Optimizing the U.S. Ground-Based Optical and Infrared Astronomy System (2015)

2
Science from Major U.S. Ground-Based OIR Investments

2.1 PROGRESS ON DECADAL SCIENCE PRIORITIES

The 2010 National Research Council (NRC) decadal survey report New Worlds, New Horizons in Astronomy and Astrophysics¹ (NWNH) laid out a broad program of astronomical research, within which it identified three overarching science themes as particularly ripe for exciting progress in the coming decade: Cosmic Dawn, New Worlds, and Physics of the Universe. Cosmic dawn involves searching for the first stars, galaxies, and black holes and understanding the formation and early evolution of structure in the universe. In the realm of new worlds, astronomers seek nearby habitable planets and explore properties of exoplanetary systems and their disk progenitors, probe the formation and evolution of stars including the Sun, and seek to understand the details of gas-stellar processes and star formation histories across the full range of galaxies including the Milky Way. The quest to understand basic scientific principles, including dark matter, dark energy, and the nature of gravity, make up the physics of the universe. The 2011 NRC decadal survey report Vision and Voyages for Planetary Science in the Decade 2013-2022² (VVPS) similarly provides a roadmap for study of the solar system, from the gas giants and rocky inner planets and their interiors, surfaces, and atmospheres, to moons and primi-

_______________

¹ National Research Council (NRC), 2010, New Worlds, New Horizons in Astronomy and Astrophysics, The National Academies Press, Washington, D.C.

² NRC, 2011, Vision and Voyages for Planetary Science in the Decade 2013-2022, The National Academies Press, Washington, D.C.

tive bodies, in order to understand their origins and evolution and the development of habitable environments.

Ground-based optical and infrared (OIR) astronomy facilities provide critical capabilities that are enabling major advances in all of these (as well as other) high-priority areas of research. Increasingly, progress in these subjects requires observations across the electromagnetic spectrum and thus entails multi-wavelength campaigns that make use of both ground-based and space-based facilities. The focus of this chapter is on the key roles that ground-based OIR facilities play in this science as well as the important synergies with observations at other wavelengths and in space. With more than 2,000 publications annually based on data from telescopes in the U.S. OIR System, it is not possible to review all of the exciting recent discoveries and breakthroughs, so instead a few highlights are presented to illustrate the breadth of the accomplishments and the progress being made on some of the key decadal science themes.

A key goal of cosmic dawn research is to understand the first galaxies and their role in emitting ultraviolet radiation that reionized the universe during the first billion years after the Big Bang. Recent observing campaigns with the Hubble Space Telescope (HUDF12, CANDELS, BoRG, CLASH, HFF)³ with longer wavelength constraints based on Spitzer Space Telescope observations have pushed the high-redshift frontier to the epoch when the universe was about 500 million years old (redshift z ~ 10),⁴ providing the first glimpses into the nature of the galaxy population at these very early times.⁵ Detailed studies of these early galaxies require ground-based spectroscopy; the Magellan telescopes have been used in recent years to provide the first spectroscopic confirmation of galaxies seen when the universe was less than 800 million years old (z ~ 7-7.5).⁶ The record for the most distant quasar (z = 7.09, 770 million years)⁷ has been pushed to the same epoch, using near-infrared (IR) and optical imaging from the United Kingdom Infrared Telescope (UKIRT) and the Sloan Digital Sky Survey (SDSS) and detailed spectroscopy from Gemini North and the ESO Very Large Telescope (VLT). Recent Magellan observa-

_______________

³ Acronyms, especially those denoting individual instruments and missions, are defined in Appendix C.

⁴ D. Coe, A. Zitrin, M. Carrasco, X. Shu, W. Zheng, M. Postman, L. Bradley, A. Koekemoer, R. Bouwens, T. Broadhurst, A. Monna, et al., 2013, CLASH: Three strongly lensed images of a candidate z 11 galaxy, The Astrophysical Journal 762:32.

