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New Windows on Star
Formation in the Cosmos
October 11-13, 2004
U. of Maryland
The Dusty and Molecular
Universe
A prelude to HERSCHEL and
ALMA
27 - 29 October 2004, Paris
ALMA Update
Al Wootten NRAO
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U. Of Md.
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Dusty04
http://aramis.obspm.fr/DUSTY04/plan.html
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Dusty04—Herschel Schedule
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HIFI
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PACS
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SPIRE
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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!
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Summary of detailed requirements
Frequency
30 to 950 GHz (initially only 84-720 GHz)
Bandwidth
8 GHz, fully tunable
Spectral resolution
31.5 kHz (0.01 km/s) at 100 GHz
Spatial resolution
<0.01” (18.5 km baseline at 650 GHz)
Dynamic range
10000:1 (spectral); 50000:1 (imaging)
Flux sensitivity
Sub-mJy in <10 min (median conditions)
Antenna complement 64 antennas of 12m diameter
Polarization
All cross products simultaneously
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Management – JAO Staffing
Joint Alma Office (JAO) in Chile:
–
–
–
–
–
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Director:
Project Manager:
Project Engineer:
Project Scientist:
Project Controller:
Logistics Officer:
Massimo Tarenghi
Tony Beasley
Rick Murowinski
Vacant
Richard Simon (interim)
Charlotte Hermant
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Agreement (2/2)
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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”.
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Primary Scientific Requirements
• The ability to detect spectral line emission from CO or CII 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°.
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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 m2.
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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 m2.
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Detecting normal galaxies at z=3
•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<εa<0.75
can be achieved (25 µm antenna
surface accuracy).
• Tsys depends on band, atmosphere, …
for 115 GHz, Tsys =67 K obtainable.
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Detecting normal galaxies at z=3
•Total CO luminosity of Milky Way: L’co(1-0) = 3.7x108 K km s-1pc2
(Solomon & Rivolo 1989).
• COBE found slightly higher luminosities in higher transitions
(Bennett et al 1994) → adopt L’co = 5x108 K km s-1pc2.
• At z=3 → 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 L’co(3-2) / L’co(1-0) = 1.
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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).
→ ND2=7300 m2.
• Achievable with N=64 antennas of D=12m
diameter.
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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.
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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.
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Design Reference Science Plan
• 128 projects; full list available from
http://www.alma.nrao.edu
• Use ALMA sensitivity calculator:
http://www.eso.org/projects/alma/science/bin
/sensitivity.html
• Total time: 3-4 years of ALMA
observing.
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Design Reference Science Plan
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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: <z>~2.4.
• Confirmation needed
with CO spectroscopy.
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Molecular line studies of submm galaxies
•
ALMA will provide 0.1” images of
submm sources found in bolometer
surveys (LABOCA/APEX, SCUBA2/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)
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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.
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Millimeter VLBI – Imaging the Galactic center black
hole (Falcke 2000)
Kerr
R_g = 3 uas
Schwarzschild
Model: opt.
thin synch
0.6 mm VLBI
1.3 mm VLBI
16uas res
33 uas res
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Enabling technology III: Wideband spectroscopy –
Redshifts for obscured/faint sources: 8 - 32 GHz
spectrometers on ALMA, LMT, GBT (Min Yun 04,
Harris 04)
L_FIR = 1e13 L_sun
ALMA
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Andre
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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.
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• Good match to
weather statistics
and science
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Frequency band capabilities
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•
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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
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Diffraction limited imaging needs phase
correction
• Water fluctuations typically 500m1000m above site
• Correct by Fast Switching of
antennas to QSO, plus Water Vapor
Radiometry
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Star Forming
Regions are
complex
• Such as DR21
at roughly 3
Kpc (Marston
et al. IRAC)
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Serpens at 3mm and 100 microns (Testi priv.comm)
n HSO Survey of Nearby SFR
OVRO 3mm
: P. Saraceno
M. Benedettini, A. di Giorgio, S.Tuesday
Molinari,
S. Pezzuto, S. Viti
Lunch - Walmsley
: L. Testi, P. Caselli
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Fundamental steps forward with Herschel
• PACS : Maps of star forming regions in continuum
and OI 63 micron line
• SPIRE : Maps on the large scale (eg of galactic plane,
see Molinari HIGAL poster)
• HIFI : Water and detailed kinematics of star forming
regions
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Initial Conditions: Pre-collapse Cores
• Strong chemical gradients
and clumpiness
• Indicates depletion and
chemical evolution
• ALMA mosaic at 3mm:
100 pointings plus singledish data needed
• ALMA can resolve 15AU
scales in nearby cores, or
study cores at 1000AU
scales out to 10kpc
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L1498: Tafalla et al.
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Small-scale
Core dynamics: infall
Extended 0.1 - 0.3 pc
Walsh et al
Di Francesco et al (2001)
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Starless Core Chemistry: probing the depletion
zones • Complete CNO depletion
CS, CO,
within 2500AU?
