From Idea to ALMA Project James Di Francesco Herzberg Institute of Astrophysics North American ALMA Science Center (thanks to Mike Rupen, Gianni Comoretto & Ray Escoffier)

The Atacama Large Millimetre Array (ALMA)

Outline ALMA CapabilitiesALMA Capabilities Correlator ModesCorrelator Modes Observing Tool (OT)Observing Tool (OT) Proposal ProcessProposal Process Early ScienceEarly Science

ALMA Capabilities NumbersNumbers

mm 350  m ALMA Capabilities Frequency CoverageFrequency Coverage

ALMA Capabilities Angular ResolutionAngular Resolution - for 12-m array:  FWHM = 0.62”(max baseline[km]) -1 ( /100 GHz) m antenna configurations will “breathe” from maximum 200 m to maximum ~18 km baselines maximum 200 m to maximum ~18 km baselines - for ACA:  FWHM = 20.6”( /100 GHz) -1 - ACA antennas will be fixed in position

ALMA Capabilities Fields of ViewFields of View = 62.9” ( /100 GHz) -1 [12m] FOV = 1.22 ( /D) = 107.8” ( /100 GHz) -1 [7m]

ALMA Capabilities Fields of ViewFields of View ~4’ Band 3 (54”) Band 6 (27”) Band 9 (9”) Band 7 (18”) FOV [12 m] B68 ALMA single pointing

ALMA Capabilities Fields of View (Mosaics)Fields of View (Mosaics) ~4’ Nyquist Spacing = 3 -1/2 ( /D) = 29.75” x ( /100 GHz) -1 ( /100 GHz) -1 = expensive! OTF mosaicking to come! to come! B68 ALMA 22-pointing mosaic

ALMA Capabilities Total Power Recovery (on scales > /b min )Total Power Recovery (on scales > /b min ) Method 1: ACA (or SMA??) - fixed configuration, more compact: - fixed configuration, more compact:  FWHM = 20.6”( /100 GHz) -1  FWHM = 20.6”( /100 GHz) -1 - for similar SNR data, t(ACA) = n x t(ALMA) - for similar SNR data, t(ACA) = n x t(ALMA) Method 2: ACA 12 m antennas in TP mode -  FWHM = 12-m array FOVs (e.g., 54” in B3) -  FWHM = 12-m array FOVs (e.g., 54” in B3) - for similar SNR data, t(ACA-12) = n x t(ALMA) - for similar SNR data, t(ACA-12) = n x t(ALMA) Method 3: build a ~25 m single dish (CCAT?)

ALMA Capabilities PolarizationPolarization - ALMA antennas have linearly polarized feeds, can recover I, Q, U and V from observed X and Y can recover I, Q, U and V from observed X and Y - not “free,” requires reducing band width by 2, some sensitivity some sensitivity - specs require <0.1% polarized flux error * - special calibration required (e.g., obs over many parallactic angles) parallactic angles) - needed for high dynamic range imaging - Band 7 will have quarter-wave plates for precise polarimetric imaging (B5 only one polzn) polarimetric imaging (B5 only one polzn)

ALMA Capabilities SensitivitySensitivity - also possible to combine ACA* with 12-m array!

ALMA Capabilities SensitivitySensitivity - ultimately depends on spectral resolution (SR) and this depends on correlator configuration and this depends on correlator configuration - correlator is powerful but has finite capacity, has 4 quadrants that can be configured independently 4 quadrants that can be configured independently - correlator resources (filters, correlator planes) allocated with trade-offs between band width, allocated with trade-offs between band width, no. of polarizations processed, sampling rate, and quantization level no. of polarizations processed, sampling rate, and quantization level

Correlator Modes

x ij (  ) Correlators, um, correlate signals from antenna pairs From the correlations, the complex visibilities can be obtained by measuring the real and imaginary parts.

