In addition to the scientific progress described in the previous chapter, considerations of programmatic context are a factor in the committee’s assessment of the agencies’ response to New Worlds, New Horizons in Astronomy and Astrophysics1 (NWNH) and in the committee’s recommendations for the remainder of the decade. These include the overall fiscal landscape and developments in three components of the overall program: ground-based activities, space-based activities, and activities with close connection to physics, such as particle astrophysics, gravitation, and cosmic microwave background (CMB) studies. These three programmatic areas are closely linked to the National Science Foundation (NSF), NASA, and the Department of Energy (DOE), respectively, but have considerable overlap and benefit from synergy between them. In each of these areas, the committee also considered developments outside the United States. In this report, as in NWNH, the committee frequently refers to “balance” in the astrophysics program; therefore, an understanding of the committee’s interpretation of balance, as discussed in NWNH, is considered to be an important part of the context. Finally, this chapter concludes with a brief discussion of the state of the profession.
1 National Research Council (NRC), 2010, New Worlds, New Horizons in Astronomy and Astrophysics, The National Academies Press, Washington, D.C.
NWNH emphasized the importance of a balanced decadal program with a mix of large- and medium-scale initiatives and a strengthening of core research infrastructure through individual grants and support for instrumentation, technology development, and theory.
For both ground and space, the top-ranked large initiative (Large Synoptic Survey Telescope [LSST] and the Wide-Field Infrared Survey Telescope [WFIRST], respectively) was a low-technical-risk facility with a relatively broad science program. WFIRST was envisioned by NWNH to be a moderate-cost mission that could be executed on a relatively short timescale, and not a “flagship” mission. The second-ranked large initiatives for the ground and for space (Mid-Scale Innovations Program [MSIP] and Explorer augmentation, respectively) were programs intended to support intermediate-scale projects that could respond quickly to new scientific and technical opportunities. The allocation of resources among the different scales was done within the framework of budget scenarios for the agencies. Relative to the budget assumptions adopted by NWNH, which were more optimistic than the budget guidance given to the survey committee by the agencies, the actual budgets of the NSF Division of Astronomical Sciences (NSF-AST) and the NASA Astrophysics Division (NASA-APD) have been considerably lower than projected.
For NSF-AST, NWNH based its recommended program on a scenario in which the NSF-AST budget approximately doubled in real-year dollars2 over the course of the decade. NSF input to NWNH suggested a more pessimistic scenario, with a budget approximately flat over the decade in fiscal year (FY) 2010 (inflation-adjusted) dollars.3,4 NWNH noted that in this scenario “the only way there can be any significant new initiative is through very large reductions in the funding for existing facilities and budget lines.”5 The NSF-AST budget through the first half of the decade has been notably worse than even this more pessimistic scenario: approximately flat in real-year dollars, with a substantial erosion of purchasing power over time (Figure 2.1). Recognizing the need to identify funds for new initiatives, NSF executed in 2012 the NWNH recommendation of a second senior review by carrying out a broad Portfolio Review of the NSF-AST program.
FINDING 2-1: The NSF-AST budget through the first half of the decade has been approximately flat in real-year dollars. This budget reality is somewhat lower than that baselined by NSF for NWNH (approximately flat in
2 Real-year dollars are unadjusted for inflation.
3 NRC, 2010, New Worlds, New Horizons, p. 187.
4 Inflation was assumed to be about 3 percent per year.
5 NRC, 2010, New Worlds, New Horizons, p. 188.
inflation-adjusted dollars) and significantly lower than that assumed by NWNH (doubling in real-year dollars).
For NASA-APD, NWNH assumed a flat budget in inflation-adjusted dollars. NASA-APD budget guidance to the survey committee was that the budget would remain flat in real-year dollars through the decade, implying a decrease in real purchasing power at the rate of inflation.6 The sum of the James Webb Space Telescope (JWST) and APD budgets has roughly tracked this assumption during the first half of the decade (although it is projected to flatten in real-year dollars in the second
6 NRC, 2010, New Worlds, New Horizons, p. 187.
half). However, the late-breaking schedule delay and associated cost increase for JWST have effectively delayed the availability of a funding wedge for new initiatives by about 4 years. In response to problems encountered in the development of JWST, NASA removed JWST management from APD and established a new, separate office (the James Webb Space Telescope Program Office) within the Science Mission Directorate responsible for completing the project. The JWST budget was also transferred to this new office. At the time that this was done, it was anticipated that the budget wedge created by the roll-off of JWST development activities as the project approached launch would be recombined with the APD budget. Thus, while the NSF-AST budget has been depressed well below NWNH expectations through the full decade, the NASA-APD budget has been shifted in time (Figure 2.2).
