Detailed study of a rare hyperluminous rotating disk in an Einstein ring 10 billion years ago

Abstract

Hyperluminous infrared galaxies (HyLIRGs) are the rarest and most extreme starbursts and found only in the distant Universe ( z ≳ 1). They have intrinsic infrared (IR) luminosities L _IR ≥ 10 ¹³ L _⊙ and are commonly found to be major mergers. Recently, the Planck All-Sky Survey to Analyze Gravitationally-lensed Extreme Starbursts project (PASSAGES) searched ~10 ⁴ deg ² of the sky and found ~20 HyLIRGs. We describe a detailed study of PJ0116-24, the brightest ( μL _IR ≈ 2.6 × 10 ¹⁴ L _⊙, magnified with μ ≈ 17) Einstein-ring HyLIRG in the southern sky, at z = 2.125, with observations from the near-IR integral-field spectrograph VLT/ERIS and the submillimetre interferometer ALMA. We detected Hα, Hβ, [N ii] and [S ii] lines and obtained an extreme Balmer decrement (Hα/Hβ ≈ 8.73 ± 1.14). We modelled the molecular-gas and ionized-gas kinematics with CO(3–2) and Hα data at ~100–300 pc and (sub)kiloparsec delensed scales, respectively, finding consistent regular rotation. We found PJ0116-24 to be highly rotationally supported ( v _rot/ σ _{0, mol. gas} ≈ 9.4) with a richer gaseous substructure than other known HyLIRGs. Our results imply that PJ0116-24 is an intrinsically massive ( M _baryon ≈ 10 ^11.3 M _⊙) and rare starbursty disk (star-formation rate, SFR = 1,490 M _⊙ yr ⁻¹) probably undergoing secular evolution. This indicates that the maximal SFR (≳1,000 M _⊙ yr ⁻¹) predicted by simulations could occur during a galaxy’s secular evolution, away from major mergers.