⁵ P.A. Oesch, R.J. Bouwens, G.D. Illingworth, I. Labbé, M. Franx, P.G. van Dokkum, M. Trenti, M. Stiavelli, V. Gonzalex, and D. Magee, 2013, Probing the dawn of galaxies at z ~ 9-12: New constraints from HUDF12/XDF and CANDELS data, The Astrophysical Journal 773:75.

⁶ J.E. Rhoads, P. Hibon, S. Malhotra, M. Cooper, and B. Weiner, 2012, A Lyα galaxy at redshift z = 6.944 in the cosmos field, The Astrophysical Journal Letters 752(2):L28.

⁷ D.J. Mortlock, S.J. Warren, B.P. Venemans, M. Patel, P.C. Hewitt, R.G. McMahon, C. Simpson, T. Theuns, E.A. Gonzáles-Solares, A. Adamson, S. Dye, et al., 2011, A luminous quasar at a redshift of z = 7.085, Nature 474(7353):616-619.

tions of Lyman-alpha absorption in the spectra of z ~ 6 quasars⁸ found by surveys such as SDSS indicate that reionization is completed by z ~ 5. The origin of black holes and their connection to galaxy formation is another focus of Cosmic Dawn. A spectroscopic survey of 700 nearby galaxies using the Hobby-Eberly telescope finds several galaxies with unusually massive black holes that do not follow the usual black hole mass-galaxy mass scaling relation.⁹

In the realm of new worlds, NWNH recommended a multi-pronged approach to taking a census of habitable worlds around other stars. In the past few years, several candidates for potentially habitable planets have been found both from ground-based radial velocity surveys and from NASA’s Kepler mission, including eight small planets orbiting G-type stars like the Sun.¹⁰ Another exoplanet, Kepler-186f (Figure 2.1) was inferred to be Earth-sized and orbiting within its M dwarf star’s habitable zone.¹¹ Observations with adaptive optics on Keck and speckle imaging on Gemini telescopes ruled out the possibility of a faint companion star mimicking the observed light curve dip, although Kepler observations supplemented by high-spatial-resolution speckle imaging on National Optical Astronomical Observatory’s (NOAO’s) Wisconsin-Indiana-Yale-NOAO Consortium 3.5-m telescope (WIYN) and Gemini telescopes have revealed that about half of exoplanet hosts are binary star systems.¹² Ground-based follow-up spectroscopy on telescopes throughout the U.S. OIR System to characterize stellar hosts and measure precise radial velocities remains critical for fully exploiting the data from present and future transiting planet detection missions.

The characterization of exoplanet atmospheres using transit techniques on both ground- and space-based telescopes has made substantial advances; the detection of emitted light and molecular absorption by giant planets close to their host stars has now been made in a number of systems. The recent deployment of the Gemini Planet Imager (GPI) adaptive optics (AO) system on Gemini South, SPHERE on the European Southern Observatory (ESO) VLT, Keck AO, the SEEDS¹³ project

_______________

⁸ G.D. Becker, J.S. Bolton, P. Madau, M. Pettini, E.V. Ryan-Weber, and B.P. Venemans, 2014, Evidence of patchy hydrogen reionization from an extreme Lyα trough below redshift six, Monthly Notices of the Royal Astronomical Society arXiv:1407.4850 [astro-ph.CO].

⁹ R.C.E. van den Bosch, K. Gebhardt, K. Gültekin, G. van de Ven, A. van der Wel, and J.L. Walsh, 2012, An over-massive black hole in the compact lenticular galaxy NGC 1277, Nature 491(7426):729-731.

¹⁰ NASA Exoplanet Archive, http://exoplanetarchive.ipac.caltech.edu/, accessed February 1, 2015.

¹¹ E.V. Quintana, T. Barclay, S.N. Raymond, J.F. Rowe, E. Bolmont, D.A. Caldwell, S. B. Howell, S.R. Kane, D. Huber, J. R. Crepp, and J. J. Lissauer, 2014, An Earth-sized planet in the habitable zone of a cool star, Science 344(6181):277-280.