FINDING 2-2: For NASA-APD, NWNH assumed a flat budget in inflation-adjusted dollars. The actual combined budget for NASA-APD and JWST has roughly tracked this assumption. However, the late-breaking schedule delay and associated budget increase of JWST have delayed the availability of funding for new initiatives by about 4 to 5 years.
For DOE, NWNH based its budget assumptions on the 2009 High Energy Physics Advisory Panel (HEPAP) report,7 considering that report’s Scenario A, in which the total budget was constant in inflation-adjusted dollars, and Scenario C, in which there is a budget doubling over the decade in inflation-adjusted dollars. NWNH recommendations are based on the more optimistic scenario. For the first half of the current decade, the Cosmic Frontier budget line in real-year dollars increased by slightly more than 50 percent, so for the DOE program, the budget reality has been much closer to the baseline plan presented in NWNH than for the other agencies.
FINDING 2-3: At DOE, support for astrophysics has been strong, and the budget reality has been close to the baseline plan presented in NWNH.
The U.S. optical and infrared (OIR) system, with its unique mix of private and public facilities, continues to produce world-leading scientific results. The ground-based system is a powerful complement to space facilities; for example, the ground-based observations confirm many Kepler exoplanet candidates and allow measurements of their density, and ground-based observations provide critical data for dark energy parameter constraints. New instrumentation on 4- to 10-meter telescopes and new analysis techniques have continued to extend the capabilities of very large telescopes built in previous decades.
However, these successes occur against a landscape of challenges. NSF funding to support public observatories has eroded, and several have been closed and others are facing federal divestment to allow NSF to achieve its other goals. NSF funding for new instrumentation for OIR telescopes is also challenging to obtain, particularly with the termination of the NSF Telescope Systems Instrumentation Program (TSIP) that had previously provided both instrumentation funding and
7 U.S. Department of Energy, Report of the HEPAP Particle Astrophysics Scientific Assessment Group (PASAG), October 23, 2009, http://www.er.doe.gov/hep/panels/reports/hepapreports.html.
a channel for public access to powerful private facilities. As a result, the access of U.S. scientists to state-of-the-art instruments will decline over the remainder of the decade. The general astrophysics community no longer has access through TSIP to the powerful Keck telescopes and other 6-10 meter telescopes, and the last TSIP-funded instruments are coming online now; no new major capability is in development for Keck, and most U.S. observatories are in a similar situation.
Offsetting declining NSF support to some extent, other federal agencies have funded ground-based capabilities that meet their science needs, with cooperative ventures between DOE and NSF proving especially important. The Dark Energy Survey (DES) on the Blanco 4-m telescope, located at the Cerro Tololo Inter-American Observatory in Chile, represents a major advance in weak-lensing measurements of cosmic structure, and the Dark Energy Camera that DOE built for DES is one of the National Optical Astronomy Observatory’s (NOAO’s) most powerful instruments for community science. Through its support of the Sloan Digital Sky Survey’s (SDSS’s) Baryon Oscillation Spectroscopic Survey (BOSS) and Extended Baryon Oscillation Spectroscopic Survey (eBOSS) projects and, on a larger scale, the Dark Energy Spectroscopic Instrument (DESI), DOE is enabling giant galaxy redshift surveys for precision measurements of cosmic acceleration and structure growth. DESI allows the Mayall 4-meter telescope at Kitt Peak National Observatory to remain a cutting-edge scientific facility following NSF divestment. DOE is building the LSST camera, which together with NSF Major Research Equipment and Facilities Construction (MREFC) funding of telescope construction has enabled LSST to stay on track for operations beginning in the early 2020s. The DOE science focus in these projects is on cosmology and neutrino physics, but the data sets produced by SDSS, DES, DESI, and LSST have applications across a wide range of astronomy and astrophysics. In addition to its direct funding of projects, DOE is playing a crucial role in sustaining the strength of the U.S. research community through its support of individual scientists and research groups.
