1. Project Overview
Eric Murphy, ngVLA Project Scientist

2. The Jansky Very Large Array
1972 – Approved by Congress
1975 – First Antenna in place
1980 – Full science operations
2001 – Complete electronics upgrade approved by NSF
2011 – Jansky VLA full science ops
~12,000 refereed papers with ~500,000 citations
~500 PhD theses
The VLA has been among the most productive telescopes ever!
Major recent science:
FRB localization of completely unknown phenomena
distance record for atomic H in emission
Investigations of solar weather.

3. A next generation VLA
Scientific Frontier: Thermal imaging at milli-arcsecond scale resolution
Design Goals
10x effective collecting area of JVLA and ALMA
10x resolution of JVLA and ALMA
Frequency range: 1.2 –116 GHz
Located in Southwest U.S. (NM+TX+?) & Mexico, building from JVLA site
Baseline design under development
Low technical risk (reasonable step beyond current state of the art)
Where we started… goals for the array.
Really started previous DS (2010) with NAA

4. Radio Facilities in the 2030’s
Complementary suite from cm to submm, appropriate for the mid-21st century
< 0.3cm: ALMA 2030 superb for chemistry, dust, fine structure lines
0.3 to 3cm: ngVLA superb for terrestrial planet formation, dense gas history, baryon cycling
> 3cm: SKA superb for pulsars, reionization, HI + continuum surveys

5. Radio Facilities in the 2030’s
Complementary suite from cm to submm, appropriate for the mid-21st century
< 0.3cm: ALMA 2030 superb for chemistry, dust, fine structure lines
0.3 to 3cm: ngVLA superb for terrestrial planet formation, dense gas history, baryon cycling
> 3cm: SKA superb for pulsars, reionization, HI + continuum surveys

6. Radio Facilities in the 2030’s
ngVLA Key Science
Cases
Complementary suite from cm to submm, appropriate for the mid-21st century
< 0.3cm: ALMA 2030 superb for chemistry, dust, fine structure lines
0.3 to 3cm: ngVLA superb for terrestrial planet formation, dense gas history, baryon cycling
> 3cm: SKA superb for pulsars, reionization, HI + continuum surveys
Stars or key science drivers

7. Bridging SKA & ALMA Scientifically
Thermal Imaging on mas Scales at λ ~ 0.3cm to 3cm
140pc
Terrestrial zone planet formation
Resolution ~ 1cm (300km)
Synergy w. ALMA submm, future ELTs
Complement to SKA low frequency capabilities
Synergies with (ALMA) sub-mm, and (ELT’s) optical/NIR high-resolution science.

8. Highly Synergistic with Other Facilities on Similar Timescales
SKA
Atomic/non-thermal
Molecular/thermal
ALMA
Warm/star-forming
Cold/dense fuel for SF
LUVOIR/HabEx
Image earth-like planets
Image terrestrial-zone planets forming
OST (FIR surveyor)
C/WNM & WIM
Cold Molecular Medium
TMT/GMT
Stellar Mass and Unobscured SF
Dense Gas and Obscured SF
JWST
Continuing its legacy in many areas of astrophysics
All science Highly synergistic with next-generation ground-based OIR and NASA missions.

9. Developing the ngVLA Science Case
Community-Driven, Growing, and Evolving
Numerous Science and Technical meetings, starting from Jan 2015 AAS
Initial Science Working Group reports covering 4 broad areas, Nov (
Cradle of Life: CoL (Isella et al): Terrestrial-zone planet formation, Massive Stars, etc.
Galaxy Ecosystems: GEco (Leroy et al): wide field, high resolution/sensitive imaging
Galaxy Formation: GFor (Casey et al): Dense gas history of the Universe
Time domain, Cosmology, and Physics: TdCP (Bower et al): Plasma physics, Exo-space weather, Strong Lensing
26 Community Design Studies in progress, partially funded by NRAO (
75 Community-Led Science Use Cases Submitted for ‘Reqs to Specs’ process
All gathered to report out and build toward a consensus vision last week of June in Socorro
A community-driven ngVLA Science Case has been being built over past 2.5 years and includes:
Really builds on NAA, which was submitted at previous DS2010
A number of science and technology workshops were held
Initial set of science WPs covering 4 broad areas
A (funded) community study program
Science use-case capture (led by SAC)
All gathered in Socorro in June to report out and discuss findings of science use case capture.
Andrea will report on the resulting key science mission.

