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Title: How Large Is a Disk—What Do Protoplanetary Disk Gas Sizes Really Mean?
Abstract

It remains unclear what mechanism is driving the evolution of protoplanetary disks. Direct detection of the main candidates, either turbulence driven by magnetorotational instabilities or magnetohydrodynamical disk winds, has proven difficult, leaving the time evolution of the disk size as one of the most promising observables able to differentiate between these two mechanisms. But to do so successfully, we need to understand what the observed gas disk size actually traces. We studied the relation betweenRCO,90%, the radius that encloses 90% of the12CO flux, andRc, the radius that encodes the physical disk size, in order to provide simple prescriptions for conversions between these two sizes. For an extensive grid of thermochemical models, we calculateRCO,90%from synthetic observations and relate properties measured at this radius, such as the gas column density, to bulk disk properties, such asRcand the disk massMdisk. We found an empirical correlation between the gas column density atRCO,90%and disk mass:Ngas(RCO,90%)3.73×1021(Mdisk/M)0.34cm2. Using this correlation we derive an analytical prescription ofRCO,90%that only depends onRcandMdisk. We deriveRcfor disks in Lupus, Upper Sco, Taurus, and the DSHARP sample, finding that disks in the older Upper Sco region are significantly smaller (〈Rc〉 = 4.8 au) than disks in the younger Lupus and Taurus regions (〈Rc〉 = 19.8 and 20.9 au, respectively). This temporal decrease inRcgoes against predictions of both viscous and wind-driven evolution, but could be a sign of significant external photoevaporation truncating disks in Upper Sco.

 
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Award ID(s):
2205617
NSF-PAR ID:
10444413
Author(s) / Creator(s):
; ; ;
Publisher / Repository:
DOI PREFIX: 10.3847
Date Published:
Journal Name:
The Astrophysical Journal
Volume:
954
Issue:
1
ISSN:
0004-637X
Format(s):
Medium: X Size: Article No. 41
Size(s):
["Article No. 41"]
Sponsoring Org:
National Science Foundation
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