Capability of quasar selection by combining SCUSS and SDSS observations

The South Galactic Cap u-band Sky Survey (SCUSS) provides a deep u-band imaging of about 5000 deg² in south Galactic cap. It is about 1.5 mag deeper than the SDSS u-band. In this article, we evaluate the capability of quasar selection using both SCUSS and SDSS data, based on considerations of the deep SCUSS u-band imaging and two-epoch u-band variability. We find that the combination of the SCUSS u-band and the SDSS griz-band allows us to select more faint quasars and more quasars at redshift around 2.2 than the selection that uses only the SDSS ugriz data. Quasars have significant u-band variabilities. The fraction of quasars with large two-epoch variability is much higher than that of stars. The selection by variability can select both low-redshift quasars with ultraviolet excess and mid-redshift (2 < z < 3:5) quasars where quasar selection by optical colors is inefficient. The above two selections are complementary and make full use of the SCUSS u-band advantages.