Antenna 1 Correlator Modes Antenna 1

Antenna 2 Correlator Modes Antenna 1Antenna 2

 =0 Correlator Modes Antenna 1Antenna 2

Correlator Modes Antenna 1 Antenna 2  =0.5

Correlator Modes Antenna 1 Antenna 2  =1

Correlator Modes Antenna 1 Antenna 2  =1.5

Correlator Modes Antenna 1 Antenna 2  =2

Correlation of Ant 1 & Ant 2 Correlator Modes

For a monochromatic signal: and the correlation function is So we need only measure with Correlator Modes

xIxI xRxR - x R and x I correspond to the amplitude and phase respectively

Correlator Modes - measured by adding phase delays (  = 1/4 ) to incoming signals, get R ij (,t) - x R and x I are measured by adding phase delays (  = 1/4 ) to incoming signals, get R ij (,t) a complex correlator

Correlator Modes - ALMA’s receivers are not monochromatic, and deliver wide-band signals to the correlator - to get spectra, use the principle that the Fourier Transform of a cross-correlation (lag) function is the frequency spectrum: - SHORT LAGS LOW FREQUENCIES - LONG LAGS HIGH FREQUENCIES

Correlator Modes - baseband pairs from antennas are 2 GHz wide - 4 baseband pairs are independently tunable LSBUSB GHz8 GHz4 GHz o e.g., Band 3: LO1

Correlator Modes The ALMA Correlator: - 32 main racks with 3,000 printed circuit cards - 32 main racks with 3,000 printed circuit cards - a total of 135,000 complex integrated circuits - a total of 135,000 complex integrated circuits - factor of 15,000 larger than the VLA correlator - factor of 15,000 larger than the VLA correlator - overall system dissipation: 170,000 W - overall system dissipation: 170,000 W one quadrant station rackcorrelator rack power supply computer

Correlator Modes - the ALMA Correlator is an “FXF” design: - F: divide incoming signal up to smaller chunks - F: divide incoming signal up to smaller chunks (sub-bands) using a Tunable Filter Bank card (sub-bands) using a Tunable Filter Bank card - X: measure the cross-correlation function over a - X: measure the cross-correlation function over a range of lags, average over time range of lags, average over time - F: Fourier Transform the CC functions to obtain - F: Fourier Transform the CC functions to obtain the frequency spectrum of each sub-band the frequency spectrum of each sub-band - stitch together the sub-bands (if necessary) - stitch together the sub-bands (if necessary)

Correlator Modes “F” “X” “F” x4 ALMA Correlator Block Diagram

Correlator Modes - Tunable Filter Bank (“F”) - divides up the input 2 GHz baseband pairs into - divides up the input 2 GHz baseband pairs into 32 sub-bands, each 62.5 MHz wide 32 sub-bands, each 62.5 MHz wide - each sub-band can be tuned independently within - each sub-band can be tuned independently within the 2 GHz baseband the 2 GHz baseband - allows quadrant to work simultaneously on many pieces of baseband - allows quadrant to work simultaneously on many pieces of baseband - no. of filters used determines band width: - no. of filters used determines band width: e.g., 32 filters  2 GHz e.g., 32 filters  2 GHz 1 filter  62.5 MHz 1 filter  62.5 MHz (NB: 2 filters used for MHz) (NB: 2 filters used for MHz)

Correlator Modes - Correlator Planes (“X”) - 32 planes per quadrant - 32 planes per quadrant - process the outputs from filters - process the outputs from filters - e.g., one plane used for each 62.5 MHz sub-band, - e.g., one plane used for each 62.5 MHz sub-band, - or, the output of fewer filters can be “stretched” - or, the output of fewer filters can be “stretched” across many planes to obtain higher spectral across many planes to obtain higher spectral resolution (SR) resolution (SR) - e.g., for 2 GHz (32 filters), get 244 kHz SR - e.g., for 2 GHz (32 filters), get 244 kHz SR for 250 MHz (4 filters), get 30 kHz SR for 250 MHz (4 filters), get 30 kHz SR

