An ALMA Molecular Inventory of Warm Herbig Ae Disks. II. Abundant Complex Organics and Volatile Sulphur in the IRS 48 Disk

Abstract

The Atacama Large Millimeter/submillimeter Array (ALMA) can probe the molecular content of planet-forming disks with unprecedented sensitivity. These observations allow us to build up an inventory of the volatiles available for forming planets and comets. Herbig Ae transition disks are fruitful targets due to the thermal sublimation of complex organic molecules (COMs) and likely H _2 O-rich ices in these disks. The IRS 48 disk shows a particularly rich chemistry that can be directly linked to its asymmetric dust trap. Here, we present ALMA observations of the IRS 48 disk where we detect 16 different molecules and make the first robust detections of ${{\rm{H}}}_{2}^{13}\,\mathrm{CO}$ , ^34 SO, ^33 SO, and c-H _2 COCH _2 (ethylene oxide) in a protoplanetary disk. All of the molecular emissions, aside from CO, are co-located with the dust trap, and this includes newly detected simple molecules such as HCO ^+ , $\mathrm{HCN}$ , and CS. Interestingly, there are spatial offsets between different molecular families, including between the COMs and sulfur-bearing species, with the latter being more azimuthally extended and radially located further from the star. The abundances of the newly detected COMs relative to CH _3 OH are higher than the expected protostellar ratios, which implies some degree of chemical processing of the inherited ices during the disk lifetime. These data highlight IRS 48 as a unique astrochemical laboratory to unravel the full volatile reservoir at the epoch of planet and comet formation and the role of the disk in (re)setting chemical complexity.

Keywords

• Planet formation
• Complex organic molecules
• Interferometry
• Chemical abundances
• Astrochemistry