Other significant support of ground-based astronomy comes from the Air Force Research Laboratory and private sources in their funding of the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) project. Pan-STARRS has surveyed three-fourths of the sky (north of declination –30) approximately 60 times. However, funding exists only to make these archival survey data available to the community for 1 year. NASA continues to operate Pan-STARRS, but only in a mode optimized for finding near-Earth objects. NASA is also funding a new instrument and associated operations costs for the Wisconsin/Indiana/Yale/ NOAO (WIYN) telescope in support of exoplanet studies. These agencies’ support of ground-based programs remains focused on their own science interests and, to a significant extent, on large-scale programs.
The international (U.S.-managed) Gemini Observatory was an area of concern for NWNH. With the deployment of the Gemini Planet Imager and plans for a
high-resolution optical spectrograph, the Gemini instrumentation suite is becoming more capable, and the management structure has been changed to be more responsive to community concerns. The greatest change in U.S. access to Gemini came in 2012 with the withdrawal of the United Kingdom from the partnership, which resulted in the U.S. share of Gemini going from 50 to 65 percent with no increase in the U.S. contribution.
At the time of NWNH, projects for the next generation of telescopes were beginning. Referred to as Extremely Large Telescopes or Giant Segmented Mirror Telescopes (GSMTs), these 20- to 40-meter instruments will be revolutionary for most of the science themes discussed here. Progress toward a U.S. GSMT is discussed in the section “The Ground-Based Program—Large Scale” in Chapter 3.
The European Very Large Telescope (VLT) and the Japanese Subaru telescopes continue to be upgraded with instrumentation programs significantly more ambitious than those of any U.S. public or private 8- to 10-meter facility. The European Extremely Large Telescope (E-ELT), a 39-meter-diameter aperture telescope under construction on Cerro Armazones in Chile, will be larger than any other planned optical-infrared telescope in the world. The E-ELT program was approved by the European Southern Observatory (ESO) in 2012; ground breaking and site preparation began in 2014, proceeding to construction was approved in December 2014, and the first suite of instruments was approved in 2015. Science operations are expected to begin in 2026.
At the time of NWNH, the U.S. radio facilities were the Very Large Array (VLA), the Very Long Baseline Array (VLBA), and the Green Bank Telescope (GBT), all operated by the National Radio Astronomy Observatory (NRAO; managed by Associated Universities, Inc.); Arecibo, operated by Cornell University; and university-operated radio facilities. The two major advances in the past half-decade are the completion of a major upgrade to the VLA, now known as the Karl Jansky Very Large Array (JVLA; completed in 2013), and the successful completion of the construction and first three cycles of observing by ALMA (construction completed in 2015). Both projects were completed within budget. Jointly operated by North America (through NRAO), Europe (through ESO), and Japan (through the Joint ALMA Observatory), ALMA is a new submillimeter/millimeter array located in the Chajnantor plateau in northern Chile, having been prioritized as the second large-class priority of the 1991 decadal survey. The first three cycles of observing with ALMA have yielded ground-breaking discoveries in planetary science, the late stages of stellar evolution, galaxy dynamics, and the morphology and kinematics of the first galaxies. Meanwhile, JVLA has enabled fundamental studies of the evolution of the gas content of galaxies and star formation in the Milky Way, among
other studies. Additionally, a consortium led by the University of Massachusetts and INOAE (Mexico) achieved first light with the Large Millimeter Telescope (LMT), which promises new advances in the study of gas and dust in galaxies across cosmic time.
FINDING 2-4: The completion and successful operation of ALMA are a remarkable success and the culmination of significant investment by NSF through the MREFC program.
While NWNH recommended investment in a new millimeter survey telescope, CCAT, to complement ALMA, there has been no new funding to enable CCAT to proceed past an initial design stage (see Chapter 3).
Since NWNH, the NSF Portfolio Review has recommended that NSF divest from the VLBA and the GBT and that it subsume any further support of university radio observatories into the MSIP. As of October 2016, the VLBA and the GBT will be operated as stand-alone facilities—the Long Baseline Observatory (LBO) and the Green Bank Observatory (GBO), respectively—for 2 years with a decreasing fraction of support from NSF-AST and an increasing contribution from private sources and other government agencies. After recompetition, a new management consortium took over the operation of Arecibo. The Portfolio Review also recommended that NSF-AST consider divestment of Arecibo later in the decade; currently, its status is under discussion within NSF-AST.
