ALMA the Atacama Large Millimetre Array

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(ESO press drawing)
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Science with the Atacama Large Millimetre Array
(ALMA)

• John Richer, Cavendish Laboratory
• UK Project Scientist for ALMA

• scientific goals
• requirements
• outline design
• project status

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15-m JCMT 0.35 to 2.0mm operation
Leading European facilities
5x15m Plateau de Bure array 1.3 to 3 mm operation
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Key Science Goals of ALMA

• ALMA will map thermal emission from cool gas
  and dust throughout the Universe at lt0.1 arcsec
  resolution

• image the gas from which the very early
  generations of stars and galaxies formed
• image in detail the formation of stars and
  structure of protoplanetary disks
• study structure of the interstellar medium in
  galaxies of all types
• image planetary atmospheres, comets and other
  solar system debris

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12 Billion
5 Billion
Time in Years
1 Billion
100 Million
300,000
Era of galaxy formation
Big Bang
Present Day
COBE
ALMA NGST Gemini
HST
Ground-Based Observatories
Fig 001
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Origins of Galaxies
Deepest optical image the Hubble Space Telescope
Deep Field
Deepest submm image the HDF at 850mm with SCUBA
on the JCMT
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40 hours, Plateau de Bure (5x15m antennas)
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Deepest submm image - the HDF at 850mm with
SCUBA. 15 nights observing 6 sources.
Confusion-limited
7mJy at 850mm
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• Model for 100,000 Orions (30Msun/yr of star
  formation - Spaans and Silk)
• Blind CO surveys possible with ALMA
• rich set of lines, especially CO
• ladder spacing 115GHz/(1z)

J6-5
ALMA mm bands
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Star Formation
wide range of angular scales involved
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Protoplanetary Discs
...observing the birth of new solar systems
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Galaxy Structure

• ALMA will provide the first high resolution
  images of the dense gas in galaxies
• normal galaxies
• Starbursts
• Galactic nuclei

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Stellar Studies
IRC10216
TT Cygni
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Solar System

• Comets
• Kuiper belt objects
• Planetary atmospheres
• Volcanoes on Io
• The Sun

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ALMA Scientific Requirements

• resolution lt 0.1
• to resolve protostellar disks and high-z galaxies
• high sensitivity, sufficient to
• image extended thermal objects
• detect modest star-forming galaxies at high-z
• 30 to 900GHz operation with km/s resolution
• peak of dust near (1z)100mm
• access to several transitions of many molecules
  to measure gas chemistry, kinematics, physical
  properties
• 50GHz sensitivity well-matched to upgraded VLA

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The Atacama Array

• international collaboration draws on wealth of
  previous submillimetre experience
• well-defined scientific aims and system concept
• massive step forward in angular resolution and
  sensitivity over current instruments (factor of
  10-100)
• biggest ground-based telescope project of the
  next 10 years
• great enthusiasm worldwide from very broad
  scientific community

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ALMA specifications

• 64 moveable 12-m antennas (7200m2 collecting
  area)
• 20-mm surface accuracy (25-mm spec.)
• 5000-m site - excellent transmission and phase
  stability
• baselines from 16m up to 10km
• resolution up to 7mas
• (30?) - 60 - 900GHz frequency coverage
• sensitive HFET/SIS receivers - several hn/k noise
• dual (linear) polarisation
• 4 to 8GHz bandwidth
• 2016 correlated baselines
• 4096 spectral channels?

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Target sensitivities

• Continuum
• 140?Jy in 1 minute at 345GHz
• 4mJy in 1 minute at 850GHz
• Lines
• 0.8mJy in 25km/s in 1 minute at 90GHz

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One source per ALMA primary beam at 850mm
detected in 3 minutes at 3-sigma!
Submm source count models (Blain)
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Timeline

• Phase 1 DD - 3 years to December 2001
• European MOU signed Jan 1 1999 (ESO countries
  PPARC)
• US-European MOU signed June 10th 1999 ALMA is
  born
• 2 prototype 12-m antennas being procured
• full merged ALMA design undertaken
• other partners join?
• continuing science definition
• realistic costing funding sought.
• Phase 2 construction, 2001-2 on
• final international agreement needed
• site development
• interferometer tests and antenna evaluation (VLA
  site?)
• antenna, receiver, correlator production
  construction begins
• Operation 2007? on
• simultaneous observing and construction?
• full operation 2010?

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Prototype 12-m antenna contracts signed 2000 Q1
delivery to New Mexico in 2001 Q4, to Chile in
2003.
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UK Involvement in ALMA

• Aiming for 10 of world project (and thus 10 of
  observing time, presumably!)
• 2M in Phase 1
• Half time Project Manager (Richard Wade) and
  Project Scientist (JSR)
• contribution to European antenna
• phase correction at 183GHz
• array configurations
• receiver, cryogenics, correlator design
• signal distribution (fibre)
• software
• scientific input - this means you!
• Phase 2 work to be decided
• Overall project cost around 500M, with 50M p.a.
  running costs - but numbers very preliminary

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The ALMA Site

• Llano de Chajnantor in the Atacama Desert of
  northern Chile
• Altitude 5000m (16,500ft) - drier than Mauna Kea
• Low snow and rainfall
• Smooth topography over 3-4km scales
• Served by international highway to Argentina
• Gas pipeline runs across site
• 40km from the tourist town San Pedro
• 100km from Calama, a major copper mining centre
  and airport
• 250km from VLT site Paranal

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Llano de Chajnantor
Simon Radfords photo
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CBI November 99
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Site Properties
t(225GHz)0.010.04pwv
2.7mm of water
1.3mm of water
0.7mm of water
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Major Challenges

• operation on 5000-m site
• health issues
• reliability
• cost
• antenna pointing, switching rate, and surface
  accuracy
• phase correction
• short spacing requirement
• receiver design
• digital correlator 1014 flops!
• astronomer interface

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ALMA site
For more details, contact me at jsr_at_mrao.cam.ac.uk
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Peak at (1z)100mm
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