The Blanco Cosmology Survey: Data Acquisition, Processing, Calibration, Quality Diagnostics, and Data Release

• Published in: The Astrophysical Journal
• Main Authors: Desai, S., Armstrong, R., Mohr, J. J., Semler, D. R., Liu, J., Bertin, E., Allam, S. S., Barkhouse, W. A., Bazin, G., Buckley-Geer, E. J., Cooper, M. C., Hansen, S. M., High, F. W., Lin, H., Lin, Y. -T., Ngeow, C. -C., Rest, A., Song, J., Tucker, D., Zenteno, A.
• Other Authors: Institut d'Astrophysique de Paris (IAP), Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2012
• Subjects: cosmology: observations; galaxies: clusters: general; methods: data analysis; surveys; techniques: image processing; Astrophysics - Cosmology and Extragalactic Astrophysics; [SDU]Sciences of the Universe [physics]; South pole
• Online Access: https://hal.science/hal-03645778; https://doi.org/10.1088/0004-637X/757/1/83

International audience The Blanco Cosmology Survey (BCS) is a 60 night imaging survey of ~80 deg 2 of the southern sky located in two fields: (α, δ) = (5 hr, -55°) and (23 hr, -55°). The survey was carried out between 2005 and 2008 in griz bands with the Mosaic2 imager on the Blanco 4 m telescope. The primary aim of the BCS survey is to provide the data required to optically confirm and measure photometric redshifts for Sunyaev-Zel'dovich effect selected galaxy clusters from the South Pole Telescope and the Atacama Cosmology Telescope. We process and calibrate the BCS data, carrying out point-spread function-corrected model-fitting photometry for all detected objects. The median 10σ galaxy (point-source) depths over the survey in griz are approximately 23.3 (23.9), 23.4 (24.0), 23.0 (23.6), and 21.3 (22.1), respectively. The astrometric accuracy relative to the USNO-B survey is ~45 mas. We calibrate our absolute photometry using the stellar locus in grizJ bands, and thus our absolute photometric scale derives from the Two Micron All Sky Survey, which has ~2% accuracy. The scatter of stars about the stellar locus indicates a systematic floor in the relative stellar photometric scatter in griz that is ~1.9%, ~2.2%, ~2.7%, and ~2.7%, respectively. A simple cut in the AstrOmatic star-galaxy classifier spread_model produces a star sample with good spatial uniformity. We use the resulting photometric catalogs to calibrate photometric redshifts for the survey and demonstrate scatter δz/(1 + z) = 0.054 with an outlier fraction η < 5% to z ~ 1. We highlight some selected science results to date and provide a full description of the released data products.