¹² E.P. Horch, S.B. Howell, M.E. Everett, and D.R. Ciardi, 2014, Most sub-arcsecond companions of Kepler exoplanet candidate host stars are gravitationally bound, The Astrophysical Journal 795(1):60.

¹³ National Astronomical Observatory of Japan, Strategic Explorations of Exoplanets and Disks with Subaru (SEEDS) Project, http://esppro.mtk.nao.ac.jp/eng/seeds, accessed February 1, 2015.

FIGURE 2.1 Kepler 186 system, with five planets orbiting an M dwarf, compared with the solar system. Kepler 186-f lies in its star’s habitable zone. SOURCE: Courtesy of NASA/Ames/Jet Propulsion Laboratory-Caltech/T. Pyle.

on Subaru, and Large Binocular Telescope (LBT) surveys LBTI and LEECH¹⁴ are enabling direct high-contrast imaging of planets around bright stars, such as Beta Pictoris b (Figure 2.2), and will enable a census of outer planets around young stars. These OIR observations are now being complemented by Atacama Large Millimeter/submillimeter Array (ALMA), which is finding regions in the disks around young stars that likely were swept clear by newly formed planets.

Ground-based OIR surveys offer powerful probes of the physics of the universe. The Baryon Oscillation Spectroscopic Survey (BOSS) galaxy redshift survey, part of SDSS-III using the Sloan 2.5-meter telescope, has made measurements of the baryon acoustic oscillation (BAO) feature in galaxy clustering that determine the cosmic distance scale with precision at the percent level. In combination with cosmic microwave background anisotropy data from the Planck Surveyor and

_________________

¹⁴ LBTI HOST (W. Danchi, V. Bailey, G. Bryden, D. Defrère, C. Haniff, P. Hinz, G. Kennedy, B. Mennesson, R. Millan-Gabet, G. Rieke, A. Roberge, et al., 2014, The LBTI hunt for observable signatures of terrestrial systems (HOSTS) survey: A key NASA science program on the road to exoplanet imaging missions, Proceedings of the SPIE 9146, Optical and Infrared Interferometry IV, 914607); LEECH (A. Skemer, D. Apai, V. Bailey, B. Biller, M. Bonnefoy, W. Brandner, E. Buenzli, L. Close, J. Crepp, D. Defrere, S. Desidera, et al., 2013, LEECH: A 100 night exoplanet imaging survey at the LBT, Proceedings of the International Astronomical Union 8(S299):70-71) surveys.

FIGURE 2.2 Image from GPI on Gemini South of Beta Pictoris b, a planet orbiting the star Beta Pictoris (masked out in the center of the image). SOURCE: Courtesy of Gemini Observatory/Association of Universities for Research in Astronomy/Processing by Christian Marois, National Research Council Canada.

ground- and space-based measurements of Type Ia supernovae, these results place high-precision constraints on cosmological parameters. This study is being continued in the extended BOSS (eBOSS) in SDSS-IV.

In 2013, the 5-year Dark Energy Survey (DES) began operation using the Dark Energy Camera on the NOAO Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory (CTIO). A forerunner of the Large Synoptic Survey Telescope (LSST), DES will map 300 million galaxies (Figure 2.3) and measure

FIGURE 2.3 NGC 1398, a spiral galaxy in the Fornax cluster imaged with the Dark Energy Camera (DECam), is one of 300 million galaxies that will be imaged by the Dark Energy Survey. SOURCE: Courtesy of the Dark Energy Survey.

