Description of the Community Studies Program
As part of the process of building towards a final concept for the ngVLA, NRAO launched the ngVLA Community Studies program, allowing members of the scientific and engineering communities to become major contributors to this effort. The initial call requested investigations on a number of scientific objectives and technical challenges that play major roles in driving the telescope design (i.e., see list of (first round) suggested topics), where community input was expected to be most constructive.
Given the success of our first round of ngVLA Community Studies, a second round was initiated aimed at tackling some of the most pressing questions unveiled by the initial studies. The primary objective for the second round of community studies is to further develop the Key Science Goals outlined in Memo #19. Studies and simulations were asked to focus on addressing these key science goals while better quantifying the expected performance of the array in order to provide additional supporting technical requirements.
Supporting materials for the ngVLA Community Studies, such as notional receiver and array configuration files, can be found on the ngVLA Tools page.
All ngVLA Community Studies are expected to:
- demonstrate the major scientific/technical advancement being advocated and put it in context for the broader astronomical community
- clearly state the impact on design choices
- produce a publication in a peer-refereed journal, or at minimum in the ngVLA memo series
All accepted Community Studies efforts from the second round are expected to write up their findings as part of a peer-refereed journal article or ngVLA memo, and present their progress/final results at the "Astronomy Frontiers in the next Decade and Beyond" Science Conference, June 26-29, 2018 in Portland, OR. Consequently, NRAO is financially supporting each study, at modest level, to offset travel expenses to present results at the June Science Meeting, and offset page charges from publications expected to result from the study. As with the first round of studies, the NRAO is supporting a number of these at a much more significant level.
First Round Awards
Description of the First Round Solicitation:
As part of the process of building a final concept for the ngVLA, NRAO launched the ngVLA Community Studies program, allowing members of the scientific and engineering communities to become major contributors. Included in a list of suggested topics where community input was expected to be most constructive, a number of scientific objective and technical challenges that played major roles driving the telescope design were investigated by experts. A list of the 26 approved scientific and technical studies from our first round of community studies are provided below. Information about the proposal selection process can be found in the initial call for proposals.
|Geoffrey Bower (ASIAA)||Galactic Center Pulsars with the ngVLA|
|Caitlin Casey (University of Texas at Austin)*||Cold Gas in the Early Universe|
|Shami Chatterjee (Cornell University)*||A NANOGrav Study of Gravitational Wave Astronomy with the ngVLA|
|Alessandra Corsi (Texas Tech University)*||Cosmic Explosions and Collisions in the ngVLA Era|
|Andrea Isella (Rice University)*||Imaging Planet Formation with the ngVLA|
|Garrett Keating (SAO)||Exploring the Cosmic History of Molecular Gas with Intensity Mapping|
|Adam Leroy (Ohio State University)||Assessing the Suitability of Proposed ngVLA Designs for Surface Brightness Science|
|Brett McGuire (NRAO)||The Detectability of Interstellar Molecules with the ngVLA|
|Kristina Nyland (NRAO)||Revolutionizing Radio AGN Science with the ngVLA|
|Rachel Osten (STScI & JHU)*||Quantifying the ngVLA's Contribution to Exo-Space Weather|
|Jorge Pineda (JPL)||Composition of the Interstellar Medium|
|Vikram Ravi (Caltech)*||Centimeter-Wavelength Observations of Compact-Object Cataclysms|
|Keren Willacy (JPL)||Protoplanetary Disk Chemistry as a Probe of Planet Formation|
|Roger Angel (University of Arizona; REhnu, Inc.)||A New Approach to Inexpensive Radio Dishes|
|Joe Campbell (UVa)*||High-Power, High-Speed Photodiodes|
|Larry D'Addario (Caltech/JPL)||Advanced Cryocooling Technologies|
|Matt Fleming (Minex Engineering Corp.)*||Proposal for Antenna Mount Study (18m) Proposal for Antenna Mount Study (15m)|
|David Frayer (GBO)||Short Spacing Requirements for the ngVLA|
|Brian Jeffs (BYU)*||Advanced Spatial Filtering Methods for RFI Mitigation at the ngVLA|
|Jeroen Koelemeij (LaserLaB and VU Amsterdam)||Sub-Nanosecond Time Accuracy and Frequency Distribution through White Rabbit Ethernet|
|Dean Chalmers (NRC Herzberg)||Offset Gregorian Antenna|
|Lewis Knee (NRC Herzberg)||ngVLA Receivers|
|Michael Rupen (NRC Herzberg)||The Scientific Drivers and Technical Requirements for the ngVLA Correlator|
|Stefano Spagna (Quantum Design Inc.)*||Smart Energy Cryocooler Technology for the ngVLA|
|Greg Taylor (UNM)||Exploring Low Frequency Options for the ngVLA: Providing a Path to a Next Generation LOw Band Observatory (ngLOBO)|
|David Woody (Caltech/Owens Valley Radio Observatory)||Impact of Fast Switching on Telescope Design|
*Requested and approved for additional funding.
