ALMA: Capabilities and Status Al Wootten NRAO, ALMA/NA Project Scientist.
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Transcript of ALMA: Capabilities and Status Al Wootten NRAO, ALMA/NA Project Scientist.
ALMA: Capabilities and Status
Al Wootten
NRAO, ALMA/NA Project Scientist
ALMA is governed by a Board, with representatives from each of the partners (Chile, NSF/NRC, ESO/Spain, NINS) [~10 folks+]
Board committees include ALMA Science Advisory Committee (ASAC) [~14 folks], AMAC
ALMA construction activities are conducted by joint teams which report to the Joint ALMA Office (Tarenghi, Director; Beasley, Project Manager) in Santiago [four+]
Regional Managers, Project Scientists, Advisory Committees (e.g. NA, EU, JP ALMA Project Manager) ;
ANASAC, ESAC, JSAC Regional ALMA Resource Centers (ARCs) in partner
regions support users in the respective astronomical communities [NAOJ, NRAO, ESO]
Who is ALMA?
ALMA Observes the Millimeter Spectrum
Millimeter/submillimeter photons are the most abundant photons in the cosmic background, and in the spectrum of the Milky Way and most spiral galaxies.
Most important component is the 3K Cosmic Microwave Background (CMB)
After the CMB, the strongest component is the submm/FIR component, which carries most of the remaining radiative energy in the Universe, and 40% of that in for instance the Milky Way Galaxy.
ALMA range--wavelengths from 1cm to 0.3 mm, covers both components to the extent the atmosphere of the Earth allows.
COBE observations
Telescope altitude diam. No. A max (feet) (m) dishes (m2) (GHz)
NMA 2,000 10 6 470 250CARMA 7,300 3.5/6/10 23 800 250IRAM PdB 8,000 15 6 1060 250SMA 13,600 6 8 230 690eSMA 13,600 6/10/15 10 490 690 ALMA 16,400 12 505700 950ACA 16,400 7 12 460 950
Summary of existing and future mm/sub-mm Summary of existing and future mm/sub-mm arraysarrays
ALMA will have >6x more collecting area, and will be 10-100 times more sensitive and 10-100 times better angular resolution compared to current mm/submm telescopes
Contributors to the Millimeter Spectrum
In addition to dominating the spectrum of the distant Universe, millimeter/submillimeter spectral components dominate the spectrum of planets, young stars, many distant galaxies.
Cool objects tend to be extended, hence ALMA’s mandate to image with high sensitivity, recovering all of an object’s emitted flux at the frequency of interest.
Most of the observed transitions of the 142 known interstellar molecules lie in the mm/submm spectral region—here some 17,000 lines are seen in a small portion of the spectrum at 2mm.
However, molecules in the Earth’s atmosphere inhibit our study of many of these molecules. Furthermore, the long wavelength requires large aperture for high resolution, unachievable from space. To explore the submillimeter spectrum, a telescope should be placed at Earth’s highest dryest site.
Spectrum courtesy B. Turner (NRAO)
Forests of Spectral Lines
Schilke et al. (2000)
N
Where is ALMA?Where is ALMA?
El llano de Chajnantor
AOS TBToco
Chajnantor
Negro
MacónHonar
Road
43km=27 miles
Chascón
OSF
5000m Chajnantor site
ALMA
APEX
CBI
Site Char
Transparent Site Allows Complete Spectral Coverage
10 Frequency bands coincident with atmospheric windows have been defined.
Bands 3 (3mm), 6 (1mm), 7 (.85mm) and 9 (.45mm) will be available from the start.
Bands 4 (2mm), 8 (.65mm) and, later, some 10 (.35mm), built by Japan, also available.
Some band 5 (1.5mm) receivers built with EU funding.
