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ELT observations of small Solar System objects: The origins of the Solar System

Additional Authors: Michael H. Wong, UC Berkeley Thomas Greathouse, SwRI Richard Cartwright, SETI Institute Nancy Chanover, NMSU Al Conrad, LBTO Eric Gaidos, University of Hawai'i Michael Lucas, University of Tennessee Karen Meech, University of Hawai`i Noemi Pinilla-Alonso, Florida Space Institute (UCF) Megan E. Schwamb, Gemini Observatory

This white paper describes how ELTs (e.g., GMT, TMT) can be used to understand the origins of our Solar System
through observations of small bodies (asteroids, comets, etc.).

Understanding the circumgalactic medium is critical for understanding galaxy evolution

Additional Authors: Many

Galaxies evolve under the influence of gas flows between their interstellar medium and their surrounding gaseous halos known as the circumgalactic medium (CGM). The CGM is a major reservoir of galactic baryons and metals, and plays a key role in the long cycles of accretion, feedback, and recycling of gas that drive star formation.In order to fully understand the physical processes at work {em within} galaxies, it is therefore essential to have a firm understanding of the composition, structure, kinematics, thermodynamics, and evolution of the CGM. In this white paper we outline connections between the CGM and galactic star formation histories, internal kinematics, chemical evolution, quenching, satellite evolution, dark matter halo occupation, and the reionization of the larger-scale intergalactic medium in light of the advances that will be made on these topics in the 2020s. We argue that, in the next decade, fundamental progress on all of these major issues depends critically on improved empirical characterization and theoretical understanding of the CGM. In particular, we discuss how future advances in spatially-resolved CGM observations at high spectral resolution, broader characterization of the CGM across galaxy mass and redshift, and expected breakthroughs in cosmological hydrodynamic simulations will help resolve these major problems in galaxy evolution.

Link to draft or additional information: https://www.overleaf.com/3275181648pknhntgttwws.

Science Platforms for Resolved StellarPopulations in the Next Decade

Additional Authors: Melissa Graham (U. Washington and LSST)

Over the past decade, research in resolved stellar populations has made great strides in exploring the nature of dark matter, in unraveling the star formation, chemical enrichment, and dynamical histories of the Milky Way and nearby galaxies, and in probing fundamental physics from general relativity to the structure of stars. Surveys have been particularly important to the biggest of these discoveries. In the coming decade, current and planned surveys will push these research areas still further through a large variety of discovery spaces, giving us unprecedented views into the low surface brightness Universe, the high surface brightness Universe, the 3D motions of stars, the time domain, and the chemical abundances of stellar populations. These discovery spaces will be opened
by a diverse range of facilities, including the continuing Gaia mission, imaging machines like LSST and WFIRST, massively multiplexed spectroscopic platforms like DESI, Subaru-PFS, and MSE, and telescopes with high sensitivity and spatial resolution like JWST, the ELTs, and LUVOIR. While we do not know which of these facilities will prove most critical for resolved stellar populations research in the next decade, we can predict that their chance of success will be maximized by granting use of the data to broad communities, that
many scientific discoveries will draw on a combination of data from them, and that advances in computing will enable increasingly sophisticated analyses of the large and complex datasets that they will produce. We recommend that Astro2020 1) acknowledge the critical role that data archives will play for stellar populations and other science in the next decade, 2) recognize the opportunity that advances in computing will bring for survey data analysis, and 3) explore investments in Science Platform technology to bring these opportunities to life.

Link to draft or additional information: https://www.overleaf.com/read/ypdwxgdfnvnn.

Ground-Based Radial Velocity as Critical Support for Future NASA Earth-Finding Missions

Future space-based direct imaging missions are poised to search for biosignatures in the atmospheres of potentially habitable planets orbiting nearby stars. Although these missions could conduct a blind survey to detect candidate Earth-like planets, conducting a precursor radial velocity (RV) survey will improve the efficiency of future direct imaging missions by identifying key targets in advance. The masses and mass upper limits resulting from an RV survey will also be useful for providing the context required to interpret future atmospheric spectra. Assuming a long-term precision of 20 cm/s, RV observations could discover Earth-mass planets in the habitable zones of 38 nearby stars accessible to space-based direct imaging. At a lower precision of 2 m/s, RV observations will be sensitive to Neptune-mass planets in the habitable zones of 78 stars, thereby revealing which candidate Earths are actually more massive planets.

Link to draft or additional information: https://docs.google.com/document/d/1O59Nd5kONlkWzuwF4zdj7Wncaw8JgcOnZjicoI-O7ao/edit.

Tracing the formation history of galaxy clusters into the epoch of reionization

Additional Authors: Nobunari Kashikawa (University of Tokyo)

Deep, wide optical surveys and multi-wavelength follow-up of, e.g., Spitzer, Herschel, Planck and South Pole Telescope selected targets have begun to deliver significant numbers of large-scale galaxy structures ("proto-clusters") at z=2-7. Spectroscopic confirmation and interpretation of these targets, however, is still challenging, and will require wide-field multi-plexed spectroscopy on >20 m-class telescopes in the optical and near-infrared. In the coming decade, detailed studies of these protoclusters will enable us, for the first time, to systematically connect these cluster progenitors in the early universe to their virialized counterparts at lower redshifts. This will allow us to address observationally the formation of brightest cluster galaxies and other cluster galaxy populations, the buildup of the intra-cluster light, the chemical enrichment history of the intra-cluster medium, and the formation and triggering of supermassive black holes in dense environments, all of which are currently almost exclusively approached either through the fossil record in clusters or through numerical simulations. Furthermore, at the highest redshifts (z~5-10), these large extended overdensities of star-forming galaxies are believed to have played an important role in the reionization of the universe, which needs to be tested by upcoming experiments. Theory and recent simulations also suggest important links between these overdensities and the formation of supermassive black holes, but observational evidence is still lacking. In this white paper we review our current understanding of this important phase of galaxy cluster history that will be explored by the next generation of large aperture ground-based telescopes such as GMT and TMT.

