GALAXY CRUISE is a citizen science project of NAOJ in which Citizen Astronomers participate in galaxy research while exploring the vast cosmic images captured by the Subaru Telescope. The 2023 Special Campaign for classifying simulated galaxies will start on September 12, 2023, at 9 a.m. in Japan Standard Time (JST). The JST time zone is UTC+9 (UTC: Coordinated Universal Time).
Figure 1: Image examples from the 2023 Special Campaign: one simulated galaxy and one real galaxy each for ellipticals (left two images) and spirals (right two images). They are hard to tell apart aren't they? (Credit: Bottrell et al./The TNG collaboration/HSC-SSP/NAOJ)
How were galaxies formed, and how have they evolved (grown)? Why do galaxies show various shapes, from featureless ellipticals to spirals with a bulge and arms? GALAXY CRUISE focuses on galaxy interaction and merging, which are believed to be a key to understanding galaxy evolution, and invites Citizen Astronomers to classify galaxies captured with Hyper Suprime-Cam (HSC) mounted on the Subaru Telescope on Maunakea, Hawai`i. This project launched in November 2019 in Japanese and in February 2020 in English as Season 1. Since April 2022, Season 2 with fainter galaxies has been on a "voyage." As of September 1, 2023, 11,734 people from 104 countries and regions have registered as Citizen Astronomers, and total classification results have exceeded 3.96 million.
GALAXY CRUISE has accumulated classification results for galaxies by Citizen Astronomers, such as morphologies (elliptical or spiral) and signs of interaction (interacting or non-interacting). These results have spawned new studies by combining them with the machine learning of AI (Artificial Intelligence). On the other hand, there are many hard-to-classify galaxies for which opinions were sharply divided on whether or not they were interacting. However, nobody has a benchmark like 'galaxies that XX % of Citizen Astronomers judge as interacting are interacting.'
In the Special Campaign, Citizen Astronomers will classify simulated galaxies reproduced in a computer using a "galaxy evolution model." The images of simulated galaxies are from the IllustrisTNG (hereafter TNG) project in Germany and the United States (Note 1).
"Because of its vastness and high resolution, TNG is the best simulation to compare with GALAXY CRUISE. Converting the simulation results into galaxy images compatible with the Subaru HSC image quality is quite time-consuming; however, our collaborator, conducting a comparative study of TNG results and HSC images, provided the images to us. Thanks to him, we can start the campaign," says Makoto Ando, a JSPS Research Fellow for Young Scientists at the University of Tokyo, who leads the campaign as a GALAXY CRUISE science team member.
When the campaign starts, the ongoing Season 2 classification will be suspended until the campaign is completed. It will continue until more than 40 classification results are collected for all 7,000 galaxy images, a mixture of simulated and real galaxies.
Kei Ito, a JSPS Research Fellow for Young Scientists at the University of Tokyo and a GALAXY CRUISE science team member, explains about the unique feature of the campaign, "To eliminate any preconceptions, we mixed real galaxies with the simulated galaxies. As they are indistinguishable, please classify the images as if all were real galaxies captured by the Subaru Telescope." For reference, images in Figure 1 are from left to right: simulated, real, simulated, and real.
Simulations in galactic astronomy, which are numerical calculations using a "galaxy evolution model" that incorporates a recipe for the formation and growth of galaxies, enable us to use an "experimental" approach to examine how a modeled galaxy in a computer evolves. As most phenomena in the Universe cannot be attempted in a flask or beaker, astronomers carry out experiments on a computer and compare the simulation results with observational data.
"I have wanted to compare observational and simulated data, because both are essential for research. Classification of simulated galaxies by Citizen Astronomers will enrich our understanding of galaxy evolution," says Captain Masayuki Tanaka, an Associate Professor at Subaru Telescope, with high expectations for the campaign.
"Even active users who have classified thousands of galaxies ask us if their classification results are correct, but nobody knows the right answer. In this campaign, Citizen Astronomers will classify simulated galaxies for which we know the answers. After the campaign is completed, we will provide "answers" to you about which galaxies are interacting so that you can compare your classification results with the answers," says Captain Tanaka.
(Note 1) Lately, the TNG simulation is being widely used in galaxy evolution research all over the world because it covers a wide area of the Universe, and its results can be seen with a high spatial resolution.
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