Reddening-independent quasar selection from a wide-field optical and near-infrared imaging survey

This is the authors' abstract. We don't add key points for this paper.

We combine deep, wide-field near-infrared (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 deg2 to a depth of mH∼ 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. Two of eight 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 per cent success rate), a high surface density of candidates and is relatively independent of reddening. We discuss the implications for star—galaxy separation for IR base surveys for quasars. We provide the coordinate list and follow-up spectroscopy for the sample of 22 confirmed quasars.