Pwv = 0.5mm 15% of time
Receivers/Front Ends
ALMABand
Frequency Range
Receiver noise temperature
Mixing scheme
Receiver technolog
yTRx over
80% of the RF band
TRx at any RF
frequency
131.3 – 45
GHz17 K 28 K USB HEMT
2 67 – 90 GHz 30 K 50 K LSB HEMT
384 – 116
GHz37 K 62 K 2SB SIS
4125 – 169
GHz51 K 85 K 2SB SIS
5163 - 211
GHz65 K 108 K 2SB SIS
6211 – 275
GHz83 K 138 K 2SB SIS
7275 – 373
GHz147 K 221 K 2SB SIS
8385 – 500
GHz98 K 147 K DSB SIS
9602 – 720
GHz175 K 263 K DSB SIS
10787 – 950
GHz230 K 345 K DSB SIS
• Dual, linear polarization channels:•Increased sensitivity•Measurement of 4 Stokes parameters
•183 GHz water vapour radiometer:•Used for atmospheric path length correction
Antennas Demanding ALMA antenna
specifications: Surface accuracy (25 µm) Absolute and offset pointing accuracy
(2 arcsec absolute, 0.6 arcsec offset) Fast switching (1.5 deg sky in 1.5 sec) Path length (15 µm non-repeatable,
20 µm repeatable)
To validate these specifications: two prototype antennas built & evaluated at ATF (VLA)
Prototype Antenna Testing at VLA
Photogrammetry,January 2005
Antenna Configurations (min)
150 m
ALMA + ACA
First ACA 12m – Dec 2007, 7m – Nov 2008
Big tractor picture These vehicles must lift the 110 ton
antenna systems and transport them over the ALMA road, often for several tens of kilometers at 7% avg grade, to and from the antenna stations and the OSF. To do this, these vehicles are equipped with twin 1340 horsepower engines; the
transporters measure 33 feet wide, 52 feet long, and 15 feet
high.
10,000m
4 mas @ 950 GHz
Antenna Configurations (max)
Site infrastructure (AOS/OSF) + inner array completed 2008
Summary of detailed requirements
Frequency 30 to 950 GHz (initially only 84-720 GHz fully instrumented)
Bandwidth 8 GHz, fully tunable
Spectral resolution 31.5 kHz (0.01 km/s) at 100 GHz
Angular resolution 30 to 0.015” at 300 GHz
Dynamic range 10000:1 (spectral); 50000:1 (imaging)
Flux sensitivity 0.2 mJy in 1 min at 345 GHz (median conditions)
Antenna complement 64 antennas of 12m diameter, plus compact array of 4 x 12m and 12 x 7m antennas (Japan)
Polarization All cross products simultaneously
Schedule
June 1998Phase I: Design & Development
November 2001Prototype antennas at VLA site
December 2001US/European ALMA Agreement
September 2004Enhanced ALMA Agreement (JP)
2005 Antenna Contract Awarded
2005-7 Prototype System Testing
2007-8 AOS/OSF completed
2009 - 2010Commissioning & early science operations
2012 Full Operations
Evaluation of Early Science
Array Complete
Projected Science Summary Schedule20072006 20092008 20112010 2012
41 2 3 41 2 3 41 2 3 41 2 3 41 2 3 41 2 3 41 2 3
(Data as of 2006Aug06)
ATF Testing Support
OS
F/A
OS
Commissioning Antenna Array – Finish dates
16th 32nd 50th
Science Verification
AT
F
`
July ’10 Early Science (+24)
Sept ’09 Early Science Decision Point
Call for Proposals / Early Science Preparation
Sept ’12 Start of Full Science
8th
OSF Integration – Start dates
1st 16th 32nd 50th3rd2nd
SE
&I
Re
fere
nc
eATF Testing
8th
Nov ’06 ATF First Fringes
SC
IEN
CE
SU
MM
AR
Y
Site Characterization
Science Support OSF
Time Now
March ’09 Limited call for SV proposals
+6 antennas
NOT YET BOARD APPROVED
3rd
Highest Level Science GoalsBilateral Agreement Annex B:“ALMA has three level-1 science requirements: 1) The ability to detect spectral line emission from CO or C+ in a
normal galaxy like the Milky Way at a redshift of z = 3, in less than 24 hours of observation.
2) The ability to image the gas kinematics in a solar-mass protostellar/ protoplanetary disk at a distance of 150 pc (roughly, the distance of the star-forming clouds in Ophiuchus or Corona Australis), enabling one to study the physical, chemical, and magnetic field structure of the disk and to detect the tidal gaps created by planets undergoing formation.
