A major asymmetric ice trap in a planet-forming disk: I. Formaldehyde and methanol

Abstract

The chemistry of planet-forming disks sets the exoplanet atmosphere composition and the prebiotic molecular content. Dust traps are of particular importance as pebble growth and transport are crucial for setting the chemistry where giant planets are forming. The asymmetric Oph~IRS~48 dust trap located at 60 au radius provides a unique laboratory for studying chemistry in pebble-concentrated environments in warm Herbig disks with low gas-to-dust ratios down to 0.01. We use deep ALMA Band~7 line observations to search the IRS~48 disk for H${}_2$CO and CH${}_3$OH line emission, the first steps of complex organic chemistry. We report the detection of 7 H${}_2$CO and 6 CH${}_3$OH lines with energy levels between 17 and 260 K. The line emission shows a crescent morphology, similar to the dust continuum, suggesting that the icy pebbles play an important role in the delivery of these molecules. Rotational diagrams and line ratios indicate that both molecules originate from warm molecular regions in the disk with temperatures $>$100 K and column densities $\sim 10^{14}$ cm${}^{-2}$ or a fractional abundance of $\sim 10^{-8}$ and with H${}_2$CO/CH${}_3$OH$\sim$0.2, indicative of ice chemistry. Based on arguments from a physical-chemical model with low gas-to-dust ratios, we propose a scenario where the dust trap provides a huge icy grain reservoir in the disk midplane or an `ice trap', which can result in high gas-phase abundances of warm COMs through efficient vertical mixing. This is the first time that complex organic molecules have been clearly linked to the presence of a dust trap. These results demonstrate the importance of including dust evolution and vertical transport in chemical disk models, as icy dust concentrations provide important reservoirs for complex organic chemistry in disks.

arXiv commentAccepted by A&A Letters. 8 pages, 4 figures, plus appendix (8 pages, 8 figures)

References in corpus (45)

• emcee: The MCMC Hammer
• Gaia Data Release 2. Summary of the contents and survey properties
• A computer program for fast non-LTE analysis of interstellar line spectra
• An atomic and molecular database for analysis of submillimetre line observations
• The Disk Substructures at High Angular Resolution Project (DSHARP): I. Motivation, Sample, Calibration, and Overview
• Observations of the Icy Universe
• Coagulation, fragmentation and radial motion of solid particles in protoplanetary disks
• Resolved Images of Large Cavities in Protoplanetary Transition Disks
• A Major Asymmetric Dust Trap in a Transition Disk
• Ring shaped dust accumulation in transition disks
• Trapping dust particles in the outer regions of protoplanetary disks
• The warm gas atmosphere of the HD 100546 disk seen by Herschel (Evidence of a gas-rich, carbon-poor atmosphere?)
• The cometary composition of a protoplanetary disk as revealed by complex cyanides
• Complex organic molecules in protoplanetary disks
• Astrochemistry and compositions of planetary systems
• Large-Scale Asymmetries in the Transitional Disks of SAO 206462 and SR 21
• Resolved gas cavities in transitional disks inferred from CO isotopologues with ALMA
• Survival of molecular gas in cavities of transition disks (I. CO)
• Organic molecules in protoplanetary disks around TTauri and HerbigAe stars
• Chemical evolution of turbulent protoplanetary disks and the Solar nebula
• Dust depleted inner disks in a large sample of transition disks through long-baseline ALMA observations
• Disk Imaging Survey of Chemistry with SMA (DISCS): I. Taurus Protoplanetary Disk Data
• Gas structure inside dust cavities of transition disks: Oph IRS 48 observed by ALMA
• CO Depletion in Protoplanetary Disks: A Unified Picture Combining Physical Sequestration and Chemical Processing
• The ice composition in the disk around V883 Ori revealed by its stellar outburst
• Sensitivity analysis of grain surface chemistry to binding energies of ice species
• Rotational quenching of H2CO by molecular hydrogen: cross-sections, rates, pressure broadening
• Detecting Weak Spectral Lines in Interferometric Data through Matched Filtering
• Rossby Wave Instability and three-dimensional vortices in accretion disks
• Gas and dust dynamics in starlight-heated protoplanetary disks
• Methanol and its relation to the water snowline in the disk around the young outbursting star V883 Ori
• Spatial separation of small and large grains in the transitional disk around the young star IRS 48
• A concentration of centimeter-sized grains in the Oph IRS 48 dust trap
• An ALMA Survey of H${}_2$CO in Protoplanetary Disks
• ALMA chemical survey of disk-outflow sources in Taurus (ALMA-DOT) II: Vertical stratification of CO, CS, CN, H${}_2$CO, and CH${}_3$OH in a Class I disk
• ALMA reveals the anatomy of the mm-sized dust and molecular gas in the HD 97048 disk
• The chemistry of disks around T Tauri and Herbig Ae/Be stars
• Low abundance, strong features: Window-dressing crystalline forsterite in the disk wall of HD 100546
• Probing the 2D temperature structure of protoplanetary disks with Herschel observations of high-J CO lines
• Transition disk chemistry and future prospects with ALMA
• Warm formaldehyde in the Oph IRS 48 transitional disk
• Solving grain size inconsistency between ALMA polarization and VLA continuum in the Ophiuchus IRS 48 protoplanetary disk
• The TW Hya Rosetta Stone Project II: Spatially resolved emission of formaldehyde hints at low-temperature gas-phase formation
• Chemical Evolution in a Protoplanetary Disk within Planet Carved Gaps and Dust Rings
• An inherited complex organic molecule reservoir in a warm planet-hosting disk