Other radio instruments considered promising by NWNH include the Event Horizon Telescope (EHT), pulsar timing detections of gravitational waves (NANOGrav), and arrays for 21 cm cosmology (Murchison Widefield Array [MWA], Precision Array to Probe Epoch of Reionization [PAPER], and Hydrogen Epoch of Reionization Array [HERA]). The EHT is moving forward with combined support from MSIP and the Gordon and Betty Moore Foundation. NANOGrav has received combined support from MSIP and from the NSF Physics Division (NSF-PHY) as a Physics Frontier Center, from the Natural Sciences and Engineering Research Council in Canada and the Research Corporation for Scientific Advancement in the United States. The NANOGrav support includes funds for purchasing time on the GBT, although the future of GBT is uncertain and the loss of access to GBT would be very detrimental to NANOGrav. The MWA and PAPER low-frequency arrays are operating, and HERA has received funding for technology development from MSIP.
A major development for radio astronomy worldwide is the initiation of the international Square Kilometer Array (SKA) project. The United States is not a member nation, but through precursor activities is contributing to some aspects of the design of SKA Phase 1. Preliminary design and prototyping of Phase 1 is complete. It consists of two arrays, SKA-low, to be built in Australia, and SKA-mid, to be built in South Africa. The SKA headquarters will be in the United Kingdom.
In China, construction of the Five hundred meter Aperture Spherical Telescope (FAST) began in 2011 with an expected completion date of 2016. Its design is similar to that of the 305-meter Arecibo telescope. With its enormous collecting area, FAST will be the most sensitive telescope in the world. As of this writing, the United States does not have significant participation in these large international radio astronomy initiatives.
Despite schedule delay and cost increase, JWST is now on track with a late 2018 launch to deliver science capabilities that will very much exceed those of the Hubble Space Telescope (HST). However, the delay and increased cost of JWST has led to delay in starting WFIRST, the top-ranked NWNH large space initiative. As a result, WFIRST had its Phase A start in 2016 and is working toward a launch in 2024-2026 rather than in 2020, as envisioned by NWNH. The Explorer program augmentation recommended by NWNH has also been delayed, with the first Small Explorers (SMEX) Missions + Mission of Opportunity (MoO) Announcement of Opportunity issued in 2014 (see further discussion in the section “The Space-Based Program—Large Scale” in Chapter 4). The Nuclear Spectroscopic Telescope Array (NuSTAR) was launched in June 2012 and is providing astronomers with their first look into the high-energy X-ray universe. The Stratospheric Observatory for Infrared Astronomy (SOFIA) reached full operational capacity in February 2014 and provides unique capabilities for mid-to-far infrared spectroscopy. Two Explorers, the Transiting Exoplanet Survey Satellite (TESS; expected launch in December 2017) and the Neutron Star Interior Composition Explorer (NICER; expected launch in February 2017), are in development. LISA Pathfinder (LPF) was launched in December 2015 (NWNH assumed launch in 2012), and initial analysis shows it has been successful thus far. NASA continues to be a partner in ESA’s Euclid observatory, which is slated for launch in 2020. NASA is also currently supporting five SMEX/MoOs.8
Recent developments in space-based astronomy in Europe and Japan are also having a significant impact on the U.S. program. At the time of NWNH, Euclid, the International X-ray Observatory (IXO), and the Laser Interferometer Space Antenna (LISA) were all NASA-ESA collaborations (and in the case of IXO, the collaboration included the Japan Aerospace Exploration Agency [JAXA]). Significant changes in the NASA-ESA context occurred around 2011 as the budgetary realities of the decade and their implications for implementation of NWNH became clear. ESA announced a “new approach” for its L-class (large) missions and formed European-led science teams to examine European-led affordable missions. This
8 SPHEREx, PRAXyS, IXPE, LiteBIRD (for U.S. participation), and GUSTO.
resulted in the Jupiter Icy moons Explorer (JUICE) mission, the Athena mission, and the gravitational wave theme, subsequently chosen for L1 (2022 launch), L2 (2028 launch), and L3 (2034 launch), respectively, by ESA.
Both LISA’s and IXO’s prioritizations in NWNH were based on near 50-50 partnerships between NASA and ESA; the impact of ESA’s decisions is discussed in the section “The Space-Based Program—Large Scale” in Chapter 4. However, in an effort to limit its exposure to the risks associated with collaboration beyond Europe, the committee was informed that ESA has instituted a 20 percent cap on the fraction of the budget of a mission provided through international collaboration.9 The series of events surrounding the NASA-ESA efforts illustrate the complexities of long-term planning for international collaborative missions.