Triggered High-Priority Observations of Dynamic Solar System Phenomena

Additional Authors: Michael H. Wong, UC Berkeley Thomas Greathouse, SwRI David Trilling, Northern Arizona University Al Conrad, LBTO Imke de Pater, UC Berkeley Eric Gaidos, University of Hawai`i Richard Cartwright, SETI Institute Michael Lucas, U Tennessee Knoxville Kunio Sayanagi, Hampton University Karen Meech, University of Hawai`i Glenn Orton, Jet Propulsion Laboratory Noemi Pinilla-Alonso, University of Central Florida Megan E. Schwamb, Gemini Observatory Matthew Tiscareno, SETI Institute Christian Veillet, LBTO

Unexpected dynamic phenomena have surprised solar system observers in the past and have led to important discoveries about solar system workings. Observations at the initial stages of these events provide crucial information on the physical processes at work. We advocate for long-term/permanent programs on ground-based telescopes of all sizes -- including Extremely Large Telescopes (ELTs) -- to conduct observations of high-priority dynamic phenomena, based on a predefined set of triggering conditions. These programs will ensure that the best initial dataset of the triggering event are taken; separate additional observing programs will be required to study the temporal evolution of these phenomena. While not a comprehensive list, the following are notional examples of phenomena that are rare, that cannot be anticipated, and that provide high-impact advances to our understandings of planetary processes. Examples include:
- new cryovolcanic eruptions or plumes on ocean worlds
- impacts on Jupiter, Saturn, Uranus, or Neptune
- extreme eruptions on Io
- convective superstorms on Saturn, Uranus, or Neptune
- collisions within the asteroid belt or other small-body populations
- discovery of an interstellar object passing through our solar system (e.g. `Oumuamua)
- responses of planetary atmospheres to major solar flares or coronal mass ejections

Link to draft or additional information: https://www.overleaf.com/9538329673xxszbzkykgmz.

Dust formation in supernovae

Additional Authors: Danny Milisavljevic (Purdue U.), Arkaprabha Sarangi (NASA/GSFC)

Whether supernovae are a significant source of dust has been a long-standing debate. The large quantities of dust observed in high-redshift galaxies raise a fundamental question as to the origin of dust in the Universe since stars cannot have evolved to the AGB dust-producing phase in high-redshift galaxies. In contrast, supernovae occur within several millions of years after the onset of star formation. This white paper will focus on dust formation in SN ejecta with US Extremely Large Telescope (ELT) perspective in the era of JWST and LSST.

Multi-Messenger Astrophysics with Low Frequency Gravitational Waves and Pulsar Timing Arrays

Additional Authors: Maria Charisi (Caltech), Sarah Burke-Spolaor (West Virginia University), Joseph Simon (Jet Propulsion Laboratory), Vivian U (University of California, Irvine), Jenny Greene (Princeton), and others

Supermassive black holes reside in the nuclei of massive galaxies where they evolve symbiotically with their hosts. In hierarchical structure formation, galaxies are built-up by frequent mergers. Following a galaxy merger, two SMBHs along with massive inflows of gas, are brought towards the center of the post-merger galaxy. Eventually these SMBHs may form bound binaries and become strong sources of gravitational waves (GW) in addition to bright active galactic nuclei which are observable across the electromagnetic (EM) spectrum. In the coming decade, Pulsar Timing Arrays (PTA) like NANOGrav will detect GWs from SMBH binaries in the nanohertz frequency band. At the same time, EM surveys are poised to discover an unprecedented number of SMBHB candidates, and place strong constraints on their population. However, confirming the binary nature of these sources will pose a significant challenge. Improvements in both PTA sensitivities and EM survey capabilities provide the potential for a low-frequency GW revolution in the 2020s and beyond. Multi-messenger observations of SMBH binaries will produce significant discoveries and insights, with impacts on a broad array of astronomy subfields. In this white-paper, we discuss the science that can be uniquely accessed by detecting both EM and GW counterparts to the self-same system.

Achieving Transformative Understanding of Extreme Stellar Explosions with ELT-enabled Late-time Spectroscopy

Additional Authors: Raffaella Margutti (Northwestern University), Ryan Chornock (Ohio University), Armin Rest (Space Telescope Science Institute), Darren Depoy (Texas A&M University), Melissa Graham (University of Washington), V. Zach Golkhou (University of Washington), J. Craig Wheeler (University of Texas Austin), Grant Williams (MMT Observatory), Jeonghee Rho (SETI Institute), Rachel Street (Las Cumbres Observatory), Warren Skidmore (TMT International Observatory), Yan Haojing (University of Missouri-Columbia), Joshua Bloom (University of California, Berkeley), Sumner Starrfield (Arizona State University), Chien-Hsiu Lee (NOAO), Philip S. Cowperthwaite (Carnegie Observatories), Guy Stringfellow (University of Colorado), Deanne Coppejans (Northwestern University), Giacomo Terreran (Northwestern University), Niharika Sravan (Purdue University)

Supernovae are among the most powerful and influential explosions in the universe. They are also ideal multi-messenger laboratories to study extreme astrophysics. However, many fundamental properties of supernovae related to their diverse progenitor systems and explosion mechanisms remain poorly constrained. Here we outline how late-time spectroscopic observations obtained during the nebular phase (several months to years after explosion) made possible with the next generation of Extremely Large Telescopes will facilitate transformational science opportunities and rapidly accelerate the community towards our goal of achieving a complete understanding of supernova explosions. We highlight specific examples of how complementary GMT and TMT instrumentation will enable high fidelity precision spectroscopy from which the line profiles and luminosities of elements tracing mass loss and ejecta can be used to extract kinematic and chemical information with unprecedented detail, for hundreds of objects. This will provide uniquely powerful constraints on the evolutionary phases stars may experience approaching a supernova explosion; the subsequent explosion dynamics; their nucleosynthesis yields; and the formation of compact objects that may act as central engines.

