Request for Information (RFI) Responses

RFI Response Abstracts

1. Theodore Gull, "How do molecules and dust form in massive interacting winds?"
   How do molecules and dust form in massive interacting winds? One of the mysteries of interstellar dust is how it forms. While prodigious amounts of dust are seen in the interstellar medium, most models assume a dust core and then proceed to build a mantle of condensed molecules around this core. This science objective tries to understand how molecules and dust cores form in massive winds. At high redshifts, evidence is that metal enrichment and dust occurred early after the first stars formed. We simply do not understand how the dust cores form in stellar atmospheres, enriched by carbon and oxygen the basic building blocks for many molecules. Yet molecular and dust formation is so robust that both form even in stars with greatly depleted amounts of carbon and oxygen, as exemplified by Eta Carinae. Massive stars, that evolved rapidly, must play a dominant role in chemical enrichment early in the Universe. By studying current day systems, we can gain insight on the earliest mixing in young galaxies.
2. Judith Provencal, "The Importance of White Dwarf Stars as Tests of Stellar Physics and Galactic Evolution"
   White dwarfs are rich forensic laboratories that provide links between the history and future evolution of the Milky Way Galaxy. The structure and composition of white dwarfs contain the records of the final stages of stellar evolution. As a newly forming white dwarf evolves through the planetary nebula phase, large quantities of processed material are injected into the interstellar medium. The chemical evolution of the Galaxy is traced through subsequent generations of stars formed from this contaminated material. The distribution of Milky Way white dwarfs in temperature constrains models of galactic and cosmological evolutionary history. Type I supernovae, in which an accreting white dwarf undergoes a thermonuclear event, are used as distance indicators demonstrating the acceleration of the universe. Underlying all these studies is the theoretical mass-radius relation for electron degenerate matter, an important consequence of which is the existence of an upper mass limit for white dwarf stars. The ultraviolet waveband is particularly important for the study of these objects. A significant fraction of white dwarf emergent flux appears in the UV, especially for the hotter stars. In addition, traces of elements heavier than hydrogen or helium are, in general, only detected in this waveband or at shorter wavelengths that are also only accessible from space. We broadly outline the importance of:
   

   1. the white dwarf mass-radius relation
   2. the white dwarf luminosity function
   3. white dwarf spectroscopy

   in understanding important cosmological questions, including questions of stellar physics in extreme conditions, galactic evolution, stellar formation and evolution, and the chemical distribution of material in our galaxy."
3. James Lawler, "The Origin of the Elements Heavier than Iron"
   Understanding the origin of the elements is one of the major challenges of modern astrophysics. This goal is expressed in several of the Cosmic Origins science questions, including how the first stars influenced their environments, how the chemical elements were dispersed through the circumgalactic medium, how galaxies and their constituent stars formed and evolved, and how baryons destined to form planets grow to heavy atoms.
4. Coralie Neiner, "UVMag: Stellar physics with UV and visible spectropolarimetry"
   We propose to study the formation, structure, evolution and environment of all types of stars in particular through the measurement of their magnetospheres, i.e., through the association of spectropolarimetry and spectroscopy in the UV and visible domains.
5. Richard Ignace, "Response to Request for Information: NNH12ZDA008L"
   This response to the RFI will emphasize the importance of times series studies and polarimetric capability for future NASA missions. The issue of "structure" in winds and disks has become of central importance of late. The clumping aspects of stellar winds has proven to be critical for obtaining better mass loss rates of massive stars, with consequences for understanding both stellar and galactic evolution. Magnetism of massive stars has matured greatly as a subfield. Detections are now regularly reported, and there have been significant successes from theory in explaining a number of phenomena associated with rotating magnetospheres and stellar winds (although it is clear that there is much work remaining). Although the ability to obtain spectral energy distributions or high quality line profiles are and will continue to be important, another "style" of observing that has proven to be of immense scientific value and highly productive has been time series studies.
