Measuring protoplanetary gas disk masses in AGE-PRO using N₂H⁺ and C18O

Measuring the gas mass of protoplanetary disks, the reservoir available for giant planet formation, has proven to be difficult. We currently lack a far-infrared observatory capable of observing HD, and the most common gas mass tracer, CO, suffers from a poorly constrained CO-to-H₂ ratio. Our recent work has shown that N2H+, a chemical tracer of CO poor gas, can be used to observationally measure the CO-to-H₂ ratio in disks and correct their CO-based gas masses. I will present the application of this new method to measure accurate protoplanetary gas disk masses of AGE-PRO, the ALMA survey of Gas Evolution in PROtoplanetary disks, a sample of 30 disks around similar spectral type (M3-K6) stars with ages between 0.1 and 10 Myr. Fitting the observations using a large grid of thermochemical models, the initial analysis shows no significant difference between gas masses of the 1-3 Myr disks in Lupus and the 5-11 Myr old disks in Upper Sco, with both regions having a similarly low median gas mass of ~4x10^-4 solar mass. Gas-to-dust mass ratios are found to decrease with age but are found to be lower than previously thought, in particular for compact disks. These results show that the AGE-PRO sample an excellent laboratory to understand giant-planet formation throughout the evolution of protoplanetary disks.