Molecules with ALMA at Planet-forming Scales (MAPS). V. CO Gas Distributions

Abstract

Here we present high-resolution (15-24 au) observations of CO isotopologue lines from the Molecules with ALMA on Planet-forming Scales (MAPS) ALMA Large Program. Our analysis employs observations of the (J = 2-1) and (1-0) lines of 13 CO and C 18 O and the (J = 1-0) line of C 17 O for five protoplanetary disks. We retrieve CO gas density distributions, using three independent methods: (1) a thermochemical modeling framework based on the CO data, the broadband spectral energy distribution, and the millimeter continuum emission; (2) an empirical temperature distribution based on optically thick CO lines; and (3) a direct fit to the C 17 O hyperfine lines. Results from these methods generally show excellent agreement. The CO gas column density profiles of the five disks show significant variations in the absolute value and the radial shape. Assuming a gas-to-dust mass ratio of 100, all five disks have a global CO-to-H 2 abundance 10-100 times lower than the interstellar medium ratio. The CO gas distributions between 150 and 400 au match well with models of viscous disks, supporting the longstanding theory. CO gas gaps appear to be correlated with continuum gap locations, but some deep continuum gaps do not have corresponding CO gaps. The relative depths of CO and dust gaps are generally consistent with predictions of planet-disk interactions, but some CO gaps are 5-10 times shallower than predictions based on dust gaps. This paper is part of the MAPS special issue of the Astrophysical Journal Supplement.

Water UV-shielding in the Terrestrial Planet-forming Zone: Implications from Water Emission

“…The disk parameters are given in Table 1. The stellar input spectrum is also taken from Zhang et al (2021) and is the combination of a stellar atmosphere model (Nextgen; Hauschildt et al 1999) and excess UV (Herczeg et al 2004;Dionatos et al 2019), which is dominated by Lyα emission, consistent with observations (Schindhelm et al 2012). The final stellar spectrum is spectral type K5 (4300 K) with a total luminosity of 1.4 L e and 0.01 L e in UV at wavelengths smaller than 200 nm.…”

“…The physical model is a smooth version of the AS 209 model from Zhang et al (2021). The disk parameters are given in Table 1.…”

“…Whereas many previous studies have assumed large grains (up to 1 mm) (e.g., Bruderer et al 2015;Bosman et al 2017;Woitke et al 2018), we only use small grains (up to 1 μm) in the inner disk surface. Dust opacities are calculated using the DSHARP dust opacity tool (Birnstiel et al 2018) and are the same as the ones used in Zhang et al (2021).…”

Chemical Feedbacks of Pebble Growth: Impacts on CO depletion and C/O ratios

“…Such observations have revealed that the chemical inventories in disks are markedly different from those seen in molecular clouds, indicating significant processing in the solids and gas that eventually are incorporated into planets. Notably, the CO abundance observed across protoplanetary disks is consistently found to be a factor of 10-100 lower than the canonical interstellar medium (ISM) value of ∼10 −4 (Favre et al 2013;Schwarz et al 2016;Miotello et al 2017;Zhang et al 2019Zhang et al , 2021. Additionally, the bright emission of hydrocarbons in disks points to significantly elevated gas-phase C/O ratios (>1) compared to the interstellar value (∼0.4; Bergin et al 2016;Cleeves et al 2018;Miotello et al 2019;Bosman et al 2021a).…”

No Significant Correlation between Line-emission and Continuum Substructures in the Molecules with ALMA at Planet-forming Scales Program

“…Okuzumi et al 2016) can contribute to the appearance of a dust ring, while chemical rings and gaps appear when the molecules freeze out beyond the icelines. However, whether the iceline coincides with the dust ring is still a matter of debate (Long et al 2018;Huang et al 2018;van der Marel et al 2019;Zhang et al 2021). On the other hand, there are also mechanisms of dust ring formation, e.g., the Secular Gravitational Instability (Tominaga et al 2020) (Jiang & Ormel 2021), which do not necessarily require that gas and dust substructures correlate spatially.…”