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

Abstract

We present the first high-resolution sub-mm 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 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-mm 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 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 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.

Far-infrared HD emission as a measure of protoplanetary disk mass

“…Deriving accurate gas-to-dust mass ratios has been one of the motivations for measuring the gas mass directly (e.g., Ansdell et al 2016;Miotello et al 2017). However, the gas-to-dust ratio could also affect the HD emission directly, e.g., by changing the coupling between the dust and the gas.…”

Disk Masses for Embedded Class I Protostars in the Taurus Molecular Cloud

“…Over the past few decades, there have been numerous studies of nearby star-forming regions at millimeter wavelengths with the aim of measuring disk masses for large samples of disks, and this work has been accelerated in recent years by the power of ALMA to quickly survey large numbers of sources (e.g., Beckwith et al 1990;Osterloh & Beckwith 1995;Dutrey et al 1996;Andrews & Williams 2005, 2007Eisner et al 2008Eisner et al , 2016Mann & Williams 2010;Andrews et al 2013;Mann et al 2014;Ansdell et al 2016Ansdell et al , 2017Barenfeld et al 2016;Pascucci et al 2016). These surveys have tended to target the population of Class II protostar disks because they are no longer embedded in an envelope, and so estimates of their disk masses are more straightforward.…”

“…It has also been shown that Class II disk masses are correlated with stellar mass (Andrews et al 2013, Ansdell et al 2016Barenfeld et al 2016;Pascucci et al 2016). As such, when comparing disk mass distributions, we must take care to ensure that our samples have similar stellar host properties; otherwise, our disk mass measurements may be biased.…”

“…Recent disk mass surveys of Class II protostars have raised concerns about whether their disks contain enough mass to form giant planets (e.g., Williams & Best 2014;Ansdell et al 2016;Eisner et al 2016). An accounting of the material in our own solar system, which is dominated by the mass of Jupiter, suggests that disk masses of   -M 0.01 0.1 are needed to form a planetary system like our own (e.g., Weidenschilling 1977;Hayashi 1981;Desch 2007).…”

“…Class II disks are the easiest to study because, without a protostellar envelope, the entirety of the submillimeter flux can be attributed to disk emission. In the past decade there has been a large effort, particularly with interferometers like the Combined Array for Research in Millimeter-wave Astronomy (CARMA), the SMA, and now ALMA, toward measuring Class II disk masses (Andrews & Williams 2005, 2007Eisner et al 2008;Mann & Williams 2010;Mann et al 2014;Ansdell et al 2016Ansdell et al , 2017Barenfeld et al 2016;Pascucci et al 2016). These studies typically find that the majority of these disks fall well below the  -M 0.01 0.1 needed to form planetary systems like our own (e.g., Weidenschilling 1977;Desch 2007).…”