MUSUBI (MegaCam Ultra-deep Survey: $u^{\ast }$-Band Imaging)-Data for the COSMOS and SXDS Fields

Abstract

The Subaru Hyper Suprime-Cam (HSC) Strategic Survey is the latest-generation multi-band optical imaging survey for galaxy evolution and structure formation. The "Ultra-Deep" component of the HSC survey provides $grizy$ broad-band images over $\sim 3.4$ deg${}^2$ to detection limits of $\sim 26$-28 AB, along with narrow-band images, in the COSMOS and the SXDS fields. These images provide an unprecedented combination of depths and area coverage, for the studies galaxies up to $z\sim 7$. However, the lack of coverage at $<4000$ Ang implies incomplete sampling of the rest-frame UV at $z\lesssim 3$, which is critically needed for understanding the buildup of stellar mass in the later cosmic time. We conducted a multi-year CFHT $u^{\ast }$-band imaging campaign in the two HSC Ultra-Deep fields with CFHT MegaCam. By including shallower archival data, we reach 5-$\ddot{I}ƒ$ depths of $u^{\ast }=28.1$ and 28.4 (AB) at the centers of the COSMOS and SXDS fields, respectively, and $u^{\ast }=27.7$ and 27.8 in the central 1 deg${}^2$ fields. The image quality is $\gtrsim 0.90$ arcsec, fairly good for the $u^{\ast }$ band. Both the photometric and astrometric quality of our data are excellent. We show that the combination of our $u^{\ast }$-band and HSC data can lead to high-quality photometric redshifts at $z=0$-3, and robust measurements of rest-frame UV on galaxies at $0.4<z<0.6$ for distinguishing green-valley galaxies from star-forming and quiescent galaxies. We publicly release our reduced $u^{\ast }$-band images and reference catalogs that can be used readily for scientific studies.

24 pages, 12 figures, accepted for publication on ApJS