Technosignatures

Additional Authors: Many, see link

The technosignatures (i.e. SETI) community is preparing a series of white papers for the Astro2020 decadal.

There is a "top-level" white paper introducing the topic here:
https://docs.google.com/document/d/1JzUwBa7hSfRhOQdLdtR6o9ODEh0dliGQ7-dF65OUTi4/edit?usp=sharing

I invite you to add your name as an endorser of this paper at the link on the first page of that document.

If you are interested in participating in and/or contributing to the effort further, you can see the full suite of papers here:
https://docs.google.com/spreadsheets/d/12oSRgkpw064evANmTzwMbCVRn8STHA6zK9UOtaW7wN8
/edit#gid=0

And we are also looking to make connections to other white papers; if you are leading one discussing topics related to the search for technosignatures, or if you are looking to bolster the science case for a proposal you describe, we would be interested in finding reciprocal language so the two white papers can support each other.

Thank you!

Link to draft or additional information:
https://docs.google.com/spreadsheets/d/12oSRgkpw064evANmTzwMbCVRn8STHA6zK9UOtaW7wN8
/edit#gid=0.

Emission Line Mapping of the Circumgalactic Medium of Nearby Galaxies

Additional Authors: Peter Behroozi (University of Arizona) Molly S. Peeples (Space Telescope Science Institute / Johns Hopkins University) Sarah Tuttle (University of Washington) Jessica Werk (University of Washington) Huanian Zhang (University of Arizona)

The circumgalactic medium (CGM), which harbors > 50% of all the baryons in a galaxy, is both the reservoir of gas for subsequent star formation and the depository of chemically processed gas, energy, and angular momentum from feedback. As such, the CGM obviously plays a critical role in galaxy evolution. We discuss the opportunity to image this component using recombination line emission, beginning with the early results coming from recent statistical detections of this emission to the final goal of realizing spectral-line images of the CGM in individual nearby galaxies. Such work will happen in the next decade and provide new insights on the galactic baryon cycle.

Observing Galaxy Evolution in the Context of Large-Scale Structure

Additional Authors: Yun Wang (Caltech/IPAC), James Bartlett (JPL), Peter Behroozi (Arizona), Jarle Brinchmann (Leiden Observatory; Porto), Peter Capak (Caltech/IPAC), Ranga Chary (Caltech/IPAC), Andrea Cimatti (Bologna; INAF), Charlie Conroy (CfA), Emanuele Daddi (CEA, Saclay), Megan Donahue (Michigan State University), Peter Eisenhardt (JPL), Henry C. Ferguson (STScI), Karl Glazebrook (Swinburne), Anthony Gonzalez (Florida), George Helou (Caltech/IPAC), Sangeeta Malhotra (GSFC), Jennifer Marshall (Texas A&M), Jeffrey A. Newman (Pittsburgh), Alvaro Orsi (CEFCA), James Rhoads (GSFC), Jason Rhodes (JPL), Alice Shapley (UCLA), Risa H. Wechsler (KIPAC/Stanford; SLAC); additional authors/signers are welcome!

Galaxies form and evolve in the context of their local and large-scale environments. Their baryonic content that we observe with imaging and spectroscopy is intimately connected to the properties of their dark matter halos, and to their location in the "cosmic web" of large scale structure. Very large spectroscopic surveys of the local universe (e.g., SDSS and GAMA) measure galaxy positions (location within large scale structure), statistical clustering (a direct constraint on dark matter halo masses), and spectral features (measuring physical conditions of the gas and stars within the galaxies, as well as internal velocities). Deep surveys with the James Webb Space Telescope (JWST) will revolutionize spectroscopic measurements of redshifts and spectral properties for galaxies out to the epoch of reionization, but with numerical statistics and over cosmic volumes that are too small to map large scale structure and to constrain halo properties via clustering. Here, we consider advances in understanding galaxy evolution that would be enabled by very large spectroscopic surveys at high redshifts: very large numbers of galaxies (outstanding statistics) over large co-moving volumes (large-scale structure on all scales) over broad redshift ranges (evolution over most of cosmic history).

Mass Spectroscopy of the Milky Way

Additional Authors: Joan R. Najita (NOAO), Sergey Koposov (CMU), Connie Rockosi (UCSC), Ting Li(FNAL), Knut Olsen (NOAO), Carlos Allende-Prieto (IAC), Ana Bonaca (CfA), Gurtina Besla (U.Arizona), Nicolas Garavito-Camargo (U. Arizona), Lori Allen (NOAO), Boris G ̈ansicke (U. War-wick), AdamBolton(NOAO)+ ...