The Astro-H mission, now renamed Hitomi, is a collaboration between JAXA and NASA. It launched in February 2016 and, despite successful initial operations, underwent a catastrophic set of operational errors on March 26, 2016, and was declared lost by JAXA on April 28. Despite the failure of the satellite, one excellent data set, an observation of the Perseus cluster, was obtained. This observation confirmed the unprecedented energy resolution in the astrophysically important iron K-alpha line as well as the existence of a wide variety of temperature, ionization, abundance, and dynamical diagnostics in X-ray spectra and demonstrated this detector technology in space for the first time. JAXA has revised the Space Infrared telescope for Cosmology and Astrophysics (SPICA) concept, and it is being considered for launch in the late 2020s. An ESA group will propose a new SPICA concept to the ESA Cosmic Visions M5 call. LiteBIRD, a CMB mission with planned sensitivity to B-mode polarization at an inflationary tensor-to-scalar ratio of r = 0.001, is also in the planning stage. India’s first space-based dedicated astronomical observatory, Astrosat, was launched in September 2015 with five astronomical instruments onboard that provide simultaneous co-aligned ultraviolet to X-ray telescope coverage. Its widefield X-ray instrument provides large-area X-ray timing capability, restoring a capability previously provided by the Rossi X-ray Timing Explorer. In December 2015, China launched the Dark Matter Particle Explorer, the first Chinese space mission for astronomy and astrophysics and one of a series of planned space science missions. In July 2011, Russia launched the RadioAstron mission, a space-based radio telescope designed for very-long-baseline interferometry at centimeter wavelengths. The Spectrum-XG mission, featuring a wide-field X-ray telescope (eRosita) developed by Germany and a hard X-ray telescope (ART-XC) developed by Russia in collaboration with NASA’s Marshall Space Flight Center, is currently scheduled for launch in 2017.
9 Within Europe, ESA manages its budget with a 5-year horizon at levels agreed to by all member states. The levels can be changed only by unanimous vote, providing stability on this timescale. The committee was informed that in executing its missions, ESA funds the spacecraft and launch and cooperates with the member states to secure the scientific instruments.
The technology for electromagnetic observations from space has improved in several ways—with programmatic implications since NWNH was written. Investment by NASA in mercury cadmium telluride (HgCdTe) detector development has resulted in wide-format infrared detectors that are background limited in space at temperatures that can be reached by passive cooling in high orbits. These arrays will be useful for wide-field infrared survey missions, including WFIRST. Rapid progress has been made in the design of pupil and focal plane masks for coronagraphs on telescopes with obscured apertures, including designs specifically for WFIRST-Astrophysics Focused Telescope Assets (AFTA). The starshade approach using an external occultor has also been significantly advanced. At X-ray energies, NuSTAR demonstrates the power of multi-layer coatings applied to highly nested, segmented glass X-ray mirrors. The X-ray calorimeter on Hitomi was providing unprecedented energy resolution in the astrophysically important iron K-alpha line, demonstrating this detector technology in space for the first time.
NWNH noted that LISA would provide insight into the early growth of black holes and the cosmological history of galaxy formation and test general relativity with exquisite precession. The potential for transformative discoveries was highlighted: “It would be unprecedented in the history of astronomy if the gravitational radiation window being opened up by LISA does not reveal new, enigmatic sources.”10 Gravitational wave detection is currently being pursued through four main efforts: ground-based interferometers (led by Advanced LIGO [Laser Interferometry Gravitational-wave Observatory]), pulsar timing arrays, space-based interferometers, and polarization measurements of the CMB. Funding for these programs comes from NSF-AST, NSF-PHY, NASA, and DOE. Advanced LIGO is part of a world-wide network of detectors under development, and operation of the two Advanced LIGO detectors in coincidence with the European Virgo and GEO600 detectors is intended to become routine. Long baseline interferometric detectors are also being planned in Japan (KAGRA) and India (LIGO India). The recent direct detection of gravitational waves by Advanced LIGO is a groundbreaking proof of principle for the interferometric technique, with implications for future directions on the ground and in space. The LISA Pathfinder (LPF) was launched in December 2015, whereas it was assumed by NWNH to be launched in 2012.11 This is several years behind the schedule assumed by NWNH, but LPF re-
10 NRC, 2010, New Worlds, New Horizons, p. 201.
11 LPF is an ESA-led mission, but the ST-7 component (colloidal thrusters and control system) are a U.S. contribution. NASA scientists are involved in the analysis of LPF data and will run the ST-7 segment of the mission.
