The ALMA Survey of Gas Evolution of PROtoplanetary disks (AGE-PRO): Evolution of dust properties from multi-wavelength observations

Résumé : Understanding the evolution of solids in protoplanetary discs is important to comprehend the formation of giant planets cores and terrestrial planets. The ALMA Large Program AGE-PRO studied key disc properties in a survey of 30 protoplanetary discs across three evolutionary stages: the embedded phase (0.5-1 Myr), the middle-age phase (1-3 Myr), and the end of the disc lifetime (2-6 Myr). Preliminary dust properties were estimated using 1.3 mm observations, but a multi-wavelength analysis provides a better constraint of important properties such as the dust disc mass, the dust temperature, and the maximum grain size. We present new ALMA 3.1 mm and 1.5 mm (Bands 3 and 5) continuum observations of the complete survey of 30 AGE-PRO discs. We fitted the observed visibilities and derived radial brightness profiles, spatially resolving 20 discs from the AGE-PRO sample at the two studied wavelengths. A multi-wavelength modelling was performed including also the radial profiles from the 1.3 mm observations. Our results replicate trends obtained from the single wavelength analysis: the dust disc size seems to be constant over age and the dust disc mass decreases with time, with a factor $\sim$10-40 uncertainty from opacity assumptions. This result implies much lower gas-to-dust mass ratios for the discs in our sample than previously reported. In addition, the derived spectral indices are consistent with optically thick emission in a large fraction of the AGE-PRO discs, in particular for the Ophiuchus and Lupus discs.