The Milky Way stars encode the history of our Galaxy’s formation and are tracers of its hidden components. The last decade has witnessed resurgent interest in studies of the Milky Way, catalyzed by imaging surveys on 2-4m class telescopes and revolutionized, most recently, by precision, all-sky astrometric data from the Gaia satellite. Ground-based imaging surveys have nowcovered the entire sky, cataloging stars to very faint magnitude limits, and unveiling structure on a range of scales, discovering faint companion dwarf galaxies, their shredded remnants, and large scale streams. In the Galactic disk, Gaia’s precision photometric and astrometric measurements have revealed substructure never before observed (e.g., snail shells, ridges, etc.) that encode perturbations to the Galactic potential. With many highly multiplexed spectroscopic instruments soon to be available on a range of telescope apertures and even more ambitious ones planned, the coming decades will be the age of spectroscopy, much as past decades have been the age of imaging. These instruments will drive discovery by enabling spectroscopic studies of the Milky Way at unprecedented scales. Here we sketch out how an all-sky spectroscopic survey of∼100,000,000 stars, in combination with Gaia, can not only produce a 6-d map of the Milky Way, but also constrain the shape and substructure of the dark matter halo, reveal the metallicity,α/Fe, and elemental abundances of stars across the Galaxy, explore the outer reaches of the Galaxy’s halo, map the intervening dust and gas distributions within the Galaxy, and ultimately lead to a more detailed understanding of the formation and evolution of the Galaxy as a whole. Realizing the full scientific potential of this opportunity for the US astronomical community will require: resources to guarantee long-term (multi-year) access to the new capabilities to enable dedicated large-scale surveys of the Milky Way; resources to carryout the necessary observations and theoretical studies, and to provide public access to the spectroscopic data; and software tools to carry out the science.

Link to draft or additional information: https://www.overleaf.com/read/gnnvfhnbycpn.

Exploring the Atmospheres of Irradiated Exoplanets at High Spectral Resolution

Additional Authors: Eliza Kempton (University of Maryland), Jacob Bean (University of Chicago), Ian Crossfield (MIT), Eric Gaidos (University of Hawaii), Nikole Lewis (Cornell University), Michael Line (Arizona State University), Roxana Lupu (BAER Institute / NASA Ames), George Zhou (Harvard CfA)

The best-characterized exoplanets to date are planets on close-in transiting orbits around their host stars. The high level of irradiation and transiting geometry of these objects make them ideal targets for atmospheric investigations. However, the modest apertures of many current telescopes allow mostly low resolution spectra to be observed for transiting planets, failing to extract key physical and chemical properties of their atmospheres. The US 30-meter class telescopes will set the stage for a substantial leap in our understanding of exoplanet atmospheres. We outline a two-pronged survey that would yield unprecedented insight into the atmospheres of close-in exoplanets via observations with the US ELTs. (1) The first opportunity involves measuring the global-scale atmospheric circulation and planetary rotation for a sample of 40 hot Jupiters to glean insight into the unique radiative forcing regime governing highly-irradiated, tidally-locked giant planets. (2) The second opporunity involves extracting atmospheric composition and abundance ratio information for $>50$ sub-Neptunes and super-Earths (including candidate disintegrating planets) to constrain their formation and evolution histories. Each of these efforts will be made possible by the unparalleled combination of high spectral resolution instrumentation (e.g. G-CLEF, GMTNIRS, MODHIS, NIRES, MICHI) and large aperture size of the US ELTs. This survey would enable the first statistical study of atmospheric circulation in extrasolar giant planets, and would provide detections of trace gases and measurements of atmospheric escape in small-planet atmospheres, far exceeding the reach of textit{JWST}.

Link to draft or additional information: https://www.overleaf.com/9351863531pqvgxkrdgnys.

Dark Matter Physics with Wide Field Spectroscopic Surveys

Additional Authors: Manoj Kaplinghat (UCI), Andrew Pace (Texas A&M) and many more. You can find the co-authors in this page: http://tinyurl.com/yxjgrvg4 You are all invited to add your name and affliation in the above URL by the end of Sunday if you support this white paper.

We discuss the potential to discover the nature of dark matter particles with spectroscopy of a large number of faint stars in the Milky Way's halo, streams and dwarf spheroidal galaxies, mapping the faint end of the luminosity function in the local volume and deep observations of galaxies further away. N-body and hydrodynamical simulations of cold, warm, fuzzy and self-interacting dark matter show that non-trivial dynamics in the dark sector will leave an imprint on structure formation, with much of this science having been developed in last few years.
Sensitivity to these imprints will require extensive and unprecedented kinematic datasets for stars down to $g sim 23$ mag and redshifts for galaxies down to $g sim 24$ mag. We conclude that a next generation spectroscopic survey is required to definitively search for deviations from the cold collisionless dark matter model.

Link to draft or additional information: https://www.overleaf.com/read/kmfzwsywnsxt.

Comments (1)

Multi-Messenger Astronomy with Extremely Large Telescopes

Additional Authors: Lots

The field of time-domain astrophysics has entered the era of Multi-messenger Astronomy. One key science goal for the next decade (and beyond) will be to characterize gravitational wave sources (GW) using the next generation of Extremely Large Telescopes (ELTs). These studies will have a broad impact across astrophysics because they will inform our knowledge of the production and enrichment history of the heaviest chemical elements, constrain the dense matter equation of state, and provide independent constraints on cosmology. Future GW detectors will greatly improve their sensitivity during coming decade, as will near-IR telescopes capable of finding kilonovae independently. However, the counterparts will be distant and faint and thus demand ELT capabilities for characterization. ELTs will be important and necessary contributors to an advanced and complete multi-messenger network.

Link to draft or additional information: https://www.overleaf.com/read/tyyfrkfqggyn.

Measuring H$_0$ near and far with ELT's

Additional Authors: Ian Dell'Antonio, Brown; Chris Fassnacht, UC Davis; Danny Goldstein, CalTech; Chien-Hsiu Lee, NOAO; Peter Nugent, LBNL; Anowar J. Shajib, UCLA; Tommaso Treu, UCLA; Others welcome!

