Here we present high-resolution (15-24 au) observations of CO isotopologue lines from the Molecules with ALMA on Planet-forming Scales (MAPS) ALMA Large Program. Our analysis employs observations of the (J = 2-1) and (1-0) lines of 13 CO and C 18 O and the (J = 1-0) line of C 17 O for five protoplanetary disks. We retrieve CO gas density distributions, using three independent methods: (1) a thermochemical modeling framework based on the CO data, the broadband spectral energy distribution, and the millimeter continuum emission; (2) an empirical temperature distribution based on optically thick CO lines; and (3) a direct fit to the C 17 O hyperfine lines. Results from these methods generally show excellent agreement. The CO gas column density profiles of the five disks show significant variations in the absolute value and the radial shape. Assuming a gas-to-dust mass ratio of 100, all five disks have a global CO-to-H 2 abundance 10-100 times lower than the interstellar medium ratio. The CO gas distributions between 150 and 400 au match well with models of viscous disks, supporting the longstanding theory. CO gas gaps appear to be correlated with continuum gap locations, but some deep continuum gaps do not have corresponding CO gaps. The relative depths of CO and dust gaps are generally consistent with predictions of planet-disk interactions, but some CO gaps are 5-10 times shallower than predictions based on dust gaps. This paper is part of the MAPS special issue of the Astrophysical Journal Supplement.

The Molecules with ALMA at Planet-forming Scales (MAPS) Large Program provides a unique opportunity to study the vertical distribution of gas, chemistry, and temperature in the protoplanetary disks around IMLup, GMAur, AS209, HD163296, and MWC480. By using the asymmetry of molecular line emission relative to the disk major axis, we infer the emission height(z) above the midplane as a function of radius(r). Using this method, we measure emitting surfaces for a suite of CO isotopologues, HCN, and C 2 H. We find that 12 CO emission traces the most elevated regions with > z r 0.3, while emission from the less abundant 13 CO and C 18 O probes deeper into the disk at altitudes of  z r 0.2. C 2 H and HCN have lower opacities and signal-to-noise ratios, making surface fitting more difficult, and could only be reliably constrained in AS209, HD163296, and MWC480, with  z r 0.1, i.e., relatively close to the planet-forming midplanes. We determine peak brightness temperatures of the optically thick CO isotopologues and use these to trace 2D disk temperature structures. Several CO temperature profiles and emission surfaces show dips in temperature or vertical height, some of which are associated with gaps and rings in line and/or continuum emission. These substructures may be due to local changes in CO column density, gas surface density, or gas temperatures, and detailed thermochemical models are necessary to better constrain their origins and relate the chemical compositions of elevated disk layers with those of planet-forming material in disk midplanes. This paper is part of the MAPS special issue of the Astrophysical Journal Supplement.

The L1544 pre-stellar core has been observed as part of the ASAI IRAM 30m Large Program as well as follow-up programs. These observations have revealed the chemical richness of the earliest phases of low-mass star-forming regions. In this paper we focus on the twenty-one sulphur bearing species (ions, isotopomers and deuteration) that have been detected in this spectral-survey through fifty one transitions: CS, CCS, C 3 S, SO, SO 2 , H 2 CS, OCS, HSCN, NS, HCS + , NS + and H 2 S. We also report the tentative detection (4 σ level) for methyl mercaptan (CH 3 SH). LTE and non-LTE radiative transfer modelling have been performed and we used the nautilus chemical code updated with the most recent chemical network for sulphur to explain our observations. From the chemical modelling we expect a strong radial variation for the abundances of these species, which mostly are emitted in the external layer where non thermal desorption of other species has previously been observed. We show that the chemical study cannot be compared to what has been done for the TMC-1 dark cloud, where the abundance is supposed constant along the line of sight, and conclude that a strong sulphur depletion is necessary to fully reproduce our observations of the prototypical pre-stellar core L1544.

