Subaru Hyper Suprime-Cam Survey of Cygnus OB2 Complex - I. Introduction, photometry, and source catalogue

Low-mass star formation inside massive clusters is crucial to understand the effect of cluster environment on processes like circumstellar disc 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 multiwavelength studies to understand the role of stellar feedback on the IMF, brown dwarf fraction and circumstellar disc properties in the region. We introduce here, the deepest and widest optical photometry of 1.5 degrees 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 catalogue generation, data quality checks, and preliminary results about the pre-main sequence sources. We obtain 713 529 sources in total, with detection down to similar to 28, 27, 25.5, and 24.5 mag in r(2), i(2), z, and Y-band, respectively, which is similar to 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 arcmin region. We find the median age of the region as similar to 5 +/- 2 Myr with an average disc fraction of similar to 9 per cent. At this age, combined with A(V) similar to 6 - 8 mag, we detect sources down to a mass range of similar to 0.01-0.17 M-circle dot. The deep HSC catalogue will serve as the groundwork for further studies on this prominent active young cluster.

Automated summary

This study focuses on investigating the impact of stellar feedback on the IMF, brown dwarf fraction, and circumstellar disc properties in the Cygnus OB2 region through deep multiwavelength observations. The research reveals the presence of a distinct pre-main sequence branch, with a median age of approximately 5 million years and an average disc fraction of around 9% in the region. With a deep HSC catalogue as the foundation, further studies on this active young cluster are facilitated.