Survey (PDR3)

Details of the instrument, survey and primary science goals are described in detail in our survey website as well as in the series of technical papers (see the top page).  Only some of the key parameters of our survey are described here.

Updates since PDR2

We lost a large number of nights due to earthquake, bad weather, and telescope trouble in 2018.  To compensate for the loss, additional 30 nights have been added to the survey.  In addition, we have slightly changed our observing strategy in November 2018 to catch up with the original survey plan.  First, we reduce the exposure time from 20min to 16.7min in izy in the Wide layer.  The reduced exposure time results in shallower depths by 0.1mag in these filters.  Note that the list of target depths shown below does not reflect this change.  Second, we relaxed the seeing constraints in the i-band in the Wide layer from <0.7 arcsec to <0.9 arcsec, although we try to observe under good seeing conditions whenever possible.  Finally, we choose to stop at around 80-90% of the original exposure times in Deep/UltraDeep.  See the data release paper for details.

Hyper Suprime-Cam Subaru Strategic Survey in a Nutshell

The HSC-SSP a three-layered, multi-band (grizy plus 4 narrow-band filters) imaging survey with the Hyper Suprime-Cam (HSC) on the 8.2m Subaru Telescope. HSC has 104 science CCDs covering a 1.5 degree diameter field of view with a 0.168 arcsec pixel scale.  The delivered image quality is excellent across the field of view; the median seeing in the i-band is about 0.6 arcsec.  Each of the Wide, Deep, and UltraDeep layer covers about 1200 deg2 (r~26),  27 deg2 (r~27), and 3.5 deg2 (r~28), respectively.  By combining data from these layers, we address some of the most pressing problems in modern cosmology and astrophysics with a particular focus on gravitational weak lensing, galaxy evolution, supernovae, and galactic structure. The survey is uniquely designed to enable various science cases, with particular attention to controlling systematic errors.  The survey is awarded 330 nights in total and it started in March 2014.

Layer Area (deg2) # of 1.8deg2 HSC fields Filters & Depth
Wide ~1200 ~800 grizy (r ~ 26)
Deep 27 15 grizy+3NBs (r ~ 27)
Ultradeep 3.5 2 grizy+3NBs (r ~ 28)

Filters and Depths

The nature, depth, and solid angle of each filter for the HSC survey are carefully determined to meet the main science requirements. The following table summarizes the filters and depths for each survey layer.  The exposure here is the total exposure time (e.g., g-band in the Wide layer is 2.5 min x 4 exposures = 10 min).  The limiting magnitudes are 5 sigma limits within 2 arcsec diameter apertures and they include effects of source confusion.  For point sources under FWHM=0.9 seeing, the depths are 0.3 mag deeper.  The filter response functions are described in detail in Kawanomoto et al. (2018)The total responses shown in the figure above are available here. For the atmosphere, we assumed airmass=1.2 (which is close to the median airmass of the survey) and PWV=1.5mm.  You can find more information about the camera responses in the observatory’s page.

Layer Filter Exptime (# of exposures) Total nights Lim. mag. Moon phase
Wide g,r 10min (4) 53 26.5, 26,1 dark
Wide i 20min (6) 53 25.9 dark
Wide z,y 20min (6) 108 25.1, 24.4 gray
Deep g,r 1.4hrs (10) 7.3 27.5, 27.1 dark
Deep i 2.1hrs (10) 5.4 26.8 dark
Deep z 3.5hrs (10) 9.1 26.3 gray
Deep y 2.1hrs (10) 5.4 25.3 gray
Deep N387 1.4hrs (10) 3.6 24.5 dark
Deep N816 2.8hrs (10) 7.2 25.8 gray/dark
Deep N921 4.2hrs (10) 11 25.6 gray/dark
UD g,r 7hrs (20) 4.8 28.1, 27.7 dark
UD i 14hrs (20) 4.8 27.4 dark
UD z,y 18.9hrs (20) 13 26.8, 26.3 gray
UD N816 10.5hrs (10) 3.6 26.5 gray/dark
UD N921 14hrs (10) 4.8 26.2 gray/dark
UD N101 17.5hrs (10) 6.1 24.8 gray/dark

Survey Fields

Wide Spring and autumn equatorial stripes, Hectomap

The fields are chosen to satisfy the following conditions:

  • The fields overlap with other multi-wavelength data sets to maximize scientific potential when combined with the HSC data. The major data sets which offer unique synergy with HSC data are the arcminute-resolution, high-sensitivity CMB survey by ACT in Chile, and its polarization extension ACTPol; X-ray surveys from XMM and eROSITA; near-/mid-infrared imaging surveys (e.g., VIKING/VIDEO and UKIDSS); and deep spectroscopic surveys (e.g., VIPERS, GAMA, COSMOS, HectoMAP).
  • The Ultradeep regions are included in the Deep fields, and the Deep fields are included in the Wide fields.  ELAIS-N1 is an exception here.
  • The fields are chosen to be low in Galactic dust extinction.