Atacama Large Millimeter Array October 2004DUSTY041 Scientific requirements of ALMA, and its capabilities for key-projects: extragalactic Carlos De Breuck (ESO)

Atacama Large Millimeter Array October 2004DUSTY042 Primary Scientific Requirements ALMA will be a flexible observatory supporting a wide range of scientific investigations in extragalactic, galactic and planetary astronomy. ALMA should be “easy to use” (i.e. you do not need to be an expert in aperture synthesis to produce images). Three scientific requirements drive the science planning. These are the “Primary Scientific Requirements”.

Atacama Large Millimeter Array October 2004DUSTY043 Primary Scientific Requirements The ability to detect spectral line emission from CO or C I in a normal galaxy like the Milky Way at a redshift of 3, in less than 24 hours of observation. The ability to image the gas kinematics in protostars and protoplanetary disks around young Sun-like stars at a distance of 150 pc, enabling one to study their physical, chemical and magnetic field structures and to detect the gaps created by planets undergoing formation in the disks. (see John Richer’s talk) The ability to provide precise images at an angular resolution of 0.1”. Here the term ‘precise images’ means representing to within the noise level the sky brightness at all points where the brightness is greater than 0.1% of the peak image brightness. This requirement applies to all sources visible to ALMA that transit at an elevation greater than 20°.

Atacama Large Millimeter Array October 2004DUSTY044 Detecting normal galaxies at z=3 CO emission now detected in 25 z>2 objects. To date only in luminous AGN and/or gravitationally lensed. Normal galaxies are 20 to 30 times fainter. Current millimeter interferometers have collecting areas between 500 and 1000 m 2.

Atacama Large Millimeter Array October 2004DUSTY045 Detecting normal galaxies at z=3 ALMA sensitivity depends on: 1.Atmospheric transparency: Chajnantor plateau at 5000m altitude is superior to all existing mm observatories. 2.Noise performance of receivers: can be reduced by factor 2 (approaching quantum limit). Also gain √2 because ALMA will simultaneously measure both states of polarization. 3.Collecting area: remaining factor of 7 to 10 can only be gained by increasing collecting area to >7000 m 2.

Atacama Large Millimeter Array October 2004DUSTY046 At z=3, the 10 kpc molecular disk of the Milky Way will be much smaller than the primary beam → single observation. Flux density sensitivity in image from an interferometric array with 2 simultaneously sampled polarizations and 95% quantum efficiency is: Aperture efficiencies 0.45<ε a <0.75 can be achieved (20 µm antenna surface accuracy). T sys depends on band, atmosphere, … for 115 GHz, T sys =67 K obtainable. Detecting normal galaxies at z=3

Atacama Large Millimeter Array October 2004DUSTY047 Detecting normal galaxies at z=3 Total CO luminosity of Milky Way: L ’ co(1-0) = 3.7x10 8 K km s -1 pc 2 (Solomon & Rivolo 1989). COBE found slightly higher luminosities in higher transitions (Bennett et al 1994) → adopt L ’ co = 5x10 8 K km s -1 pc 2. At z=3 → observe (3-2) or (4-3) transition in the GHz atmospheric band → need to correct, but also higher T CMB providing higher background levels for CO excitation. Different models predict brighter or fainter higher-order transitions. Few measurements of CO rotational transitions exist for distant quasars and ULIRGs, but these are dominated by central regions. → Assume L ’ co(3-2) / L ’ co(1-0) = 1.

Atacama Large Millimeter Array October 2004DUSTY048 Detecting normal galaxies at z=3 For ΛCDM cosmology, Δv=300 km/s, the expected peak CO(3-2) flux density is 36 µJy. Require 5σ detection in 12h on source (16h total time). → ND 2 =7300 m 2. Achievable with N=64 antennas of D=12m diameter.

Atacama Large Millimeter Array October 2004DUSTY049 Precise 0.1” resolution images 0.1” resolution needed to complement contemporary facilities: JWST, eVLA, AO with 8-10m telescopes, … High angular resolution and sensitivity complementary. High fidelity images require a sufficiently large number of baselines to fill >50% of the uv-plane. Short tracking (<2 hours) to reduce atmospheric variations → requires ND > 560 for a maximum baseline of 3 km. Achievable with 64 12m antennas.