6. Kenneth Carpenter, "Mass Transport Processes and their Roles in the Formation, Structure, and Evolution of Stars and Stellar Systems"
   Understanding the formation, structure, and evolution of stars and stellar systems remains one of the most basic pursuits of astronomical science, and is a prerequisite to obtaining an understanding of the Universe as a whole. The evolution of structure and transport of matter within, from, and between stars are controlled by dynamic processes, such as variable magnetic fields, accretion, convection, shocks, pulsations, and winds. Future long-baseline (0.5-1.0 km) observatories (i.e., space-based interferometers and sparse aperture telescopes) will achieve resolutions of 0.1 milli-arcsec (mas), a gain in spatial resolution comparable to the leap from Galileo to HST. As a result, spectral imaging observations from such facilities will enable a quantum leap in our understanding of stars and stellar systems. In this whitepaper, we discuss the compelling new scientific opportunities for understanding the formation, structure, and evolution of stars and stellar systems that can be enabled by dramatic increases in UV-Optical angular resolution to the sub-mas level. An Ultraviolet-Optical Interferometer (UVOI) with apertures on that order would provide direct spectral imaging of spatial structures and dynamical processes in the various stages of stellar evolution for a broad range of stellar types.
7. Paul Scowen, "Understanding Global Galactic Star Formation"
   We propose to the community a comprehensive UV/optical/NIR imaging survey of Galactic star formation regions to probe all aspects of the star formation process, a listed key question in the Cosmic Origins science goals: what are the mechanisms by which stars and their planetary systems form? The primary goal of such a study is to understand the evolution of circumstellar protoplanetary disks and other detailed aspects of star formation in a wide variety of different environments. This goal requires a comprehensive emission-line survey of nearby star-forming regions in the Milky Way, where a high spatial resolution telescope+camera will be capable of resolving circumstellar material and shock structures. In addition to resolving circumstellar disks themselves, such observations will study shocks in the jets and outflows from young stars, which are probes of accretion in the youngest protoplanetary disks still embedded in their surrounding molecular clouds. These data will allow the measurement of proper motions for a large sample of stars and jets/shocks in massive star-forming regions for the first time, opening a new window to study the dynamics of these environments. It will require better than 30 mas resolution and a stable PSF to conduct precision astrometry and photometry of stars and nebulae. Such data will allow production of precise color-color and color-magnitude diagrams for millions of young stars to study their evolutionary states, while also providing stellar rotation, multiplicity, and clustering statistics as functions of environment and location in the Galaxy. For the first time, one would be able to systematically map the detailed excitation structure of HII regions, stellar winds, supernova remnants, and supershells/superbubbles. This survey will provide the basic data required to understand star formation as a fundamental astrophysical process that controls the evolution of the baryonic contents of the Universe.
8. Paul Scowen, "The Magellanic Clouds Survey—a Bridge to Nearby Galaxies"
   To address several key Cosmic Origins program science questions, such as 1) "How are chemical elements distributed in galaxies and dispersed into the circumgalactic and intergalactic medium" and 2) "how does baryonic matter flow from the intergalactic medium to galaxies and ultimately into planets", we outline to the community the value of a three-phase Magellanic Clouds Survey. This survey consists of three components: I) a complete-area, high resolution, multi-band UV-near-IR broadband survey; II) a narrowband survey in 7 key nebular filters to cover a statistically significant sample of representative HII regions and a large-area, contiguous survey of the diffuse, warm ISM; and III) a comprehensive FUV spectroscopic survey of 1300 early-type stars. The science areas enabled by such a dataset are as follows: A) assessment of massive star feedback in both HII regions and the diffuse, warm ISM; B) completion of a comprehensive study of the 30 Doradus giant extragalactic HII region (GEHR); C) development and quantitative parameterization of stellar clustering properties; D) extensive FUV studies of early-type stellar atmospheres and their energy distributions; and E) similarly extensive FUV absorption-line studies of molecular cloud structure and ISM extinction properties.
9. Aida Wofford, "Massive Stars: Key to Solving the Cosmic Puzzle"
   We describe observations in the nearby universe (<100 Mpc) with a ≥ 10-m spacebased telescope having imaging and spectral capabilities in the range 912–9000 Å that would enable advances in the fields of massive stars, young populations, and star-forming galaxies, that are essential for achieving the Cosmic Origins Program objectives i) how are the chemical elements distributed in galaxies and dispersed in the circumgalactic and intergalactic medium; and ii) when did the first stars in the universe form, and how did they influence their environments. We stress the importance of observing hundreds of massive stars and their descendants individually, which will make it possible to separate the many competing factors that influence the observed properties of these systems (mass, composition, convection, mass-loss, rotation rate, binarity, magnetic fields, and cluster mass).
