Protoplanetary Disk Demographics with ALMA.

Abstract

The recent successes of exoplanet surveys have resulted in thousands of planetary systems being discovered and characterized. Yet exactly how these planets formed remains unclear, as similar demographic surveys of the preceding protoplanetary disks were, until recently, hindered by the limited sensitivity and resolution of (sub-)mm telescopes. The revolutionary Atacama Large Millimeter/sub-millimeter Array (ALMA) has overcome these observational barriers, freeing observers from the need to focus on only the brightest disks, which likely do not represent the typical pathways to planet formation. This work leverages the power of ALMA to conduct the rst large-scale, high-sensitivity surveys of (sub-)mm continuum and line emission for complete samples of protoplanetary disks at distinct stages of disk evolution. These observations are capable of placing statistical constraints on the evolution of fundamental disk properties, thereby providing new insights into how protoplanetary disks evolve into the observed exoplanet population. We focus on obtaining bulk disk masses in both dust and gas, as these fundamental properties are thought to strongly in uence subsequent planetary architectures, yet remain poorly understood on a population level. We utilize a well-established method of translating (sub-)mm continuum

ux into dust mass, and apply a recently developed technique for e ciently inferring gas mass from CO isotopologue line emission. Our ALMA surveys reveal a clear decline in disk dust mass with age, along with a potentially swifter decline in gas mass, both of which indicate that giant planet formation is either rare or rapid|the former being more consistent with exoplanet trends. We also nd that in OB clusters external photoevaporation driven by the highest-mass stars enhances both dust and gas depletion much more severely than previously thought. Our surveys illustrate the power of disk population studies in furthering our understanding of \typical" disk evolution and ultimately the most common pathways to planet formation.