Context. The specific location from where molecules emit in a protoplanetary disk depends on the system properties. Therefore, directly constraining the emitting regions radially, azimuthally and vertically is key towards studying the environment of planet formation. Due to the difficulties and lack of high resolution observations, most of the current observational constraints for the vertical distribution of molecular emission rely on indirect methods. Aims. We aim to directly trace the vertical location of the emitting surface of multiple molecular tracers in protoplanetary disks. Our sample of disks includes Elias 2-27, WaOph 6 and the sources targeted by the MAPS ALMA Large Program. The set of molecules studied include CO isotopologues in various transitions, HCN, CN, H 2 CO, HCO + , C 2 H and c-C 3 H 2 . Methods. The vertical emitting region is determined directly from the channel maps using the geometrical method described in Pinte et al. (2018a). This method has been used in previous studies, however we implement an accurate masking of the channel emission in order to recover the vertical location of the emission surface even at large radial distances from the star and for low-SNR lines. Parametric models are used to describe the emission surfaces and characterize any structure within the vertical profile.Results. The vertical location of the emitting layer is obtained for 10 different molecules and transitions in HD 163296. In the rest of the sample it is possible to vertically locate between 4-7 lines. Brightness temperature profiles are obtained for the entire sample and for all CO isotopologues. IM Lup, HD163296 and MWC 480 12 CO and 13 CO show vertical modulations, which are characterized and found to be coincident with dust gaps and kinematical perturbations. We also present estimates of the gas pressure scale height in the disks from the MAPS sample. Compared to physical-chemical models we find good agreement with the vertical location of CO isotopologues. In HD 163296 CN and HCN trace a similar intermediate layer, which is expected from physical chemical models. For the other disks, we find that UV flux tracers and the vertical profiles of HCN and C 2 H are lower than predicted in theoretical models. HCN and H 2 CO show a highly structured vertical profile, possibly indicative of different formation pathways in the case of H 2 CO. Conclusions. It is possible to trace the vertical locations of multiple molecular species that trace a wide variety of physical and chemical disk properties. The distribution of CO isotopologues is in agreement with theoretical predictions and the emission is found at a wide range of vertical heights z/r = 0.5-0.05. The vertical location of CO may be inversely related to the stellar mass. Other molecular lines are mostly found at z/r ≤0.15. The vertical layering of molecules is in agreement with theoretical predictions in some systems, but not in all, therefore dedicated chemical-physical models are needed to further study and understand the diversity of the emission surf...
Context. CN emission is expected to originate in the upper layers of protoplanetary disks, tracing UV-irradiated regions. This hypothesis, however, has been observationally tested only in a handful of disks. Elias 2-27 is a young star that hosts an extended, bright and inclined disk of dust and gas. The inclination and extreme flaring of the disk make Elias 2-27 an ideal target to study the vertical distribution of molecules, particularly CN. Aims. We aim to directly trace the emission of CN in the disk around Elias 2-27 and compare it to previously published CO isotopologue data of the system. Both tracers can be combined and used to constrain the physical and chemical properties of the disk. Through this analysis we can test model predictions of CN emission and compare observations of CN in other objects to the massive, highly flared, asymmetric and likely gravitationally unstable protoplanetary disk around Elias 2-27. Methods. We analyze CN N = 3 − 2 emission in two different transitions J = 7/2 − 5/2 and J = 5/2 − 3/2, for which we detect two hyperfine group transitions. The vertical location of CN emission is traced directly from the channel maps, following geometrical methods that have been previously used to analyze the CO emission of Elias 2-27. Simple analytical models are used to parametrize the vertical profile of each molecule and study the extent of each tracer. From the radial intensity profiles we compute radial profiles of column density and optical depth. Results. We show that the vertical location of CN and CO isotopologues in Elias 2-27 is layered and consistent with predictions from thermochemical models. A north/south asymmetry in the radial extent of the CN emission is detected, which is likely due to shadowing in the north side of the disk. Combining the information from the peak brightness temperature and vertical structure radial profiles, we find that the CN emission is mostly optically thin and constrained vertically to a thin slab at z/r ∼0.5. A column density of 10 14 cm −2 is measured in the inner disk which for the north side decreases to 10 12 cm −2 and for the south side to 10 13 cm −2 in the outer regions. Conclusions. In Elias 2-27, CN traces a vertically elevated region above the midplane, very similar to that traced by 12 CO. The inferred CN column densities, low optical depth (τ ≤1) and location near the disk surface are consistent with thermo-chemical disk models, in which CN formation is initiated by the reaction of N with UV-pumped H 2 . The observed north/south asymmetry may be caused by either ongoing infall or by a warped inner disk. This study highlights the importance of tracing the vertical location of various molecules to constrain the disk physical conditions.
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