10. Martin Barstow, "Conditions for Life in the Local Universe"
    This response to the RFI addresses the "local" aspect of the cosmic feedback and flow of baryons to support life, assuming that other elements will be considered in complementary submissions.
11. Thomas Brown, "The History of Star Formation in Galaxies"
    If we are to develop a comprehensive and predictive theory of galaxy formation and evolution, it is essential that we obtain an accurate assessment of how and when galaxies assemble their stellar populations, and how this assembly varies with environment. There is strong observational support for the hierarchical assembly of galaxies, but our insight into this assembly comes from sifting through the resolved field populations of the surviving galaxies we see today, in order to reconstruct their star formation histories, chemical evolution, and kinematics. To obtain the detailed distribution of stellar ages and metallicities over the entire life of a galaxy, one needs multi-band photometry reaching solar-luminosity main sequence stars. The Hubble Space Telescope can obtain such data in the low-density regions of Local Group galaxies. To perform these essential studies for a fair sample of the Local Universe, we will require observational capabilities that allow us to extend the study of resolved stellar populations to much larger galaxy samples that span the full range of galaxy morphologies, while also enabling the study of the more crowded regions of relatively nearby galaxies. With such capabilities in hand, we will reveal the detailed history of star formation and chemical evolution in the universe.
12. Paul Goudfrooij, "Space-Based UV/Optical Wide-Field Imaging and Spectroscopy: Near-Field Cosmology and Galaxy Evolution Using Globular Clusters in Nearby Galaxies"
    Star formation plays a central role in the evolution of galaxies and of the Universe as a whole. Studies of star-forming regions in the local universe have shown that star formation typically occurs in a clustered fashion. Building a coherent picture of how star clusters form and evolve is therefore critical to our overall understanding of the star formation process. Most clusters disrupt after they form, thus contributing to the field star population. However, the most massive and dense clusters remain bound and survive for a Hubble time. These globular clusters provide unique observational probes of the formation history of their host galaxies. In particular, the age and metallicity can be determined for each globular cluster individually, allowing the distribution of ages and metallicities within host galaxies to be constrained. We show how space-based UV-to-Near-IR imaging covering a wide field of view ( >≅20' per axis) and deep UV/Optical multi-object spectroscopy of globular cluster systems in nearby galaxies would allow one to place important new constraints on the formation history of early-type galaxies and their structural subcomponents (e.g., bulge, halo).
13. Benjamin Williams, "The Crucial Role of High Spatial Resolution, High Sensitivity UV Observations to Galaxy Evolution Studies"
    Models of galaxy formation and evolution are only as reliable as our knowledge of the individual stars responsible for the light we detect. From the prescriptions for stellar feedback, to numerical simulations, to the interpretation of galaxy colors and spectra, galaxy evolution research depends at its core on reliable star formation and evolution models. These models are calibrated using observations of resolved stellar populations in a wide range of environments. Studies of stellar populations in the UV have made great strides in the past decade with the GALEX UV surveys and the UV-sensitive WFC3 camera on HST. With the phenomenal data that these instruments have provided, we have learned surprising UV properties of the stellar populations of galaxies and star clusters. While these observations have certainly shed light on the evolution of stars and star clusters, the picture is still far from complete. To fully understand the processes that shape star formation of clusters and OB associations in galaxies with a range of masses, metallicities, and gas content will require the next generation of UV telescopes and instrumentation. To make significant progress, goals for this future instrumentation will need to include improved spatial resolution to resolve individual stars in crowded extragalactic environments and a larger field of view to cover nearby galaxies with fewer pointings. Future observations will then be able to produce the required libraries of resolved stars in carefully selected UV bands to reveal the physical properties of the stars and properly making the necessary observations.
