ALMA surveys of planet-forming disks

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1 ALMA surveys of planet-forming disks ILARIA PASCUCCI Lunar and Planetary Laboratory, Department of Planetary Sciences The University of Arizona

2 Questions that can be answered in a disk survey: Which are the typical disk properties? What is their spread? When combining multiple regions: How do disk properties evolve with time?

3 ALMA high-resolution observations of disks Lupus survey, Ansdell et al. (2016)

4 Region d (pc) Age(Myr) λ(mm) Res. ( ) rms(mjy) Ref. Orion 400 ~1 0.9 ~0.1(~40au) ρoph (~30au) 0.2 Eisner et al. sub. Cox et al Taurus 140 ~ Andrews et al Lupus ~ ~0.3(~50au) Ansdell et al Cha I 160 ~ ~0.6(96au) Pascucci et al σori 385 ~ ~0.28(100au) 0.15 Ansdell et al USco 145 ~ ~0.45(60au) 0.2 Barenfeld et al Taurus : new SMA@1.3mm + archival Orion : mosaic of the central 1.5 x1.5 of the ONC Cha II, see poster by Villenave All other surveys targeted known disks (mostly ClassII)

5 NOTE: ρoph no Mstar available VLT/XShooter spectroscopy to homogeneously re-classify stars and measure mass accretion rates (Alcala et al. 2017,Manara et al. 2017) NIR spectroscopy for embedded sources (Fang et al. in prep.)

6 Properties inferred from moderate resolution surveys Fmm ( Lmm Mdust for ~80% of the sources) Rdust (Rgas) for a subset (~20%) FCO ( Mgas for ~20-40% of the sources) Macc-Mdust (or Mgas) for ChaI and Lupus Cavity size for a few transition disks

7 Millimeter continuum and dust disk masses

8 Optically thin dust emission in the mm Disk mass Rout F υ = cosθ d B 2 υ (T d )(1 e τ υ )2π RdR Rin τ υ = κ υσ cosθ ifτ υ < 1 F υ = B υ (T d ) κ d 2 υ M dust

9 The absolute value of k ν is uncertain by 1dex (e.g. Beckwith et al. 2000) But k ν ~ ν β and F ν ~ ν (β+2)=α. As α does not change much from disk to disk (Ricci et al. 2010) relative disk mass measurements are less uncertain (Ricci et al. 2010)

10 Which Tdust should we take and does it scale with Lstar? Tdust = 20K for disks around solar-mass stars (e.g. Williams & Cieza 2011) Tdust ~ (Lstar) 1/4 (Andrews et al. 2013, from RT models with fixed outer radius) Tdust ~ (Lstar) Tdust ~ (Lstar) 1/4 Hendler et al. (2017) see also van der Plas et al. (2016)

11 Ansdell et al. (2017) lower sensitivity due to distance lower sensitivity survey (SMA) Orion - Eisner et al. sub.

12 Evolution of dust disk masses within 10Myr IP: including Orion Mdust~Mstar 2 Mdust~Mstar 0.25 The dust disk stellar mass relation steepens with time Mdust~Mstar 2.5 Ansdell et al. (2016, 2017); Barenfeld et al. (2016); Pascucci et al. (2016)

13 growth fragmentation radial drift Pascucci et al. (2016) with models by S. Krijt et al. (2016) credit: B. Ercolano &T. Birnstiel The time for radial drift to remove the largest grains is faster around lower mass stars Implication: dust disks around lower mass stars are smaller than those around higher mass stars

14 How dust disk masses compare to the mass in solids in planetary systems? What about Kepler planetary systems? ChaI, Pascucci et al. (2016) S S Solar System T T TRAPPIST-1: Seven Earthsize planets orbiting a 0.08 solar mass star (Gillon et al. 2017)

15 The paucity of pebbles in ~2Myr-old disks around low-mass stars is most likely due to faster inward migration (fewer giants?) toward the star Pascucci et al. (2016) dust disk masses in ChaI Mulders et al. (2015) T exoplanet mass in solids Cuzzi & Zahnle (2004)

16 Transition disks with ALMA TDs = disks with a dust cavity 29 disks from different star-forming regions (ALMA Cycle 0 to 3) Pinilla et al. sub.