• ALMA can study this
region, in objects as far as
the GC, in H2D+
HCO+
NH3, N2H+
H2 D +
D2 H +
2,500AU
8,000AU
372GHz line
15,000AU
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Walmsley et al. 2004; Caselli et al 2003
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Role of Magnetic Fields?
(Figure by A. Chrysostomou)
L1544: Ward-Thompson et al 2000
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(Crutcher et al)
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Star formation in crowded environments
Bate 2002
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Protostars and Clumps in Perseus: Hatchell et al 2005.
• 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 on43AU
scales
Molecular Outflows
Chandler & Richer 1999
170AU resolution
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•
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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
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Beuther et al, 2002
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Spatially-resolved Spectral Surveys
Kuan et al 2004
8GHz bandwidth
Schilke et al
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Disk around young stars
• Current arrays have done
about 20 sources... (e.g.
IRAM PdB Survey)
• ALMA sensitivity 50 times
better ...
• ALMA could do hundreds
of sources in continuum, to
a much better level, and at
much higher angular
resolution
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Zooming on inner disks
• Nice, circularly symmetric,
Keplerian disks don’t really exist
• E.g. AB Aur 1.3 mm image at 0.6”
resolution: “spiral” density
enhancements 100 AU from the star
(black: IR from Fukagawa et al
2004, White: mm from Piétu et al
2004)
• Are such phenomena common?
Long-lived ?
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Stellar Masses (and
more)
• From the (Keplerian) rotation curve,
measured from CO (Simon et al
2000)
• Temperature from CO isotopes
(Dartois et al 2003)
• A sample of 40 sources, in CO and
its isotopes at 0.2” resolution
requires 2600 hours of ALMA !
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Transition Disks ?
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•
•
ALMA can image the “débris” disks around (young) stars
But also perhaps unveil the transition stage between proto-planetary disks and
“débris” disks
Small disks just being found: e.g. BP Tau (Dutrey et al 2003)
But studies will require long integration time even with ALMA (>> 10 hours /
object)
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Long term schedule
• Proper motions can be measured with ALMA
• Clumps in “debris” disks ( evidence for planets ?)
• Orbital motions of proto-stellar condensations in massive
star forming regions
• Plan in advance and for the long term...
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Imaging Protoplanetary Disks
• Protoplanetary disk at 140pc, with
Jupiter mass planet at 5AU
• ALMA simulation
Gueth, Henning,
– 428GHz, bandwidth 8GHz Wolf,
& Kley 2002, ApJ 566, L97
– total integration time: 4h
– max. baseline: 10km
• Contrast reduced at higher
frequency as optical depth
increases
• Will push ALMA to its limits
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“Debris” disk spectroscopy with Spitzer
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Rieke et al 2004
“Debris” Disk imaging with ALMA
Fomalhaut (Greaves et al)
Vega (Holland 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
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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
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SCUBA 450 micron
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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Site – Road Construction 1
Road Construction
• There are 42Km of road being constructed between Highway 23
outside San Pedro de Atacama to the AOS via the OSF giving
ALMA its own private road network.
• Initial construction started in 2003 and the road was opened in
time for the Ground Breaking ceremony in November.
• Commencing in June 2004 the final construction is now taking
place to consolidate the existing road and make it suitable for the
main construction and operations phases.
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GPS track
on site
image
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Site – Road Construction 2
Right of Way
Concession
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Site – Road Construction 3
To AOS
OSF Site
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Site – Road Construction 4
View West
Road at 18Km
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View East
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Site – ALMA Camp 1
ALMA Camp
• The permanent ALMA camp at the OSF is currently being used by
members of the site IPT. Further expansion is planned over the
following year to allow accommodation of all ALMA staff during
the main integration phase.
• The camp will also be used during the operations phase and it is
planned to augment the facilities with a Residence building
housing about 100 visiting staff and observers.
• At the same time a Contractors camp is being built nearby to house
the contractors workforce during the construction phase.
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Site – ALMA Camp 2
Inner Court
ALMA Camp – General View
Typical Office
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ALMA Board at ALMA Camp Grill
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Site – OSF 1
Operations Support Facility
• The OSF is the main facility for operations and maintenance of the
array. Situated at 2900m it will offer a modern, comfortable and
safe environment from which both scientific observation and
routine maintenance can be conducted.
• The design of the OSF encompasses workshop facilities,
integration facilities and maintenance areas for both the current
baseline ALMA and the enhanced design to include the
contribution of Japan. In addition the array operations centre and
associated observing facilities are all contained within the same
campus.
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Visitors Center
Residence Area
OSF
Camps
and
Technical
Facilities
Access Road to Visitors Center
Contractors Camp
ALMA Camp
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Site – AOS 1
Array Operation Site
• The AOS complex houses the Correlator and Local Oscillator
equipment together with limited workshop facilities and emergency
overnight accommodation. It is not intended to have any staff
permanently stationed at the AOS and all operations will be
conducted remotely from the AOS.
• The layout of the array foundations has been completed with a total
of 216 pads. The original compliment of 256 pads has been
reduced with no compromise to the ALMA science.
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Site – AOS Building 1
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