14. Karl Gordon, "A Census of Local Group Ultraviolet Dust Extinction Curves"
    Interstellar dust plays a central role in shaping the detailed structure of the interstellar medium, thus strongly influencing star formation and galaxy evolution. Ultraviolet extinction curves provide one of the main pillars of our understanding of interstellar dust while also being one of the limiting factors when interpreting observations of distant galaxies. Our observational picture of extinction curves is strongly biased to nearby regions in the Milky Way. However, the few extinction curves measured in the Magellanic Clouds show curves that are quite different from those seen in the Milky Way. We propose an observational program to obtain a census of ultraviolet dust extinction curves in the Local Group by measuring large, statistically significant samples of extinction curves in each Local Group galaxy. This program requires sensitive medium-band UV and blue-optical imaging and followup R~1000 spectroscopy of 1000s of sources. This census will, for the first time, provide a full census of dust and its variation with environment and galaxy type. It would simultaneously generate one of the largest ultraviolet spectral libraries ideal for a range of hot star studies. Such a census will revolutionize our understanding of the dependence of dust properties on local environment providing both an empirical description as well as strong constraints on dust grain and evolution models.
15. Michael Shull, "The Baryon Census in a Multiphase Intergalactic Medium"
    In this white paper, we summarize the current observations of the baryon census at low redshift (Shull, Smith, & Danforth 2012). We then suggest improvements in measuring the baryons in major components of the IGM and CGM with future UV and X-ray spectroscopic missions that could find and map the missing baryons, the fuel for the formation and chemical evolution of galaxies.
16. Todd Tripp, "Quasar Absorption Lines in the Far Ultraviolet: An Untapped Gold Mine for Galaxy Evolution Studies"
    Most of the baryons are exceedingly difficulty to observe, at all epochs. Theoretically, we expect that the majority of the baryonic matter is located in low-density, highly ionized gaseous envelopes of galaxies—the "circumgalactic medium"—and in the highly ionized intergalactic medium. Interactions with the CGM and IGM are thought to play crucial roles in galaxy evolution through accretion, which provides the necessary fuel to sustain on-going star formation, and through feedback-driven outflows and dynamical gas-stripping processes, which truncate and regulate star formation as required in various contexts (e.g., low- mass vs. high-mass galaxies; cluster vs. field). Due to the low density and highly ionized condition of these gases, quasar absorption lines in the rest-frame ultraviolet and X-ray regimes provide the most efficient observational probes of the CGM and IGM, but ultraviolet spectrographs offer vastly higher spectral resolution and sensitivity than X-ray instruments, and there are many more suitable targets in the UV, which enables carefully designed studies of samples of particular classes of objects. This white paper emphasizes the potential of QSO absorption lines in the rest-frame far/extreme UV at 500 <≅ λ_rest <≅ 2000 Å. In this wavelength range, species such as Ne VIII, Na IX, and Mg X can be detected, providing diagnostics of gas with temperatures >>10⁶ K, as well as banks of adjacent ions such as O I, O II, O III, O IV, O V, and O VI (and similarly N I – N V; S II – S VI; Ne II – Ne VIII, etc.), which constrain physical conditions with unprecedented precision. A UV spectrograph with good sensitivity down to observed wavelengths of 1000 Å can detect these new species in absorption systems with redshift z_abs >≅ 0.3, and at these redshifts, the detailed relationships between the absorbers and nearby galaxies and large-scale environment can be studied from the ground. By observing QSOs at z = 1.0–1.5, HST has started to exploit extreme-UV QSO absorption lines, but HST can only reach a small number of these targets. A future, more sensitive UV spectrograph could open up this new discovery space.
17. Ana Gomez de Castro, "Seeking into the anthropic principle"
    The anthropic principle is about the emergence of life, of complex and intelligent life. For that, nucleosynthesis needs to have proceeded to enrich significantly the interstellar medium and guarantee that carbon, nitrogen, oxygen and phosphor are widespread in the Universe. Studies of the metal abundance variation up to redshift 5 are showing that the metallicity increases steadily with the age of the Universe. However there are numerous evidences of a large scatter in the metallic properties of matter for any given z; non metal-enriched clouds have been detected and chemically processed material has been found in the voids of the Comic Web. Meanwhile, the star formation rate seems, to be decaying from z=1. Important clues on the metal enrichment spreading on the Universe hang on inter-galactic transport processes such as galactic winds or the effect of galactic interaction in halos that are poorly studied because of the lack of high sensitivity imaging capabilities to detect the warm/hot plasma emission from galactic halos. Current information comes from absorption spectroscopy that it is a rather inefficient technique to map the large scales involved and requires the presence of strong background sources. Moreover, most of the emission is expected to come from filaments and chimneys that will require a high sensitivity imaging capability with resolutions at least ten times better than those provided by the GALEX mission.
