The ALMA Survey of Gas Evolution of PROtoplanetary Disks (AGE-PRO): III. Dust and Gas Disk Properties in the Lupus Star-forming Region

Abstract: We present Band 6 and Band 7 observations of 10 Lupus disks around M3-K6 stars from the ALMA survey of Gas Evolution in PROtoplanetary disks (AGE-PRO) Large Program. In addition to continuum emission in both bands, our Band 6 setup covers the $\mathrm{{}^{12}CO}$, $\mathrm{{}^{13}CO}$ and $\mathrm{C^{18}O}\,J$=2-1 lines, while our Band 7 setup covers the $\mathrm{N_2H^+}\,J$=3-2 line. All of our sources are detected in $\mathrm{{}^{12}CO}$ and $\mathrm{{}^{13}CO}$, 7 out of 10 are detected in $\mathrm{C^{18}O}$, and 3 are detected in $\mathrm{N_2H^+}$. We find strong correlations between the CO isotopologue line fluxes and the continuum flux densities. With the exception of one disk, we also identify a strong correlation between the $\mathrm{C^{18}O}\,J$=2-1 and $\mathrm{N_2H^+}\,J$=3-2 fluxes, indicating similar CO abundances across this sample. For the two sources with well-resolved continuum and $\mathrm{{}^{12}CO}\,J$=2-1 images, we find that their gas-to-dust size ratio is consistent with the median value of $\sim 2$ inferred from a larger sample of Lupus disks. We derive dust disk masses from continuum flux densities. We estimate gas disk masses by comparing $\mathrm{C^{18}O}\,J$=2-1 line fluxes with those predicted by the limited grid of self-consistent disk models of Ruaud et al. (2022). A comparison of these mass estimates with those derived by Trapman et al. (2025), using a combination of CO isotopologue and $\mathrm{N_2H^+}$ line emission, shows that the masses are consistent with each other. Some discrepancies appear for small and faint disks, but they are still within the uncertainties. Both methods find gas disk masses increase with dust disk masses, and gas-to-dust mass ratios are between $10-100$ in the AGE-PRO Lupus sample.

• The paper leverages ALMA Band 6/7 observations to characterize gas and dust properties in Lupus protoplanetary disks.
• It applies self-consistent thermodynamic models to derive dust and gas mass estimates, showing a close correlation and a median gas-to-dust size ratio of about 2.0.
• The study’s high-resolution CO isotopologue analysis distinguishes uniform gas distributions and identifies effects from dust opacity and intrinsic variability.

Analysis of the ALMA Survey of Gas Evolution of Protoplanetary Disks (AGE-PRO): Dust and Gas Disk Properties in the Lupus Star-forming Region

The paper "The ALMA Survey of Gas Evolution of PROtoplanetary Disks (AGE-PRO): Dust and Gas Disk Properties in the Lupus Star-forming Region" presents an in-depth investigation of protoplanetary disks within the Lupus Star-forming Region employing data from the Atacama Large Millimeter/submillimeter Array (ALMA). Authored by Deng et al., this study forms part of a broader initiative, aiming to elucidate the evolutionary aspects of gas and dust in young stellar objects.

Study Context and Methodology

The research utilizes Band 6 and Band 7 ALMA observations targeting ten protoplanetary disks surrounding M3-K6 stars. These disks were selected to represent a spectrum of properties, particularly in terms of disk mass and size, within the Lupus region, which is noted for its active star formation and proximity to the Scorpius-Centaurus OB association.

Key observations involve the analysis of continuum emission alongside emission lines from CO isotopologues (including $^{12}CO$, $^{13}CO$, and $C^{18}O$) and the $N_2H^+$ line. These observations have been facilitated by high-resolution imaging capabilities and the application of advanced data calibration and analysis techniques to discern the continuum and line emissions effectively.

Results

The study reports several significant findings:

1. Line Emission Analysis: All surveyed sources were detected in $^{12}CO$ and $^{13}CO$ emissions, while the detection of $C^{18}O$ and $N_2H^+$ was achieved for a subset of sources. The detected correlations between CO isotopologues' fluxes and continuum emissions suggest uniform gas distributions in most of the disks, but highlight variability attributable to either dust opacity effects or intrinsic gas distribution differences.
2. Disk Mass and Size Estimations: Utilizing self-consistent thermodynamic disk models, the authors derived dust and gas mass estimations. The calculated disk masses correlate positively with dust masses, indicating that dust continuum emission remains a reliable proxy for gas disk properties granted the assumption of a constant gas-to-dust ratio within the sample.
3. Significant Disk Size Ratio Observations: For two well-resolved sources, gas-to-dust size ratios were consistent with the median value of approximately 2.0, as derived from a greater sample of Lupus disks. This ratio provides insights into the radial drift of dust particles and the prevalence of pressure bumps that could impede such drift.

Implications and Future Directions

This study contributes valuable insights into the dynamics and physical conditions prevailing in the protoplanetary disks of young star-forming regions. The results emphasize the capability to effectively use emissions such as $C^{18}O$ as mass tracers when appropriately contextualized within theoretical models. Moreover, the investigation reveals nuanced information about the interaction between gas and dust components, crucial for understanding planet formation mechanisms.

The findings pave the way for future research to further explore disk properties across varied stellar environments. Particularly, this work suggests that expanded multi-line observations alongside enhanced computational modeling will refine gas mass estimations and elucidate elemental depletion mechanisms. Furthermore, pairing these observations with studies focused on older stellar regions might shed light on the evolutionary transitions from protoplanetary disks to fully-fledged planetary systems.

In summary, this comprehensive analysis of the Lupus star-forming region advances the understanding of disk evolution, presenting robust methodologies and frameworks that can be leveraged in subsequent observational and theoretical studies in astrophysics.