Correlator Modes - a quick side-discussion on digitization: - Sampling: signals ( v(t), 0 ≤ ≤  ) are lossless if sampled - Sampling: signals ( v(t), 0 ≤ ≤  ) are lossless if sampled at the Nyquist rate,  t < 1/2(  ) at the Nyquist rate,  t < 1/2(  ) - Quantization: chosen level (2-bit, 4-bit) can induce - Quantization: chosen level (2-bit, 4-bit) can induce offsets (noise), v(t)  v(t) +  offsets (noise), v(t)  v(t) +  - higher sampling rate and quantization level better - higher sampling rate and quantization level better reproduce input signal, improves S/N, at a cost to reproduce input signal, improves S/N, at a cost to SR (correlator resources) SR (correlator resources) - can choose sampling rate (1N or 2N, for factor 2 SR) and - can choose sampling rate (1N or 2N, for factor 2 SR) and quantization level (2-, (3-), 4-bit, for factor 4 SR) quantization level (2-, (3-), 4-bit, for factor 4 SR)

Correlator Modes 1. Time Division Modes - total band width of 2 GHz (continuum only) - total band width of 2 GHz (continuum only) - filters divide up 1 ms of integration into 32 - filters divide up 1 ms of integration into 32 smaller time blocks smaller time blocks - planes process each time block, allows faster - planes process each time block, allows faster integration times of 16 ms integration times of 16 ms - only Nyquist sampling possible - only Nyquist sampling possible - SR depends on no. of polzns (1, 2 or 4) and - SR depends on no. of polzns (1, 2 or 4) and quantization level (2-bit or 3-bit) quantization level (2-bit or 3-bit) - e.g., 128 x 15.6 MHz SR for 2 polzns - e.g., 128 x 15.6 MHz SR for 2 polzns

Correlator Modes Example of Time Division Modes (Band 6): - 1 quadrant observes 2 GHz of LSB ( GHz), 2 polzns, 2-bit, Nyq., get 128 spectral points each 15.6 MHz wide 2-bit, Nyq., get 128 spectral points each 15.6 MHz wide - 1 quadrant observes 2 GHz of LSB ( GHz), 4 polzns, 2-bit, Nyq., get 64 spectral points each MHz wide 2-bit, Nyq., get 64 spectral points each MHz wide - 1 quadrant observes 2 GHz of USB ( GHz), 2 polzns, 2-bit, Nyq., get 128 spectral points each 15.6 MHz wide 2-bit, Nyq., get 128 spectral points each 15.6 MHz wide - 1 quadrant observes 2 GHz of USB ( GHz), 4 polzns, 2-bit, Nyq., get 64 spectral points each MHz wide 2-bit, Nyq., get 64 spectral points each MHz wide

Correlator Modes 2. Frequency Division Modes - filters used to obtain MHz - 2 GHz BWs, - filters used to obtain MHz - 2 GHz BWs, all planes work on filtered BW to improve SR all planes work on filtered BW to improve SR - spectral resolution (SR) depends on: - spectral resolution (SR) depends on: - no of polarizations (1, 2, or 4) - no of polarizations (1, 2, or 4) - quantization level (2-bit or 4-bit)* - quantization level (2-bit or 4-bit)* - sampling rate (1 Nyq. or 2 Nyq.) - sampling rate (1 Nyq. or 2 Nyq.) - 1 spectral “window” per quadrant - 1 spectral “window” per quadrant - slower integration times: ms - slower integration times: ms * Correlation efficiency is 0.88 for 2-bit x 2-bit, increases to 0.94 (2N) or 0.99 (4- bit), yielding respectively 14% and 27% reductions in observing time.

Correlator Modes

Example of Frequency Division Modes (Band 6): - 1 quadrant observes (in USB) CO 2-1 at GHz over 125 MHz; mode 61 yields 512 spectral points with MHz; mode 61 yields 512 spectral points with 0.32 km s -1 resolution, 2 polzns, 4-bit, 2 x Nyq. km s -1 resolution, 2 polzns, 4-bit, 2 x Nyq. - 1 quadrant observes (in LSB) C 18 O 2-1 at GHz over MHz; mode 63 yields 1024 spectral points with MHz; mode 63 yields 1024 spectral points with 0.04 km s -1 resolution, 2 polzns, 4-bin, 2 x Nyq. km s -1 resolution, 2 polzns, 4-bin, 2 x Nyq. - 2 quadrants observe continuum over 2 GHz each (one in USB, one in LSB) in time division mode; mode 69 yields 128 USB, one in LSB) in time division mode; mode 69 yields 128 spectral points, 20.4 km s -1 resolution, 2 polzns, 2-bit, Nyq. spectral points, 20.4 km s -1 resolution, 2 polzns, 2-bit, Nyq.