PRIMARY COAUTHOR: Simon Birrer, UCLA (sibirrer@astro.ucla.edu)

An adaptation of the US ELT KSP developed of the same title. The paper describes how ELTs complement smaller facilities to enable robust determination of the Hubble Constant. Three independent techniques are discussed -- (i) standard candles via a two-step distance ladder applied to metal, poor stellar populations, (ii) standard clocks via gravitational lens cosmography, and (iii) standard sirens via gravitational wave sources -- each of which can reach 1% with relatively modest investment from 30-m class facilities.

Under Active Revision -- co-authors welcome, please contact Simon (sibirrer@astro.ucla.edu) or Rachael (rbeaton@princeton.edu) for more information. Or come aboard via the #ExpansionHistory channel in the USELTP Slack.

Comments (1)

*willing to collaborate

The production and escape of ionizing photons over cosmic time

Additional Authors: Rongmon Bordoloi (NCSU) John Chisholm (UCSC) Michael Florian (NASA GSFC, USRA) T. Emil Rivera-Thorsen (ITA-UiO)

The ionizing photons produced by massive stars are key actors in galaxy evolution. Ionizing photon production and escape is poorly understood. Improved space-based, spatially-resolved, multiplexed spectroscopic capabilities covering λobs = 1000-3000 Å, in concert with spectroscopy from the ELTs and JWST, would lead to definitive answers as to how ionizing photons are produced and leaked, what populations of galaxies are responsible for ionizing photon leakage, what determines whether escape is possible, and how ionizing galaxy populations evolve over cosmic time.

Link to draft or additional information: https://docs.google.com/document/d/12B_L9kIIqhW_Ri2viFgf6bY4AvHYXDMdRD-Kye9B23Q/edit.

Comments (1)

*willing to collaborate

Fundamental physics with brown dwarfs: M/R relation

Additional Authors: Isabelle Baraffe (University of Exeter) Adam Burrows (Princeton University) Gilles Chabrier (University of Exeter) Michelle Creech-Eakman (New Mexico Tech) Nicolas Lodieu (IAC) Peter Plavchan (George Mason University) Michael Rich (UCLA) Keivan Stassun (Vanderbilt University) Johanna M. Vos (American Museum of Natural History) Rakesh Yadav (Harvard University)

The lowest-mass stars, brown dwarfs and giant planets span a minimum of the mass-radius relationship that probes the fundamental physics of extreme states of matter. This White Paper outlines scientific opportunities and critical resources for measuring the mass-radius relationship in this regime.

Link to draft or additional information: https://docs.google.com/document/d/1qfRv4HDcF2n9C4ZUNfV6p2X-QxTlslBowyPLADKiyP8/edit?usp=sharing.

The Critical, Strategic Importance of Adaptive Optics-Assisted, Ground-Based Telescopes for the Success of Future NASA Exoplanet Direct Imaging Missions

Additional Authors: Ruslan Belikov (NASA-Ames Research Center), Olivier Guyon (Subaru Telescope), N. Jeremy Kasdin (Princeton University), Christian Marois (NRC-Herzberg), Mark S. Marley (NASA-Ames Research Center), Kerri Cahoy (Massachusetts Institute of Technology), Dimitri Mawet (California Institute of Technology), Michael McElwain (NASA-Goddard Spaceflight Center), Eduardo Bendek (NASA-Ames Research Center), Marc J. Kuchner (NASA-Goddard Spaceflight Center), Michael R. Meyer (University of Michigan)

Ground-based telescopes coupled with adaptive optics (AO) have been playing a leading role in exoplanet direct imaging science and technological development for the past two decades and will continue to have an indispensable role for the next decade and beyond.

Over the next decade, Extreme AO systems on 8-10m telescopes will: 1) mature novel technological improvements useful for space, 2) validate performance requirements and motivate improvements to atmosphere models needed to unambiguously characterize solar system-analogues from space, and 3) mitigate risk for WFIRST-CGI by identifying numerous planets the mission can recover.
Extremely Large Telescopes can deliver the first thermal infrared (10 $mu m$) images of rocky planets around Sun-like stars. These data provide a future NASA direct imaging flagship mission (i.e. HabEx, LUVOIR) with numerous exo-Earth candidates and critical ancillary information that can help clarify whether these planets are habitable.

Link to draft or additional information: https://www.overleaf.com/read/zrsmwgpggmqz.

Black Hole Growth in Mergers and Dual AGN

Additional Authors: M. Koss (Eureka), J. Kartaltepe (RIT), D. Kocevski (Colby), J. M. Comerford (CU Boulder), R. S. Barrows (CU Boulder), S. Satyapal (GMU), Adi Foord (UMich), L. Blecha (UF), and more

Hierarchical models of galaxy formation predict that galaxy mergers represent a significant transitional stage in galaxy evolution where supermassive black hole (SMBH) growth proceeds at a very rapid rate. Yet, the connection between the merging process and enhanced active galactic nuclei (AGN) activity as well as the timescale of SMBH mergers remain highly uncertain. The breakthrough in reconciling the importance of galaxy mergers with black hole growth lies in a well-established and thoroughly-studied census of dual AGN across cosmic history, which will be enabled by next-generation observational capabilities, theoretical advances, and simulations. This white paper outlines the key issues involving galaxy mergers, dual and offset AGN, and proposes solutions from the high-resolution multiwavelength perspective shared by a myriad of upcoming facilities.

Revealing the Origins of Planetary Systems: Protoplanetary Disk Science Enabled by Extremely Large Telescopes

Additional Authors: Go to https://goo.gl/forms/saqGLp9rBPpoPhXu2 to be added as a co-author.

