Frequently Asked Questions


The next-generation VLA (ngVLA) is a future centimeter-to-millimeter wave interferometer that builds on the legacy of the JVLA and ALMA, as the next major facility in ground-based U.S. radio astronomy. The ngVLA is optimized for observations at wavelengths between the superb performance of ALMA at sub-mm wavelengths, and the future SKA1-MID at longer (decimetric) wavelengths. The ngVLA opens a new window on the Universe through ultra-sensitive imaging of thermal line and continuum emission down to milliarcecond resolution, as well as unprecedented broad band continuum polarimetric imaging of non-thermal processes. The ngVLA will perform transformational science covering areas of terrestrial planet formation to the first generation of molecules.

The current baseline design for the main array consists of 214 18m dishes, providing 10x the effective collecting area of the JVLA at 40GHz. Presently, an offset-Gregorian geometry is preferred, with its feed-arm low, similar to the choice for the South African MeerKAT dishes.

An additional 19 6m dishes will make up a short-spacing array (SSA) and will be sensitive to a portion of the larger angular scales undetected by the main array. The SSA may be combined with 4 18m (main-array) antennas used in total power mode to completely fill in the central hole in the (u, v)-plane left by the 6m dishes.

The ngVLA will nominally operate from 1.2 – 116 GHz.

We are also exploring the option for potential commensal observations at lower frequencies that leverage the ngVLA infrastructure (e.g., ngLOBO) that would both cover 5 – 150 MHz (20 – 150 MHz for astronomy) with a multi-beam dipole array at ngVLA long-baseline stations and commensal prime focus feeds on the ngVLA antennas covering ~150 – 800 MHz. Funding for this commensal system is outside the scope of the ngVLA baseline design.

 

 

The resolution of an interferometer is determined by the observed wavelength and its longest baseline. With up to ~1000 km baselines, the ngVLA will achieve an angular resolution ranging between ~0.5 and 50 mas at 2.6 mm (116 GHz) and 25cm (1.2 GHz), respectively. Even higher angular resolution imaging will be possible by combining the ngVLA with existing VLBA antennas into a continental-scale array.

In addition to the main array, we are also exploring the option of using the ngVLA project as a means to initiate an expansion of U.S. VLBI capabilities by replacing existing VLBA antennas/infrastructure with ngVLA technology. Funding for this option is outside the scope of the ngVLA baseline design.

The ngVLA will be centered at the location of the VLA site on the plains of San Agustin, with additional long-baseline stations currently spread over greater New Mexico, Texas, and Mexico.

The VLA has been the workhorse of radio astronomy since its inception in the late 1970s, consisting of 27 movable 25 m symmetric antennas, with maximum baselines of 30 km. The VLA underwent a major electronics upgrade, completed in 2011, which provided contiguous frequency coverage between 1 50 GHz. The ngVLA, by comparison, will consist of 214 18 m dishes extending up to ~1000 km baselines. The ngVLA will extend the operational frequency range from 1.2 116 GHz.

ALMA is a radio interferometer optimized to take advantage of the sub-mm (THz) windows that are only accessible at high, dry sites such as the Chajnantor plateau, which is at ~5000 m altitude. While ALMA operates in the 3mm band, the ngVLA (at an altitude of ~2100 m) can both access the 3mm atmospheric window and will provide a factor of ~10 times better sensitivity and baselines that are ~60x longer than ALMA.

As currently envisioned, SKA1-MID will be the premier radio interferometer at decimetric wavelengths, consisting of up to 133 15m (+ 64 13.5m MeerKAT) dishes with a maximum baseline of up to ~150 km and eventually covering a frequency range spanning 350 MHz (85 cm) to 14 GHz (2 cm). The ngVLA, on the other hand, is being optimized to cover and complement the frequency range above the highest SKA1-MID band, while also achieving much higher angular resolution.

Yes. The project office is currently in the process of exploring international and domestic (academic and industrial) partnerships. If interested in discussing partnership options, please contact our project director. We anticipate a name change for the instrument once the project enters into its design and development phase, allowing our international partners to participate in this important activity.

The scientific and technical difference between the arrays is apparent – ngVLA focusing on cm/mm emission, in particular, thermal gas/dust emission on milliarcsecond scales and redshifted molecular emission. SKA1 is planning to observe at meter thru centimeter wavelengths, expanding on the scientific legacy of instruments like the VLA.

ngVLA strongly complements SKA1 and ALMA, providing key sensitivity and resolution to pursue new scientific goals and interests while bridging the capabilities of those facilities.