18. Claudia Scarlata, "The escape fraction of ionizing photons from dwarf galaxies"
    Measuring the escape fraction of ionizing photons from galaxies is a crucial step in understanding the reionization of the Universe, a central question in the COR program. We highlight how this goal can be achieved with deep imaging down to 2000Å (reaching NUV~32, i.e., about 10 times deeper than the currently deepest HST observations), over a large field of view (a few times Hubble's WFC3). We also briefly discuss the importance of deep spectroscopy in the NUV, to understand the mechanisms that allow the escape of ionizing radiation and to constrain the line-of-sight specific IGM absorption.
19. David Schiminovich, "Science from IGM/CGM Emission Mapping"
    How does baryonic matter collapse, cool, form and fuel galaxies over cosmic time?" While the road to this answer may be tortuous, IGM emission mapping will provide a new perspective that could lead to fundamental breakthroughs by addressing these questions:
    

    1. How strong is IGM emission, what is its relationship with absorption, and can emission mapping offer a new and powerful cosmological tool?
    2. What is the total baryon content of the dark matter halos hosting galaxies in a 10⁴–10⁶K phase, and how does this gas content vary with redshift, galaxy type, evolutionary stage, and halo mass and environment?
    3. How much CGM gas is inflowing to the galaxies, outflowing due to winds or AGN, replenished by inflow from the IGM? Do these gas flows regulate SF history, or are they regulated by star formation?
20. Stephan McCandliss, "Project Lyman: Quantifying 11 Gyrs of Metagalactic Ionizing Background Evolution"
    The timing and duration of the reionization epoch is crucial to the emergence and evolution of structure in the universe. The relative roles that star-forming galaxies, active galactic nuclei and quasars play in contributing to the metagalactic ionizing background across cosmic time remains uncertain. Deep quasar counts provide insights into their role, but the potentially crucial contribution from star-formation is highly uncertain due to our poor understanding of the processes that allow ionizing radiation to escape into the intergalactic medium (IGM). The fraction of ionizing photons that escape from star-forming galaxies is a fundamental free parameter used in models to "fine-tune" the timing and duration of the reionization epoch that occurred somewhere between 13.4 and 12.7 Gyrs ago (redshifts between 12 > z > 6). However, direct observation of Lyman continuum (LyC) photons emitted below the rest frame H I ionization edge at 912 Å is increasingly improbable at redshifts z > 3, due to the steady increase of intervening Lyman limit systems towards high z. Thus UV and U-band optical bandpasses provide the only hope for direct, up close and in depth, observations of the types of environment that favor LyC escape. By quantifying the evolution over the past 11 billion years (z < 3) of the relationships between LyC escape and local and global parameters such as: metallicity, gas fraction, dust content, star formation history, mass, luminosity, redshift, over-density and quasar proximity, we can provide definitive information on the LyC escape fraction that is so crucial to answering the question of, how did the universe come to be ionized? Here we provide estimates of the ionizing continuum flux emitted by "characteristic" (L*uv) star-forming galaxies as a function of look back time and escape fraction, finding that at z = 1 (7.6 Gyrs ago) L*uv galaxies with an escape fraction of 1% have a flux of 10^-19 ergs cm^-2 s^-1 Å^-1.
21. Gerard Kriss, "Synergistic Astrophysics in the Ultraviolet using Active Galactic Nuclei"
    Observing programs comprising multiple scientific objectives will enhance the productivity of NAS' s next UV/Visible mission. Studying active galactic nuclei (AGN) is intrinsically important for understanding how black holes accrete matter, grow through cosmic time, and influence their host galaxies. At the same time, the bright UV continuum of AGN serves as an ideal background light source for studying foreground gas in the intergalactic medium (IGM), the circumgalactic medium (CGM) of individual galaxies, and the interstellar medium (ISM) and halo of the Milky Way. A well chosen sample of AGN can serve as the observational backbone for multiple spectroscopic investigations including quantitative measurements of outflows from AGN, the structure of their accretion disks, and the mass of the central black hole.
