Molecules with ALMA at Planet-forming Scales (MAPS) XII: Inferring the C/O and S/H ratios in Protoplanetary Disks with Sulfur Molecules

Abstract

Sulfur-bearing molecules play an important role in prebiotic chemistry and planet habitability. They are also proposed probes of chemical ages, elemental C/O ratio, and grain chemistry processing. Commonly detected in diverse astrophysical objects, including the Solar System, their distribution and chemistry remain, however, largely unknown in planet-forming disks. We present CS ($2-1$) observations at $\sim 0."3$ resolution performed within the ALMA-MAPS Large Program toward the five disks around IM Lup, GM Aur, AS 209, HD 163296, and MWC 480. CS is detected in all five disks, displaying a variety of radial intensity profiles and spatial distributions across the sample, including intriguing apparent azimuthal asymmetries. Transitions of C${}_2$S and SO were also serendipitously covered but only upper limits are found. For MWC 480, we present complementary ALMA observations at $\sim 0."5$, of CS, ${}^{13}$CS, C${}^{34}$S, H${}_2$CS, OCS, and SO${}_2$. We find a column density ratio N(H${}_2$CS)/N(CS)$\sim 2/3$, suggesting that a substantial part of the sulfur reservoir in disks is in organic form (i.e., C${}_x$H${}_y$S${}_z$). Using astrochemical disk modeling tuned to MWC 480, we demonstrate that $N$(CS)/$N$(SO) is a promising probe for the elemental C/O ratio. The comparison with the observations provides a super-solar C/O. We also find a depleted gas-phase S/H ratio, suggesting either that part of the sulfur reservoir is locked in solid phase or that it remains in an unidentified gas-phase reservoir. This paper is part of the MAPS special issue of the Astrophysical Journal Supplement.

Accepted for publication in The Astrophysical Journal Supplement (27 pages, 13 figures, 5 tables)

References in corpus (40)

• The NumPy array: a structure for efficient numerical computation
• A Unified Representation of Gas-Phase Element Depletions in the Interstellar Medium
• Coagulation, fragmentation and radial motion of solid particles in protoplanetary disks
• The Critical Density and the Effective Excitation Density of Commonly Observed Molecular Dense Gas Tracers
• X-Shooter spectroscopy of young stellar objects in Lupus: Accretion properties of class II and transitional objects
• Polycylcic Aromatic Hydrocarbons (PAH's) in dense cloud chemistry
• Molecules with ALMA at Planet-forming Scales (MAPS) I: Program Overview and Highlights
• Binding energies: new values and impact on the efficiency of chemical desorption
• Constraining the X-ray and Cosmic Ray Ionization Chemistry of the TW Hya Protoplanetary Disk: Evidence for a Sub-interstellar Cosmic Ray Rate
• Meridional flows in the disk around a young star
• Direct mapping of the temperature and velocity gradients in discs. Imaging the vertical CO snow line around IM Lupi
• Modeling Sulfur Depletion in Interstellar Clouds
• Water in star-forming regions (WISH): Physics and chemistry from clouds to disks as probed by Herschel spectroscopy
• Low sulfur depletion in the Horsehead PDR
• CO and dust properties in the TW Hya disk from high-resolution ALMA observations
• Parameters of Herbig Ae/Be and Vega-type stars
• An interferometric study of the low-mass protostar IRAS 16293-2422: small scale organic chemistry
• Molecules with ALMA at Planet-forming Scales (MAPS) XIV: Revealing disk substructures in multi-wavelength continuum emission
• Sulphur-bearing molecules in diffuse molecular clouds: new results from SOFIA/GREAT and the IRAM 30 m telescope
• Sulfur chemistry in protoplanetary disks: CS and H2CS
• Cold CO in circumstellar disks: On the effects of photodesorption and vertical mixing
• A survey of C2H, HCN, and C18O in protoplanetary disks
• An ALMA survey of DCN/H${}^{13}$CN and DCO${}^{+}$/H${}^{13}$CO${}^{+}$ in protoplanetary disks
• Molecules with ALMA at Planet-forming Scales (MAPS). VII. Sub-stellar O/H and C/H and super-stellar C/O in planet feeding gas
• Gas phase Elemental abundances in Molecular cloudS (GEMS). II. On the quest for the sulphur reservoir in molecular clouds: the $H_{2}S$ case
• First detection of interstellar S2H
• Molecules with ALMA at Planet-forming Scales (MAPS). IX. Distribution and Properties of the Large Organic Molecules HC${}_3$N, CH${}_3$CN, and $c$-C${}_3$H${}_2$
• Stacking Spectra in Protoplanetary Disks: Detecting Intensity Profiles from Hidden Molecular Lines in HD 163296
• An unbiased ALMA spectral survey of the LkCa 15 and MWC 480 protoplanetary disks
• H2S in the L1157-B1 Bow shock
• The role of C/O in nitrile astrochemistry in PDRs and planet-forming disks
• Molecules with ALMA at Planet-forming Scales (MAPS) XVI: Characterizing the impact of the molecular wind on the evolution of the HD 163296 system
• Using FUV to IR Variability to Probe the Star-Disk Connection in the Transitional Disk of GM Aur
• Spatially resolved HCN J=4--3 and CS J=7--6 emission from the disk around HD 142527
• A new study of the chemical structure of the Horsehead nebula: the influence of grain-surface chemistry
• The essential elements of dust evolution: A viable solution to the interstellar oxygen depletion problem?
• The nitrogen carrier in protoplanetary disks
• Importance of the H2 abundance in protoplanetary disk ices for the molecular layer chemical composition
• Time evolution of a viscous protoplanetary disk with a free geometry: toward a more self-consistent picture
• Protoplanetary disks: Sensitivity of the chemical composition to various model parameters

Cited by in corpus (1)

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