The processes that transform gas and dust in circumstellar disks into the diverse exoplanets in our Galaxy remain poorly understood. One key pathway is to study exoplanets as they form in their young (~few Myr) natal disks. Extremely Large Telescopes (ELTs) such as GMT or TMT, can be used to establish the chemical initial conditions, locations, and timescales of planet formation, via (1) infrared spectroscopy to measure the physical and chemical conditions in protoplanetary disks and (2) studying of planet-disk interactions using imaging and spectro-astrometry. Our current knowledge is based a limited sample of targets, representing the brightest, most extreme cases, and/or most massive systems, and thus almost certainly represents an incomplete understanding. ELTs will play a transformational role in this arena, thanks to the supremely high spatial and spectral resolution data they will deliver. A key science program to conduct a volume-limited survey of high-resolution spectroscopy and high-contrast imaging of the nearest protoplanetary disks would result in an unbiased, holistic picture of planet formation as it occurs.

Link to draft or additional information: https://www.overleaf.com/read/yvwmvttprcgg.

Precision Analysis of Evolved Stars

Evolved stars dominate galactic spectra, enrich the galactic medium, expand to change their planetary systems, eject winds of a complex nature, produce spectacular nebulae and illuminate them, transfer material between binary companions. While doing this, they fill the HR diagram with diagnostic streaks and loops that write the story of late stellar evolution. Evolved stars sometimes release unfathomable amounts of energy in neutrinos, light, kinetic flow, and gravitational waves. During these late-life times, stars evolve complexly, with expansion, convection, mixing, pulsation, mass loss. Some processes have virtually no spatial symmetries, and are poorly addressed with approximate measurements and analysis. Even the "simple" question of how to model mass loss resists verification. However, new methods now offer highly diagnostic tools. Astrometry reveals populations and associations. Pulsations/oscillations support study of stellar interiors. Optical/radio interferometry enable 2-3d imagery of atmospheres and shells. Bright stars with rich molecular spectra and spatially variable velocity fields are a ripe opportunity for imaging with high spatial and spectral resolution, supporting observation, modeling and interpretation of the physics of later stellar evolution.

The First Luminous Quasars and Their HostGalaxies

Additional Authors: Aaron Barth (UCI), Eduardo Banados (MPIA), Gisella De Rosa (STScI), Anna-Christina Eilers (MPIA), Emanuele Paolo Farina (MPIA & MPA), Jenny Greene (Princeton), Melanie Habouzit (Flatiron), Linhua Jiang (PKU), Hyunsung D. Jun (KIAS), Saengeeta Melhorara (GSFC), Chiara Mazzucchelli (ESO), Fabio Pacucci (Kapteyn, Yale) Dominik Riechers (Cornell, MPIA), Michael A. Strauss (Princeton), Marta Volonteri (IAP), Jinyi Yang (Arizona), Feige Wang (UCSB)

The discovery of luminous quasars at redshifts up to 7.5 demonstrates the existence of several billion $M_{odot}$ supermassive black holes (SMBHs) less than a billion years after the Big Bang. They are accompanied by intense star formation in their host galaxies, pinpointing sites of massive galaxy assembly in the early universe, while their absorption spectra reveal an increasing neutral intergalactic medium (IGM) at the epoch of reionization.
Extrapolating from the rapid evolution of the quasar density at $z=5-7$, we predict that there is only one luminous quasar powered by a billion $M_{odot}$ SMBH in the entire observable universe at $zsim 9$.
In the next decade, new wide-field, deep near-infrared (NIR) sky surveys will push the redshift frontier to the first luminous quasars at $zsim 9 - 10$; the combination with new deep X-ray surveys will probe fainter quasar populations that trace earlier phases of SMBH growth. The identification of these record-breaking quasars, and the measurements of their BH masses and accretion properties require sensitive spectroscopic observations with next generation of ground-based and space telescopes at NIR wavelengths. High-resolution integral-field spectroscopy at NIR, and observations at millimeter and radio wavelengths will provide a panchromatic view of the quasar host galaxies and their galactic environment at cosmic dawn, connecting SMBH growth with the rise of the earliest massive galaxies. Systematic surveys and multiwavelength follow-up observations of the earliest luminous quasars will place strong observational constraints on the seeding and growth of the first SMBHs in the universe, and provide the best lines of sight to study the history of reionization.

Link to draft or additional information: https://www.overleaf.com/7228568256cdgnjbpqkbvf.

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Rest-frame UV Diagnostics of Galaxies: fromthe Peak of Star-Formation to the Epoch ofReionization

Additional Authors: Dan Stark (Arizona), Steve Finkelstein (UT Austin), Nimish Hathi (STScI), Ryan Endsley (University of Arizona), Swara Ravindranath (STScI), Taylor Hutchison (Texas A&M University), Intae Jung (University of Texas at Austin), Naveen Reddy (UC Riverside) and others

The rest-frame UV emission from massive stars contains a wealth of information about the physical nature and conditions in stellar populations in distant galaxies (z > 3). Using studies of the rest-frame UV, the past decade has witnessed the beginning of knowledge about the existence and properties of galaxies during the first few billion years after the Big Bang. This period of history corresponds to the formation of the first stars, the rapid formation of galaxy stellar populations, the ionization of the IGM, the production and dissemination of heavy elements, and the formation and growth of the first black holes. Massive stars in these galaxies drive all of these events, and their light dominates the spectra and spectral energy distributions of galaxies. Looking to the 2020s, fundamental questions remain about the nature of these stellar populations and their evolution, from just before the peak of the cosmic star formation density (z~3), up to the epoch of reionization (z > 6). This next decade will provide transformative gains both in our ability to identify star-forming galaxies and accreting supermassive black holes at these early epochs with imaging surveys in the rest-frame UV (e.g., LSST, WFIRST), and to study the astrophysical nature of these sources with follow-up UV spectroscopy (with gains in spectroscopic sensitivity on 25-30~m class telescopes, e.g., the GMT and TMT). Rest-frame UV spectroscopy offers the ability to study the evolution in galaxy stellar populations, ionization, metallicity, and gas kinematics/covering fractions, enabling an understanding of the astrophysical conditions in galaxies at the earliest cosmic times.

