ngVLA Reference Design Development & Performance Estimates (June 2018)

 
Preliminary (revB) ngVLA Configuration

A preliminary (revB, Apr. 2018) configuration map for all 214 antennas included in the main array.

The predicted performance of the array, based on feedback from the community following the June 2017 ngVLA Science and Technology meeting in Socorro, is summarized below, and is described in more detail and originally documented in ngVLA Memo 17.  Updated numbers are given below and in a Technical Overivew to be published in the  proceedings of the 2018 SPIE Astronomical Telescopes and Instrumentation conference (Selina et al. 2018 -- arXiv:1806.0840).  

The array collecting area is distributed to provide high surface brightness sensitivity on a range of angular scales spanning from approximately 1000 to 10 mas. In practice, this means there is a core with a large faction of the collecting area in a randomized distribution to provide high snapshot imaging fidelity, and arms extending asymmetrically out to ~1000 km baselines, filling out the (u,v)‐plane with Earth rotation and frequency synthesis.

The present concept is a homogeneous array of 214, 18m apertures. The selection of the number of apertures and the antenna diameter is supported by parametric cost estimation. The antenna locations are fixed, with no reconfiguration capability. All antennas are outfitted with front ends that provide access to the atmospheric windows spanning 1.2 GHz to 50.5 GHz and 70 GHz to 116 GHz.

The first table below provides the current baseline receiver configuration, while second table gives the key imaging performance. While the values are more representative of the current design than those previously reported (e.g., ngVLA Memo 5), the table is by necessity a simplification. As the configuration and our understanding of its performance evolve with design refinements and modeling, most factors in this table can be expected to change as future work on the imaging performance of the array continues.

A sensitivity calculator is currently being developed based on such investigations and will eventually supersede the values included in performance metric table below.

The implementation of Very Long Baseline Interferometry (VLBI) on the timescale of the ngVLA is being actively investigated to enable science that requires baselines out to transcontinental distances.

 

ngVLA Baseline Receiver Configuration

Band # Dewar fL
GHz
fM
GHz
fH
GHz
fH:fL BW
GHz
1 A 1.2 2.35 3.5 2.91 2.3
2 B 3.5 7.90 12.3 3.51 8.8
3 B 12.3 16.4 20.5 1.67 8.2
4 B 20.5 27.3 34.0 1.66 13.5
5 B 30.5 40.5 50.5 1.66 20.0
6 B 70.0 93.0 116 1.66 46.0

 

 

Next Generation VLA Key Performance Metrics
Parameter [units] 2.4 
GHz

GHz
16
GHz
27
GHz
41
GHz
93
GHz
Notes
Band Lower Frequency, fL [GHz] 1.2 3.5 12.3 20.5 30.5 70.0 a
Band Upper Frequency, fH [GHz] 3.5 12.3 20.5 34.0 50.5 116.0 a
Field of View FWHM [arcmin] 24.4 7.3 3.7 2.2 1.4 0.6 b
Aperture Efficiency [%] 0.78 0.77 0.86 0.85 0.81 0.60 b
Effective Area, Aeff x 103 [m2] 42.2 41.7 46.8 46.0 44.0 32.4 b
System Temp, Tsys [K] 23 25 22 33 45 62 a, f
Max Inst. Bandwidth [GHz] 2.3 8.8 8.2 13.5 20.0 20.0 a
Antenna SEFD [Jy] 328.6 361.8 283.2 432.4 617.0 1153.7 a, b
Resolution of Max. Baseline θmax [mas] 26 8 4 2.3 1.5 0.7 c
 
Naturally Weighted Sensitivity
            c, d
Continuum rms, 1 hr [μJy/beam] 0.41 0.23 0.19 0.22 0.26 0.48 d
Line Width, 10 km/s [kHz] 80.0 266.67 533.33 900.0 1366.67 3100.0  
Line rms, 1 hr, 10 km/s [μJy/beam] 69.0 41.6 23.0 27.1 31.3 38.9 d
Projected Imaging Sensitivity
 
 
Resolution θ1/2 [mas]
1000
 
Continuum rms, 1 hr, Robust [μJy/beam] 0.80 0.50 0.43 0.53 0.64 1.28 e
Line rms 1 hr, 10 km/s Robust [μJy/beam] 135.6 91.0 53.3 65.2 77.9 102.6 e
Brightness Temp (TB) rms continuum, 1 hr, Robust [K] 0.1688 0.0095 0.002 0.0009 0.0005 0.0002 e
TB rms line, 1 hr, 10 km/s, Robust [K] 28.62 1.73 0.25 0.11 0.06 0.01 e
Resolution θ1/2 [mas]
100
 
Continuum rms, 1 hr, Robust [μJy/beam] 0.63 0.40 0.35 0.44 0.53 1.07 e
Line rms 1 hr, 10 km/s Robust [μJy/beam] 106.4 73.4 43.5 53.8 64.7 86.1 e
Brightness Temp (TB) rms continuum, 1 hr, Robust [K] 13.25 0.77 0.17 0.07 0.04 0.02 e
TB rms line, 1 hr, 10 km/s, Robust [K] 2245.9 139.4 20.7 9.0 4.7 1.2 e
Resolution θ1/2 [mas]
10
 
Continuum rms, 1 hr, Robust [μJy/beam] - 0.31 0.27 0.35 0.43 0.87 e
Line rms 1 hr, 10 km/s Robust [μJy/beam] - 55.8 33.8 42.3 51.4 69.7 e
Brightness Temp (TB) rms continuum, 1 hr, Robust [K] - 58.3 13.0 5.8 3.1 1.2 e
TB rms line, 1 hr, 10 km/s, Robust [K] - 10595 1605 706 372 98 e
(a)  6-band 'baseline' receiver configuration.
(b) Reference design concept of 214 18m aperture antennas. Unblocked aperture with 160um surface.
(c) 'Spiral214' Configuration.
(d) Using Natural Weights, dual pol, and all baselines. A full width half max is not given as it is ill defined for this tri-scale array.
(e) Using Weights as described in ngVLA Memo #16, scaled by frequency.
(f) At the nominal mid-band frequency shown. Assumes 1mm PWV for W-band, 6mm PWV for others; 45 deg elev. on sky for all.