22. Steven Kraemer, "Active Galactic Nuclei and their role in Galaxy Formation and Evolution"
    Nuclear super-massive black holes (SMBH) seem to be a fundamental constituent of galaxies. Their growth as active galactic nuclei (AGN) produces a significant fraction of the luminosity in the universe. Moreover, the masses of galactic bulges and SMBHs appear to correlated, which suggests the importance of the AGN in galaxy evolution (e.g., via AGN feedback). However, we face a basic limitation. AGN have been the archetypical "point sources" for 50 years: no spatial structure has been resolved in the inner regions in which the winds and jets involved in feedback processes arise. Space-based UV/optical interferometry is the only technologically feasible means to probe these inner regions.
23. Bradley Peterson, "UV Spectroscopic Time Domain Studies of Active Galactic Nuclei"
    "Reverberation mapping" (Blandford & McKee 1982; Peterson 1993) is a spectroscopic time-domain technique that can be used to determine the structure and dynamics of the broad-line region (BLR) of AGNs. Reverberation mapping can provide us (a) with insights into mass outflows and mass accretion on microarcsecond scales, too small to be resolved by any other direct method, and (b) a means to directly measure the masses of the central black holes in these objects. Moreover, secondary methods anchored by reverberation mapping results allow us to estimate masses in active nuclei to arbitrarily large cosmic distances, addressing the Cosmic Origins goals of determining when supermassive black holes form and how have they affected the evolution of galaxies in which they are found. Indeed, all black hole mass estimates beyond the local universe are based on scaling relationships anchored by reverberation. In addition, the luminosities of AGNs can be inferred by BLR sizes determined by reverberation mapping, providing a direct measure of luminosity distances to quasars and allowing determination of cosmological parameters at redshifts as high as z = 3 or more.
24. Matthew Hayes, "Extragalactic Lyman-alpha Experiments in the Nearby Universe"
    The universe has been statistically studied in the Hi Lyman-alpha emission line only at redshifts (z) above 2. Thus despite living in a universe where Ly-α is the brightest spectral feature of the most abundant species of baryonic matter, 75 per cent of our cosmic history is left unexplored. Here we outline the scientific case and approximate requirements for a space-based UV facility that could efficiently cover the remainder. Ly-α is the most important spectral beacon in high-z astrophysics, where studies of galaxy formation, the cosmic web, and the epoch of reionization all rely upon Ly-α population statistics. The unbiased assembly and study of a large sample of Ly-galaxies at low and moderate redshifts is the only method through which we can truly rely upon Ly-α as cosmological diagnostic tool. Simultaneously such observations would enable unprecedented studies of galaxy evolution and massive star formation across the latter 3/4 of cosmic time. A new UV-optimized mission with spectroscopic (R ~ 10,000) and spectrophotometric capabilities at λ = 1200–3500Å is the only way that these goals can be realized. We therefore strongly recommend the inclusion of these capabilities in a future facility, and we are willing and able to contribute more detailed goals, requirements, and specifications and realistic simulations.
