Resolved carbon monoxide observations of protoplanetary discs in ophiuchus

Abstract

The $^{12}$CO rotational lines in protoplanetary discs are good tracers of the total spatial extension of the gas component and potentially planet-disc interactions. This work analyses ALMA long-baseline observations of the $^{12}$CO($J$=2$-$1) line, aiming to provide new observational constraints on the gas distribution of ten discs from the "Ophiuchus DIsc Survey Employing ALMA" (ODISEA) project. This Ophiuchus sample is diverse in terms of SED Class and mm-continuum morphologies. The position angle is inferred for five sources using high-velocity channels, and it is compared to the orientation of the continuum. A significant difference in orientation for DoAr\,44 was found, which is evidence of a tilted inner disc. In addition, a tentative misalignment of the components was found for discs WSB\,82 and RXJ1633.9-2442. We also measure the gas disc size and R$_{gas}$/R$_{dust}$ ratio for the two discs less affected by contamination from the cloud. These ratios are consistent with ratios found in the literature. Further, an interesting finding is that all the discs are detected in $^{12}$CO, except ISO-Oph\,196, which displays a compact signal inside its dust cavity. The lack of extended emission might indicate that the disc dispersal process has already started. Eight discs show evidence of gas inside inner dust cavities or dust gaps, and the possibility that the substructures seen in the mm are the result of planet formation processes remains open. Further research can investigate the hypothesis of planet-disc interaction using new $^{12}$CO line observations with higher spectral resolution. Finally, our observations also point out a possible outflow in WLY\,2-63 that can be confirmed with new observations at larger angular scales.