Second Round Awards
Description of the Second Round Solicitation:
As part of the process of building a final concept for the ngVLA, NRAO launched the ngVLA Community Studies program, allowing members of the scientific and engineering communities to become major contributors to this effort. Given the success of our first round of ngVLA Community Studies, a second round was initiated. Aimed at tackling some of the most pressing questions unveiled by the initial studies, the primary objective for the second round of community studies is to further develop the Key Science Goals outlined in Memo #19. Studies and simulations were asked to focus on addressing these key science goals while better quantifying the expected performance of the array in order to provide additional supporting technical requirements. A list of the 12 approved studies from our second round of community studies are provided below. Information the proposal selection process can be found in the associated call for proposals.
|Sarah Burke Spolaor (WVU)||Exploring Nanohertz Multi-messenger Capabilities of the ngVLA|
|Laura Chomiuk (Michigan State)* and Tom Maccarone (Texas Tech)*||The Formation and Evolution of Stellar and Supermassive Black Holes in the Era of Multi-Messenger Astronomy|
|Richard Dodson (ICRAR, UWA)||Enhancing ngVLA capabilities using multiple frequencies|
|Justin Linford (George Washington)*||Classical Novae: A Test Case for ngVLA Stellar Outflow Imaging Capabilities|
|Liton Majumdar (JPL)||HOCO+ emission as a diagnostic of planet-forming regions of disks: Bridging ngVLA and JWST|
|Carl Melis (UCSD)*||Astrometry with the ngVLA|
|Kristina Nylan (NRAO)||Imaging Fidelity and Detectability of Cold Gas with the ngVLA|
|Luca Ricci (CSUN/JPL)*||Witnessing the Origin of Solar System Analogues with the ngVLA|
|Mark Sargent and Anna Cibinel (University of Sussex)||Tracing the build-up of mass inside galaxies: using ngVLA to map the SFR distributions of distant galaxies|
|Sascha Schediwy (ICRAR, UWA)||Phase synchronization of the ngVLA|
|Gregory Taylor (UNM)*||Taking a Census of Supermassive Binary Black Holes with the ngVLA|
|Peter Teuben (U. Maryland)* and Daniel Dale (U. Wyoming)*||Short Spacing Issues for the Mapping of Milky Way Extended Emission and Nearby Galaxies|
*Requested and approved for additional funding.
Suggested Topics for First Round (2016) Community Studies
Science Studies Topics
Terrestrial Planet Formation and Astrochemistry: imaging of the dust continuum at optically thin frequencies (typically < 50GHZ) at 1AU resolution at 130pc (=10mas), plus astrochemistry, in particular the pathway to biochemistry. Areas of interest for further study include:
- imaging capabilities of different configurations using CASA simulator and disk models
- number of systems that can be imaged in the dust continuum at 1AU resolution at 130pc (Taurus, Rho Oph); possibilities for imaging at distance of Orion (500pc).
