Elias 2-27 CO and CN ALMA datacubes

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. We analyzed 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 was traced directly from the channel maps, following geometrical methods that had been previously used to analyze the CO emission of Elias 2-27.

Simple analytical models were used to parameterize the vertical profile of each molecule and study the extent of each tracer. From the radial intensity profiles we computed radial profiles of column density and optical depth. We show that the vertical location of CN and CO isotopologs 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 on 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.

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 ({tau}<=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.