2022MNRAS.511.1462M

Cool gas (T∼10⁴ K) traced by hydrogen Ly α emission is now routinely detected around z ∼ 3 quasars, but little is known about their molecular gas reservoirs. Here, we present an APEX spectroscopic survey of the CO(6-5), CO(7-6), and [C I](2-1) emission lines for nine quasars from the QSO MUSEUM survey, which have similar UV luminosities, but very diverse Ly α nebulae. These observations (≲ngle ∼ rms~>=2.6 mJy in 300 km s^–1) detected three CO(6-5) lines with 3.4<=I_CO(6–5) <=5.1 Jy km s^–1, 620<=FWHM<=707 km s^–1, and three [C I](2-1) lines with 2.3≤I_ [C I](2-1)_ ≤15.7 Jy km s^–1, 329<=FWHM<=943 km s^–1. For the CO and [C I] detected sources, we constrain the molecular gas reservoirs to be M_H2 = (0.4-6.9) ×10¹¹ M_☉, while the non-detections imply M_H2 < 1.1×10¹¹ M_☉. We compare our observations with the extended Ly α properties to understand the link between the cool and the molecular gas phases. We find large velocity shifts between the bulk of Ly α and the molecular gas systemic redshift in five sources (from ∼-400 to ∼+1200 km s^–1). The sources with the largest shifts have the largest Ly α line widths in the sample, suggesting more turbulent gas conditions and/or large-scale inflows/outflows around these quasars. We also find that the brightest (I_[C I](2-1)_=15.7±3.7∼ Jy∼km∼s^–1) and the widest (FWHM∼900 km s^–1) lines are detected for the smallest and dimmest Ly α nebulae. From this, we speculate that host galaxy obscuration can play an important role in reducing the ionizing and Ly α photons able to escape to halo scales, and/or that these systems are hosted by more massive haloes.