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ALMA Design Reference Science Plan

Scientific requirements of ALMA, and its capabilities for key-projects: Galactic John Richer, Cavendish Laboratory, Cambridge. ALMA Design Reference Science Plan. Galaxies and Cosmology Previous talk Star and Planet Formation “Initial conditions” Envelopes Disks Chemistry

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ALMA Design Reference Science Plan

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  1. Scientific requirements of ALMA, and its capabilities for key-projects: GalacticJohn Richer, Cavendish Laboratory, Cambridge

  2. ALMA Design Reference Science Plan • Galaxies and Cosmology • Previous talk • Star and Planet Formation • “Initial conditions” • Envelopes • Disks • Chemistry • Stars and their Evolution • The Sun, mm-continuum emission from stars, Circumstellar Envelopes, AGB stars, Supernovae,… • Solar System • Planetary Atmospheres, Surfaces, Comets, Exosolar Planets, …

  3. ALMA “Level 0” Requirements • Image gas kinematics in protostars and protoplanetary disks around Sun-like stars at 140pc distance, enabling one to study their physical, chemical and magneticfield structures and to detect the gaps created by planets undergoing formation in the disk. • Provide precise images at 0.1 arcsec resolution. Precise means representing within the noise level the sky brightness at all points where the brightness is greater than 0.1% of the peak image brightness. This applies to all objects transiting at >20 degree elevation.

  4. ALMA: Current Definition • 64 moveable 12-m antennas: ‘100-m class telescope’ • Baselines from 15m to 15km • Angular resolution ~40 mas at 100 GHz (5mas at 900GHz) • Strong implications for atmospheric phase correction scheme • Receivers: low-noise, wide-band (8GHz), dual-polarisation, SSB • Many spectral lines per band • Digital correlator, >=8192 spectral channels, 4 Stokes • very high spectral resolution (up to 15kHz) • Short spacing data provided by 12-m antennas in single-dish mode • Critical for objects bigger than the primary beam • Requirements for star formation and high-z studies are remarkably similar!

  5. Good match to weather statistics and science

  6. Frequency band capabilities • Band 3: 84-116GHz. FOV = 60 arcsec • Continuum: ff/dust separation, optically-thin dust, dust emissivity index, grain size • SiO maser, low excitation lines CO 1-0 (5.5K), CS 2-1, HCO+ 1-0, N2H+… • Band 6: 211-275GHz. FOV = 25 arcsec • Dust SED • Medium excitation lines: CO 2-1 (16K), HCN 3-2, … • Band 7: 275-373GHz. FOV = 18 arcsec • Continuum: most sensitive band for dust. • Wave plate at 345GHz for precision polarimetry • Medium-high excitation lines: CO 3-2 (33K), HCN 4-3, N2D+, … • Band 9: 602-720GHz. FOV = 9 arcsec • Towards peak of dust SED, away from Rayleigh Jeans; hence T(dust) • High excitation lines e.g. CO 6-5 (115K), HCN 8-7 in compact regions

  7. Aperture Synthesis with ALMA 12-m cross-correlations from 60 dishes measure spacings from 12m up to maximum baseline e.g. 10km Auto-correlations from 4 12-m dishes measure from zero up to ~6m spacings 12m Extra measurements here help imaging precision: • Cross-correlations from 7-m dishes, or • Large single dish observations Up to 15km

  8. Diffraction limited imaging needs phase correction • Water fluctuations typically 500m-1000m above site • Correct by Fast Switching of antennas to QSO, plus Water Vapour Radiometry

  9. Initial Conditions: Pre-collapse Cores • Strong chemical gradients and clumpiness • Indicates depletion and chemical evolution • ALMA mosaic at 3mm: 100 pointings plus single-dish data needed • ALMA can resolve 15AU scales in nearby cores, or study cores at 1000AU scales out to 10kpc L1498: Tafalla et al.

