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ESAC report
Rebaselining Time Allocation procedure Other items
ARC, EU-FP6: see T. Wilson
I. ALMA Rebaseling
Most of the ESAC and ASAC discussions over the last year focussed on the ALMA rebaselining; see ASAC reports October 2004, March 2005 and October 2005
At each of their face-to-face meetings, the ASAC/ESAC was presented with various options for re-scoping of the project. The latest set of Baseline Change Proposals (BCPs) by the JAO was received on September 8.
ESAC/ASAC reaction to BCPs ESAC and ASAC discussed all science-related BCPs; obtained
clarifications from project where needed ESAC grouped BCPs in 4 categories, with increasing severity of
impact on science RE, PR, MA, U(nacceptable) ASAC decided on 3 categories, where MA implies Unacceptable
Terminology ‘defer’ unclear ESAC assumed that ‘defer’ implies that the BCP may be realized in the
first ~3-4 yr after completion of full array, either through development funding in operations budget or additional money
Because of strict US-NSF rules which prevent moving scope from construction to operations, it is more likely that defer implies an indefinite delay. ASAC has therefore moved several of these BCPs into MA category.
BCP discussion
1. 50 antennas: MA N=50 antennas is a reduction compared with 50
operational antennas, as recommend by ASAC in March 2005 report 50 antennas endorsed by STC
ALMA science driven by sensitivity and image quality Sensitivity ~ N => integration time ~N2
Factor 1.5 in time for N=50, 2.3 for N=40 compared with N=60
Image quality ~N(N-1) ~N2, or even N3 as stressed in Blandford committee report
Milky Way galaxy at high redshift
- ALMA-60 takes 24 hrs to detect CO in Milky Way galaxy at z=3- This becomes 55 hrs with ALMA-40, far from routine!- Will take 200 hrs to observe 4 objects
Gas kinematics in disksCO 3-2 in TW Hya disk with SMA
- constrain physical and chemical structure- constrain kinematics, radial and vertical turbulence- requires >50 hrs with ALMA-60 at highest spatial resolution
Linewidth < 1 km/s => need ~0.1 km/s resolution!
Obs
Mod
Qi et al. 2004
Imaging quality
- Image fidelity = model * beam / (reconstructed image – model * beam)- Simulation includes thermal noise, but not other types of noise- Single configuration image; M51 scaled to ~6” and observed at 0.1”
=> Image quality strong function of N
Simulations M. Holdaway
M51 H image
BCP discussion (cont’d)
2. Long baselines (>4 km): MA Long baselines are a level 1 science driver for ALMA
Imaging gaps on AU scale in protoplanetary disks Imaging CO lines in high-z galaxies (requires 3 mm band)
Some delay O.K., but should never be fully excluded; see ASAC March 2005 report
3+4: OSF facilities: PR/RE Don’t make OSF facilities too basic, since it may
hamper attracting astronomers to Chile
Protoplanetary disks
- Origin of gaps, rings and holes in debris disks => planet formation?- Typical integration times with ALMA 60 ~8 hr continuum-only
Augereau 2005
Protoplanetary disks
- More distant objects being discovered with Spitzer => ALMA follow-up
Beichman et al. 2004Rieke et al. 2005
MIPS 70 m
T
Need long baselines toimages gaps and perhaps
protoplanets in disks
Wolf & D’Angelo (2004)
Maximum baseline: 10 km, 850 GHz, t int=8h,
30deg phase noise
Mplanet / Mstar = 1.0MJup / 0.5 Msun
Orbital radius: 5 AU50 pc
100 pc
High-redshift galaxies CO at z=6.4
VLA
- Need long baselines to image CO at high-z at <0.2” resolution (4 km at 3 mm corresponds to 0.18’’)
Walter et al. 2004VLA and IRAM PdB
Walter et al. 2003
CO 3-2 map, SDSS J1148+5251
0.3’’
BCP discussion (cont’d)
5. WVR: MA WVR are critical for phase correction, even on baselines as short as
300 m, see ASAC October 2002 report Can significantly enhance efficiency of array
6a. Solar filters: MA Possible to defer half of solar filters Removal of solar filters would disenfranchise an entire community
6b. Quarter-wave plates: PR ¼ wave plate ensures higher precision on weak polarization signals,
but can be deferred 7a. Removal 1 IF: MA
Removal one 1 IF reduces sensitivity by 40% for continuum and most line projects, see ASAC March 2005 report
Phase Stability Variations
36° el.
Annual variation
Diurnal variation
night day
11.2
GH
z
<100 m needed to image to 0.2” at 345 GHz without phase correction
400
800
25%
75%
Weather statistics indicate that phase correction is almost always needed on baselines >300m, even with good transparency!!!
Transparency and phase stability
Median
Note tail in statistics of periods with good transparency but large phase rms ¬> phase correction essential!
WVRs correct phase on ~1 s timescale; fast switching on 10’s of seconds
BCP discussion (cont’d)
7b: Defer 2 of 4 subarrays: PR Defer 2 of 4 subarrays O.K., but array more efficient with 4 Can significantly affect Band 5 operation if only 2 subarrays
7c + 7d: ?? Need more technical information, especially on magnitude of phase
loss; not ready for scientific discussion
8: Defer 3 of 4 receiver bands: MA-U Receivers 6, 7 and 9 integral part of ALMA science, see ASAC
October 2004 and March 2005 reports
Motivation for at least 4 receiver bands
Coverage of CO and C+ lines over a large range of z
Dust SEDs, dust properties Ability to probe range in physical conditions
(10-1000 K, 102 – 109 cm-3) Ultimate spatial resolution at the highest
frequencies Large variety of molecules, hydrides
(out of 10 originally planned => major descope has already occurred)
Different lines probe different conditions
ncrit~23
Higher frequencytransitions probe higherdensities and temperatures
Band
9
763CO principle tracer
of H2 gas
Cold tenuous gas vs warm dense gas
CO excitation Milky Way galaxies different from starbursts
Milky Way galaxy
Starburst nucleus
Nearby Galaxy: NGC6090
HST: Dinshaw et a. 1999HST: Dinshaw et a. 1999 SMA: J. WangSMA: J. Wang
CO 2-1CO 2-1
CO 3-2CO 3-2
[C II] detection at z=6.4!
