Subaru Hyper Suprime-Cam Survey of Cygnus OB2 Complex -- I:
  Introduction, Photometry and Source Catalog
  Low mass star formation inside massive clusters is crucial to understand the
effect of cluster environment on processes like circumstellar disk evolution,
planet and brown dwarf formation. The young massive association of Cygnus OB2,
with a strong feedback from massive stars, is an ideal target to study the
effect of extreme environmental conditions on its extensive low-mass
population. We aim to perform deep multi-wavelength studies to understand the
role of stellar feedback on the IMF, brown dwarf fraction and circumstellar
disk properties in the region. We introduce here, the deepest and widest
optical photometry of 1.5$^\circ$ diameter region centred at Cygnus OB2 in
r$_{2}$, i$_{2}$, z and Y-filters using Subaru Hyper Suprime-Cam (HSC). This
work presents the data reduction, source catalog generation, data quality
checks and preliminary results about the pre-main sequence sources. We obtain
713,529 sources in total, with detection down to $\sim$ 28 mag, 27 mag, 25.5
mag and 24.5 mag in r$_{2}$, i$_{2}$, z and Y-band respectively, which is
$\sim$ 3 - 5 mag deeper than the existing Pan-STARRS and GTC/OSIRIS photometry.
We confirm the presence of a distinct pre-main sequence branch by statistical
field subtraction of the central 18$^\prime$ region. We find the median age of
the region as $\sim$ 5 $\pm$ 2 Myrs with an average disk fraction of $\sim$
9$\%$. At this age, combined with A$_V$ $\sim$ 6 - 8 mag, we detect sources
down to a mass range $\sim$ 0.01 - 0.17 M$_\odot$. The deep HSC catalog will
serve as the groundwork for further studies on this prominent active young
cluster.