3,500 Type Ia supernovae to probe the accelerated expansion of the universe. Now in its second year, the survey has, among its initial results,¹⁵ discovered 1,000 high-redshift supernovae and scores of high-redshift galaxy clusters, made weak-lensing maps of clusters, discovered new outer solar system bodies, and discovered ultra-faint dwarf galaxies that may account for some local dark matter.¹⁶ These projects will be complemented by the Hobby-Eberly Telescope Dark Energy Experiment¹⁷ (HETDEX), which should begin taking BAO spectroscopic data of a million galaxies with a massively replicated integral field unit (IFU) system in 2015.

In the realm of solar system studies envisioned by VVPS, Keck and Gemini carried out complementary infrared (1-4 micron) studies of three successive violent

_______________

¹⁵ The Dark Energy Survey, http://www.darkenergysurvey.org, accessed February 1, 2015.

¹⁶ S.E. Koposov, V. Belokurov, G. Torrealba, and N. Wyn Evans, 2015, Beasts of the southern wild. Discovery of a large number of ultra faint satellites in the vicinity of the Magellanic clouds, submitted to The Astrophysical Journal arXiv:1503.02079 [astro-ph.GA]; and K. Bechtol, A. Drlica-Wagner, E. Balbinot, A. Pieres, J.D. Simon, B. Yanny, B. Santiago, R.H. Wechsler, J. Frieman, A.R. Walker, P. Williams, E. Rozo, E.S. Rykoff, A. Queiroz, E. Luque., et al., 2015, Eight new Milky Way companions discovered in first-year Dark Energy Survey data, submitted to The Astrophysical Journal arXiv:1503.02584 [astro-ph.GA].

¹⁷ The Hobby-Eberly Telescope Dark Energy Experiment, http://hetdex.org/, accessed February 1, 2015.

volcanic eruptions on Jupiter’s moon Io, which were more massive and frequent than previously expected. This work provides insights into Io’s thermal processes.¹⁸ The NASA Dawn mission achieved orbit around the dwarf planet Ceres in March 2015 in order to study its differentiation and composition. This study, along with Dawn’s mapping of Vesta in 2011, provides important perspectives for ground-based OIR characterizations of Kuiper Belt objects. Dynamical cloud features on Saturn, Neptune, and Uranus have been studied with adaptive optics on telescopes such as Keck, Gemini, and Subaru.¹⁹

Trans-Neptunian Objects (TNOs), which are primitive bodies that provide insight on conditions in the early solar system, have been the subject of many ground- and space-based surveys to understand their properties and distribution.²⁰ The Next Generation Virgo Cluster Survey, a high-resolution study using the MegaPrime camera on the CFHT 3.6-meter telescope, discovered nearly 100 new objects, including a very distant TNO that suggests an extensive population of more than 11,000 such objects in the inner Oort Cloud.²¹

2.2 POSITIONING THE OIR SYSTEM TO COMPLEMENT NON-OIR ASTRONOMY

OIR astronomy spans only a few octaves of the electromagnetic spectrum, but often anchors astronomy that originates at other wavelengths. It is no accident that the human eye is tuned to detect starlight. Setting aside the cosmic microwave background, most of the light in the universe is starlight, and the infrared background is largely radiation from dust heated by stars. X-ray astronomers and radio astronomers need to know what kind of optical and infrared light is associated with their sources in order to understand their nature. A growing trend in astronomical research is the synergy between observations with different telescopes and instruments in the study of astrophysical phenomena. This includes coordinated use of multiple ground-based OIR facilities with complementary capabilities, use of OIR facilities in combination with ground-based observations at other wavelengths,

_______________

¹⁸ I. de Pater, A.G. Davies, A. McGregor, C. Trujillo, M. Ádámkovics, G.J. Veeder, D.L. Matson, G. Leone, and the Gemini Io Team, 2014, Global near-IR maps from Gemini-N and Keck in 2010, with a special focus on Janus Patera and Kanehekili Fluctus, Icarus 242:379-395.

¹⁹ H.B. Hammel, M.L. Sitko, D.K. Lynch, G.S. Orton, R.W. Russell, T.R. Geballe, and I. de Pater, 2007, Distribution of ethane and methane emission on Neptune, The Astronomical Journal 134(2):637.

