Capability of Quasar Selection by Combining the SCUSS and SDSS Observations

TL;DR

Combining deep SCUSS u-band imaging with SDSS data enhances quasar detection, especially for faint and mid-redshift quasars, by utilizing color and variability information.

Contribution

This study demonstrates that integrating SCUSS and SDSS data improves quasar selection efficiency, particularly for faint and redshift-specific quasars, leveraging deep u-band imaging and variability analysis.

Findings

Enhanced detection of faint quasars using combined data.

Significant u-band variability distinguishes quasars from stars.

Complementary selection methods improve overall quasar identification.

Abstract

The South Galactic Cap $u$-band Sky Survey (SCUSS) provides a deep $u$-band imaging of about 5000 deg$^2$ in south Galactic cap. It is about 1.5 mag deeper than the SDSS $u$-band. In this paper 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 only with 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.