Rich and diverse molecular gas environments of closely-separated dual quasars viewed by ALMA

TL;DR

This study uses ALMA to investigate molecular gas in five closely-separated dual quasars at redshifts 0.4-0.8, revealing substantial gas reservoirs and complex interactions, with implications for galaxy evolution and quasar fueling.

Contribution

First detailed ALMA observations of molecular gas in closely-separated dual quasars, providing insights into gas properties and feedback processes during galaxy interactions.

Findings

Most quasars have significant molecular gas reservoirs.

Gas-to-stellar mass ratios are similar to star-forming galaxies.

Evidence of AGN feedback and matter transfer in individual systems.

Abstract

We present a study of the molecular gas in five closely-spaced ($R_{\perp}<20$ kpc) dual quasars ($L_{\rm bol}\gtrsim10^{44}~\mathrm{erg~s}^{-1}$) 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 Program, with confirmatory spectroscopic validation. Based on the detection of the CO J=2--1 emission line with Band 4, we derived key properties including CO luminosities, line widths, and molecular gas masses for these systems. Among the ten quasars of the five pairs, eight have line detections exceeding $5\sigma$. The detected sources prominently harbor substantial molecular gas reservoirs, with molecular gas masses ($M_{\text{molgas}}$) between $10^{9.6-10.5}~\mathrm{M_{\odot}}$, and molecular gas-to-stellar mass ratios ($\mu_{\text{molgas}}$) spanning $18-97\%$. The overall $\mu_{\text{molgas}}$ of these dual quasars agrees with that of inactive star-forming main-sequence galaxies at comparable redshifts, indicating no clear evidence of quenching. However, intriguing features in each individual system show possible evidence of AGN feedback, matter transfer, and compaction processes.