²⁰ E. Vilenius, C. Kiss, T. Müller, M. Mommert, P. Santos-Sanz, A. Pál, J. Stansberry, M. Mueller, N. Peixinho, E. Lellouch, S. Fornasier, et al., 2014, “TNOs are cool”: A survey of the trans-Neptunian region, Astronomy and Astrophysics 564(A35):1-18.

²¹ Y.-T. Chen, J.J. Kavelaars, S. Gwyn, L. Ferrarese, P. Côté, A. Jordán, V. Suc, J.-C. Cuillandre, and W.-H. Ip, 2013, Discovery of a new member of the inner Oort cloud from the next generation Virgo cluster survey, The Astrophysical Journal 775:L8.

and use of OIR facilities in combination with space-based facilities. In the era of LSST, this trend will expand tremendously; follow-up of objects discovered by LSST will be important at many ground- and space-based astronomical facilities in the decade of the 2020s. A ground-based OIR strategy must mesh with developments beyond the OIR spectral range. This section mentions some of the ground-based OIR capabilities that are in use now or will be needed in the future to maximize science from observations at other wavelengths. Section 4.1 addresses more details of the OIR instrumentation, with conclusions and recommendations in Chapters 4 and 5.

Radio and Submillimeter Studies

The National Radio Astronomy Observatory (NRAO) scientific staff and NRAO User Committee identified a number of OIR capabilities important to radio, millimeter, and submillimeter (RMS) studies in achieving the goals of NWNH (using an NRAO poll for this report).²² Studies of disk gaps formed by planetesimals, disk kinematics, and disk chemistry in protoplanetary disks, accretion and infall in young stellar objects, and gas-giant exoplanets all require OIR imaging capabilities with resolutions better than about 0.1 arcsecond to match the VLA and ALMA, with a field of view (FOV) of approximately 3 arcminutes. Such capabilities are important for studying galaxies too; for example, ALMA and the VLA observed a pair of gravitationally lensed merging galaxies at high redshift that were subsequently studied using Hubble Space Telescope (HST) and the Keck 10-meter with adaptive optics.²³

The infrared sensitivity to warmer material complements the radio/ submillimeter sensitivity to cold material, providing a complete picture of the constituents of these systems. Radio-variable objects identified in radio time domain surveys, such as M stars, active galactic nuclei (AGN) flares, and gamma-ray bursts (GRBs), need rapid OIR follow-up to allow identification with optical counterparts and characterization. A spectrograph with very wide wavelength coverage (from the blue end of optical light through the near-IR, like ESO’s X-shooter), giving as many diagnostics as possible in a single observation, would be ideal.

The NRAO User Committee²⁴ made two specific suggestions for augmenting Gemini South:

_________________

²² Tony Beasley, National Radio Astronomy Observatory, presentation to the committee on August 1, 2014.

²³ H. Messias, S. Dye, N. Nagar, G. Orellana, R.S. Bussmann, J. Calanog, H. Dannerbauer, H. Fu, E. Ibar, A. Inohara, R.J. Ivison, et al., 2014, Herschel-ATLAS and ALMA HATLAS J142935.3-002836, a lensed major merger at redshift 1.027, Astronomy and Astrophysics 568(A92):1-20.

²⁴ Tony Beasley, National Radio Astronomy Observatory, presentation to the committee on August 1, 2014.