Link to draft or additional information: https://www.overleaf.com/read/kbbythfnykks.

Searching for Earth-like Biosignatures onRocky Planets around Nearby Stars

Additional Authors: Thayne Currie (NASA-Ames/Subaru Telescope), Johanna Teske (Carnegie Observatories), Eric Gaidos (U. of Hawaii), Eliza Kempton (U. of Maryland), Jared Males (U. of Arizona), Nikole Lewis (Cornell University), Sagi Ben-Ami (Smithsonian Astrophysical Observatory), Jayne Birkby (U. of Amsterdam, Netherlands), David Charbonneau (Harvard University), Laird Close (U. of Arizona), Mark Dickinson (NOAO), Jeff Crane (Carnegie Observatories), Courtney Dressing (U. of California Berkeley), Cynthia Froning (U. of Texas at Austin),Yasuhiro Hasegawa (NASA-JPL/Caltech), Quinn Konopacky (U. of California San Diego), Ravi K. Kopparapu (NASA-GSFC), Dimitri Mawet (California Institute of Technology),Bertrand Mennesson (Caltech/NASA-JPL), Benjamin Rackham (U. of Arizona), Ramses Ramirez(ELSI/Tokyo Institute of Technology), Deno Stelter (U. of California Santa Cruz), AndrewSzentgyorgyi (Smithsonian Astrophysical Observatory), Ji Wang (Ohio State University), Andrea Dupree (Smithsonian Astrophysical Observatory), Amit Levi (Smithsonian Astrophysical Observatory), Chima McGruder (Harvard University), Sarah Rugheimer (U. of Oxford, UK)

As we begin to discover rocky planets in the habitable zone of nearby stars with missions like TESS and CHEOPS, we will need quick advancements on instrumentation and observational techniques that will enable us to answer key science questions, such asWhat are the atmospheric characteristics of habitable zone rocky planets? How common are Earth-like biosignatures in rocky planets? How similar or dissimilar are those planets to Earth?The expectation for the next decade is that observations with JWST will probe the atmospheres of small planets in search forEarth-like biomarkers (i.e.H2O,CH4,O3,CO2, andO2), but these observations will be challenging even for a superb telescope like JWST. JWST will only be able to observe the atmospheres of a very small number of small planets, given the large amount of telescope time required and expected noise floor limits. In addition,O2will be very difficult to detect with JWST, since its most prominent absorption appears at visible wavelengths for which JWST is not optimized. We expect to have discovered several Earth-analog candidates within the next decade, but we will not have the tools to study the atmospheres of all of them in detail. Therefore, we make the following recommendations to the Astro2020 Decadal Survey Committee: Support (1) the search for Earth-like biosignatures on rocky planets around nearby stars as a key science case, (2) the construction over the next decade of ground-based Extremely Large Telescopes (ELTs), which will provide the large aperture and spatial resolution necessary to start revealing the atmospheres of Earth-analogsaround nearby stars, (3) the development of instrumentation that optimizes the detection of biosignatures, and (4) the generation of accurate line lists for potential biosignature gases, which are needed as model templates to detect those molecules.

Link to draft or additional information: https://www.overleaf.com/read/bzpwvprgnxyt.

Tracing the Origins of Small Planets using Their Orbital Obliquities

Additional Authors: George Zhou (CfA), David R. Ciardi (IPAC/Caltech), Diana Dragomir (MIT/New Mexico), Yasuhiro Hasegawa (JPL/Caltech), Eve Lee (McGill), Lauren Weiss (Hawaii)

We recommend an intensive effort to survey and understand the obliquity distribution of small close-in extrasolar planets over the coming decade. The orbital obliquities of exoplanets--i.e., the relative orientation between the planetary orbit and the stellar rotation--is a key tracer of how planets form and migrate. While the orbital obliquities of smaller planets are poorly explored today, a new generation of facilities coming online over the next decade will make such observations possible en masse. Transit spectroscopic observations with the extremely large telescopes will enable us to measure the orbital obliquities of planets as small as ~2 REarth around a wide variety of stars, opening a window onto the orbital properties of the most common types of planets. This effort will directly contribute to understanding the formation and evolution of planetary systems, a key objective of the National Academy of Sciences's Exoplanet Science Strategies report.

Link to draft or additional information: https://www.overleaf.com/read/jbbzpkqwtwhs.

US-ELT, LSST, and Explosive Transients

Additional Authors: Danny Milisavljevic (Purdue University); Ryan Chornock (Ohio University); Raffaella Margutti (Northwestern University); Armin Rest (Space Telescope Science Institute); J.~Craig Wheeler (University of Texas at Austin); and more.

We focus on five open science questions for which progress will be enabled by the combination of LSST and US-ELT observations throughout the 2020s.

Establishing an Empirical Substellar Sequence to Planetary Masses

Additional Authors: C. Theissen (UCSD); more welcome

Mass is the most fundamental parameter governing the life-history of all gaseous objects from stars to brown dwarfs and giant planets. Extending measurements of mass to the regime of directly imaged gas-giants, and spectroscopically characterizing this mass sample, will require the new capabilities offered by ELTs.

Link to draft or additional information: https://www.overleaf.com/read/nzhhprdrdxtv.

Probing Dark Matter with ELTs

A white paper based on the dark matter key science program developed as part of the US ELT program.

Link to draft or additional information: https://www.overleaf.com/read/rwyvhvjkwqjc.