NRAO and its international partners will be building upon their ALMA experience and success in developing the ngVLA project definition. Many projects undergo scoping revisions before and during construction to address planning shortcomings, changes in assumptions or external conditions, new constraints etc. NRAO rebaselined ALMA in 2005, eventually completing the project within 0.5% of the revised budget estimate. SKA1 recently completed a second rebaselining (2017).

The technologies and approaches developed for ngVLA will have application well beyond the project, enabling many different futures.

The U.S. government has never been asked to fund SKA in any significant way; SKA was unable to gather scientific community support in the ASTRO2010 Decadal Survey due to uncertainties in the scientific requirements and technical definition of the project at that time. NSF’s withdrawal from supporting overall SKA development in the U.S. was a consequence of funding shortfalls in U.S. science early this decade and a recognition that the project was not broadly supported in the U.S. astronomy community. Since 2010, the scientific goals of SKA1 have narrowed, and engagement with the broader U.S. community has further declined. The fact that U.S. science funding agencies are not engaging with SKA arises from several factors, including funding shortages.

The ngVLA concept has been developed to explore new horizons in cm radio astronomy, synergistic with other existing, under construction or planned instruments in the U.S. in coming years, and focused on our PI-driven science interests. ngVLA can address many of the goals of the ASTRO2010 Decadal Survey, and will be even more relevant (we believe) to the science priorities identified for the 2020s in ASTRO2020.

ngVLA may eventually be considered as an element of an SKA global program, thereby engaging all parts of the U.S. RMS community in new opportunities in the 2020s.

 

Similar to current ALMA operations, we anticipate ngVLA users will be delivered Science Ready Data Products (SRDPs), rather than raw data, due to the sheer volume of data and computing resources that will be required to reduce data. However, raw visibilities will still be available for advanced users. Using ALMA and the VLA as test beds, we are building up our expertise and knowledge base of the best methods/practices/deliverables for SRDPs in preparation for the ngVLA.

The ngVLA data processing implementation will be based on the CASA package, providing continuity with JVLA and ALMA and continuing to provide a flexible data reduction package for experts in the community. As part of the construction project, CASA will evolve both in the implementation of cutting edge algorithms and the infrastructure needed for broad scale parallelization in order to support the ngVLA.

The Science Ready Data Products (SRDPs) produced by the ngVLA will be available through the NRAO Archive interface, providing a single access point for ALMA and ngVLA data products.  After the proprietary period, these SRDPs will be available to the full community, providing a rich archive of images ready for study.  Capabilities for inspection and selection prior to download will assist in mitigating download times.

Depending on the recommendation for the Astro2020 Decadal Survey, we expect to enter the MREFC design phase in late 2021 and have a final design completed by late 2023. Procurement and construction would then commence in 2024 and should be completed by 2034.

With construction commencing in 2024, we would anticipate a notional Early Science start date in 2028, with full array operations beginning in 2034.

 

We have instituted an internal cost cap of $1.5B (2016) for construction funds, and a corresponding operational cost cap of $75M (2016) per year (i.e., <3x current VLA operations). Of the $1.5B in construction, we anticipate the U.S. to be the majority partner, paying roughly half of the total cost (i.e., $750M), with the other half covered by a combination of international and multi-agency partnerships that are actively being pursued. For context, construction costs for the ngVLA are anticipated to be comparable to those for ALMA.  

 

The ngVLA project includes a Science Advisory Council (SAC) and Technical Advisory Council (TAC) to guide the science case and technical implementation of the array. To date, the ngVLA Science Working Groups (SWGs) have prepared of order 80 science use cases that were subsequently prioritized by the SAC. These form the highest-level requirements for the system, and have significantly impacted the design concept as it has matured from 2015 through 2018. Examples of community driven changes are the inclusion of 1.2 10 GHz frequency coverage, a short spacing array of 6m apertures, and the total power antennas.

Likewise, the ngVLA TAC has also influenced key design decisions, including the feed design for Band 1 and 2, and the selection of the optical design for the ngVLA antenna reference design.

If you are interested in providing scientific or technolgiical input to help guide the design of the ngVLA, please contact the respective council chairs.

The ngVLA reference design includes an assessment of the technological readiness of each major element in the system. With the exception of the imaging pipeline and the data archive, all ngVLA systems could be built with 2018 technology. The imaging pipeline and archive will require continued advances in processing power and storage technology from 2018 through first science in 2028 in order to achieve our current science goals within the allowable cost.

If Moore’s Law fails within this time interval, a descope of the post-processing pipeline and archive system could be required.

For other systems, while they can be achieved with present technology, a core goal with ngVLA development is to find solutions that allow for volume manufacture, improved performance, increased reliability, and reduced lifecycle cost. There is ample scope for advances in technology to improve the value of the array over the course of the design.

Yes, we planning to operate the ngVLA as an Open Skies observatory.