1. An integral field spectrograph with an FOV of at least 1 arcminute, similar to the Denspak instrument of WIYN (no longer available), ESO’s Multi-Unit Spectroscopic Explorer (MUSE), and the Keck Cosmic Web Imager (KCWI), would enable the study of ionized emission lines in starburst galaxies and the characterization of outflows and shocks, using optical emission line tracers in concert with molecular line tracers from ALMA.
2. A high-throughput multi-object spectrograph with a 5-10 arcminute FOV, similar to the Deep Imaging Multi-Object Spectrograph (DEIMOS) on Keck, would provide characterization of the faint centimeter-wave radio source population, both in terms of its makeup (fractions of star-forming galaxies and AGNs, both radio-quiet and radio-loud) and its redshift distribution. This is particularly important for future radio surveys with, for example, the Square Kilometer Array (SKA), which seek to use radio sources for constraining cosmology through clustering and radio weak lensing. Although getting a redshift for every galaxy in a radio survey would be prohibitively expensive, an accurate redshift distribution would be very useful, both for statistical applications and for validating photometric redshifts.

X-Ray and Gamma Ray Studies

Much of the science carried out with NASA’s Chandra X-ray Observatory and the Nuclear Spectroscopic Telescope Array (NuSTAR) depends upon OIR capabilities for a wide range of complementary observations. These include direct imaging weak-lensing studies of clusters of galaxies to determine the total mass fraction of hot gas and multi-object spectroscopy to determine cluster membership. Deep IR spectroscopy will characterize high redshift and heavily obscured active galactic nuclei (AGNs) and quasars, while multi-epoch spectroscopy will constrain accretion disk models of their variability. IFU spectroscopy of nearby galaxies is needed to study winds and feedback in nearby star-forming galaxies and AGNs. The combination of X-ray observations with optical transients discovered in wide-field synoptic surveys will help discriminate among progenitor models for supernovae. As in the radio regime, wide-field multi-object spectroscopy is needed to identify and characterize sources such as AGNs and galaxy clusters found in deep X-ray surveys. These studies will be complemented by the Astro-H mission to be launched by the Japan Aerospace Exploration Agency in 2016, with NASA contributing a high-resolution soft X-ray spectrometer for measuring gas near black holes, active galaxies, and supernovae.

The European Space Agency’s (ESA’s) Athena X-ray mission, scheduled to launch in 2028, will yield high signal-to-noise spectra of AGNs and clusters of galaxies. NASA is expected to play a substantial role in Athena, and U.S. astronomers will consequently have access to Athena data. Ground-based OIR observations

needed to complement Athena will be similar to those that presently complement Chandra. Conversely, Athena has a goal of a 2-hour response to targets of opportunity, many of which might be expected to come from LSST.

Gamma ray bursts detected by NASA’s Swift and Fermi satellites require contemporaneous OIR imaging and spectroscopy to elucidate the connection between GRBs and supernovae. A gamma-ray flare in the Crab Nebula was followed up with the VLA, Keck Observatory, and Chandra X-ray observations to study details of the synchrotron emission associated with the nebula (see Figure 2.4).²⁵ Gamma-ray emission from novae and recurrent novae, discovered with Fermi²⁶ and studied with Swift, also require OIR follow-up observations.

There does not appear to be an outstanding unmet need for a specific ground-based OIR capability to complement present X-ray and gamma-ray missions, nor would planned missions appear to require more than the generic capabilities likely to be implemented over the course of the next decade.

Gravitational Wave Studies

Gravitational waves are perturbations in spacetime caused by accelerating masses, just as electromagnetic waves are emitted by accelerating charges. The first science data from the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) is expected in 2015. LIGO will work in concert with the Virgo interferometer in Italy. There are two approaches to ground-based OIR cross-identification. The first involves prompt searches with wide-field telescopes for LIGO-triggered events. Subsequent spectroscopic follow-up would be similar to GRB and supernova follow-up. The second involves optical triggering, with regular monitoring (at least nightly, perhaps more often) of the 5,000 or so nearest galaxies, which are the ones most likely to harbor detectable events. This would probably require facilities much like those of the Las Cumbres Observatory Global Telescope (LCOGT) network. Such monitoring would permit the post hoc search of LIGO data for optically triggered events.²⁷

_______________

²⁵ M.C. Weisskopf, A.F. Tennant, J. Arons, R. Blandford, R. Buehler, P. Caraveo, C.C. Cheung, E. Costa, A. De Luca, C. Farrigno, H. Fu, et al., 2013, Chandra, Keck, and VLA observations of the Crab Nebula during the 2011 April gamma-ray flare, The Astrophysical Journal 765(1):56.