sults inform this report and will inform the next decadal survey. U.S. (NANOGrav) and international pulsar timing arrays continue to make precise timing observations, and recent limits on gravitational wave backgrounds at periods of months to years are beginning to challenge the simplest cosmological models. Measurements of the B-mode polarization patterns of the CMB are being made from the South Pole, high-altitude sites in Chile, and balloon platforms (see the sections “The Space-Based Program—Large Scale” and “The Space-Based Program—Medium Scale” in Chapter 4 for further discussion).
Particle astrophysics observatories and experiments in the United States are supported by NSF-PHY, NSF-AST, and DOE on the ground, and by NASA for suborbital and space missions. At the time of NWNH, the operating facilities for gamma-ray astronomy included Fermi, Swift, Integral, and AGILE in space, and VERITAS, HESS, MAGIC, and Milagro on the ground. All of these continue to operate, except for Milagro, which has been succeeded by the High-Altitude Water Cherenkov Observatory (HAWC). HAWC construction in Mexico was completed in 2014, and it is now carrying out a high-sensitivity synoptic survey of the gamma-ray and cosmic ray sky at energies between 100 GeV and 100 TeV with a very large field of view.
NSF-AST participation in the Cherenkov Telescope Array (CTA) has not occurred because of budgetary constraints and programmatic choices vis a vis NWNH rankings. CTA, referred to as ACTA in NWNH, is the leading next-generation gamma-ray instrument designed to increase sensitivity by an order of magnitude as compared to the currently operating observatories VERITAS, HESS, and MAGIC. It would observe gamma rays over a wide range of energies (20 GeV to above 300 TeV). It is being developed by a large international consortium as an open observatory with one array in each hemisphere. In 2010, the U.S. Advanced Gamma-ray Imaging System effort merged into CTA, as recommended by NWNH. The NSF Major Research Instrumentation program funded a prototype SCT [Schwarzschild-Couder Telescope] in 2012 designed to perform near the theoretical limit for a Cherenkov Telescope. Construction of CTA is expected to start in 2017 with completion in 2024 (see the section “The Ground-Based Program—Large Scale” in Chapter 3 for further discussion).
In neutrino astronomy, IceCube, under construction at the time of NWNH, is funded in the United States by NSF-PHY and the NSF Division of Polar Programs. After IceCube’s important discovery of peta-electronvolt (PeV) neutrinos in 2013, several upgrade plans are being considered. At ultrahigh energies (exa-electronvolt, EeV), where neutrinos produced by photo-pion production of ultrahigh-energy cosmic rays should be observed, a number of prototypes have been built, including the Askaryan Radio Array (ARA) and Antarctic Ross Iceshelf Antenna Neutrino Array (ARIANNA) in Antarctica and the balloon payload ANITA (Antarctic Impulse Transient Antenna).
A number of observatories for cosmic rays of different energies are now operating. At lower energies, the leading detector is AMS-02 (Alpha Magnetic Spectrometer), which was deployed on the International Space Station (ISS) in 2011. AMS confirmed the PAMELA positron excess and is precisely measuring spectra of many cosmic ray primaries including anti-protons. The CALET, a JAXA-led electron calorimeter, joined AMS on the ISS in 2015, and in 2017 ISS-CREAM should also be deployed on the ISS to study cosmic rays at higher energies. Rare heavy primaries are currently being studied through the NASA balloon program with Super-TIGER. At higher energies, cosmic rays are studied by ground arrays up to 1020 eV. At the ultrahigh energies, the leading experiments are the Pierre Auger Observatory, covering 3,000 km2 in Argentina and the Telescope Array (TA) observatory, covering 700 km2 in Utah. During NWNH, the Particle Astrophysics and Gravitation panel recommended that Auger North be built if budgets allowed. The budgetary constraints did not allow this project to go forward, but an expansion of TA to match the size of Auger South, named Tax4, was recently approved by the Japanese funding agencies.