Correlator Modes 3. Multiple Region Modes - for frequency division modes with BWs of - for frequency division modes with BWs of 125 MHz - 1 GHz, can divide up BW… 125 MHz - 1 GHz, can divide up BW… - allows multiple lines within BW to be observed - allows multiple lines within BW to be observed simultaneously within the 2 GHz baseband, if: simultaneously within the 2 GHz baseband, if: - region BW must be a multiple of 62.5 MHz - region BW must be a multiple of 62.5 MHz - other parameters (SR, no. of polzns, quant. - other parameters (SR, no. of polzns, quant. level and sampling rate) must be the same level and sampling rate) must be the same for all regions for all regions - trade-off between no. of regions and SR! - trade-off between no. of regions and SR!

Correlator Modes Example of Multiple Region Modes (Band 6): - 1 quadrant observes (in USB) uses mode 47, 125 GHz BW, 1024 spectral points at 0.16 km s -1 SR, 2 polzns, 4-bit, Nyq.: 1024 spectral points at 0.16 km s -1 SR, 2 polzns, 4-bit, Nyq.: 1/4 for CO 2-1 at GHz, 1/4 for CO 2-1 at GHz, 1/4 for N 2 D+ 3-2 at GHz, 1/4 for N 2 D+ 3-2 at GHz, 1/4 for CH 3 OH E at GHz, 1/4 for CH 3 OH E at GHz, 1/4 for SO 2 11(5,7) - 12(4,8) at GHz, 1/4 for SO 2 11(5,7) - 12(4,8) at GHz, for 4 windows each with 256 spectral points (BW: 164 km s -1 ) for 4 windows each with 256 spectral points (BW: 164 km s -1 ) - 1 quadrant observes (in LSB) C 18 O 2-1, 13 CO 2-1, SO and CH 3 OH E also in mode 47, as above CH 3 OH E also in mode 47, as above - 2 quadrants: LSB/USB continuum in time division mode (69)

Correlator Modes 4. Multi-resolution Modes - implement frequency division modes over fewer - implement frequency division modes over fewer than 32 correlator planes than 32 correlator planes - correlator resources can be fully divided up for - correlator resources can be fully divided up for multiple windows with different SR multiple windows with different SR - allows zoom in into features seen in wide band - allows zoom in into features seen in wide band - lower SR for a given BW - lower SR for a given BW - only 2-bit quantization available, mostly 1 Nyq. - only 2-bit quantization available, mostly 1 Nyq. available (three 2 Nyq. Modes) available (three 2 Nyq. Modes) - no more than 16 filters can be used! - no more than 16 filters can be used!

Correlator Modes * na = correlator fraction cannot maintain BW with minimum feasible resolution

Correlator Modes Example of Multi-Resolution Modes (Band 6): - 1 quadrant observes (in USB) uses: - mode 3, 500 GHz BW with 8 planes, gets 2048 spectral - mode 3, 500 GHz BW with 8 planes, gets 2048 spectral points, 1 polzn, 2-bit, Nyq. (wide-band?) points, 1 polzn, 2-bit, Nyq. (wide-band?) - mode 6, 62.5 MHz BW with 8 planes, gets 2048 spectral - mode 6, 62.5 MHz BW with 8 planes, gets 2048 spectral points, 1 polzn, 2-bit, Nyq. (CO 2-1) points, 1 polzn, 2-bit, Nyq. (CO 2-1) - mode 25, MHz BW with 16 planes, gets 4096 spec. - mode 25, MHz BW with 16 planes, gets 4096 spec. points, 1 polzn, 2-bit, 2 x Nyq. (N 2 D + 3-2) points, 1 polzn, 2-bit, 2 x Nyq. (N 2 D + 3-2) - windows put anywhere in the 2 GHz input baseband - windows put anywhere in the 2 GHz input baseband - total BW used < 1 GHz (16 filters; NB: if mode 2 is - total BW used < 1 GHz (16 filters; NB: if mode 2 is included, filters are shared; BW of m2 window < 1 GHz) included, filters are shared; BW of m2 window < 1 GHz) each of other 3 quadrants are set up independently!

