New Constraints on Protoplanetary Disk Gas Masses in Lupus
Abstract

Gas mass is a fundamental quantity of protoplanetary disks that directly relates to their ability to form planets. Because we are unable to observe the bulk H2content of disks directly, we rely on indirect tracers to provide quantitative mass estimates. Current estimates for the gas masses of the observed disk population in the Lupus star-forming region are based on measurements of isotopologues of CO. However, without additional constraints, the degeneracy between H2mass and the elemental composition of the gas leads to large uncertainties in such estimates. Here, we explore the gas compositions of seven disks from the Lupus sample representing a range of CO-to-dust ratios. With Band 6 and 7 ALMA observations, we measure line emission for HCO+, HCN, and N2H+. We find a tentative correlation among the line fluxes for these three molecular species across the sample, but no correlation with13CO or submillimeter continuum fluxes. For the three disks where N2H+is detected, we find that a combination of high disk gas masses and subinterstellar C/H and O/H are needed to reproduce the observed values. We find increases of ∼10–100× previous mass estimates are required to match the observed line fluxes. This work highlights how multimolecular studies are essential more »

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Award ID(s):
Publication Date:
NSF-PAR ID:
10364360
Journal Name:
The Astrophysical Journal
Volume:
927
Issue:
2
Page Range or eLocation-ID:
Article No. 229
ISSN:
0004-637X
Publisher:
DOI PREFIX: 10.3847
We use ALMA observations of CO(2–1) in 13 massive (M*≳ 1011M) poststarburst galaxies atz∼ 0.6 to constrain the molecular gas content in galaxies shortly after they quench their major star-forming episode. The poststarburst galaxies in this study are selected from the Sloan Digital Sky Survey spectroscopic samples (Data Release 14) based on their spectral shapes, as part of the Studying QUenching at Intermediate-z Galaxies: Gas, angu$L→ar$momentum, and Evolution ($SQuIGGL⃗E$) program. Early results showed that two poststarburst galaxies host large H2reservoirs despite their low inferred star formation rates (SFRs). Here we expand this analysis to a larger statistical sample of 13 galaxies. Six of the primary targets (45%) are detected, with$MH2≳109$M. Given their high stellar masses, this mass limit corresponds to an average gas fraction of$〈fH2≡MH2/M*〉∼7%$or ∼14% using lower stellar masses estimates derived from analytic, exponentially declining star formation histories. The gas fraction correlates with theDn4000 spectral index, suggesting that the cold gas reservoirs decrease with time since burst, as found in local K+A galaxies. Star formation histories derived from flexible stellar population synthesis modeling support thismore »