- sensitivity and spectral requirements for large molecule chemistry
Chemistry of the Early Universe: study of the molecular gas content, dynamics, and ISM physics of galaxies back to the epoch of reionization. Areas of interest for further study include:
- prospects for molecular deep fields and mapping out the dense gas history of the Universe using low order CO transitions
- sensitivity required for imaging dense gas tracers, such as HCN and HCO+
- imaging capabilities to study the dynamics, spatial distribution, and temperature distribution of molecular gas in main sequence galaxies at high redshift
Exo-space Weather: study of stellar phenomena related to space weather and its potential impact on the development of life. Areas of interest for further study include:
- flares on dwarf stars: sensitivity vs. number of systems vs. time scales
- stellar winds: sensitivity vs. mass loss rate
- exo-aurorae: star - planet magnetospheric interactions: statistics and implications
- imaging stellar photospheres: number of supergiants that can be resolved; simulations of imaging capabilities; temporal changes (rotation)
- radio HR diagram: number of stars that can be detected vs. type
- radio novae: late time mass loss; imaging capabilities and temporal variations
The Dynamic Sky: time domain astronomy is a major growth area, with the advent of, e.g., LSST, Euclid, WFIRST, etc.; areas of interest for further study with the ngVLA include:
- capabilities and requirements for triggered fast response
- possibility of finding EM counterparts to gravitational wave sources
- searching for millisec bursts: Localizing FRBs
- targeted search for millisecond pulsars at the galactic center
- feasibility study of wide-area pulsar searches (including for example, effect of available frequency ranges, array configuration, field of view, correlator and computational requirements)
- pulsar timing; complementarity with current and future GHz-frequency instruments
- active stars and stellar systems (flare stars, active binaries, T Tau objects, LMXRBs, …)
- novae, supernovae
- extreme scattering events
Near Earth Sensing: the ngVLA will offer significant opportunity into the field of Near Earth Sensing, which includes studies related to near Earth asteroids, space debris, and artificial satellites; at least 4 methods are possible and require further study:
- passive thermal observations; at the cm and millimeter wavelengths imaging ambient (200K) objects at 30 mas resolution will be possible. This resolution is equivalent to ~10cm at low earth orbit, 6m at geosynchronous orbit, and 50m at a lunar distance. Spin states, orientation, heat capacity, and material properties of satellites and asteroids could be probed at these scales. Such observations require no cooperation on behalf of the targets or other facilities.
- passive observing of satellite transmissions; functioning artificial satellites invariably transmit in the radio band. Observing such transmissions could be used for radio "fingerprinting" and precise state vector determination.
- passive illumination of space debris; radio transmissions of existing high-elevation satellites can illuminate known and unknown space debris. Training a small number of ngVLA antennas on the direct transmission of a satellite and the remaining away from the direct transmission one could perform a cross-correlation analysis and determine states of debris through time of arrival analysis.