²⁶ M. Ackermann, M. Ajello, A. Albert, L. Baldini, J. Ballet, G. Barbiellini, D. Bastieri, R. Bellazzini, E. Bissaldi, R.D. Blandford, E.D. Bloom, et al., 2014, Fermi establishes a classical novae as a distinct class of gamma-ray sources, Science 345(6196):554-558.

²⁷ L.P. Singer, L.R. Price, B. Farr, A.L. Urban, C. Pankow, S. Vitale, J. Veitch, W.M. Farr, C. Hanna, K. Cannon, T. Downes, et al., 2014, The first two years of electromagnetic follow-up with advanced LIGO and Virgo, The Astrophysical Journal 795(2):105.

FIGURE 2.4 The Crab Nebula, shown as a composite with images from the Chandra X-ray satellite (blue), Spitzer Space Telescope (red), and Hubble Space Telescope (green). SOURCE: Courtesy of NASA/Jet Propulsion Laboratory-Caltech/European Space Agency/Chandra X-ray Center/University of Arizona/University of Szeged.

Technology for a future ESA space mission to detect gravitational waves will be tested with a planned launch of the LISA Pathfinder (named after a previously planned mission, the Laser Interferometer Space Antenna) in 2015. As an example of gravitational waves that might be detected, a recent study using the Gemini multi-object spectrograph (GMOS) on Gemini North and the Blue Channel spectrograph on the MMT (formerly the Multiple Mirror Telescope) found that what was thought for the past 30 years to be a binary system consisting of a white dwarf and an

M dwarf instead was a white dwarf binary system.²⁸ These white dwarf binary stars are spiraling inward and should eventually merge, producing gravitational waves.

2.3 FUTURE SYNERGIES BETWEEN GROUND-BASED AND SPACE-BASED OIR FACILITIES

Powerful science comes from combining space-based observations with data from the OIR System. This combination has proved profoundly productive—sensitive imaging from unique instruments in space combined with imaging surveys and spectra from large telescopes on the ground has revealed the nature of faint objects both near (such as field brown dwarfs) and far (such as supernovae to trace the history of cosmic expansion). In the 1990s, the Hubble Space Telescope (HST), along with Keck, the Hobby-Eberly Telescope, Gemini, Magellan, and other large ground-based telescopes worked effectively to exploit these opportunities. In the 2020s, the James Webb Space Telescope (JWST) along with LSST and other large telescopes and the Giant Segmented Mirror Telescopes will combine to solve a new set of cosmic mysteries.

Gaia

One space observatory that will provide a rich source of scientific opportunities is the ESA satellite Gaia, launched in 2013. By the end of its mission, Gaia will have imaged a billion stars 70 times each to measure their brightnesses, colors, parallaxes, and motions. Gaia will determine the positions of stars brighter than 15th magnitude to 40 microarcseconds; this will provide parallax distances with 10 percent precision to almost 100 million stars in the Milky Way. European colleagues are already using ESO facilities to follow up 100,000 stars that represent various Milky Way populations.²⁹ Some of these will be individual targets, while others will need observations over wide fields to study clusters and coherent kinematic structures. Gaia has begun to report discoveries of transients, including supernovae, which demand prompt OIR follow-up spectroscopy.

_______________

²⁸ M. Kilic, W.R. Brown, A. Gianninas, J.J. Hermes, C.A. Prieto, and S.J. Kenyon, 2014, A new gravitational wave verification source, Monthly Notices Letters of the Royal Astronomical Society 444(1):L1-L5.

²⁹ G. Gilmore, S. Randich, M. Asplund, J. Binney, P. Bonifacio, J. Drew, S. Feltzing, A. Ferguson, R. Jeffries, G. Micela, I. Negueruela, et al., 2012, The Gaia-ESO public spectroscopic survey, The Messenger 147:25.

