ALMA Survey of Lupus Protoplanetary Disks. I. Dust and Gas Masses

Abstract

We present the first high-resolution sub-millimeter survey of both dust and gas for a large population of protoplanetary disks. Characterizing fundamental properties of protoplanetary disks on a statistical level is critical to understanding how disks evolve into the diverse exoplanet population. We use the Atacama Large Millimeter/Submillimeter Array (ALMA) to survey 89 protoplanetary disks around stars with M∗ > 0.1 M⊙ in the young (1–3 Myr), nearby (150–200 pc) Lupus complex. Our observations cover the 890 μm continuum and the ^(13)CO and C^(18)O 3–2 lines. We use the sub-millimeter continuum to constrain M_(dust) to a few Martian masses (0.2–0.4 M⊕) and the CO isotopologue lines to constrain M_(gas) to roughly a Jupiter mass (assuming an interstellar medium (ISM)-like [CO]/[H_2] abundance). Of 89 sources, we detect 62 in continuum, 36 in ^(13)CO, and 11 in C^(18)O at >3σ significance. Stacking individually undetected sources limits their average dust mass to ≾6 Lunar masses (0.03 M⊕), indicating rapid evolution once disk clearing begins. We find a positive correlation between M_(dust) and M∗, and present the first evidence for a positive correlation between M_(gas) and M∗, which may explain the dependence of giant planet frequency on host star mass. The mean dust mass in Lupus is 3× higher than in Upper Sco, while the dust mass distributions in Lupus and Taurus are statistically indistinguishable. Most detected disks have M_(gas) ≾ 1 M(Jup) and gas-to-dust ratios <100, assuming an ISM-like [CO]/[H_2] abundance; unless CO is very depleted, the inferred gas depletion indicates that planet formation is well underway by a few Myr and may explain the unexpected prevalence of super-Earths in the exoplanet population.