Abstract
In galaxy mergers, dual quasars — two actively accreting supermassive black holes (SMBHs) — provide a unique opportunity to study the interplay between galaxy dynamics and quasar activity. However, very little is known about their molecular gas, which fuels star formation and quasar activity. In this study, we map the kinematics of the cold molecular gas in J0749+2255, a 3.8 kpc separation dual quasar at z = 2.17 using the Atacama Large Millimeter Array (ALMA) Band 4. We detect CO(4−3)λ650µm, which shows remarkably complex morphological and kinematic structures. While the integrated CO map suggested a lens-like ring, this feature disappears with kinematic decomposition. The kinematic analysis with ALMA resolves the ambiguities introduced by previous observations, further supporting the dual quasar interpretation of J0749+2255. We find two kinematically distinct molecular gas components: spatially extended, yet dynamically complex slow-moving gas (FWHM ∼ 130 km s−1), and a compact, blueshifted, fast-moving, turbulent gas (FWHM ∼ 300 km s−1). The disturbed kinematics, likely driven by the merger, show hints of rotation but no molecular outflows, suggesting circumnuclear flows. We estimate a large molecular gas reservoir (MH2 ∼ 1010M⊙), yet the starburst activity appears to exceed the available fuel. We detect an extended continuum in excess at rest-frame 455 GHz. The kinematic complexity of CO implicates the connection of mergers on the starburst and quasar activity in J0749+2255, yet whether J0749+2255 represents the dual quasar population remains unclear. Targeted kinematic studies of larger dual quasar samples will be essential to disentangling the nature of dual quasars.