  10. Core dynamics: infall Small-scale Extended 0.1 - 0.3 pc Walsh et al Di Francesco et al (2001)

  11. Starless Core Chemistry: probing the depletion zones • Complete CNO depletion within 2500AU? • ALMA can study this region, in objects as far as the GC, in H2D+ CS, CO, HCO+ NH3, N2H+ H2D+ D2H+ 2,500AU 8,000AU 372GHz line 15,000AU Walmsley et al. 2004; Caselli et al 2003

  12. Role of Magnetic Fields? (Figure by A. Chrysostomou) (Crutcher et al) L1544: Ward-Thompson et al 2000

  13. Star formation in crowded environments • ALMA can resolve 15AU scales at Taurus • Clump mass function down to 0.1 Jupiter masses • Onset of multiplicity • BD formation • Internal structure of clumps • Turbulence on AU scales Bate 2002 Protostars and Clumps in Perseus: Hatchell et al 2005.

  14. Cores and Filaments: Are Hydrodynamical Simulations Realistic? Motte et al • Clump mass spectrum • Relation to IMF? • Low mass limit? • Dependence on age? • Clump structure – transient or bound? • Filaments • are they omnipresent? • thermal/density structure Klessen 2004

  15. Molecular Outflows Chandler & Richer 1999 • Origin of flows down to 1.5AU scales • 10 mas resolution at 345 GHz: • 24 hours gives 5K rms at 20 km/s resolution • Resolve magnetosphere: X or disk winds? • Flow rotation? • Proper motions • 0.2 arcsec per year for 100km/s at 100pc • Resolve the cooling length • Resolve multiple outflow regions 170AU resolution Beuther et al, 2002

  16. Spatially-resolved Spectral Surveys 8GHz bandwidth Kuan et al 2004 Schilke et al

  17. Imaging Protoplanetary Disks • Protoplanetary disk at 140pc, with Jupiter mass planet at 5AU • ALMA simulation • 428GHz, bandwidth 8GHz • total integration time: 4h • max. baseline: 10km • Contrast reduced at higher frequency as optical depth increases • Will push ALMA to its limits Wolf, Gueth, Henning, & Kley 2002, ApJ 566, L97

  18. “Debris” disk spectroscopy with Spitzer Rieke et al 2004

  19. “Debris” Disk imaging with ALMA Fomalhaut (Greaves et al) • Wyatt (2004) model: dust trapped in resonances by migrating planets in disk • ALMA will revolutionise studies of the large cold grains in other planetary systems Vega (Holland et al)

  20. Pierce-Price, Richer, et al 2000 Star Formation at the Galactic Centre SCUBA 850 micron: Pierce-Price et al 2000 • ALMA could map one square degree at 350GHz in 180 hours to • 0.7mJy sensitivity • This is 0.15 solar masses at 20K • confusion limited unless resolution high • 1 arcsec beam (8500AU) would give • ΔT=0.6K at 1 km/s resolution • Possible lines in 2x4GHz passband: • USB: SiO 8-7, H13CO+ 4-3, H13CN 4-3, CO 3-2 • LSB: CH3CN, CH3OH • Or • USB: HCN 4-3, HCO+ 4-3 • LSB: H13CN 4-3, CS 7-6, CO 3-2 SCUBA 450 micron

  21. Final Remarks • ALMA’s unique role will be imaging down to few AU scales in nearby star forming regions with a sensitivity of a few Kelvin • Protostellar and protoplanetary disks • Accretion, rotation and outflow deep in the potential well • Chemistry and dust properties at high spatial resolution • Will require excellent operation on long baselines • Study star formation across the Galaxy • Modest resolution observations (0.5 arcsec or so) will be important too • Good brightness sensitivity • ALMA has a narrow field of view • Need surveys with single dishes to feed ALMA • Many targets extended over several primary beams • Need high-quality short spacing data to make precise images and for flux ratio experiments

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