1. Scientific requirements of ALMA, and its capabilities for key-projects: Galactic John 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 magnetic field 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, N 2 H+… 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, N 2 D +, … 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. Synthesising the Aperture: “Homogeneous Imaging” weight uv distance U=D/λ Single dish Cross correlation mosaic Reduced sensitivity at D/2

8. 12m 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 Extra measurements here help imaging precision: Cross-correlations from 7-m dishes, or Large single dish observations Up to 15km

9. 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

10. Initial Conditions: Pre-collapse Cores L1498: Tafalla et al. 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

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

12. 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 H 2 D + CS, CO, HCO + NH 3, N 2 H + H2D+D2H+H2D+D2H+ Walmsley et al. 2004; Caselli et al 2003 372GHz line 8,000AU 2,500AU 15,000AU

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

14. CO polarisation: Goldreich-Kylafis effect Detection of polarised CO J=2-1 NGC2024FIR5 Greaves et al (2001)

15. 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.

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

17. Molecular Outflows 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 Beuther et al, 2002 Chandler & Richer 1999 170AU resolution

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

19. Looney et al, 2000 “Hot Core” chemistry around low mass protostars 300AU sized molecular structures around protostellar candidates Different chemical signatures

20. Circumstellar Disks: Structure and Evolution Dutrey et al

21. 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 Imaging Protoplanetary Disks

22. See Sebastian Wolf’s talk Direct detection of proto-Jovian planets? Wolf et al 2004

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

24. “Debris” Disk imaging with ALMA 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) Fomalhaut (Greaves et al)

25. 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, H 13 CO + 4-3, H 13 CN 4-3, CO 3-2 LSB: CH 3 CN, CH 3 OH Or USB: HCN 4-3, HCO + 4-3 LSB: H 13 CN 4-3, CS 7-6, CO 3-2 Pierce-Price, Richer, et al 2000 SCUBA 850 micron: Pierce-Price et al 2000 SCUBA 450 micron Star Formation at the Galactic Centre

26. 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