Third Data Release of the Hyper Suprime-Cam Subaru Strategic Program (2108.13045v1)

Abstract: The paper presents the third data release of Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP), a wide-field multi-band imaging survey with the Subaru 8.2m telescope. HSC-SSP has three survey layers (Wide, Deep, and UltraDeep) with different area coverages and depths, designed to address a wide array of astrophysical questions. This third release from HSC-SSP includes data from 278 nights of observing time and covers about 670 square degrees in all five broad-band filters at the full depth ($\sim26$~mag at $5\sigma$) in the Wide layer. If we include partially observed area, the release covers 1,470 square degrees. The Deep and UltraDeep layers have $\sim80\%$ of the originally planned integration times, and are considered done, as we have slightly changed the observing strategy in order to compensate for various time losses. There are a number of updates in the image processing pipeline. Of particular importance is the change in the sky subtraction algorithm; we subtract the sky on small scales before the detection and measurement stages, which has significantly reduced false detections. Thanks to this and other updates, the overall quality of the processed data has improved since the previous release. However, there are limitations in the data (for example, the pipeline is not optimized for crowded fields), and we encourage the user to check the quality assurance plots as well as a list of known issues before exploiting the data. The data release website is https://hsc-release.mtk.nao.ac.jp/.

• The paper introduces the third HSC-SSP data release, emphasizing enhanced imaging techniques and expanded survey coverage.
• It details the implementation of advanced sky subtraction and precise photometric and astrometric calibrations across three survey layers.
• The release provides value-added products and collaborative datasets that boost reliability for cosmological and extragalactic research.

Third Data Release of the Hyper Suprime-Cam Subaru Strategic Program

The third data release from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) provides a substantial addition to the astrophysical datasets available from this extensive wide-field imaging survey. Conducted using the Subaru Telescope, the HSC-SSP aims to address a spectrum of cosmological and extragalactic questions through its three-tiered survey approach: Wide, Deep, and UltraDeep layers.

Survey Coverage and Data

This release encompasses data collected over 278 nights and covers approximately 670 square degrees at full depth across the five primary broadband filters used in the Wide layer, namely $grizy$. With the inclusion of areas partially observed, the total coverage extends to 1,470 square degrees. The Deep and UltraDeep layers have reached about 80% of the initially planned integration times, signifying their near completion.

The Deep layer comprises four separate fields with coverage in both broad and narrow bands, while the UltraDeep fields focus on extended observations in the COSMOS and Subaru XMM-Newton Deep Field (SXDS) areas. The survey's design enables a comprehensive investigation into astrophysical phenomena ranging from weak gravitational lensing to cosmic structure characterization and high-redshift galaxy studies.

Image Processing and Updates

Significant advancements in image processing are reflected in this data release. Notably, the sky subtraction algorithm has undergone enhancements to reduce false detections and improve the fidelity of data for scientific analysis. This development is pivotal in advancing data quality, reducing noise, and offering cleaner source detections.

The photometric and astrometric calibration improvements further ensure higher precision in the dataset; however, users are cautioned to review known issues and quality assurance plots provided alongside the dataset. These plots assist in assessing data integrity and reliability before drawing scientific conclusions.

Value-added Products and Collaborating Surveys

In addition to raw and processed survey data, this release includes several value-added products. These span public spectroscopic redshifts, COSMOS Wide-depth stacks, and random point catalogues, enhancing the usability and scientific output potential of the dataset. Collaborations have further enriched the survey coverage, notably through the provision of deep U-band data from the Canada-France-Hawaii Telescope (CFHT) and upcoming IR catalogues from the UKIRT and CFHT near-infrared surveys.

Future Implications and Final Data Release

The upcoming observations aim to expand the full-color, full-depth map to an anticipated 1,200 square degrees, focusing solely on completing the Wide layer. This would constitute the final data compilation from the HSC-SSP and present an unparalleled resource for both current studies and future queries in the field of cosmology.

In conclusion, this third data release from the HSC-SSP marks a critical milestone in providing a comprehensive, multi-tiered astrophysical survey. With its detailed imaging and expansive data coverage, it creates a robust foundation for concerted cosmological investigation and exploration, setting the stage for future advancements and in-depth studies in the field.