Imaging the distribution of water vapour in planet-forming disks with ALMA

Imaging the distribution of water vapour in planet-forming disks with ALMA Stefano Facchini University of Milan UNVEIL 101076613 Distribution of water vapour in protoplanetary disks Static disk model, passively heated by a central Herbig star: defines a clear snow surface (snowline in the disk midplane) Notsu+2017 A “blurred” snow surface When including more physics beyond a static model, the transition between gas and ice reservoirs becomes more blurred Banzatti+in prep., ARA&A review Image credit: Banzatti+, Gordon conference Different reservoirs of water gas in a disk gas H α Reservoir 1: thermally desorbed water gas H α gas H α Reservoir 2: photodesorbed water Reservoir 3: reformed water Image credit: M. Leemker water snowline ~ 1-10 au Three different reservoirs of water vapour depending on T and UV penetration depth A thermal gradient in the snow surface Kamp+2021, Banzatti+2023a,b Distinct wavelength regimes typically sensitive to different upper energy levels, tracing different radial ranges Why do we care? Water snowline can promote planetesimal formation. High H2O abundance in inner regions may be due to high pebble flux, a key parameter regulating pebble accretion in the formation of planetary cores and rocky planets. Location of water snowline leads to drastic changes in elemental ratios (e.g., C/O) of ice and solid phases. Water isotopologue ratio is a key tracer of ice reprocessing during the disk formation phase. Why do we care? Water snowline can promote planetesimal formation High H2O abundance in inner regions may be due to high pebble flux, a key parameter regulating pebble accretion in the formation of planetary cores and rocky planets Location of water snowline leads to drastic changes in elemental ratios (e.g., C/O) of ice and solid phases Water isotopologue ratio is a key tracer of ice reprocessing during the disk formation phase. Complementary approaches to constrain water vapour extent Banzatti+2023, Brittan+2016, Leemker+in prep. JWST: multiple transitions in NIR-MIR, thermally “resolve” gradients from excitation studies i-Shell, CRIRES+: High-res NIR spectroscopy, spectrally resolve individual lines, reconstruct intensity profile with Doppler tomography ALMA: high angular resolution in (sub-)mm regime, spectrally and spatially resolve individual lines, and access to isotopologues Complementary approaches to constrain water vapour extent Banzatti+2023, Brittan+2016, Leemker+in prep. JWST: multiple transitions in NIR-MIR, thermally “resolve” gradients from excitation studies i-Shell, CRIRES+: High-res NIR spectroscopy, spectrally resolve individual lines, reconstruct intensity profile with Doppler tomography ALMA: high angular resolution in (sub-)mm regime, spectrally and spatially resolve individual lines, and access to isotopologues Detection of water main isotopologue with ALMA in HL Tau Eup ~ 205 K Eup ~ 470 K Eup ~ 1860 K 60 mas resolution Facchini+2024, Nat. Ast. , 183 GHz , 325 GHz , 321 GHz 500 mas resolution 500 mas resolution Conclusions •Disks are largely substructured in their kinematical pattern, spirals being more common than in mm continuum and scattered light emission •Signatures of Jupiter mass planet-disk interactions in outer regions •Evidence of disk dynamics yet to be identified •New methodology of estimating disk masses with new orthogonal approaches •Planet-induced structure can affect the chemistry of the hosting disk •Main H2O isotopologue can be used to map water vapour in bright disks Credit: ALMA (ESO/NAOJ/NRAO)/S. Facchini et al. New 50mas data of the 183 GHz line Leemker+subm. We detect water out to large radii (snowline at ~5 au), above the water snow-surface Lines look close to thermal, but hard to fully constrain. The role of continuum optical depth Leemker+subm. The role of continuum optical depth Leemker+subm. The role of continuum optical depth Leemker+subm. Excitation seems reasonably close to LTE when accounting for continuum optical depth. Lines in the FIR are sensitive to <1% of the water, in the mm to ~50%. A directly-irradiated cavity wall Rampinelli+subm. Spatially resolved H216O detected in the cavity of the HD 100546 disk. A directly-irradiated cavity wall Leemker+2021, Rampinelli+subm. The profile of the water emission peaks just inside the dust cavity wall: RT models indicate dust temperatures above H2O sublimation temperature What is the scalability of these observations? This study can be performed only on brightest disks (~10 not outbursting, ~20 outbursting), the limit is line sensitivity. Simplistic arguments yield: (scaling is steep with …) FH2O∼L1/2 * M* We need a massive boost in line sensitivity/collecting area, a next-generation ALMA: CAD model of ng-VLA antenna, courtesy of mtex industry; SKA-mid antenna design Conclusions 1) Water isotopologues (H2O, H218O, HDO, D2O) can be detected in bright planet-forming disks 2) Thermally desorbed gas indicates inheritance scenario (D2O/H2O) 3) (Sub-)mm lines are optimal to probe the bulk of water column density and get close to the midplane water snowline 4) Transition disks (with warm cavity walls) are optimal targets to constrain H2O/ COM ratios in thermally desorbed gas. 5) A radically upgraded mm interferometer needed in the future to extend the study to large samples.