exoALMA. XIII. Gas Masses from N2H+ and C18O: A Comparison of Measurement Techniques for Protoplanetary Gas Disk Masses

exoALMA. XIII. Gas Masses from N2H+ and C18O: A Comparison of Measurement Techniques for Protoplanetary Gas Disk Masses

The gas masses of protoplanetary disks are important but elusive quantities. In this work we present new Atacama Large Millimeter/submillimeter Array (ALMA) observations of N _2 H ^+ (3–2) for 11 exoALMA disks. N _2 H ^+ is a molecule sensitive to CO freeze-out and has recently been shown to signifi...

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Main Authors: Leon Trapman, Cristiano Longarini, Giovanni P. Rosotti, Sean M. Andrews, Jaehan Bae, Marcelo Barraza-Alfaro, Myriam Benisty, Gianni Cataldi, Pietro Curone, Ian Czekala, Stefano Facchini, Daniele Fasano, Mario Flock, Misato Fukagawa, Maria Galloway-Sprietsma, Himanshi Garg, Cassandra Hall, Jane Huang, John D. Ilee, Andres F. Izquierdo, Kazuhiro Kanagawa, Geoffroy Lesur, Giuseppe Lodato, Ryan A. Loomis, Ryuta Orihara, Teresa Paneque-Carreno, Christophe Pinte, Daniel Price, Jochen Stadler, Richard Teague, Sierk van Terwisga, Leonardo Testi, Hsi-Wei Yen, Gaylor Wafflard-Fernandez, David J. Wilner, Andrew J. Winter, Lisa Wölfer, Tomohiro C. Yoshida, Brianna Zawadzki, Ke Zhang
Format: Article
Language:English
Published: IOP Publishing 2025-01-01
Series:The Astrophysical Journal Letters
Subjects:
Protoplanetary disks
Astrochemistry
Interferometry
Radio interferometry
Online Access:https://doi.org/10.3847/2041-8213/adc430
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Summary:The gas masses of protoplanetary disks are important but elusive quantities. In this work we present new Atacama Large Millimeter/submillimeter Array (ALMA) observations of N _2 H ^+ (3–2) for 11 exoALMA disks. N _2 H ^+ is a molecule sensitive to CO freeze-out and has recently been shown to significantly improve the accuracy of gas masses estimated from CO line emission. We combine these new observations with archival N _2 H ^+ and CO isotopologue observations to measure gas masses for 19 disks, predominantly from the exoALMA large program. For 15 of these disks the gas mass has also been measured using gas rotation curves. We show that the CO + N _2 H ^+ line emission-based gas masses typically agree with the kinematically measured ones within a factor of 3 (∼1 σ –2 σ ). Gas disk masses from CO + N _2 H ^+ are on average a factor of ${2.3}_{-1.0}^{+0.7}\times $ lower than the kinematic disk masses, which could suggest slightly lower N _2 abundances and/or lower midplane ionization rates than typically assumed. Herbig disks are found to have CO gas abundances at the level of the interstellar medium based on their CO and N _2 H ^+ fluxes, which sets them apart from T Tauri disks, where abundances are typically ∼3−30× lower. The agreement between CO + N _2 H ^+ -based and kinematically measured gas masses is promising and shows that multimolecule line fluxes are a robust tool to accurately measure disk masses at least for extended disks.
ISSN:2041-8205

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