3) The ability to provide precise images at an angular resolution of 0.1". Here the term precise image means accurately representing 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 degrees. These requirements drive the technical specifications of ALMA. “
A detailed discussion of them may be found in the new ESA publication Dusty and Molecular Universe on ALMA and Herschel.
ALMA Design Reference Science Plan(DRSP)
Goal: To provide a prototype suite of high-priority ALMA projects that could be carried out in ~3 yr of full ALMA operations
Started planning late April 2003; outline + teams complete early July; submitted December 2003; updated periodically
128 submissions received involving ~75 astronomers Review by ASAC members completed; comments
included Current version of DRSP on Website at:
http://www.strw.leidenuniv.nl/~alma/drsp.html New submissions continue to be added.
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,
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
12m
Aperture Synthesis with ALMA12-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 observationsUp to 15km
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
Core dynamics: infall
Di Francesco et al (2001)
Small-scaleExtended 0.1 - 0.3 pc
Walsh et al
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 H2D+
CS, CO, HCO+
NH3, N2H+
H2D+
D2H+
Walmsley et al. 2004; Caselli et al 2003
372GHz line8,000AU
2,500AU
15,000AU
Polarized CO Line Emission
NFC1333IRAS4A Goldreich-Kylafis
Effect
Girart, Crutcher, Rao 1999
SiO J=1-0 Choi 2005
A1
A2
Polarization and the Role of Magnetic Fields
Girart, Rao, Marrone 2006
•Polarization hole•Polarization peak is offset•Hour glass shape of the magnetic field structure in the circumbinary envelope•The large scale field is well aligned with the minor axis•We will need some higher angular resolution observations to map the structure of the field between the two cores
•Contours - I•Pixel - polarized flux density sqrt(Q^2+U^2)•RMS = 3 mJy/bm•Peak pol = 9 % at PA 153 degrees•At the peak of Stokes I - pol = 1%•Averaged pol = 4.7% @ 145 degrees
E-Vectors
B-Vectors
The data indicate that, in the case of IRAS 4A, magnetic pressure is more influential than
turbulence in slowing star formation within the cloud core. The same likely is true for similar
cloud cores elsewhere.
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.
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
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
Spatially-resolved Spectral Surveys
8GHz bandwidth
Schilke et al
Kuan
et a
l 200
4
Kuan
et a
l 200
4
Loon
ey e
t al,
2000
“Hot Core” chemistry around low mass protostars
300AU sized molecular structures around protostellar candidates
Different chemical signatures
= 333m = 870m
Mplanet / Mstar = 0.5MJup / 1.0 Msun
Orbital radius: 5 AU
Disk mass as in the circumstellar disk as
around the Butterfly Star in Taurus
Maximum baseline: 10km,
tint=8h,
30deg phase noise
pointing eror 0.6“
Tsys = 1200K (333mu) / 220K
(870mu)Sebastian Wolf (2005)
50 pc
50 pc
100 pc
“Debris” disk spectroscopy with Spitzer
Rieke et al 2004
“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)Fom
alhaut (Greaves et al)
Science group suggestions:
* predictions about how gas lifts off of the surface of the disk and what the physical conditions of that gas might be - we need to know what tracers ALMA can use are likely to probe this effect and how those tracers are likely to evolve as the protostar heats up or for higher luminosity protostars. * when the material accretes from the "envelope" to the disk and starts to "pile-up” in the disk (in the scenario for episodic accretion), there should be a second, lower energy accretion shock in the outer disk. What are the atomic/molecular/continuum diagnostic of that shock? Any chance we could observe it with ALMA?
www.alma.info
The Atacama Large Millimeter Array (ALMA) is an international astronomy facility. ALMA is a partnership between Europe, North America and Japan, in cooperation with the Republic of Chile. ALMA is funded in North America by the U.S. National Science Foundation (NSF) in cooperation with the National Research Council of Canada (NRC), in Europe by the European Southern Observatory (ESO) and Spain. ALMA construction and operations are led on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI), on behalf of Europe by ESO, and on behalf of Japan by the National Astronomical Observatory of Japan.