Reddening-Independent Quasar Selection from a Wide-Field Optical and Near-IR Imaging Survey

Abstract

We combine deep, wide-field near-IR and optical imaging to demonstrate a reddening-independent quasar selection technique based on identifying outliers in the (g-z) / (z-H) colour diagram. In three fields covering a total of ~0.7 deg^2 to a depth of m_H~18, we identified 68 quasar candidates. Follow-up spectroscopy for 32 objects from this candidate list confirmed 22 quasars (0.86<z<2.66), five with significant IR excesses. 2 of 8 quasars from a subsample with U band observations do not exhibit UVX colours. From these preliminary results, we suggest that this combined optical and near-IR selection technique has a high selection efficiency (> 65% success rate), a high surface density of candidates, and is relatively independent of reddening. We discuss the implications for star/galaxy separation for IR based surveys for quasars. We provide the coordinate list and follow-up spectroscopy for the sample of 22 confirmed quasars.