H 2 CO is one of the most abundant organic molecules in protoplanetary disks and can serve as a precursor to more complex organic chemistry. We present an ALMA survey of H 2 CO towards 15 disks covering a range of stellar spectral types, stellar ages, and dust continuum morphologies. H 2 CO is detected towards 13 disks and tentatively detected towards a 14th. We find both centrally-peaked and centrally-depressed emission morphologies, and half of the disks show ring-like structures at or beyond expected CO snowline locations. Together these morphologies suggest that H 2 CO in disks is commonly produced through both gas-phase and CO-ice-regulated grain-surface chemistry. We extract disk-averaged and azimuthally-averaged H 2 CO excitation temperatures and column densities for four disks with multiple H 2 CO line detections. The temperatures are between 20-50K, with the exception of colder temperatures in the DM Tau disk. These temperatures suggest that H 2 CO emission in disks is generally emerging from the warm molecular layer, with some contributions from the colder midplane. Applying the same H 2 CO excitation temperatures to all disks in the survey, we find that H 2 CO column densities span almost three orders of magnitude (∼ 5×10 11 −5×10 14 cm −2 ). The column densities appear uncorrelated with disk size and stellar age, but Herbig Ae disks may have less H 2 CO compared to T Tauri disks, possibly because of less CO freeze-out. More H 2 CO observations towards Herbig Ae disks are needed to confirm this tentative trend, and to better constrain under which disk conditions H 2 CO and other oxygen-bearing organics efficiently form during planet formation.

The Molecules with ALMA at Planet-forming Scales (MAPS) Large Program provides a detailed, high-resolution (∼10–20 au) view of molecular line emission in five protoplanetary disks at spatial scales relevant for planet formation. Here we present a systematic analysis of chemical substructures in 18 molecular lines toward the MAPS sources: IM Lup, GM Aur, AS 209, HD 163296, and MWC 480. We identify more than 200 chemical substructures, which are found at nearly all radii where line emission is detected. A wide diversity of radial morphologies—including rings, gaps, and plateaus—is observed both within each disk and across the MAPS sample. This diversity in line emission profiles is also present in the innermost 50 au. Overall, this suggests that planets form in varied chemical environments both across disks and at different radii within the same disk. Interior to 150 au, the majority of chemical substructures across the MAPS disks are spatially coincident with substructures in the millimeter continuum, indicative of physical and chemical links between the disk midplane and warm, elevated molecular emission layers. Some chemical substructures in the inner disk and most chemical substructures exterior to 150 au cannot be directly linked to dust substructure, however, which indicates that there are also other causes of chemical substructures, such as snowlines, gradients in UV photon fluxes, ionization, and radially varying elemental ratios. This implies that chemical substructures could be developed into powerful probes of different disk characteristics, in addition to influencing the environments within which planets assemble. This paper is part of the MAPS special issue of the Astrophysical Journal Supplement.

We explore the dynamical structure of the protoplanetary disks surrounding HD 163296 and MWC 480 as part of the Molecules with ALMA at Planet-forming Scales (MAPS) large program. Using the J = 2-1 transitions of 12 CO, 13 CO, and C 18 O imaged at spatial resolutions of ∼0 15 and with a channel spacing of 200 m s −1 , we find perturbations from Keplerian rotation in the projected velocity fields of both disks (5% of the local Keplerian velocity), suggestive of large-scale (tens of astronomical units in size), coherent flows. By accounting for the azimuthal dependence on the projection of the velocity field, the velocity fields were decomposed into azimuthally averaged orthogonal components, v f , v r , and v z . Using the optically thick 12 CO emission as a probe of the gas temperature, local variations of ≈3 K (≈5% relative changes) were observed and found to be associated with the kinematic substructures. The MWC 480 disk hosts a suite of tightly wound spiral arms. The spirals arms, in conjunction with the highly localized perturbations in the gas velocity structure (kinematic planetary signatures), indicate a giant planet, ∼1 M Jup , at a radius of ≈245 au. In the disk of HD 163296, the kinematic substructures were consistent with previous studies of Pinte et al. and Teague et al. advocating for multiple ∼1 M Jup planets embedded in the disk. These results demonstrate that molecular line observations that characterize the dynamical structure of disks can be used to search for the signatures of embedded planets. This paper is part of the MAPS special issue of the Astrophysical Journal Supplement.

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In this paper, we present preliminary results illustrating the effect of cosmic rays on solid-phase chemistry in models of both TMC-1 and several sources with physical conditions identical to TMC-1 except for hypothetically enhanced ionization rates. Using a recent theory for the addition of cosmic ray-induced reactions to astrochemical models, we calculated the radiochemical yields, called G values, for the primary dust grain ice-mantle constituents. We show that the inclusion of this nonthermal chemistry can lead to the formation of complex organic molecules from simpler ice-mantle constituents, even under cold core conditions. In addition to enriching ice-mantles, we find that these new radiation-chemical processes can lead to increased gas-phase abundances as well, particularly for HOCO, NO 2 , HC 2 O, methyl formate (HCOOCH 3 ), and ethanol (CH 3 CH 2 OH). These model results