25. Paul Scowen, "Galaxy Assembly and SMBH/AGN-growth from Cosmic Dawn to the End of Reionization"
    In order to address the key Cosmic Origins science question "How did galaxies evolve from the very first systems to the types we observe nearby?", we propose to the community a systematic and comprehensive UV-near-IR cosmological broad- and medium-band imaging and grism survey that covers a wide area on the sky in multiple epochs. Specifically we advocate a tiered survey that covers ~10 deg² in two epochs to m_AB ~28 mag, ~3 deg² in seven epochs to m_AB ~29 mag, and ~ 1 deg² in 20 epochs to m_AB ~30 mag, each at 10σ point source sensitivity. Such a survey would provide spectrophotometric redshifts accurate to σ_z/(1 + z) <≅ 0.02 and faint source variability measurements for >≅ 5 × 10⁶ galaxies and QSOs, and would be an essential complement to JWST surveys (<≅ 0.1 deg² to m_AB <≅ 31mag at λ >1100 nm). This rich data set would allow: (1) study of faint Lyα-emitting and Lyman-break galaxies at 5.5 <≅ z <≅ 8 to understand how galaxies formed from primordial density perturbations and to trace the metal enrichment of the intergalactic medium (IGM); (2) measuring the evolution of the faint end of the galaxy luminosity function (LF) from z ~ 8 to z ~ 0 by mapping the ramp-up of Pop II star formation, (dwarf) galaxy formation and assembly, and hence, the objects that likely completed the Hydrogen reionization by z ≅ 6; (3) direct study of the λ < 91.2 nm escape fractions of galaxies and weak AGN from z ~ 4.0–2.5, during the epoch of Helium reionization; (4) measuring the mass and environment-dependent galaxy assembly process for >≅ 5 × 10⁶ galaxies from z ≅ 5 to z ≅ 0; (5) tracing the strongly epoch-dependent galaxy merger rate and constraining how Dark Energy affected galaxy assembly and the growth of super-massive black holes (SMBHs); (6) the study of >≅ 10⁵ weak AGN, including faint variable objects (feeding SMBHs in the faint end of the QSO LF), over 10 deg² to measure how SMBH growth kept pace with galaxy assembly and spheroid growth, and how this process was shaped by various feedback processes over cosmic time. The proposed study is not feasible with current instrumentation but argues for a wide-field (>≅ 250 arcmin²), high resolution (<≅0″.1), UV-near-IR imaging facility on a 2.4–4m class space-based observatory.
26. Sara Heap, "A UV/Optical/Near-IR Spectroscopic Sky Survey for Understanding Galaxy Evolution"
    We outline the scientific benefits of a very large UV/Optical/near-IR spectroscopic survey for understanding the evolution of galaxies, circumgalactic medium, and intergalactic medium in the era of galaxy assembly (z > 1).
27. Olivier Doré, "An Optical and Ultraviolet Cosmological Mapper"
    Working in the "intensity mapping regime"—large scale, low spatial resolution, moderate spectral resolution—optical and UV surveys offer a potentially very powerful, yet economical, avenue to map cosmological scales. The idea consists in mapping the aggregated line emission of many galaxies in a given frequency/redshift range rather than the emission of individual galaxies. To not aim at resolving individual galaxies naturally allows the use of a smaller telescope and also increases the signal strength, thus decreasing sensitivity requirements.
28. Charley Noecker, "Exoplanet Science of Nearby Stars on a UV/Visible Astrophysics Mission"
    Direct imaging of nearby planetary systems will enable three broad science areas: (1) detection of individual exoplanets; (2) spectral characterization of those exoplanets, including searching for signs of life; and (3) investigation of the origin and ultimate fate of planetary systems. 1) The detection of individual exoplanets requires a high contrast imaging capability (e.g. internal coronagraph or external starshade), and can be accomplished with only a few snapshot images of the area around a star. 2) The spectral characterization of individual exoplanets begins with a longer observation for modest resolution spectroscopy (λ/δλ ~ 70–100), and should be followed by observations over a time span approaching or exceeding an orbital period, to obtain position, photometry, and spectroscopy as a function of time. 3) The investigation of the origin and evolution of planetary systems combines the information from the detection and characterization phases with our experience with the thousands of planets and candidates in the Corot, Kepler, RV, and gravitational microlensing surveys, and our knowledge of the specific planet-disk and planet-planet orbital interactions that are implied from many of the precise timing events from Kepler.
29. Timothy Cook, "Ultraviolet imaging of exoplanets"
    Direct exoplanet observations are nominally the province of the EXOPAG and are thus beyond the scope of this RFI. However, the authors feel that given the synergy between exoplanet observations in general, and direct ultraviolet imaging of exoplanets in particular, and ultraviolet astrophysics that this response is warranted. The study of extrasolar planets is one of the most exciting endeavors of modern science. The statistics are familiar and impressive. To date over 750 planets have discovered in about 600 planetary systems—and that is not counting the thousands of Kepler planet candidates awaiting confirmation. The advent of high quality ultraviolet transiting observations and possibly more, better, ultraviolet observations in the future go a long way to furthering our understanding of the diverse properties of exoplanetary atmospheres. They have given us information about the composition, ionization, and dynamics (including the rates of atmospheric escape) of the atmospheres of a few planets.
