Observational constraints on evolution of dust disc properties in Upper Scorpius

ABSTRACT Protoplanetary discs in the Upper Scorpius star-forming region are excellent laboratories to investigate late stages of planet formation. In this work, we analyse the morphology of the dust continuum emission of 121 discs from an Atacama Large Millimeter Array (ALMA) Band 7 survey of the Upper Scorpius region. This analysis is done in the visibility plane, to measure the flux, geometry and characterize potential structures. We compare the results with state-of-the art gas and dust evolution models that include external photoevaporation, with mild values of the $F_{\rm {UV}}$ of 1–40 $G_0$. From the visibility analysis, 52 of the 121 discs are resolved (43 per cent). From the resolved discs, 24 discs have structures and 28 remain as smooth discs at the mean resolution scale of ${\sim} 0.1\,\mathrm{ arcsec}$ ($\sim$14 au). Our results show no significant dust disc size evolution of the surviving discs in UpperSco when compared to discs in younger star-forming regions, such as Lupus. We find a strong, steeper-than-previously-reported correlation between dust disc size and disc millimetre continuum luminosity, in agreement with drift-dominated dust evolution models. We also find positive correlations between the dust disc mass versus stellar mass and dust disc size versus stellar mass. The slope of the dust disc size versus stellar mass relationship is steeper compared to younger star forming regions. Additionally, we observe no significant correlation between dust disc properties and the environmental $F_{\rm {UV}}$, consistent with models predicting that dust disc properties are primarily shaped by drift and dust traps. Our models predict that gas disc masses and sizes should be highly affected by the moderate $F_{\rm {UV}}$ values that Upper Scorpius discs experience in contrast to the dust. This highlights the need for deeper and higher-resolution ALMA observations of gas in these discs exposed to mild external photoevaporation to further constrain their evolution and fate.