10. Community-Led Advisory Councils
ngVLA Science Advisory Council
ngVLA Technical Advisory Council
Interface between the science community & NRAO
Recent/Current Activities:
Science working groups: science use cases  telescope requirements
SOC for science meeting in June
Lead Science case development  ‘science book’ & DS2020 White Papers
Interface between the engineering & computing community and NRAO
Membership covers a broad range of expertise in relevant technical areas including:
Antennas, low-noise receiver systems, cryogenics, data transmission, correlators, and data processing
Alberto Bolatto    (University of Maryland: co-Chair)
Andrea Isella    (Rice University : co-Chair)
Brenda Matthews    (NRC-Victoria: SWG1 Chair)
Cornelia Lang    (University of Iowa: SWG2 Chair)
Dominik Riechers (Cornell: SWG3 Chair)
Joseph Lazio    (JPL: SWG4 Chair)
James Lamb (Caltech : co-Chair)
Melissa Soriano (JPL : co-Chair)
ngVLA Project Office has been relying on input gathered by our two advisory councils.
Will hear form both SAC and TAC co-charis later.

11. ngVLA Key Science Mission (ngVLA memo #19)
Unveiling the Formation of Solar System Analogues
Probing the Initial Conditions for Planetary Systems and Life with Astrochemistry
Charting the Assembly, Structure, and Evolution of Galaxies Over Cosmic Time
Using Pulsars in the Galactic Center as Fundamental Tests of Gravity
Understanding the Formation and Evolution of Stellar and Supermassive BH’s
Uncovering the Violent Sky in the Era of Multi-Messenger Astronomy
Highly synergistic with next-generation ground-based OIR and NASA missions.
ngVLA 100hr 25GHz 10mas
rms = 90nJy/bm = 1K
Isella Dust Model
0.1” = 13AU
Gas
ALMA
NGVLA
Decarli+2016
HI + CO(1-0)
CO(2-1)

12. Science Use Case Parameterization (ngVLA memo #18)
75 Science Use Cases developed into 180 discrete observations.
Derived a number of parameters from each observation to determine what the community needs from this array.
Andrea’s Talk will summarize the process/findings.
All feedback was distilled and uniformly parametrized into a spreadsheet
Large number of slices in paramter space (resolution, frequency, sensitivity, etc.) was looed at
see talk posted online form meeting and ngVLA memo 18.

14. Significant Requirements & Take-Aways
ngVLA 100hr 25GHz 10mas
rms = 90nJy/bm = 1K
Isella Dust Model
0.1” = 13AU
Significant Requirements & Take-Aways
PI driven / pointed operations model.
Need full 1.2 – 116 GHz Frequency coverage across the full array.
Most science achievable with ~300 – 1000 km scale array, with a long tail extending out to VLBI scales.
Gas
ALMA
NGVLA
HI + CO(1-0)
CO(2-1)
Decarli+2016
Most importantly, we can’t predict how the intellectual curiosity of the community will drive this array, likely leading to a lot of exciting science that has not yet been captured.

15. Operating Modes / Functional Capabilities
Spectral Line & Continuum Modes
Time Domain Capabilities
VLBI Capabilities
Phased Array Capability
Total Power Measurements
Sub-Array Capabilities
Solar Observation Capabilities
Goal to maximize flexibility of both modes. Both equally represented.
Time domain search capabilities on msec scales.
Combine with other antennas out to continental scale baselines.
Operate as both an interferometer and phased array.
Need a solution to recover total flux.
Flexible sub-array capability.
Analog dynamic range for bright sources.

16. Requested Key Technical Parameters
Frequency Range – 1.2 – 116GHz
Requested 30 GHz
Continuum Imaging Sensitivity – 0.08 uJy/bm
Line Imaging Sensitivity – 10 uJy/bm/km/s
Surface Brightness Sensitivity – 1 1 arcsec
Angular Resolution – < 30GHz
Dynamic Range – <~105
Polarization – 0.1% Purity, 1-degree
An artist’s rendering of the ngVLA core, centered on the current JVLA site, which may include ~85 of the ~214 18m diameter dishes that comprise the array.
Dynamic range: 90% cases require DR < 40 dB
0.2 uJy/bm in 10hr => 100% of all driving science cases and ~80% of all science cases submitted.

17. Current Reference Design Specifications (ngVLA Memo #17)
214 18m offset Gregorian (feed-low) Antennas
Supported by internal costing exercise
Fixed antenna locations across NM, TX, MX
~1000 km baselines being explored
1.2 – 50.5 GHz; 70 – 116 GHz
Single-pixel feeds
6 feeds / 2 dewar package
Short-spacing/total power array under consideration
Receiver Configuration
Band #
Dewar
fL GHz
fM GHz
fH GHz
fH: fL
BW GHz 1 A
1.2
2.55
3.9
3.25
2.7 2
8.25
12.6
3.23
8.7 3 B
16.8
21.0
1.67
8.4 4
28.0
35.0
14.0 5
30.5
40.5
50.5
1.66
20.0 6
70.0
93.0
116
46.0
Continuum Sensitivity: 1cm, 10mas, 10hr => TB ~ 1K
Line sensitivity: 1cm/bm, 10 km/s, 1” => TB ~ 25mK
- Where we ended up based on a very successful meeting in June in Socorro.
- Registration was a oversubscribed.
- Included breakout sessions of SWGs.
- Settled on a reference design to focus on for DS2020.