There has been considerable progress in CMB instrumentation and measurement since NWNH. WMAP published its final maps and cosmological analyses in 2013. Planck measurements have extended full-sky temperature and polarization maps to higher angular resolution, higher sensitivity, and greater frequency range, including high frequencies where galactic dust emission dominates. Planck temperature maps show the expected signature of gravitational lensing by foreground structure at a significance of 40 σ, allowing precise new tests of cosmological predictions for structure growth. Ground-based experiments, notably the South Pole Telescope (SPT) and Atacama Cosmology Telescope (ACT), complement Planck by reaching higher angular resolution, which is especially valuable for lensing and Sunyaev-Zeldovich measurements. In addition to showing beautiful agreement with the expected E-mode polarization signal, the ACTpol, SPTpol, BICEP2/Keck, and PolarBear experiments show clear detection of the B-mode polarization expected from gravitational lensing. BICEP2/Keck initially announced detection of large angle B-mode polarization from inflationary gravitational waves, but subsequent joint analysis with Planck indicates that this signal is dominated (and probably entirely explained) by polarized dust foregrounds. While the BICEP2 experience demonstrates the challenge of isolating the primordial gravity wave signal, many ground- and balloon-based experiments are pressing ahead to achieve the sensitivity and frequency coverage needed to detect large-angle B-modes at the level expected for inflationary tensor-to-scalar ratios as low as r ≈ 10-3. Current upper limits at r ~ 0.05 already rule out interesting inflationary models. Current and near-term efforts on the ground include SPTpol, SPT3G, ACTpol, Adv ACTpol, PolarBear, the Simons Array, BICEP3, the Keck Array, and ABS. Balloon-borne experiments include CASS, EBEX, Spider, and PIPER. NASA is supporting a near-term plan for
higher sensitivity with observations from long-duration balloon flights. To date, several groups have made long-duration balloon flights around the South Pole with polarization sensitive radiometers at multiple wavelengths. In space, the CMB mission LiteBird has been selected for a SMEX phase A study as a MoO with JAXA.
CMB experiments receive support from the Physics and Astronomy divisions of the NSF, NASA, and the DOE Office of Science. DOE and NSF’s Particle Physics Project Prioritization Panel (P5), a subcommittee of HEPAP, has recommended exploring a larger role for DOE in next-generation CMB experiments, drawing on the unique fabrication capabilities at the DOE national laboratories to implement a “Stage IV” CMB effort named CMB-S4.12
A central and recurring theme of NWNH is “balance,” and, although it is articulated as a guiding principle more than 30 times throughout the document, not all readers interpret balance in a consistent manner. Therefore, it is important to clarify the meaning of balance in this report. The committee interprets balance to refer to a viable mix of small, medium, and large initiatives on the ground and in space that optimizes the overall scientific return of the entire U.S. astronomy enterprise viewed collectively. It does not refer to a balance of wavelengths, nor of astronomy subtopics.
NASA’s smaller core research programs include support for individual investigator grants, data management, theoretical studies, innovative technology development, the suborbital and balloon programs, archiving, and analysis of data realized from the missions. NWNH considered these initiatives “fundamental to mission development and essential for scientific progress”13 that “must be protected from overruns elsewhere.”14 NWNH goes on to state: “Maintaining these core activities, even in the face of cost overruns from major missions, has high priority and is the most effective way to maintain balance in the research program.”15 Moreover, NWNH highlighted “the impressive science value per dollar achieved with a healthy Explorer program,”16 and as a result, an enhancement to the medium-scale Explorer program was its second-ranked space project recommendation. Hence, it was a clear conclusion of NWNH that balance is achieved, in part, through a diversified portfolio including large flagship missions, medium-scale Explorer missions and
12 Particle Physics Project Prioritization Panel, 2014, Building for Discovery: Strategic Plan for U.S. Particle Physics in the Global Context, Department of Energy, Washington, D.C., p. 5, http://science.energy.gov/~/media/hep/hepap/pdf/May-2014/FINAL_P5_Report_Interactive_060214.pdf.
13 NRC, 2010, New Worlds, New Horizons, p. 219.
14 NRC, 2010, New Worlds, New Horizons, p. 175.
15 NRC, 2010, New Worlds, New Horizons, p. 219.
16 NRC, 2010, New Worlds, New Horizons, p. 175.
technology development, and smaller suborbital, data analysis, theory, and laboratory astrophysics programs.