- radar observations; very precise astrometry of test mass satellites such as LAGEOS, which are intended for precise tests of gravity using laser ranging, could be used to improve frame ties between optical sensors, radio telescopes, and the quasar reference frame. Broad-band centimeter-wave radar imaging of near-earth asteroids could be used to complement passive thermal observations for improved material analysis
Baryon Cycling: map the total and dense molecular gas content within nearby galaxies for a full census of mass cycles in galaxies. The ngVLA will enable local group-type ISM studies out to the Virgo cluster, using the suite of available diagnostic lines in the 3mm band; areas of interest for further study include:
- array design required for low surface brightness sensitivity: antenna sizes, (re)configurations, total power
- simulations of ngVLA capabilities to image the line and continuum emission on sub-arcsecond scales with sub-K sensitivity
VLBI/Astrometry: microarcsec astronometry using VLBI has revolutionized the fields of Galactic structure, supermassive black studies, and determination of Ho; the ngVLA will play an anchoring role as the mega-element in a global VLBI array, pushing this field to new horizons; areas of interest for further study include:
- simulation of astrometric performance of core ngVLA plus VLBI stations to transcontinental baselines
- calculations of accuracy that can be obtained on spiral structure across the galaxy using masers
- local group dynamics; explore possibility of determining 3D motions of local group galaxies
- real time cosmology; explore possibility of detecting the expansion of the Universe in real-time using VLBI astrometry
Plasma Physics: use of the Sun, stars, supernovae, radio galaxies, ISM, and IPM as laboratories for understanding magnetic energy storage and release, particle acceleration and transport, shock formation and propagation, plasma turbulence, kinetic plasma processes, emission mechanisms; areas of interest for further study include:
- required development for solar observing with ngVLA core
- required development for time and spectral domain observations of the above objects
- potential study targets include:
- Pulsar radio emission mechanisms; especially new insights that may come from sensitive, wide-band >10 GHz observations.
- solar wind tomography with the ngVLA
- magnetic energy release on the Sun and starts using time-resolved imaging spectroscopy
- magnetic reconnection in galactic and extragalactic sources using imaging spectroscopy
- the SZ effect as a means of diagnosing shocks in clusters
- radio filaments in radio galaxies and their relation to magnetic flux ropes
- termination shocks in flares on the Sun and stars
- spatiotemporal evolution of the electron distribution function in flares using imaging spectroscopy – the solar-stallar connection
- coronal magnetography on the Sun and stars
- coherent emission mechanisms and kinetic plasma processes on the Sun
- a taxonomy of radio bursts on stars and stellar systems
Technical Studies Topics
Advanced Cryo-cooling Options: In addition to standard cryo techniques that are currently being pursued at NRAO and elsewhere, we are interested to see if there are substantial gains to be made through modifications to the Gifford-McMahon cycle, or the use of completely different thermodynamic cycles. Areas of interes for further study include:
- optimization of system power consumption to meet dynamic cooling requirements (cooldown, steady-state, standby modes) for individual receivers; technology development to support this involves variable-speed drives for both cryocoolers and compressors, and intelligent monitor and control software.
- investigation of alternative (more theoretical/futuristic) thermodynamic cycles that will result in a system that is more efficient, has increased intervals between maintenance, easily serviceable, and delivers significant power savings
Ultra-wideband Feed Tradeoffs: The community has a strong interest in ultra-wideband feed antennas for use in cryogenic receivers. Ongoing research and development in this area is currently going on at Caltech, NASA/JPL and CSIRO, among others. The advantages of such wide-band feeds include multi-octave signal bandwidths, which adds new science capabilities (spectral line searches, transient sources), and significant reduction in the receiver count, especially for low-frequency bands. This could dramatically reduce receiver construction and operations costs, with fewer cryocoolers per antenna. The challenges/areas that require further study include:
- achieving good aperture efficiency over multiple octaves (~6:1 bandwidth); ongoing work with dielectrically-loaded quad-ridge feeds is promising, but needs additional development and testing.
- minimizing conductor loss; for quad-ridge feeds, the coax transitions could contribute significant additional noise. Noise calibrator injection is another challenge, particularly at high frequencies, because of coupler loss. Need to investigate alternatives.
- cooling the feed, particularly if it's large; may need more development on dewars with large windows and IR filters. Feeds have to be cooled, because of the coax terminations and their associated losses.
Phase Calibration Options: There are a number of choices for the phase calibration of ngVLA observations (e.g., fast switching, water vapor radiometer, and a stand-alone calibration array), each of which has a different suite of advantages and disadvantages. Areas that require additional study include:
- a detailed investigation of the trade-offs (e.g., cost, observing efficience, etc.) amongst these various options.