This is all very challenging, but it is important to figure it all out before proposals are written! “I think anyone who does not take full advantage of the correlator deserves to be publicly ridiculed.” - Anonymous

ALMA Observing Tool - the interface for planning ALMA observations - the interface for planning ALMA observations - will be used to define “minimally schedulable - will be used to define “minimally schedulable blocks” (MSBs) for execution at ALMA blocks” (MSBs) for execution at ALMA - contains: - contains: - sensitivity calculator tool - sensitivity calculator tool - calibrator selection tool - calibrator selection tool - pointing visualization tools - pointing visualization tools - spectral region visualization tools - spectral region visualization tools - not yet ready for prime time (this workshop): - not yet ready for prime time (this workshop):

Proposal Process - a Call for Proposals will be likely issued annually, will detail available modes will detail available modes - “Phase I” prepared using ALMA Observing Tool - proposal review process is not yet solid, probably a single Proposal Review Committee with subject sub-panels will meet and offer recommendations a single Proposal Review Committee with subject sub-panels will meet and offer recommendations - these recommendations are harmonized with partner share by a higher committee partner share by a higher committee - partner of PI will be charged for observing time - time allocated, work on “Phase II” proposal with ARC support ARC support

Proposal Process

Early Science What about Early Science? - “shared-risk” observing, ie., no guarantees - “shared-risk” observing, ie., no guarantees - 33% of available time over 1 year, time shared - 33% of available time over 1 year, time shared with ALMA commissioning team with ALMA commissioning team - Timeline: - Timeline: - Decision point: Q Decision point: Q Call for Proposals issued: Q Call for Proposals issued: Q Proposals due: Q1 2011? - Proposals due: Q1 2011? - Observations: Q Q Observations: Q Q3 2012

Early Science - at least sixteen 12 m antennas fully commissioned - Bands 3, 6, 7, 9 on all antennas (some 4, 8?) - baselines out to 1 km - single fields + pointed mosaics - basic set of spectral modes (7, 9, 12, 18, 70) - linear/circular polzn of compact sources - SD mapping of extended objects in OTF mode - calibration to levels comparable to existing arrays - software for proposal preparation, planning and execution + off-line data reduction execution + off-line data reduction

Further Reading - ALMA Capabilities Correlator Modes - “Synthesis Imaging in Radio Astronomy II,” ASP Vol. 180, proceedings - “Synthesis Imaging in Radio Astronomy II,” ASP Vol. 180, proceedings of NRAO Aperture Synthesis School, chapter on correlators of NRAO Aperture Synthesis School, chapter on correlators - M. Rupen’s talk on Correlators from same (available on-line on - M. Rupen’s talk on Correlators from same (available on-line on NRAO website: NRAO website: - Escoffier, R. P. et al., “The ALMA Correlator” 2007, A&A, 462, Escoffier, R. P. et al., “The ALMA Correlator” 2007, A&A, 462, ALMA Memo 556, “Observational Modes Supported by the ALMA - ALMA Memo 556, “Observational Modes Supported by the ALMA Correlator” Correlator”

From Idea to ALMA Project Given the unprecedented capabilities of ALMA, the time to start thinking of science is NOW!Given the unprecedented capabilities of ALMA, the time to start thinking of science is NOW! ALMA’s correlator is particularly complex, requiring careful planning to exploit its potential (OT will help)ALMA’s correlator is particularly complex, requiring careful planning to exploit its potential (OT will help) Early Science will commence in Q3 2011, even then ALMA will be the most sensitive and flexible mm-array on the planetEarly Science will commence in Q3 2011, even then ALMA will be the most sensitive and flexible mm-array on the planet