The CFHT large area U-band deep survey (CLAUDS)

Marcin Sawicki, Stephane Arnouts, Jiasheng Huang, Jean Coupon, Anneya Golob, Stephen Gwyn, Sebastien Foucaud, Thibaud Moutard, Ikuru Iwata, Chengze Liu, Lingjian Chen, Guillaume Desprez, Yuichi Harikane, Yoshiaki Ono, Michael A. Strauss, Masayuki Tanaka, Nathalie Thibert, Michael Balogh, Kevin Bundy, Scott ChapmanJames E. Gunn, Bau Ching Hsieh, Olivier Ilbert, Yipeng Jing, Olivier LeFèvre, Cheng Li, Yuichi Matsuda, Satoshi Miyazaki, Tohru Nagao, Atsushi J. Nishizawa, Masami Ouchi, Kazuhiro Shimasaku, John Silverman, Sylvain De la Torre, Laurence Tresse, Wei Hao Wang, Chris J. Willott, Toru Yamada, Xiaohu Yang, Howard K.C. Yee

Research output: Contribution to journalArticlepeer-review

65 Scopus citations


The Canada–France–Hawaii Telescope (CFHT) Large Area U-band Deep Survey (CLAUDS) uses data taken with the MegaCam mosaic imager on CFHT to produce images of 18.60 deg2 with median seeing of FWHM = 0.92 arcsec and to a median depth of U = 27.1 AB (5σ in 2 arcsec apertures), with selected areas that total 1.36 deg2 reaching a median depth of U = 27.7 AB. These are the deepest U-band images assembled to date over this large an area. These data are located in four fields also imaged to comparably faint levels in grizy and several narrowband filters as part of the Hyper Suprime–Cam (HSC) Subaru Strategic Program (HSC-SSP). These CFHT and Subaru data sets will remain unmatched in their combination of area and depth until the advent of the Large Synoptic Survey Telescope. This paper provides an overview of the scientific motivation for CLAUDS and gives details of the observing strategy, observations, data reduction, and data merging with the HSC-SSP. Three early applications of these deep data are used to illustrate the potential of the data set: deep U-band galaxy number counts, z ∼ 3 Lyman break galaxy selection, and photometric redshifts improved by adding CLAUDS U to the Subaru HSC grizy photometry.

Original languageEnglish (US)
Pages (from-to)5202-5217
Number of pages16
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
StatePublished - 2019

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Cosmology: observations
  • Dark matter
  • Galaxies: formation
  • Galaxies: haloes
  • Galaxies: statistics
  • Large-scale structure of universe


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