A variable active galactic nucleus at z = 2.06 triply-imaged by the galaxy cluster MACS J0035.4-2015
Koekemoer, Anton M.; Charlot, Stéphane; Chevallard, Jacopo; Donahue, Megan; Frye, Brenda L.; Fujimoto, Seiji; Kohno, Kotaro; Stark, Daniel P.; Caputi, Karina I.; Curtis-Lake, Emma; Suess, Katherine A.; Ueda, Yoshihiro; Nelson, Erica J.; Zitrin, Adi; Coe, Dan; Andrade-Santos, Felipe; Sharon, Keren; Mainali, Ramesh; Bauer, Franz E.; Vidal-García, Alba; Magdis, Georgios E.; Bradley, Larry D.; Kokorev, Vasily; Furtak, Lukas J.; Knudsen, Kirsten K.; Plat, Adèle; Espada, Daniel; Umehata, Hideki; Lee, Minju M.; Lemaux, Brian C.; Laporte, Nicolas; Su, Yuanyuan; Caminha, Gabriel B.; Uematsu, Ryosuke; Wu, John F.
Israel, United States, Chile, Japan, Germany, Netherlands, Denmark, France, United Kingdom, Spain, Sweden
Abstract
We report the discovery of a triply imaged active galactic nucleus (AGN), lensed by the galaxy cluster MACS J0035.4-2015 (zd = 0.352). The object is detected in Hubble Space Telescope imaging taken for the RELICS program. It appears to have a quasi-stellar nucleus consistent with a point-source, with a de-magnified radius of re ≲ 100 pc. The object is spectroscopically confirmed to be an AGN at zspec = 2.063 ± 0.005 showing broad rest-frame UV emission lines, and detected in both X-ray observations with Chandra and in ALCS ALMA band 6 (1.2 mm) imaging. It has a relatively faint rest-frame UV luminosity for a quasar-like object, MUV, 1450 = -19.7 ± 0.2. The object adds to just a few quasars or other X-ray sources known to be multiply lensed by a galaxy cluster. Some diffuse emission from the host galaxy is faintly seen around the nucleus, and there is a faint object nearby sharing the same multiple-imaging symmetry and geometric redshift, possibly an interacting galaxy or a star-forming knot in the host. We present an accompanying lens model, calculate the magnifications and time delays, and infer the physical properties of the source. We find the rest-frame UV continuum and emission lines to be dominated by the AGN, and the optical emission to be dominated by the host galaxy of modest stellar mass $M_{\star }\simeq 10^{9.2}\, \mathrm{M}_{\odot }$ . We also observe some variation in the AGN emission with time, which may suggest that the AGN used to be more active. This object adds a low-redshift counterpart to several relatively faint AGN recently uncovered at high redshifts with HST and JWST.