TESS

Another mission that will have rich interactions with ground-based OIR facilities is NASA’s Transiting Exoplanet Survey Satellite (TESS). This Explorer-class mission is scheduled for launch in 2017. The principal goal of the TESS mission is to detect small planets with bright host stars in the solar neighborhood. TESS stars will be 30-100 times brighter than those surveyed by the Kepler satellite, so TESS planets should be far easier to characterize with follow-up observations. These follow-up observations, with JWST and with large ground-based telescopes, will provide refined measurements of the planets’ masses, sizes, densities, and atmospheric properties. NASA is already planning a new precision radial velocity instrument for the WIYN 3.5-meter telescope as well as continued access to the much larger Keck telescope. The legacy of TESS will be a catalog of the nearest and brightest stars that host transiting exoplanets, which should be excellent targets for detailed investigations in the coming decades. The Kepler 2 mission of the Kepler spacecraft is providing a preview of TESS science and generating planet candidates along the ecliptic plane.

JWST

NASA’s upcoming flagship astrophysics mission in space is JWST. This observatory will have a 6.5-meter aperture and will have passive cooling of the optics to a temperature of 39 K behind a large sunshield. An ambitious set of instruments using infrared array detectors will provide unprecedented sensitivity in the near- and mid-IR at the diffraction limit of about 0.1 arcsecond. The JWST project is working to a 2018 launch date. The scientific program of JWST will be exceptionally broad, and, like HST, it will open up a cornucopia of rewarding follow-up with complementary facilities on the ground, especially with the most sensitive OIR instruments. As noted in VVPS, JWST will be important for near- and mid-IR imaging and spectroscopy of solar system planets, particularly Neptune and Saturn, as well as smaller bodies such as comets and Kuiper Belt objects, and will complement several NASA planetary missions. NWNH highlights science priorities across astrophysics fields from protoplanetary and circumstellar disks and exoplanet atmospheres and surfaces, to star formation and galaxy evolution, to the early universe that will require JWST for near- and mid-IR imaging and spectroscopy. Science returns from JWST will be enhanced through complementary ground-based observations on large and giant telescopes in addition to LSST.

WFIRST

After JWST, NASA plans to focus on the Wide-Field Infrared Survey Telescope (WFIRST), the mission endorsed by NWNH as the top-ranked, large-scale, space-based priority for the coming decade. Assuming a 2017 start for WFIRST, the telescope could be operating in 2024. The present design takes advantage of a 2.4-meter telescope assembly that was built for another government agency but that has been transferred to NASA for this use. The main instrument is a wide-field detector array in the near-IR that can be used to obtain images and spectra. This mission will conduct a wide-field survey enabling a wide range of science, including investigations of dark energy using supernovae, weak lensing, and clusters of galaxies. Exoplanets will be detected by gravitational microlensing signals and probably directly imaged with a coronagraph. In addition, there will be a guest investigator program.

One interesting aspect of the planned work is that the WFIRST observations will overlap significantly with the areas studied by LSST. This overlap will provide the opportunity to use the optical data from the ground in conjunction with the near-IR for more reliable measurements of galaxy redshifts as well as enabling sophisticated reanalysis of the LSST data informed by the superior resolution of the space-based data. It also creates the possibility for WFIRST follow-up studies of transient events discovered from the ground.

Euclid

ESA aims to launch Euclid, an M-class (medium-scale) mission, in 2020. Its science mission is to probe dark matter and dark energy by mapping cosmic structure through weak gravitational lensing using optical imaging complementary to the near-IR imaging of WFIRST. Euclid will also obtain near-IR spectroscopy and photometry and study baryon acoustic oscillations in the near-IR using detectors provided by NASA. Like WFIRST, Euclid will be synergistic with LSST through observations of large-scale structure and variable sources.