APEX at the QSO MUSEUM: molecular gas reservoirs associated with z ∼3 quasars and their link to the extended Ly α emission

Abstract

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 (〈rms〉 = 2.6 mJy in 300 km s-1) detected three CO(6-5) lines with 3.4≤ICO(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[CI](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 MH2 = (0.4-6.9) × 1011M⊙, while the non-detections imply MH2 < 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[CI](2-1)=15.7± 3.7Jy 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.