17 The dust disk stellar mass relation for TDs Pinilla et al. sub. Flatter dust disk-stellar mass relation (these TDs are not more evolved than full disks, e.g. Owen & Clarke 2012) Explanation: 1. optically thick mm emission (especially for massive disks) 2. particle trapping in pressure maxima (only growth and fragmentation)

18 Dust disk sizes

19 Is there a sharp dust edge? How should we measure it? Barenfeld et al. (2017): 57 disks in USco. Truncated power-law for the dust surface density, full radiative transfer Tazzari et al. (2017): 36 spatially resolved disks in Lupus (no TDs). Two layer approximation and self-similar solution for the gas surface density. Rout contains 90% of the total flux Tripathi et al. (2017): 50 nearby disks many in Taurus. Nuker profile for the intensity (TDs included) to fit observed visibilities. Rout contains 68% of the total flux

20 Tripathi et al. (2017) Correlation between Lmm and outer radius: grain growth and drift or optically thick rings? Tazzari et al. (2017) Rd ~ (Lmm) 0.5

21 Disks in USco are three times smaller than younger disks Usco: the median Rout for the 25 highest S/N sources is 21au Barenfeld et al. (2017) (Tripathi et al. younger disks around more massive stars)

22 CO emission and gas disk masses

23 M gas ~ F iso f CO/iso f H2 /CO CO is second in abundance to H2, possible optically thin CO tracers: 13 CO, C 18 O, C 17 O Note that [ 12 C]/[ 13 C]=77, [ 16 O]/[ 18 O]=560, and [ 16 O]/[ 17 O] =1792 (e.g. Wilson & Rood 1994) What is the fh2/co in disks? fh2/co~10-4 in the ISM Further complications: optical depth, gas temperature, CO freeze out, isotope-selective dissociation

24 Gas disk masses rely on disk models Miotello et al. (2017) Williams & Best (2014) Note: the models by Miotello et al. have a self-consistent temperature determination as well as a full chemical calculation

25 using the models by Williams & Best (2014) Lupus, Ansdell et al. (2016)

26 The mean F13CO is higher in Lupus but the two samples are statistically indistinguishable (discrepancy at low flux due to different sensitivities) ChaI, Long et al. (2017)

27 Is the gas mass really low or is the CO abundance low? Most likely CO is under-abundant, see the 3 disks with HD detections (e.g. McClure et al. 2016) and CO isotopes in TWHya (Zhang et al. 2017)

28 Chemical processing alone cannot explain the low CO abundance Schwarz et al. (2018) Chemical processing: CO converted into less volatile ices, e.g. CO2, on the grain surface Easier to deplete CO in the outer than in the inner disk (inner disk requires high CR) but few models have log(co/h2) < -5

29 Mass accretion rates vs Disk masses

30 Correlation between disk masses and mass accretion rates Does the correlation prove that disks are viscously evolving? CO gas masses: most sources are undetected Dust disk masses: most sources are detected Lupus, Manara et al. (2016)

31 Observations Simulations with tvis~1myr Mulders et al. (2017) Simulations with tvis~0.1myr The scatter in Macc-Mdust can be reproduced IF the viscous timescale is long (a few Myr), i.e. disks have not substantially evolved in the ChaI and Lupus star-forming regions. (see also Lodato et al. 2017)

32 Take home messages Surveys are necessary to establish what are the typical disk properties (ad their spread) The dust disk-stellar mass scaling relation steepens with time (lower masses around low-mass stars at later times): more efficient inward drift? thick disks? more efficient planetesimal formation? Dust disk masses decline with stellar mass while the mass in solids in planetary systems increases toward low-mass stars: redistribution of solids facilitated by few giants around low-mass stars? The dust disk-stellar mass relation of disks with large cavities is rather flat: mm grains trapped in pressure bumps? thick disks around the more massive stars? Dust disk sizes ~ (Lmm) 0.5 : grain growth and drift? optically thick rings and gaps? Usco disks are smaller than younger disks (but they are mostly around lower mass stars) Gas disk masses using CO are, in most cases, lower than 1MJup. Most likely CO is depleted but chemical processing alone cannot explain depletions larger than a factor of 10 Mass accretion rates and dust disk masses are correlated but with a large spread. IF dust disk masses are a good proxy of total disk masses, 1-3Myr-old disks should not have viscously evolved significantly