PASSAGES: The Discovery of a Strongly Lensed Protocluster Core Candidate at Cosmic Noon

Investigating the processes by which galaxies rapidly build up their stellar mass during the peak of their star formation (z = 2–3) is crucial to advancing our understanding of the assembly of large-scale structures. We report the discovery of one of the most gas- and dust-rich protocluster core candidates, PJ0846+15 (J0846), from the Planck All-Sky Survey to Analyze Gravitationally lensed Extreme Starbursts (PASSAGES) sample. The exceedingly high total star formation rate (SFR) uncorrected for lensing magnification (μ) of μSFR = 39900⁺_{12900 _}²³⁰⁰⁰ M yr⁻¹ is the result of a foreground cluster lensing at least 11 dusty star-forming galaxies between z = 2.660 and 2.669, where the intrinsic value is estimated to be SFR = 5200⁺_{2000 _}³²⁰⁰ M yr⁻¹. Atacama Large Millimeter/submillimeter Array observations uncovered 18 CO(3–2) emission-line detections, some of which are multiply imaged systems, lensed by a foreground cluster at z = 0.77. We present the first multiwavelength characterization of this field, constructing a lens model that predicts that these 11 galaxies (μ ≃ 1.5–25) are contained within a projected physical extent of 280 × 150 kpc, with a velocity dispersion of σ_v = 246 ± 72 km s⁻¹. J0846 exhibits the rare case of a protocluster candidate whose core is strongly lensed, offering a magnified view of the rapid stellar buildup within an overdense environment at Cosmic Noon.