Polycyclic aromatic hydrocarbon ionization as a tracer of gas flows through protoplanetary disk gaps

Abstract

Planet-forming disks of gas and dust around young stars contain polycyclic aromatic hydrocarbons (PAHs). We aim to characterize how the charge state of PAHs can be used as a probe of flows of gas through protoplanetary gaps. In this context, our goal is to understand the PAH spectra of four transitional disks. In addition, we want to explain the observed correlation between PAH ionization (traced by the 6.2/11.3 feature ratio) and the disk mass (traced by the 1.3 mm luminosity). We implement a model to calculate the charge state of PAHs in the radiative transfer code MCMax. The emission spectra and ionization balance are calculated. A benchmark modeling grid is presented that shows how PAH ionization and luminosity behave as a function of star and disk properties. The PAH ionization is most sensitive to ultraviolet (UV) radiation and the electron density. In optically thick disks, where the UV field is low and the electron density is high, PAHs are predominantly neutral. Ionized PAHs trace low-density optically thin disk regions where the UV field is high and the electron density is low. Such regions are characteristic of gas flows through the gaps of transitional disks. We demonstrate that fitting the PAH spectra of four transitional disks requires a contribution of ionized PAHs in gas flows through the gap. The PAH spectra of transitional disks can be understood as superpositions of neutral and ionized PAHs. For HD97048, neutral PAHs in the optically thick disk dominate the spectrum. In the cases of HD169142, HD135344B and Oph IRS 48, small amounts of ionized PAHs located in the gas flows through the gap are strong contributors to the total PAH luminosity. The observed trend between the disk mass and PAH ionization may imply that lower-mass disks have larger gaps. Ionized PAHs in gas flows through these gaps contribute strongly to their spectra.

16 pages, 23 figures, Accepted for publication in A&A

References in corpus (15)

• Infrared Emission from Interstellar Dust. IV. The Silicate-Graphite-PAH Model in the Post-Spitzer Era
• Ring shaped dust accumulation in transition disks
• A Submillimeter View of Circumstellar Dust Disks in $\rho$ Ophiuchus
• Dust filtration at gap edges: Implications for the spectral energy distributions of discs with embedded planets
• Variations of the Mid-IR Aromatic Features Inside and Among Galaxies
• Radiative transfer in very optically thick circumstellar disks
• Spectro-astrometric imaging of molecular gas within protoplanetary disk gaps
• Spatially extended PAHs in circumstellar disks around T Tauri and Herbig Ae stars
• PAH chemistry and IR emission from circumstellar disks
• Polycyclic aromatic hydrocarbon ionization as a tracer of gas flows through protoplanetary disk gaps
• Spatial separation of small and large grains in the transitional disk around the young star IRS 48
• The characteristics of the IR emission features in the spectra of Herbig Ae stars: Evidence for chemical evolution
• What can we learn about protoplanetary disks from analysis of mid-infrared carbonaceous dust emission?
• Evidence of a discontinuous disk structure around the Herbig Ae star HD 139 614
• The Vertical Structure of Planet-induced Gaps in Proto-Planetary Discs

Cited by in corpus (49)

