Second Data Release of the Hyper Suprime-Cam Subaru Strategic Program (1905.12221v2)

Abstract: This paper presents the second data release of the Hyper Suprime-Cam Subaru Strategic Program, a wide-field optical imaging survey on the 8.2 meter Subaru Telescope. The release includes data from 174 nights of observation through January 2018. The Wide layer data cover about 300 deg^2 in all five broadband filters (grizy) to the nominal survey exposure (10min in gr and 20min in izy). Partially observed areas are also included in the release; about 1100 deg^2 is observed in at least one filter and one exposure. The median seeing in the i-band is 0.6 arcsec, demonstrating the superb image quality of the survey. The Deep (26 deg^2) and UltraDeep (4 deg^2) data are jointly processed and the UltraDeep-COSMOS field reaches an unprecedented depth of i~28 at 5 sigma for point sources. In addition to the broad-bands, narrow-band data are also available in the Deep and UltraDeep fields. This release includes a major update to the processing pipeline, including improved sky subtraction, PSF modeling, object detection, and artifact rejection. The overall data quality has been improved, but this release is not without problems; there is a persistent deblender problem as well as new issues with masks around bright stars. The user is encouraged to review the issue list before utilizing the data for scientific explorations. All the image products as well as catalog products are available for download. The catalogs are also loaded to a database, which provides an easy interface for users to retrieve data for objects of interest. In addition to these main data products, detailed galaxy shape measurements withheld from the Public Data Release 1 (PDR1) are now available to the community. The shape catalog is drawn from the S16A internal release, which has a larger area than PDR1 (160 deg^2). All products are available at the data release site, https://hsc-release.mtk.nao.ac.jp/.

• The paper reports an expanded data release (PDR2) with 174 observation nights and 300 sq deg coverage in five broad-band filters.
• It details a refined data processing pipeline featuring advanced sky subtraction, PSF modeling, and artifact rejection for superior data quality.
• The release underpins future cosmological studies by enabling deeper weak-lensing analyses and precise galaxy shape measurements.

An Analysis of the Second Data Release of the Hyper Suprime-Cam Subaru Strategic Program

The paper concerning the second public data release (PDR2) of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) outlines a substantial expansion of observational data collected by the 8.2-meter Subaru Telescope. This release marks a significant enhancement both in terms of observational depth and quality, reflecting improvements and updates in the data processing pipeline compared to the first release (PDR1).

Data Collection and Coverage

PDR2 consists of data from an impressive 174 nights of observation, extending the previous release's coverage substantially. The Wide layer data encompass approximately 300 square degrees in all five broad-band filters ($grizy$), which is a significant increase from previous figures. Moreover, partially observed areas total approximately 1100 square degrees, signifying that observations have been made in at least one filter and one exposure. This considerable data collection effort represents two-thirds of the total allocated observing time, demonstrating effective use of resources.

Improvements and Challenges

One of the notable enhancements in PDR2 is the updated data processing pipeline, now version 6 of the HSC pipeline (hscPipe). This version includes advanced features such as improved sky subtraction, more sophisticated PSF modeling, and artifact rejection capabilities, leading to superior data quality. Nevertheless, the release acknowledges unresolved issues, notably with the deblender and masks around bright stars, which users must consider before diving into scientific analyses.

Scientific Implications and Future Work

The updated data products enable a wide range of scientific investigations, especially due to the unprecedented depth achieved in certain fields, such as the UltraDeep-COSMOS field reaching an $i$-band depth of $i\sim28$ at $5\sigma$ for point sources. The availability of detailed galaxy shape measurements, critical for weak-lensing studies, serves as a foundation for further exploration in cosmology.

PDR2 notably continues to rely on external catalogs, such as Pan-STARRS1, for zero-point calibrations, highlighting ongoing interdependence within the astronomical community. Moving forward, anticipated improvements will address current calibration discrepancies, notably those arising from the combination of $i$ and $i2$ filters.

Conclusion

Overall, PDR2 of HSC-SSP represents a substantial advancement in both scope and capability compared to its predecessor. The efforts to improve data reduction pipelines and expand observational coverage form a crucial foundation for enhancing our understanding of solar system bodies, stars, galaxies, and the cosmos at large. As HSC-SSP progresses toward its future data releases, it promises to resolve existing challenges while setting new standards for astronomical data quality and accessibility. This data release significantly contributes to the infrastructure essential for ongoing and forthcoming cosmological surveys, underpinning the work of a broad range of astrophysical research endeavors.