2020

Preprint

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We report an automated morphological classification of galaxies into S-wise spirals, Zwise spirals, and non-spirals using big image data taken from Subaru/Hyper Suprime-Cam (HSC) Survey and a convolutional neural network(CNN)-based deep learning technique. The HSC i-band images are about 25 times deeper than those from the Sloan Digital Sky Survey (SDSS) and have a two times higher spatial resolution, allowing us to identify substructures such as spiral arms and bars in galaxies at z > 0.1. We train CNN classifiers by using HSC images of 1447 S-spirals, 1382 Z-spirals, and 51,650 non-spirals. As the number of images in each class is unbalanced, we augment the data of spiral galaxies by horizontal flipping, rotation, and rescaling of images to make the numbers of three classes similar. The trained CNN models correctly classify 97.5% of the validation data, which is not used for training. We apply the CNNs to HSC images of a half million galaxies with an i-band magnitude of i < 20 over an area of 320 deg 2 . 37,917 S-spirals and 38,718 Z-spirals are identified, indicating no significant difference between the numbers of two classes. Among a total of 76,635 spiral galaxies, 48,576 are located at z > 0.2, where we are hardly able to identify spiral arms in the SDSS images. Our attempt demonstrates that a combination of the HSC big data and CNNs has a large potential to classify various types of morphology such as bars, mergers and strongly-lensed objects.

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“…It has been generally believed that the spiral structure of galaxies is in general "trailing" rather than "leading." Iye et al (2019) found corroborative evidence from their survey of 146 spiral galaxies that all spiral structure in these galaxies is indeed "trailing." This confirmation provides a basis for us to use the spiral winding direction projected on the sky, either S-wise spirals or Z-wise spirals, to judge the sign of the line-of-sight component Ω d of a galaxy's spin vector.…”

Section: Introductionmentioning

confidence: 58%

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

Iye,

Yagi,

Fukumoto

2020

Preprint

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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 (2017a) 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-spirals, 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 does 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.

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Spin Parity of Spiral Galaxies. I. Corroborative Evidence for Trailing Spirals

Cited by 23 publications

References 194 publications

Asymmetry between galaxies with different spin patterns: A comparison between COSMOS, SDSS, and Pan-STARRS

Asymmetry between galaxies with different spin patterns: A comparison between COSMOS, SDSS, and Pan-STARRS

Spin Parity of Spiral Galaxies II: A catalogue of 80k spiral galaxies using big data from the Subaru Hyper Suprime-Cam Survey and deep learning

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

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