A Survey for High-redshift Gravitationally Lensed Quasars and Close Quasar Pairs. I. The Discoveries of an Intermediately Lensed Quasar and a Kiloparsec-scale Quasar Pair at z ∼ 5

We present the first results from a new survey for high-redshift (z ≳ 5) gravitationally lensed quasars and close quasar pairs. We carry out candidate selection based on the colors and shapes of objects in public imaging surveys, then conduct follow-up observations to confirm the nature of high-priority candidates. In this paper, we report the discoveries of J0025-0145 (z = 5.07), which we identify as an intermediately lensed quasar, and J2329-0522 (z = 4.85), which is a kiloparsec-scale close quasar pair. The Hubble Space Telescope (HST) image of J0025-0145 shows a foreground lensing galaxy located 0.″6 away from the quasar. However, J0025-0145 does not exhibit multiple lensed images of the quasar, and we identify J0025-0145 as an intermediate lensing system (a lensing system that is not multiply imaged but has a significant magnification). The spectrum of J0025-0145 implies an extreme Eddington ratio if the quasar luminosity is intrinsic, which could be explained by a large lensing magnification. The HST image of J0025-0145 also indicates a tentative detection of the quasar host galaxy in the rest-frame UV, illustrating the power of lensing magnification and distortion in studies of high-redshift quasar host galaxies. Object J2329-0522 consists of two resolved components with significantly different spectral properties and a lack of lensing galaxy detection under subarcsecond seeing. We identify it as a close quasar pair, which is the highest confirmed kiloparsec-scale quasar pair to date. We also report four lensed quasars and quasar pairs at 2 < z < 4 and discuss possible improvements to our survey strategy.