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

Abstract

Recent observations using several different telescopes and sky surveys showed patterns of asymmetry in the distribution of galaxies by their spin directions as observed from Earth. These studies were done with data imaged from the Northern hemisphere, showing excellent agreement between different telescopes and different analysis methods. Here, data from the DESI Legacy Survey was used. The initial dataset contains $\sim\!2.2\times 10^7$ galaxy images, reduced to $\sim\!8.1\times 10^5$ galaxies annotated by their spin direction using a symmetric algorithm. That makes it not just the first analysis of its kind in which the majority of the galaxies are in the Southern hemisphere, but also by far the largest dataset used for this purpose to date. The results show strong agreement between opposite parts of the sky, such that the asymmetry in one part of the sky is similar to the inverse asymmetry in the corresponding part of the sky in the opposite hemisphere. Fitting the distribution of galaxy spin directions to cosine dependence shows a dipole axis with probability of 4.66 $\sigma$ . Interestingly, the location of the most likely axis is within close proximity to the CMB Cold Spot. The profile of the distribution is nearly identical to the asymmetry profile of the distribution identified in Pan-STARRS, and it is within 1 $\sigma$ difference from the distribution profile in SDSS and HST. All four telescopes show similar large-scale profile of asymmetry.

New evidence and analysis of cosmological-scale asymmetry in galaxy spin directions

“…The DECam image data was retrieved through the DESI Legacy Survey API (Dey et al, 2019). The description of the dataset and the way it was acquired and annotated is provided in (Shamir, 2021b). In summary, the initial list of objects was taken from Data Release 8 of the DESI Legacy Survey, and included all objects imaged by DECam identified as galaxies, and had magnitude of 19.5 or less in either the g, r or z band.…”

“…Downloading such a high number of galaxies naturally required nine months, from June 4th 2020 to March 4th, 2021. The data is described in (Shamir, 2021b).…”

“…After removing neighboring objects, 807,898 galaxies were left in the dataset. More information about that dataset is provided in (Shamir, 2021b). galaxies.…”

“…The slope of that line indicates the curve of the arms, and consequently the spin directions of the galaxies. More information about Ganalyzer and detailed performance analysis can be found in (Shamir, 2011;Dojcsak and Shamir, 2014;Shamir, 2017cShamir, ,a,b, 2019Shamir, , 2020cShamir, , 2021b. Since not all galaxies are spiral galaxies, and since not all spiral galaxies have an identifiable spin direction, it is clear that the majority of the galaxies cannot be used for the analysis.…”

“…Evidence of non-random distribution has been proposed by numerous previous studies (Longo, 2007(Longo, , 2011Shamir, 2012Shamir, , 2013Shamir, , 2016Shamir, , 2017bShamir, ,c,a, 2019Shamir, , 2020aLee et al, 2019a,b;Shamir, 2021a,b). These observations include several different telescopes such as the Sloan Digial Sky Survey (Shamir, 2012(Shamir, , 2020c(Shamir, , 2021a, the Panoramic Survey Telescope and Rapid Response System (Shamir, 2020c), the Hubble Space Telescope (Shamir, 2020a), and the Dark Energy Camera (Shamir, 2021b). The different telescopes show very similar patterns regardless of the telescope being used, and regardless of whether the galaxies images were analyzed manually or automatically (Shamir, 2021b).…”