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

Abstract

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.

Tracking Supermassive Black Hole Mergers from kpc to sub-pc Scales with AXIS

“…There have been many optical searches for quasar pairs in the high-redshift Universe, where tens of candidates have been identified (z > 1; e.g., [119][120][121][122][123]). Most recently, two of the highest-z dual AGN candidates (z > 5) were detected via optical spectroscopy and photometry [124,125], and new observational techniques that leverage the angular resolution of Gaia have been effective first steps for detecting the dual AGN population at high-z (i.e., [126,127]). However, large surveys with wide-area coverage are necessary to find large samples of dual AGN candidates.…”

Detecting and Characterizing Young Quasars. III. The Impact of Gravitational Lensing Magnification

“…One possible way to find these lensed quasars is to identify quasars with large apparent SMBH masses and Eddington ratios and carry out follow-up high-resolution imaging with HST or JWST. This method has been used in the discovery of the currently only known lensed quasar at z > 5 (Fan et al 2019) and provided promising lensed quasar candidates (Yue et al 2023).…”

Discovery of Merging Twin Quasars at z = 6.05

“…On the other hand, no pairs were found by Sandoval et al (2023) in their search from a large X-ray catalog at z ∼ 3. There are also projects to search for quasar pairs motivated by investigation of gravitational lensing (e.g., Richards et al 2006;Inada et al 2012;Yue et al 2023). From such a project based on the Dark Energy Survey (Abbott et al 2018), Yue et al (2021) found a candidate of quasar pair at z = 5.66, with a separation of 7.3 kpc.…”