Hyper Suprime-Cam (HSC), an ultra-wide-field prime focus camera mounted on the Subaru Telescope, has 870 million pixels and can observe an area equivalent to nine full Moons at a time. About 10 nights around the new moon are assigned to HSC observations every month, and various astronomical objects are observed. Part of the HSC observing time is assigned to the "Subaru Strategic Program" (SSP) led by the observatory, and the rest of the time is allocated to general open-use observations. Each observer processes his/her own data, but the processed data are not always released to the public. However, the scientific value of these data is high and they can be used for purposes other than the originally intended ones. In order to fully exploit the HSC data, the observatory launched the Hyper Suprime-Cam Legacy Archive (HSCLA), where processed, science-ready data from open-use programs are available to the world-wide researchers. Raw data from open-use observations are processed with the latest version of the data reduction pipeline and artifacts such as instrument specific features and atmospheric signatures are removed to unveil the deep Universe. A variety of celestial objects are detected, and their brightness, colors, sizes, and shapes are carefully measured and catalogued.
Figure 1: NGC4244, an edge-on galaxy at about 4 Mpc (13 million light-years away). Individual stars are resolved as shown in the blow-up. (Credit: NAOJ)
The HSCLA release in 2021 included only the data acquired in 2014. This new release adds data taken in 2015 and 2016, and it includes about 20,000 exposures in total, amounting to 800 hours of observation executed under good conditions. It covers approximately 3400 square degrees (approximately 8 % of the sky) and as many as 770 million objects are detected and measured. The total data volume, including intermediate data products, is about 450 terabytes, which demonstrates the 'big data' nature of modern astronomy. Figures 1 and 2 illustrate the grandeur of the data in this release.
Figure 2: Sculptor Dwarf Galaxy. This is a satellite galaxy of the Milky Way Galaxy. Its apparent extent is about the size of the Moon. (Credit: NAOJ)
Sumiko Harasawa, a data processing specialist at Subaru Telescope, expects the new release to be widely used for research: "HSCLA is a rich resource for astronomical research, and we offer tools to efficiently analyze the big data. I am looking forward to seeing news of big discoveries from HSCLA soon!"
Guidelines for Use