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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 disks CO 3-2 in TW Hya disk with SMA Obs Mod Qi et al. 2004 • 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!
Imaging quality M51 Ha image Simulations M. Holdaway • 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
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 Augereau 2005 • Origin of gaps, rings and holes in debris disks => planet formation? • Typical integration times with ALMA 60 ~8 hr continuum-only
Protoplanetary disks MIPS 70 mm Beichman et al. 2004 Rieke et al. 2005 • More distant objects being discovered with Spitzer • => ALMA follow-up
T Need long baselines toimages gaps and perhaps protoplanets in disks Mplanet / Mstar = 1.0MJup / 0.5 Msun Orbital radius: 5 AU 50 pc Maximum baseline: 10 km, 850 GHz, t int=8h, 30deg phase noise 100 pc Wolf & D’Angelo (2004)
High-redshift galaxies CO at z=6.4 CO 3-2 map, SDSS J1148+5251 0.3’’ VLA VLA and IRAM PdB Walter et al. 2004 Walter et al. 2003 - Need long baselines to image CO at high-z at <0.2” resolution (4 km at 3 mm corresponds to 0.18’’)
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 Weather statistics indicate that phase correction is almost always needed on baselines >300m, even with good transparency!!! Annual variation Diurnal variation 36° el. day night 11.2 GHz 800 75% 400 25% f<100 mm needed to image to 0.2” at 345 GHz without phase correction
Transparency and phase stability Note tail in statistics of periods with good transparency but large phase rms ¬> phase correction essential! Median 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 (out of 10 originally planned => major descope has already occurred) • 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
Different lines probe different conditions Cold tenuous gas vs warm dense gas Band 9 • ncrit~m2n3 • Higher frequency transitions probe higher densities and temperatures 7 6 CO principle tracer of H2 gas 3
CO excitation Milky Way galaxies different from starbursts Starburst nucleus Milky Way galaxy
Nearby Galaxy: NGC6090 CO 2-1 CO 3-2 SMA: J. Wang HST: Dinshaw et a. 1999
[C II] detection at z=6.4! • Band 9: [C II] at z=1-1.5 • Band 7: [C II] at z=4-6 Maiolino et al. 2005
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
ESAC iniitial reaction Reduction comp. with 50 operating Delay, but never excluded Don’t make facilities too basic MA 50% MA U Defer ? ? U U U Small campaigns
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
2008 2009 2006 2007 2010 2011 2012 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1.09 Science Summary Schedule (Data from IPS as of 2005Oct06) ATF Testing Prototypes & Pre-Production June ’06 ATF First Fringes SE&I Reference OSF Integration – Start dates 50th 32nd 1st 2nd 3rd 8th 16th ATF Testing Support ATF Site Characterization Science Support OSF Commissioning Antenna Array – Finish dates SCIENCE SUMMARY ` AOS 6 Ant Array Evaluation Complete 50th 32nd 8th 16th Science Verification / Demonstration Science OSF/AOS Feb ’09 Early Science Decision Point Call for Proposals / Early Science Preparation Dec ’09 Early Science Subject to change! March 31 ’12 Start of Full Science
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 IRAM PdB Massive gas-rich disk 12CO 2-1 Superposed on HST-STIS Debris disk When does gas disappear from disk? => constraints on time scale giant planet formation Augereau, Dutrey et al. 2004, in prep
Redshifted CO with frequency bands Starburst galaxies Milky-way galaxies
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 ‘What science would be lost if band not or only partially available’ • 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 2s detection (calibration overheads?) • SiO 86 GHz maser
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 Measuring the ionization degree in the midplane TW Hya CSO data DM Tau • 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 Ceccarelli et al. 2004
Band 9 • Local CO 6-5 • High excitation lines • Dust SED • C+ at z=1.0-1.5 • Ultimate spatial resolution
High excitation lines Local starburst vs z=6.4 quasar Bertoldi et al. 2003
Mapping warm gas in disks Probing the radial and vertical temperature structure 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
Ultimate spatial resolution: Need for long baselines and Band 9 Massive gas-rich disks • 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 gas + dust interstellar Tenuous debris disks