Molecules with ALMA at Planet-forming Scales (MAPS) III: Characteristics\n of Radial Chemical Substructures

Abstract

The Molecules with ALMA at Planet-forming Scales (MAPS) Large Program\nprovides a detailed, high resolution (${\\sim}$10-20 au) view of molecular line\nemission in five protoplanetary disks at spatial scales relevant for planet\nformation. Here, we present a systematic analysis of chemical substructures in\n18 molecular lines toward the MAPS sources: IM Lup, GM Aur, AS 209, HD 163296,\nand MWC 480. We identify more than 200 chemical substructures, which are found\nat nearly all radii where line emission is detected. A wide diversity of radial\nmorphologies - including rings, gaps, and plateaus - is observed both within\neach disk and across the MAPS sample. This diversity in line emission profiles\nis also present in the innermost 50 au. Overall, this suggests that planets\nform in varied chemical environments both across disks and at different radii\nwithin the same disk. Interior to 150 au, the majority of chemical\nsubstructures across the MAPS disks are spatially coincident with substructures\nin the millimeter continuum, indicative of physical and chemical links between\nthe disk midplane and warm, elevated molecular emission layers. Some chemical\nsubstructures in the inner disk and most chemical substructures exterior to 150\nau cannot be directly linked to dust substructure, however, which indicates\nthat there are also other causes of chemical substructures, such as snowlines,\ngradients in UV photon fluxes, ionization, and radially-varying elemental\nratios. This implies that chemical substructures could be developed into\npowerful probes of different disk characteristics, in addition to influencing\nthe environments within which planets assemble. This paper is part of the MAPS\nspecial issue of the Astrophysical Journal Supplement.\n