Cited by in corpus (31)

• A major asymmetric ice trap in a planet-forming disk: III. First detection of dimethyl ether
• Sulphur monoxide emission tracing an embedded planet in the HD 100546 protoplanetary disk
• Transition disks: the observational revolution from SEDs to imaging
• SO and SiS Emission Tracing an Embedded Planet and Compact ${}^{12}$CO and ${}^{13}$CO Counterparts in the HD 169142 Disk
• Tracing snowlines and C/O ratio in a planet-hosting disk: ALMA molecular line observations towards the HD169142 disk
• Importance of source structure on complex organics emission. I. Observations of CH${}_3$OH from low-mass to high-mass protostars
• If you like C/O variations, you should have put a ring on it
• Investigating the asymmetric chemistry in the disk around the young star HD 142527
• FAUST XVII: Super deuteration in the planet forming system IRS 63 where the streamer strikes the disk
• Eccentric Dust Ring in the IRS 48 Transition Disk
• Shocking Sgr B2(N1) with its own outflow: A new perspective on segregation between O- and N-bearing molecules
• A major asymmetric ice trap in a planet-forming disk IV. Nitric oxide gas and a lack of CN tracing sublimating ices and a C/O ratio $<1$
• The rapid formation of macromolecules in irradiated ice of protoplanetary disk dust traps
• The Molecular Composition of Shadowed Protosolar Disk Midplanes beyond the Water Snowline
• Radial and vertical constraints on the icy origin of H${}_2$CO in the HD 163296 Protoplanetary Disk
• ALMA reveals thermal and non-thermal desorption of methanol ice in the HD 100546 protoplanetary disk
• On the origin of the lump in circumbinary discs
• An SMA Survey of Chemistry in Disks around Herbig AeBe Stars
• Infall and Disk Processes - the Message from Meteorites
• Pristine ices in a planet-forming disk revealed by heavy water
• A deep search for Complex Organic Molecules toward the protoplanetary disk of V883 Ori
• Infrared action spectroscopy as tool for probing gas-phase dynamics: Protonated Dimethyl Ether, (CH${}_3$)${}_2$OH${}^{+}$, formed by the reaction of CH${}_3$OH${}_2^{+}$ with CH${}_3$OH
• A major asymmetric ice trap in a planet-forming disk: II. prominent SO and SO2 pointing to C/O < 1
• The GUAPOS project. VI: the chemical inventory of shocked gas
• A deep Search for Ethylene Glycol and Glycolonitrile in the V883 Ori Protoplanetary Disk
• Molecules with ALMA at Planet-forming Scales (MAPS) III: Characteristics of Radial Chemical Substructures
• Models and Observational Predictions of Dust Traps in Protoplanetary Discs
• Observational evidence for a possible link between PAH emission and dust trap locations in protoplanetary disks
• Hunting for methanol in the water rich, planet forming disk around HL Tau
• Linking Outer Disk Pebble Dynamics and Gaps to Inner Disk Water Enrichment
• Protoplanetary Disk Chemistry