Measurement of Circumstellar Disk Sizes in the Upper Scorpius OB Association with ALMA

Abstract

We present detailed modeling of the spatial distributions of gas and dust in 57 circumstellar disks in the Upper Scorpius OB Association observed with ALMA at submillimeter wavelengths. We fit power-law models to the dust surface density and CO J=3-2 surface brightness to measure the radial extent of dust and gas in these disks. We found that these disks are extremely compact: the 25 highest signal-to-noise disks have a median dust outer radius of 21 au, assuming an R 1 -dust surface density profile. Our lack of CO detections in the majority of our sample is consistent with these small disk sizes assuming the dust and CO share the same spatial distribution. Of seven disks in our sample with well-constrained dust and CO radii, four appear to be more extended in CO, although this may simply be due to the higher optical depth of the CO. Comparison of the Upper Sco results with recent analyses of disks in Taurus, Ophiuchus, and Lupus suggests that the dust disks in Upper Sco may be approximately three times smaller in size than their younger counterparts, although we caution that a more uniform analysis of the data across all regions is needed. We discuss the implications of these results for disk evolution.

Formation of planetary populations − II. Effects of initial disc size and radial dust drift

“…These observed disks surrounding a range of host-stellar masses have gas radii in the range of 63-500 AU at an age of ∼ 1-3 Myr. We emphasize, however, that these large, extended disks are the exception and are not indicative of typical disks that are much more compact, as indicated by numerous observations showing dust radii of 20 − 30 AU (Barenfeld et al 2016(Barenfeld et al , 2017Cox et al 2017;Hendler et al 2017;Tazzari et al 2017;Cieza et al 2019;Long et al 2019).…”

On the diversity and statistical properties of protostellar discs

“…In Class II objects where both the gas and dust are observed it is common for the radius of the gas disc to be larger than that of the (sub-)mm dust disc (e.g. Piétu et al 2007Piétu et al , 2014Isella et al 2007;Panić et al 2009;Andrews et al 2012;Rosenfeld et al 2013;de Gregorio-Monsalvo et al 2013;Walsh et al 2014;Pineda et al 2014;Cleeves et al 2016;Barenfeld et al 2017). For example, in the Class II object IM Lupus, the gas disc extends to ≈ 1000 au while the mm dust disc is truncated at ≈ 300 au ).…”

“…All of these studies consider radii based on dust profiles, but in the ONC they are derived from optical dust absorption (discs seen in sillouhette against background nebulosity), whereas in all the other surveys they are based on millimetre dust emission. Barenfeld et al (2017) measures both dust and gas radii for seven discs, finding that the radii of the gas discs (30 − 170 au) are larger than those measured using the dust in four of the seven cases. At face value, Barenfeld et al find that the dust disc radii in Upper Scorpius are three times smaller than those found in the other regions (median radii of 21 au).…”

“…26 we plot the cumulative distributions of disc sizes of the observed samples, excluding that of Barenfeld et al (2017), and two distributions derived from the simulation. From the simulation, we plot the distribution obtained using all protostellar systems (solid line) and the distribution obtained only from protostars that have not had encounters with other protostars closer than 2000 au.…”

“…The radii of discs of Class II objects have been studied in the Orion Nebula Cluster (ONC; Vicente & Alves 2005), Ophiuchus (Andrews et al 2009(Andrews et al , 2010, Lupus , and the Upper Scorpius OB Association (Barenfeld et al 2017). In addition, Tripathi et al (2017) study a collection of 50 discs that are mostly from Taurus and Ophiuchus, but with 9 that are in other regions or in isolation.…”