ngVLA Performance Estimates (December 2021)

The Next Generation Very Large Array (ngVLA) is an astronomical observatory designed to operate in a frequency coverage of ~1.2 –116 GHz with up to 20 GHz of instantaneous sampled bandwidth per polarization. The observatory will be a fixed-position (non-reconfigurable) synthesis radio telescope operating in a phased or interferometric mode. The ngVLA is designed to accommodate a wide variety of scientific observations at centimeter-to-millimeter wavelengths aiming to deliver high sensitivity over a wide range of resolutions. The ngVLA array design includes three fundamental subarrays: the main interferometric array, the short baseline array, and the long baseline array. 

Antennas within the main array are distributed over a range of physical scales and with different geometries: (a) a dense core which provides high surface brightness sensitivity at ~1,000 mas resolution; (b) a multi-arm spiral capable of high-fidelity imaging at ~10 mas scales; and (c) longer arms which provide mid-scale baselines for imaging at ~1 mas.

The main array will be augmented by a very compact array of smaller antennas (SBA) which will provide sensitivity on larger angular scales, and four antennas of the main array will be equipped to measure total power in order to fill in the center of the (u,v)-plane.  Additionally, a long baseline array (LBA) consisting of several outlying stations will provide intercontinental-scale baselines for achieving resolutions of ~0.1 mas. The design of the array configuration is practical, accounting for logistic limitations such as topography, utility access, local RFI sources, and land management and availability.

The first table below provides the current baseline receiver configuration, while the second table gives the key imaging performance. Imaging sensitivity is estimated based on a procedure as shown in ngVLA Memo #16 and provided as a function of angular resolution in the key performance metrics table. The table is by necessity a simplification, and the imaging sensitivity will vary from these reported values depending on the quality of the (sculpted) synthesized beam required to support the science use case. 

The next generation Exposure Calculator Tool (ngECT) is a web interface that can be used  to estimate the performance sensitivity for many representative subarrays of the ngVLA (including point source and surface brightness sensitivities for lines and continuum).

 

ngVLA Baseline Receiver Configuration
Band #	Dewar	fL GHz	fM GHz	fH GHz	fH:fL	BW GHz
1	A	1.2	2.0	3.5	2.92	2.3
2	B	3.5	6.6	12.3	3.51	8.8
3	B	12.3	15.9	20.5	1.67	8.2
4	B	20.5	26.4	34.0	1.66	13.5
5	B	30.5	39.2	50.5	1.66	20.0
6	B	70.0	90.1	116.0	1.66	46.0

 

ngVLA Key Performance Metrics
Parameter [units]	2.4  GHz	8  GHz	16 GHz	27 GHz	41 GHz	93 GHz	Notes
Band Lower Frequency, fL [GHz]	1.2	3.4	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]	24.852	7.440	3.561	2.143	1.442	0.628	b
Aperture Efficiency [%]	0.828	0.936	0.941	0.920	0.886	0.648	b
Effective Area, Aeff x 103 [m2]	51.41	58.15	58.42	57.10	55.03	40.25	b
System Temp, Tsys [K]	17.07	22.00	24.40	32.42	47.41	65.37	a, f
Max Inst. Bandwidth [GHz]	2.3	8.8	8.2	13.5	20.0	20.0	a
Antenna SEFD [Jy]	232.3	264.8	292.2	397.3	602.8	1136.3	a, b
Resolution of Max. Baseline θmax [mas]	2.97	0.89	0.43	0.26	0.17	0.08	c
Naturally Weighted Sensitivity
Continuum rms, 1 hr [μJy/beam]	0.24	0.14	0.16	0.17	0.21	0.40	d
Line Width, 10 km/s [kHz]	78.39	261.85	547.05	908.96	1350.93	3102.15
Line rms, 1 hr, 10 km/s [μJy/beam]	35.46	23.90	19.85	18.77	22.26	31.34	d
Projected Imaging Sensitivity
Resolution θ1/2 [mas]	1000
Continuum rms, 1 hr [μJy/beam]	0.32	0.21	0.28	0.36	0.57	2.02	e
Line rms 1 hr, 10 km/s  [μJy/beam]	47.20	36.40	35.02	40.37	60.96	159.35	e
Brightness Temp (TB) rms continuum, 1 hr [K]	0.0700	0.0042	0.0013	0.0006	0.0004	0.0003	e
TB rms line, 1 hr, 10 km/s [K]	9.965	0.692	0.166	0.067	0.044	0.022	e
Resolution θ1/2 [mas]	100
Continuum rms, 1 hr [μJy/beam]	0.27	0.17	0.21	0.23	0.29	0.62	e
Line rms 1 hr, 10 km/s  [μJy/beam]	39.78	29.41	25.71	25.19	30.88	49.04	e
Brightness Temp (TB) rms continuum, 1 hr [K]	5.90	0.34	0.09	0.04	0.02	0.01	e
TB rms line, 1 hr, 10 km/s [K]	839.77	55.88	12.21	4.20	2.23	0.69	e
Resolution θ1/2 [mas]	10
Continuum rms, 1 hr [μJy/beam]	0.26	0.15	0.17	0.19	0.25	0.49	e
Line rms 1 hr, 10 km/s  [μJy/beam]	38.36	25.86	21.74	21.24	26.01	39.00	e
Brightness Temp (TB) rms continuum, 1 hr [K]	579.29	29.74	7.90	3.13	1.82	0.69	e
TB rms line, 1 hr, 10 km/s [K]	80987.2	4912.7	1032.8	354.3	188.1	54.8	e
Resolution θ1/2 [mas]	1
Continuum rms, 1 hr [μJy/beam]	--	3.20	0.24	0.17	0.22	0.43	e
Line rms 1 hr, 10 km/s  [μJy/beam]	--	510.47	31.79	18.85	23.01	34.00	e
Brightness Temp (TB) rms continuum, 1 hr [K]	--	63233.37	1102.96	277.02	161.18	60.51	e
TB rms line, 1 hr, 10 km/s [K]	--	9.7E6	1.5E5	31449.93	16647.83	4779.54	e
Resolution θ1/2 [mas]	0.1
Continuum rms, 1 hr [μJy/beam]	--	--	--	--	--	4.50	e
Line rms 1 hr, 10 km/s  [μJy/beam]	--	--	--	--	--	355.29	e
Brightness Temp (TB) rms continuum, 1 hr [K]	--	--	--	--	--	63241.08	e
TB rms line, 1 hr, 10 km/s [K]	--	--	--	--	--	5E6	e
(a)  6-band "baseline" receiver configuration.
(b) Reference design concept of 244 18m aperture antennas. Unblocked aperture with 160 µm surface.
(c) Current reference design configuration (Rev. D). Resolution in EW axis.
(d) Point source sensitivity using natural imaging weights, dual polarization and all baselines
(e) Using Weights  scaled by frequency.
(f) Averaged over the receiver band. Assumes 1mm PWV for 6-band, 6mm PWV for others; 45 deg elev. on sky for all.