ALMA observations of dual quasars: evidence of rich and diverse molecular gas environments

We present a study of the molecular gas in five closely separated (R_⊥ < 20 kpc) dual quasars (L_bol ≳ 10⁴⁴ erg s⁻¹) at redshifts 0.4 < z < 0.8 with the Atacama Large Millimeter/submillimeter Array. The dual quasar phase represents a distinctive stage during the interaction between two galaxies for investigating quasar fueling and feedback effects on the gas reservoir. The dual quasars were selected from the Sloan Digital Sky Survey and Subaru/Hyper Suprime-Cam Subaru Strategic Programme, with confirmatory spectroscopic validation. Based on the detection of the CO J = 2–1 emission line with Band 4, we derive key properties including CO luminosities, line widths, and molecular gas masses for these systems. Eight quasars, of the 10 in pairs, have line detections exceeding 5σ that result in molecular gas masses (M_molgas) between 10^9.7−10.7 M_☉. The molecular gas-to-stellar mass ratios (μ_molgas) of these dual quasars are typically between 18–50 per cent, which are similar to the single quasars in mergers and inactive star-forming galaxies. The resultsindicate no clear evidence of molecular gas depletion attributed to dual quasar activities on global scale. However, intriguing gas features in certain systems appear to show possible signatures of active galactic nucleus (AGN) feedback effect.