Reconfigurability/Configuration/Total Power: The straw-man ngVLA contains ~300 18-m telescopes arranged in concentric fat rings. Its 300 km maximum baseline achieves ~10 mas resolution at 30 GHz to image the "dust" continuum of a nearby (130 pc) protoplanetary nebula and resolve gaps of AU width. Additionally, it is centrally concentrated, with ~60% of the collecting area <15 km from the center and 30% in a 1 km core, which improves the surface-brightness sensitivity enough for the ngVLA to image thermal spectral lines from cold molecular gas in high-redshift galaxies with ~100 mas to ~1 arcsec resolution, a few kpc at any 0.4 < z < 8. Areas that require further investigations include:
- the impact on point source sensitivity due to various of weighting schemes that are able to yield a wide range of clean synthesized beamwidths
- the effectiveness of the compact core to be phased to search for pulsars near the Galactic Center or anchor a VLBA array measuring precise positions of simple compact sources such as masers
- the inclusion of longer north-south baseines that couple to make the ngVLA a better "SKA-High" to bridge the frequency gap between the SKA and ALMA for a larger number of southern hemisphere sources
- the use of a small array of tiny dishes or the GBT as a way to fill in the missing baselines smaller than 18m for studies of nearby galaxies
- given the range or resolution and surface brightness sensitivity requirements of particular investigations, which could result in losing a factor of ~2 in effective collecting area, the option of reconfiguring the central array within a 15km radius warrants careful study
Data Backhaul: The data transmission system on the ngVLA includes the digitization of the RF signal from the antenna receivers and the transmission of the digitized signal via optical fiber to a central processing facility. Specific areas of data transmission that may require further investigation include:
- establishment of the functional requirements for the ngVLA data transmission system, to include an analysis of the analog bandwidth, bit depth, sampling rate of digitizers, and how signals might be organized for the long distance transfer of wideband data; investigate current and future technologies that might be implemented to address these requirements
the transmission medium for the ngVLA fiber optic system may be a combination of observatory-owned fiber, leased dark fiber, and commercial network bandwidth, due to expected the scale (~300km baselines). This arrangement will introduce issues with the time stamping of data. The system may need to cope with data packets arriving out of order and to provide padding for lost packets. Similarly, the technology adopted for the data transmission system at the center of the array may be different from that for the most distant antenna stations.
Time and Frequency Distribution: the time and frequency distribution system of an interferometer provides clock signals for digital samplers and coherent frequency references for the up/down conversion of analog signals; strict requirements are placed on the phase noise of these signals in order to preserve coherence. The signal phase should be stable on the timescale of an observation’s integration time in order to preserve the visibility phase. Phase noise degrades the sensitivity, spatial resolution, and dynamic range of an observation. The total phase noise should be dominated by that of the atmosphere, and not that of the instrument. Specific areas in time and frequency distribution that may require further investigation include:
- propose the stability requirement for the ngVLA local oscillator (LO); since the highest frequency on the ngVLA is higher than that for EVLA and SKA, the LO stability requirement for the ngVLA should be more stringent than that for those instruments. However, there is no point in making the LO stability requirement better than the uncorrelated atmospheric stabilities on the longest baselines. Should the specified stability be a function of baseline length, allowing degraded stability on the longer baselines?
- several technical solutions may exist for a given stability requirement; are the implementation and operations costs of a particular solution likely to be less than another? Should fixed tones be distributed and then synthesized at each antenna? Or should the tones be synthesized at a central location?
- polarization effects can become important for an LO stability specification of less than about 1 psec; if that is the case, then it is best not to transmit signals of different wavelengths because of differential delays. A conservative approach might be to limit the fiber-transmitted LO to a maximum frequency of 10 GHz; although, this might be expensive since it requires a synthesizer at each antenna. Alternatively, one could transmit a tunable LO that is a sub-multiple of the desired first LO, and then perform a simple multiplication at the antenna.