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Scientific requirements of ALMA, and its capabilities for keyprojects: extragalactic

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Current millimeter interferometers have collecting areas between 500 and 1000 m2. ... plateau at 5000m altitude is superior to all existing mm observatories. ... – PowerPoint PPT presentation

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Title: Scientific requirements of ALMA, and its capabilities for keyprojects: extragalactic


1
  • Scientific requirements of ALMA, and its
    capabilities for key-projects extragalactic

Carlos De Breuck (ESO)
2
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.

3
Primary Scientific Requirements
  • The ability to detect spectral line emission from
    CO or CI 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 Richers 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.

4
Detecting normal galaxies at z3
  • CO emission now detected in 25 zgt2 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 m2.

5
Detecting normal galaxies at z3
  • ALMA sensitivity depends on
  • Atmospheric transparency
    Chajnantor plateau at
    5000m
    altitude is superior to all
    existing mm
    observatories.
  • Noise performance of receivers can be reduced by
    factor 2 (approaching quantum limit). Also gain
    v2 because ALMA will simultaneously measure both
    states of polarization.
  • Collecting area remaining factor of 7 to 10 can
    only be gained by increasing collecting area to
    gt7000 m2.

6
Detecting normal galaxies at z3
  • At z3, 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 0.45ltealt0.75
  • can be achieved (20 µm antenna
    surface
    accuracy).
  • Tsys depends on band, atmosphere,
    for 115 GHz, Tsys 67 K
    obtainable.

7
Detecting normal galaxies at z3
  • Total CO luminosity of Milky Way Lco(1-0)
    3.7x108 K km s-1pc2 (Solomon Rivolo 1989).
  • COBE found slightly higher luminosities in
    higher transitions (Bennett et al 1994) ? adopt
    Lco 5x108 K km s-1pc2.
  • At z3 ? observe (3-2) or (4-3) transition in
    the 84-116 GHz atmospheric band ? need to
    correct, but also higher TCMB 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 Lco(3-2) / Lco(1-0) 1.

8
Detecting normal galaxies at z3
  • For ?CDM cosmology, ?v300 km/s, the expected
    peak CO(3-2) flux density is 36 µJy.
  • Require 5s detection in 12h on source (16h total
    time).
  • ? ND27300 m2.
  • Achievable with N64 antennas of D12m diameter.

9
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 gt50 of the
    uv-plane.
  • Short tracking (lt2 hours) to reduce atmospheric
    variations
  • ? requires ND gt 560 for a maximum baseline of 3
    km.
  • Achievable with 64 12m antennas.

10
Precise 0.1 resolution images
  • Array cannot measure smallest spatial
    frequencies (ltD).
  • 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.

11
Summary of detailed requirements

12
(No Transcript)
13
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 2012. 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.
14
Design Reference Science Plan
  • 128 projects full list available from
    http//www.eso.org/projects/alma
  • Use ALMA sensitivity calculator
  • http//www.eso.org/projects/alma/science/bin/sensi
    tivity.html
  • Total time 3-4 years of ALMA observing.

15
Design Reference Science Plan
16
Molecular line studies of submm galaxies
  • gt50 of the FIR/submm background are submm
    galaxies.
  • Trace heavily obscured star-forming galaxies.
  • Optical/near-IR identification very difficult.
  • Optical spectroscopy ltzgt2.4.
  • Confirmation needed
    with CO spectroscopy.

17
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
    84-116 GHz band ? at least one CO line. (1h per
    source)
  • Confirm with observation of high/lower order CO
    line. (1h per source)

18
Molecular line studies of submm galaxies
  • Follow-up with ALMA
  • High resolution CO imaging to determine
    morphology (mergers?), derive rotation curves ?
    Mdyn, 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.

19
Construction has begun!
20
ALMA FE key specifications
- between 370 373 GHz Trx is less then 300 K
  • Dual, linear polarization channels
  • Increased sensitivity
  • Measurement of 4 Stokes parameters
  • 183 GHz water vapour radiometer
  • Used for atmospheric path length correction
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