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 apparent star formation rate of up to ($\mu$SFR) $\sim 93600{\mathrm{M}}_{\odot }{\text{yr}}^{-1}$ is a result of a foreground cluster lens magnifying at least 11 dusty star-forming galaxies between $z=2.660$–$2.669$. Atacama Large Millimeter Array (ALMA) observations revealed 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 multi-wavelength characterization of this field, constructing a lens model that predicts that these 11 systems (magnification factor, $\mu \simeq 1.5$–$25$) are contained within a projected physical extent of $280\times 150$ kpc, with a velocity dispersion of ${\sigma }_v=246\pm 72$ km s${}^{-1}$ and a total intrinsic star formation rate of up to (SFR) $\sim 10400{\mathrm{M}}_{\odot }{\text{yr}}^{-1}$. J0846 is one of the most unique, lensed, protocluster core candidates ever reported, and offers a magnified glimpse into the rapid buildup of massive local galaxy clusters.