18. Estimated Price Tag (Internal Preliminary Costing Exercise)
Target construction baseline budget ~ (2016) $1.5B
Target operations budget of < (2016) $75M (< 3x current VLA)
Operations, maintenance, computing, archiving, etc.: optimize as part of design
Partnerships
Possible U.S. Multiagency Interest [including VLBI option]
ICRF – DOD/Navy, Air Force
Spacecraft tracking/imaging, `burst-telemetry’ (mission-critical events) – NASA, DOD
Space situational awareness – DOD
Strong International Partnership critical for success:
Current International Involvement in SAC/TAC/Community Studies:
Canada, Mexico, Japan, Germany, Netherlands, Taiwan
Current Industrial Involvement through Community Studies:
REhnu Inc., Minex Engineering Corp, LaserLaB, Quantum Design
Anticipating “Open Skies” policy
Is this SKA-High? Scientifically, the same direction.

19. Key Open Questions – Specification Decisions
Recovering Large Scale Structure
Is a 30m minimum spacing good enough?
Large single dish w/ FPA (e.g., 45m x 20 beams – D. Frayer, ngVLA memo 14)?
Short-spacing array of small dishes + TP mode (e.g., 6m – Murphy/Condon+, Sci. Case NGA-3)?
Distribution of collecting area – sensitivity over a range of angular scales needed.
Maximum baseline in the reference design.
300 – 500 km. Up to 1000 km?
How far should we go with connected elements?

20. Science Options Commensal Low Frequency Science (Taylor & Kassim)
Leverage ngVLA infrastructure (land/fiber/power) for commensal LF capabilities (ngLOBO)
5 – 150 MHz: multi-beam dipole arrays alongside ngVLA long-baseline stations (e.g., LWA style).
150 – 800 MHz commensal prime focus feeds on ngVLA antennas (e.g., VLITE style)
U.S. VLBI Expansion of Capabilities (Brisken)
Replace existing VLBI antennas/infrastructure with ngVLA technology
Introduce new ~1000 km baseline stations to bridge gap between ngVLA & existing VLBA baselines
Cross correlate VLBI antennas with phased ngVLA
LWA: all sky w/ multiple beams

21. www.nrao.edu science.nrao.edu
public.nrao.edu
The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

22. Band 6 Band 5 Band 4 Band 3 Band 2 Band 1
Band definitions purely illustrative at this point, not final.
Definition of Color Coding:
* Red: Drivers are key science cases currently identified by SAC as essential
* Green: Science Cases that strongly support the key science drivers
* Blue: The remaining science cases received
Main takeaway – key science needs

23. Band 6 Band 5 Band 4 Band 3 Band 2 Band 1 30 km 300 km
How does frequency request look as a function of requested resolution (max baseline)
Conclusion – need both low and high frequency bands across the full angular scales supported by the array.
* Implies outfitting all antennas with full suite of receivers.

24. 80 nJy/bm Conclusion: sensitivity is a driving requirement!
All Driving Science achieved with ~0.08 uJy/bm and 80% of all cases.
~100hr integration with current incarnation, pessimistically assuming factor of x2 above NA sensitivity
=> 25 hr with Natural Weighting.
Stresses importance of imaging performance studies to improve weighting factors.

25. 10 uJy/bm/km/s
Conclusion: Cases are split roughly 52% continuum and 48% spectral line.
Need demanding sensitivity for spectral line work too!
Cannot sacrifice sensitivity at narrow bandwidths.
Achieve 90% of science drivers w/ ~10 uJy/bm/km/s
~720hr integration with current incarnation, pessimistically assuming factor of x2 above NA sensitivity
=> 180hr with Natural Weighting.
~ Upside, other half of driving requirements needs ~80uJy/bm/km/s, so ~10hr integration

26. 300 km
30 km
1"
1"
300 km
30 km
Continuum and spectral line cases separated.
Conclusion – need to get to ~ mK surface brightness sensitivity in the compact core of the array. (Can achieve 90% of all line and continuum science cases)
Conclusion – need to get to ~ mK surface brightness sensitivity on ~1” angular scales in the compact core of the array. (Can achieve 80% of all science cases) -- one outlier is large scale HI emission.

27. 30 km
300 km
100% of all major science drivers achieved with ~300 km baselines
80% of all science cases achieved within ~300 km baselines
~60% of all science drivers achieved within existing VLA footprint.
Plot has structure – emphasis on 1-2km scale and km scale.
Noise or signal? Something to ponder in configuration design….