Beschreibung:
<jats:title>Abstract</jats:title>
<jats:p>The Subaru Hyper Suprime-Cam (HSC) Strategic Survey is the latest-generation multiband optical imaging survey for galaxy evolution and structure formation. The “Ultra-deep” component of the HSC survey provides <jats:italic>grizy</jats:italic> broadband images over ∼3.4 deg<jats:sup>2</jats:sup> to detection limits of ∼26–28 AB, along with narrowband images, in the COSMOS and SXDS fields. These images provide an unprecedented combination of depths and area coverage, for studies of galaxies up to <jats:italic>z</jats:italic> ∼ 7. However, the lack of coverage at <4000 Å implies an incomplete sampling of the rest-frame UV at <jats:italic>z</jats:italic> ≲ 3, which is critically needed for understanding the buildup of stellar mass in later cosmic time. We conducted a multiyear CFHT <jats:italic>u</jats:italic>*-band imaging campaign in the two HSC Ultra-deep fields with CFHT MegaCam. By including shallower archival data, we reached 5<jats:italic>σ</jats:italic> depths of <jats:italic>u</jats:italic>* = 28.1 and 28.4 (AB) at the centers of the COSMOS and SXDS fields, respectively, and <jats:italic>u</jats:italic>* = 27.7 and 27.8 in the central 1 deg<jats:sup>2</jats:sup> fields. The image quality is ≳ 0.″90, fairly good for the <jats:italic>u</jats:italic>* band. Both the photometric and astrometric quality of our data are excellent. We show that the combination of our <jats:italic>u</jats:italic>*-band and HSC data can lead to high-quality photometric redshifts at <jats:italic>z</jats:italic> = 0–3, and robust measurements of rest-frame UV on galaxies at 0.4 < <jats:italic>z</jats:italic> < 0.6 for distinguishing green-valley galaxies from star-forming and quiescent galaxies. We publicly release our reduced <jats:italic>u</jats:italic>*-band images and reference catalogs, which can be used readily for scientific studies.</jats:p>