Discovery of a gravitational arc candidate at photometric redshift 4.4 in MACS J0308.9+2645 from a catalogue-based search of JWST imaging
Abstract
We report a strong gravitational arc (A1) in the massive Reionization Lensing Cluster Survey (RELICS) cluster MACS J0308.9+2645 (zl = 0.356), identified in public JWST/NIRCam imaging from programme GO-5293. A1 is an extended, curved, tangentially aligned source (axis ratio a/b = 6.5, catalogue length 3.9 arcsec) located 50.9 arcsec from the cluster X-ray centre. Its six-band (1.15-4.10 micron) photometry yields a photometric redshift of zphot = 4.4 (+0.1/-0.3), with P(z > 3) = 0.99. Using the public Zitrin-LTM-Gauss lens model, A1 lies at a median projected separation of 4.6 arcsec from the tangential critical curve for a source at z = 4.4 and is predicted to have a median absolute magnification of |mu| = 7, providing quantitative support for the lensing interpretation from a model built independently of this work. A fainter arclet (A2) at a comparable radius is reported as a secondary candidate. A1 is absent from the cluster's published multiple-image inventory and from the SIMBAD, NED, and VizieR databases. Spectroscopic redshift determination and dedicated lens modelling are required for confirmation.
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