Atacama Large Millimeter Array October 2004DUSTY0410 Precise 0.1” resolution images Array cannot measure smallest spatial frequencies (<D). Solve by having four antennas optimized for total power measurements (nutating secondaries). Remaining gap in uv-plane filled in by Atacama Compact Array (ACA): 12 antennas 7m diameter.

Atacama Large Millimeter Array October 2004DUSTY0411 Summary of detailed requirements Frequency30 to 950 GHz (initially only GHz) Bandwidth8 GHz, fully tunable Spectral resolution31.5 kHz (0.01 km/s) at 100 GHz Spatial resolution<0.01” (18.5 km baseline at 650 GHz) Dynamic range10000:1 (spectral); 50000:1 (imaging) Flux sensitivitySub-mJy in <10 min (median conditions) Antenna complement64 antennas of 12m diameter PolarizationAll cross products simultaneously

Atacama Large Millimeter Array October 2004DUSTY0412

Atacama Large Millimeter Array October 2004DUSTY0413 Design Reference Science Plan DISCLAIMER: The Design Reference Science Plan has been set up by expert scientists to serve as a quantitative reference for developing the science operations plan, for performing simulations, and for software design. It assumes the full 64-antenna array ready in The DRSP does not form the basis for any definition of ALMA early science observing, nor for any priority claims on key or similar projects.

Atacama Large Millimeter Array October 2004DUSTY0414 Design Reference Science Plan 128 projects; full list available from Use ALMA sensitivity calculator: Total time: 3-4 years of ALMA observing.

Atacama Large Millimeter Array October 2004DUSTY0415 Design Reference Science Plan

Atacama Large Millimeter Array October 2004DUSTY0416 Molecular line studies of submm galaxies >50% of the FIR/submm background are submm galaxies. Trace heavily obscured star-forming galaxies. Optical/near-IR identification very difficult. Optical spectroscopy: ~2.4. Confirmation needed with CO spectroscopy.

Atacama Large Millimeter Array October 2004DUSTY0417 Molecular line studies of submm galaxies ALMA will provide 0.1” images of submm sources found in bolometer surveys ( LABOCA/APEX, SCUBA-2/JCMT ) or with ALMA itself. 3 frequency settings will cover the entire GHz band → at least one CO line. (1h per source) Confirm with observation of high/lower order CO line. (1h per source)

Atacama Large Millimeter Array October 2004DUSTY0418 Molecular line studies of submm galaxies Follow-up with ALMA: High resolution CO imaging to determine morphology (mergers?), derive rotation curves → M dyn, density, temperature,... (1h per source) Observe sources in HCN to trace dense regions of star-formation. (10h per source, 20 sources) Total: 12h per source, 170h for sample of 50 sources.

Atacama Large Millimeter Array October 2004DUSTY0419 Construction has begun!

Atacama Large Millimeter Array October 2004DUSTY0420 ALMA FE key specifications ALMA Band Frequency Range Receiver noise temperature Mixing scheme Receiver technology T Rx over 80% of the RF band T Rx at any RF frequency – 45 GHz17 K28 KUSBHEMT 267 – 90 GHz30 K50 KLSBHEMT 384 – 116 GHz37 K62 K2SBSIS 4125 – 169 GHz51 K85 K2SBSIS GHz65 K108 K2SBSIS 6211 – 275 GHz83 K138 K2SBSIS 7275 – 373 GHz*147 K221 K2SBSIS 8385 – 500 GHz98 K147 KDSBSIS 9602 – 720 GHz175 K263 KDSBSIS – 950 GHz230 K345 KDSBSIS Dual, linear polarization channels: Increased sensitivity Measurement of 4 Stokes parameters 183 GHz water vapour radiometer: Used for atmospheric path length correction * - between 370 – 373 GHz T rx is less then 300 K