• Consistent dust and gas models for protoplanetary disks. I. Disk shape, dust settling, opacities, and PAHs
• External photoevaporation of protoplanetary discs in sparse stellar groups: the impact of dust growth
• Fingerprints of giant planets in the photospheres of Herbig stars
• An Enigmatic Pointlike Feature within the HD 169142 Transitional Disk
• A cavity and further radial substructures in the disk around HD~97048
• The structure of disks around intermediate-mass young stars from mid-infrared interferometry. Evidence for a population of group II disks with gaps
• Consistent dust and gas models for protoplanetary disks III. Models for selected objects from the FP7 DIANA project
• Polycyclic aromatic hydrocarbon ionization as a tracer of gas flows through protoplanetary disk gaps
• Polycyclic Aromatic Hydrocarbon in Protoplanetary Disks around Herbig Ae/Be and T Tauri Stars
• Shadows and cavities in protoplanetary disks: HD163296, HD141569A, and HD150193A in polarized light
• SEEDS Adaptive Optics Imaging of the Asymmetric Transition Disk Oph IRS 48 in Scattered Light
• The structure of disks around Herbig Ae/Be stars as traced by CO ro-vibrational emission
• Mass constraints for 15 protoplanetary disks from HD 1-0
• A 80 au cavity in the disk around HD 34282
• Variability of Disk Emission in Pre-Main Sequence and Related Stars. III. Exploring Structural Changes in the Pre-transitional Disk in HD 169142
• Examining the class B-to-A shift of the 7.7 $\mu$m PAH band with the NASA Ames PAH IR Spectroscopic Database
• Herbig Stars: A Quarter Century of Progress
• Observing the linked depletion of dust and CO gas at 0.1-10 au in disks of intermediate-mass stars
• Destruction and multiple ionization of PAHs by X-rays in circumnuclear regions of AGNs
• A single-armed spiral in the protoplanetary disk around HD34282 ?
• Mid-IR spectra of Pre-Main Sequence Herbig stars: an explanation for the non-detections of water lines
• A multi-instrument and multi-wavelength high angular resolution study of MWC614: quantum heated particles inside the disk cavity
• Large dust gaps in the transitional disks of HD 100453 and HD 34282
• A catalog of early-type Hα emission line stars and 58 newly confirmed Herbig Ae/Bes from LAMOST DR7
• A JWST/MIRI analysis of the ice distribution and PAH emission in the protoplanetary disk HH 48 NE
• Nano carbon dust emission in proto-planetary disks: the aliphatic-aromatic components
• Location and sizes of forsterite grains in protoplanetary disks: interpretation from the Herschel DIGIT programme
• Interferometric Evidence for Quantum Heated Particles in the Inner Region of Protoplanetary Disks around Herbig Stars
• A proposed new diagnostic for Herbig disc geometry: FWHM versus J of CO ro-vibrational lines
• Search for Polycyclic Aromatic Hydrocarbons in the Outflows from Dust-Producing Wolf-Rayet Stars
• Spinning dust emission from circumstellar disks and its role in excess microwave emission
• Dust and Polycyclic Aromatic Hydrocarbon in the Pre-Transitional Disk around HD 169142
• A resolved and asymmetric ring of PAHs within the young circumstellar disk of IRS 48
• A study of dust properties in the inner sub-au region of the Herbig Ae star HD 169142 with VLTI/PIONIER
• The spatial extent of Polycyclic Aromatic Hydrocarbons emission in the Herbig star HD 179218
• The GRAVITY Young Stellar Object survey VIII. Gas and dust faint inner rings in the hybrid disk of HD141569
• X3: a high-mass Young Stellar Object close to the supermassive black hole Sgr~A*
• Turbulent processing of PAHs in protoplanetary discs -- Coagulation and freeze-out leading to depletion of gas-phase PAH
• The Mid-Infrared Polarization of the Herbig Ae Star WL 16: An Interstellar Origin?
• XUE. JWST spectroscopy of externally irradiated disks around young intermediate-mass stars
• An Incipient Debris Disk in the Chamaeleon I Cloud
• Spatially resolving polycyclic aromatic hydrocarbons in Herbig Ae disks with VISIR-NEAR at the VLT
• Tiny Grains Shining Bright in the Gaps of Herbig Ae Transitional Discs
• Spitzer/IRS full spectral modeling to characterize mineralogical properties of silicate dust in heavily obscured AGNs
• New Mid-Infrared Imaging Constraints on Companions and Protoplanetary Disks around six Young Stars
• Radial distribution of the carbonaceous nano-grains in the protoplanetary disk around HD 169142
• Molecular formation along the atmospheric mass loss of HD 209458 b and similar Hot Jupiters
• Polycyclic aromatic hydrocarbon (PAH) abundances in the disk around T Chamaeleontis (T Cha): PAH sizes, ionization fraction, and mass during JWST observations
• Observational evidence for a possible link between PAH emission and dust trap locations in protoplanetary disks