30. Kevin France, "From Protoplanetary Disks to Extrasolar Planets: Understanding the Life Cycle of Circumstellar Gas with Ultraviolet Spectroscopy"
    Few scientific discoveries have captured the public imagination like the explosion of exoplanetary science during the past two decades. This work has fundamentally changed our picture of Earth's place in the Universe and led NASA to make significant investments towards understanding the demographics of exoplanetary systems and the conditions that lead to their formation. The story of the formation and evolution of exoplanetary systems is essentially the story of the circumstellar gas and dust that are initially present in the protostellar environment; in order to understand the variety of planetary systems observed, we need to understand the life cycle of circumstellar gas from its initial conditions in protoplanetary disks to its endpoint as planets and their atmospheres. In this white paper response to NASA's Request for Information "Science Objectives and Requirements for the Next NASA UV/Visible Astrophysics Mission Concepts (NNH12ZDA008L)", we describe scientific programs that would use the unique capabilities of a future NASA ultraviolet (UV)/visible space observatory to make order-of-magnitude advances in our understanding of the life cycle of circumstellar gas.
31. Michael Wong, "Solar System Science Objectives with the Next UV/Optical Space Observatory"
    NASA's Great Observatories (and smaller space telescopes) enable a wide range of solar system science investigations, particularly in the ultraviolet, optical, and infrared ranges. These investigations are an important part of the Cosmic Origins program, providing a local reference point for the origin and evolution of stars and planetary systems. The next UV/optical space observatory can drive fresh insights into the origin and evolution of the solar system, if the technical requirements for planetary observations are met. These requirements are easily achieved via the groundwork that has already been done for HST and JWST.
32. Patrick Côté, "Science Drivers for a Wide-Field, High-Resolution Imaging Space Telescope Operating at UV/Blue Optical Wavelengths"
    A wide-field (0.5–1 deg²), ~1m-class space telescope that provides nearly diffraction-limited imaging (FWHM ~ 0.153) at UV/blue optical wavelengths (0.15–0.55 μm) has the potential to make a unique, powerful, and lasting contribution to modern astrophysics. Such a mission would be a natural successor to both the Hubble Space Telescope (HST) and the Galaxy Evolution Explorer (GALEX), and would far surpass any ground-based optical telescope in terms of angular resolution. It would also provide crucial "UV/blue" imaging to supplement longer-wavelength data from future dark energy space missions (Euclid, WFIRST) as well as from the ground-based Large Synoptic Survey Telescope (LSST). For maximum scientific impact and complementarity with Euclid/WFIRST, the facility should allow the implementation of GO/PI programs, but concentrate initially on a small number of "legacy" surveys–including a "wide survey" that would cover an area of at least ≈5000 deg², in three filters, to depths of ≈25.8 mag (UV), 27.1 (u) and 27.8 (g). We review the rich and diverse science investigations that such a wield-field imaging facility would enable, which include (but are not limited to) dark energy, galaxy evolution, near-field cosmology, stellar astrophysics, the outer solar system, and time-domain astronomy.
33. Jason Tumlinson, "Unique Astrophysics in the Lyman Ultraviolet"
    There is unique and groundbreaking science to be done with a new generation of UV spectrographs that cover wavelengths in the "Lyman Ultraviolet" (LUV; 912–1216 Å). There is no astrophysical basis for truncating spectroscopic wavelength coverage anywhere between the atmospheric cutoff (3100 Å) and the Lyman limit (912 Å); the usual reasons this happens are all technical. The unique science available in the LUV includes critical problems in astrophysics ranging from the habitability of exoplanets to the reionization of the IGM. Crucially, the local Universe (z <≅ 0.1) is entirely closed to many key physical diagnostics without access to the LUV. These compelling scientific problems require overcoming these technical barriers so that future UV spectrographs can extend coverage to the Lyman limit at 912 Å.
34. Melville Ulmer, "White Paper In Response To NSPIRES RFI For The Next Generation Space UV-Vis Space Observatory (NG-SUVO)"
    This paper describes how it is possible to gain better than a factor of 10 in sensitivity with the same size mirror as HST. Technology investments are needed, however. I further list a few science drivers for a new improved UV-Vis mission.