In the NSF context, NWNH found that maintaining balance required wise stewardship of the NSF facilities portfolio, which involves both continued support for older facilities and the development and operation of newer ones. To accommodate new facilities and their operations costs, NWNH strongly advocated the senior review process “to determine which, if any, facilities NSF-AST should cease to support in order to release funds for (1) the construction and ongoing operation of new telescopes and instruments and (2) the science analysis needed to capitalize on the results from existing and future facilities.”17 NWNH noted that there is a “trade-off between investing in the development and construction of ambitious new telescopes and supporting broad-ranging observational and theoretical research that optimizes the return from operating facilities”18 and that this trade-off must be made while maintaining balance between large facilities initiatives and the many small research initiatives.
In summary, as envisioned by NWNH, balance requires that the uniquely capable major initiatives, with their high cost and low cadence, be complemented with both (1) innovative mid-scale initiatives, with their more modest cost and higher cadence, and (2) smaller initiatives, with their lower cost and higher cadence. NWNH considered such balance to be necessary to optimize the scientific return of U.S. investments and to maintain the health of the U.S. astronomical research community.
NWNH includes a discussion of the demographics of the astronomy profession, informed by a panel that reported to the subcommittee on state of the profession. NWNH noted continuing trends of a slowly increasing total number of astronomers, as measured by membership in astronomical societies and rates of degrees granted. Combined with flat or declining rates of tenure-track faculty positions available, this creates a concern about long-term job prospects, which was only partially offset by larger numbers of grant-funded positions and research staff positions. It was recognized that the skill sets required for astronomy research have application to non-astronomy employment, and NWNH recommended that the American Astronomical Society and the American Physical Society “should make both undergraduate and graduate students aware of the wide variety of rewarding career opportunities enabled by their education, and be supportive of students’ career decisions that go beyond academia.”19
17 NRC, 2010, New Worlds, New Horizons, p. 32.
18 NRC, 2010, New Worlds, New Horizons, pp. 14-15.
19 NRC, 2010, New Worlds, New Horizons, p. 30.
NWNH also discussed underrepresented groups, noting that only 4 percent of astronomy Ph.D.s and only 3 percent of faculty are African American, Hispanic, or Native American. NWNH concluded that “agencies, astronomy departments, and the community as a whole need to refocus their efforts toward attracting members of underrepresented minorities to the field”20 through targeted mentorship programs, joint internship programs with minority-serving institutions, family-friendly policies, and so on. Similarly, although there has been some overall progress on gender balance, only a small fraction of senior positions in astronomy are held by women—only 11 percent of full professorships were held by women as of NWNH.
The committee lacked the resources to explore demographic questions extensively, but there is little evidence that the situation for underrepresented groups has improved. Statistics from the American Institute of Physics21 indicate that underrepresented minorities still account for only 3 percent of faculty positions in astronomy. The longitudinal study by the Committee on Status of Women in Astronomy22 has only 10-year resolution but shows mild improvement in gender balance from 2003 to 2013, with the fraction of female faculty at all levels increasing from 13 to 17 percent. One encouraging result is that the rate of advancement from graduate student positions to tenure-track faculty positions is becoming more equal for women and men. However, critical issues remain, as highlighted by multiple recent news items about sexual harassment in academic research institutions.
The low rate of success for grant proposals is a serious a concern for the health of the profession. The Astronomy and Astrophysics Advisory Committee (AAAC), which advises NSF, NASA, and DOE on mutual agency issues within the fields of astronomy and astrophysics, is engaged in studying the reasons for the low grant success rate. No single cause has emerged, but this is a significant issue for the community because successful proposals are a key step towards tenure for grant-funded non-tenure-track positions and for training the next generation of scientists through graduate and post-doctoral fellowships at universities.
Chapter 5 of this report notes that the health of the profession is an important consideration in the planning for the next decadal survey.
20 NRC, 2010, New Worlds, New Horizons, p. 127.
21 American Institute of Physics, 2014, African Americans and Hispanics among Physics and Astronomy Faculty, Collage Park, Md., https://www.aip.org/sites/default/files/statistics/faculty/africanhisp-facpa-123.pdf.
22 American Astronomical Society, 2014, Status: A Report on Women in Astronomy, http://www.aas.org/cswa/status/Status_2014_Jan.pdf.