Maiolino et al. 2005
-Band 9: [C II] at z=1-1.5-Band 7: [C II] at z=4-6
BCP discussion (cont’d) 9: Drop one polarization: MA-U
Loss of one polarization leads to loss of sensitivity by 40%, see ASAC March 2005 report
10. Software descopes: MA-U Unacceptable as proposed; ALMA presented to
community as easy-to-use instrument, also for non-experts More modest savings could be discussed
11. - 12. Site testing: PR
Need to keep some minor funding for short testing campaigns
MA
U
U
U
MA50%
??
Defer
Small campaigns
Delay, but never excluded
Reduction comp. with 50 operating
U
Don’t make facilities too basic
ESAC iniitial reaction
Other ASAC charges
Charge 2: Time allocation procedure for large and/or joint projects ALMA needs large projects, but no need to
make formal distinction with small programs
Large programs should not start too soon (wait for array to have large fraction of its capabilities)
…….
Other ESAC topics Demonstration science: see upcoming ASAC report
Largely same as Science Verification in ESO terminology See updated schedule
ARC update: see report T. Wilson EU MC-RTN proposal: submitted Sept. 28; training students in
submm astronomy, i.p. interferometry ‘Star Formation throughout the Universe’ (led by S. Aalto)
EU ALMA workshops ALMA and modeling of galactic + extragalactic ISM, Sweden October
13-16 2005 Complex molecules/line surveys with ALMA, Denmark, May 8-10 2006
ALMA worldwide meeting, Madrid , November 2006
1.09 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 from IPS as of 2005Oct06)
ATF Testing Support
OS
F/A
OS
Commissioning Antenna Array – Finish dates
16th 32nd 50th
Science Verification / Demonstration Science
AT
F
`
Dec ’09 Early Science
Feb ’09 Early Science Decision Point
Call for Proposals / Early Science Preparation
March 31 ’12 Start of Full Science
AOS 6 Ant Array
Evaluation Complete
8th
OSF Integration – Start dates
1st 16th 32nd 50th3rd2nd
SE
&I
Re
fere
nc
eATF Testing Prototypes & Pre-Production
8th
June ’06 ATF First Fringes
SC
IEN
CE
SU
MM
AR
Y Site Characterization
Science Support OSF
Subject to change!
Image quality (cont’d) ALMA-40 requires a different set of configurations
from zoomed spiral (e.g., rings or Y-shaped) Multi-configuration observations Different mode of operations
Array not continuously reconfigurable Risk of systematic errors (e.g. calibration) Long time scale for completion project Smaller number of objects
HD 141569 transitional disk: dust and cold gas
Augereau, Dutrey et al. 2004, in prep
When does gas disappear from disk? => constraints on time scalegiant planet formation
IRAM PdB12CO 2-1
Superposed onHST-STIS
Massive gas-rich disk
Debris disk
Redshifted CO with frequency bands
Starburstgalaxies
Milky-waygalaxies
Dust SEDs => photometric redshifts
P. Cox, priv. comm.
Band 6
Local CO 2-1 Bulk of medium excitation lines
Workhorse frequency for line observations in DRSP
Dust SED High-z CO at z=0.4-2.5 C+ at z=6-8
Band 3
Local CO 1-0 => tracer of cold gas Bulk of low excitation lines High-z CO at z=0-3 in MW galaxies
MW galaxy at z=3 has ~0.007 Jy km/s => requires 24 hr with full array to get 2 detection (calibration overheads?)
SiO 86 GHz maser
‘What science would be lost if band not or only partially available’
Band 7
Local CO 3-2 Bulk of medium excitation lines Dust SED and maps
Workhorse band for bulk of continuum observations in DRSP
Dust polarization High-z dust search C+ at z=4-6 H2D+ 372 GHz => cold clouds and disks with
heavy freeze-out
H2D+ in disks
TW HyaCSO data
DM Tau
Ceccarelli et al. 2004
Measuring the ionization degree in the midplane
- Expected strength ~4 K for 4” diameter disk => need to reach 0.4 K rms in <1 km/s bin at ~0.2” spatial resolution to image H2D+ => ~8 hr
Band 9
Local CO 6-5 High excitation lines Dust SED C+ at z=1.0-1.5 Ultimate spatial resolution
High excitation linesLocal starburst vs z=6.4 quasar
Bertoldi et al. 2003
Mapping warm gas in disks
AB Aur
LkCa15
-Optically thin lines ~few K => require 0.3 K rms on 0.1” scales to map
Van Zadelhoff et al. 2001, Dartois et al. 2003
Probing the radial and vertical temperature structure
Ultimate spatial resolution: Need for long baselines and Band 9
Massive gas-rich disks
Tenuous debris disks
gas + dust interstellar
-Driven by need to resolve protoplanetary disks on scales of 1 AU (1 AU at 140 pc = 7 marcsec)-Lines typically 10-50 K (optically thick) to few K (optically thin) => drives also sensitivity/collecting area