Star Formation in Different Environments: The Stellar Initial Mass Function

Additional Authors: Jessica Lu, UC Berkeley Morten Andersen, Gemini Observatory Tuan Do, UCLA Dongwon Kim, UC Berkeley Nicholas Rui, UC Berkeley Peter Boyle, UC Berkeley

The stellar initial mass function (IMF) is a fundamental property of star formation, offering key insight into the physics driving the process as well as informing our understanding of stellar populations, their by-products, and their impact on the surrounding medium. While the IMF appears to be fairly uniform in the Milky Way disk, it is not yet known how the IMF might behave across a wide range of environments, such as low metallicities, high pressures, and extreme gas temperatures and densities. We discuss new opportunities for measuring the IMF in such environments in the coming decade, in particular with JWST and thirty-meter class telescopes. For the first time, we will be able to measure the high-mass slope and peak of the IMF via direct star counts for massive star clusters and ultra-faint dwarf galaxies across the Milky Way and Local Group, providing stringent tests for star formation theory and laying the groundwork for understanding distant unresolved stellar systems.

[Note: this white paper is an adaptation from a US-ELT Key Science Project. Link below is a read-only link; please contact me if you would like to be a co-author and get the editing link]

Link to draft or additional information: https://www.overleaf.com/read/xtwprhqbtxgg.

Unveiling the Phase Transition of the Universe During the Reionization Epoch with Ly-alpha

Additional Authors: Marusa Bradac (University of California, Davis) Mark Dickinson (National Optical Astronomy Observatory) Ryan Endsley (University of Arizona) Nimish Hathi (STScI) Taylor Hutchison (Texas A&M University) Intae Jung (The University of Texas at Austin) Jeyhan Kartaltepe (Rochester Institute of Technology) Rebecca Larson (The University of Texas at Austin) Charlotte Mason (Harvard/Smithsonian CfA) Casey Papovich (Texas A&M University) Swara Ravindranath (STScI) Dan Stark (University of Arizona)

The epoch of reionization (roughly 6 < z < 10) marks the period in our universe when the large galaxies grew to fruition, and began to affect the universe around them. Massive stars, and potentially accreting supermassive black holes, filled the universe with ionizing radiation, burning off the haze of neutral gas which had filled the intergalactic medium (IGM) since recombination (z~1000). The evolution of this process thus constrains key properties of these earliest luminous sources, thus observationally constraining reionization is a key science goal for the next decade. The measurement of Ly-alpha emission from photometrically identified galaxies is a highly constraining probe of reionization, as a neutral IGM will resonantly scatter these photons, reducing detectability. While significant work has been done with modern 8-10m telescopes, these observations require extremely large telescopes (ELTs) – the flux limits available from today’s 10m class telescopes are sufficient for only the brightest known galaxies (m < 26). Ultra-deep surveys with the US-ELTs (the Giant Magellan Telescope and the Thirty Meter Telescope) will, if equipped with the proper instrumentation, be capable of detecting Ly-alpha emission from galaxies 2-3 magnitudes fainter than today's deepest surveys. When equipped with fiber systems, these observations can followup ~degree scale deep imaging surveys with the Wide Field Infrared Space Telescope, encompassing the expected size of ionized bubbles throughout the epoch of reionization. These data will provide the first Ly-alpha-based maps of the ionized intergalactic medium throughout the epoch of reionization, constraining models of both the temporal and spatial evolution of this phase change.

Local Dwarf Galaxy Archaeology

Additional Authors: Joshua Simon (Carnegie), Ian Roederer (Michigan), Marla Geha (Yale), Evan Kirby (Caltech), Ting Li (Fermilab), Anna Frebel (MIT)

Nearby dwarf galaxies are local analogues of high-redshift and metal-poor stellar populations. Most of these systems ceased star formation long ago, but they retain signatures of their past that can be unraveled by detailed study of their resolved stars. Archaeological examination of dwarf galaxies with resolved stellar spectroscopy provide key insights into the first stars and galaxies, galaxy formation in the smallest dark matter halos, stellar populations in the metal-free and metal-poor universe, the nature of the first stellar explosions, and the origin of the elements. Extremely large telescopes with multiobject R=5,000-30,000 spectroscopy are needed to enable such studies for galaxies of different luminosities throughout the Local Group.

Multiple systems of brown dwarfs

Additional Authors: Adam Burgasser, UC San Diego, La Jolla, CA Trent Dupuy, Gemini Observatory, Hilo, HI Christopher Gelino, IPAC, Pasadena, CA Jacqueline Faherty, AMNH, New York, NY Quinn Konopacky, UC San Diego, La Jolla, CA Federico Marocco, JPL, Pasadena, CA Kimberly Ward-Duong, Amherst College, Amherst, MA

Stellar and substellar multiplicity are direct outcomes of the formation process, particularly the statistical distributions of the orbital parameters of the population of multiple systems (i.e. separation, eccentricity, mass ratio, etc). While brown dwarfs may be the lowest-mass products of star formation, substellar formation at the nominal mass boundary between brown dwarfs and giant planets is still poorly understood, nor we understand the role of environmental conditions at the formation stage, or dynamics in the disruption of multiple systems over time. Signatures of stellar- or planetary-like formation vanish within a few million years, and we are lacking statistical samples of objects at different ages to connect the outcomes of formation with the field after dynamical evolution. Additionally, characterizing the components of multiple systems themselves provides stringent constraints and tests of substellar evolutionary models. In this white paper we advocate for a comprehensive characterization of both the statistical distributions of the population of ultracool dwarf binary and higher order systems and the fundamental properties of their individual components as a function of age.

Link to draft or additional information: https://www.overleaf.com/project/5c6da18e780df52ad8a98080.

The Demographics and Atmospheres of Giant Planets with the US ELTs

Additional Authors: Coordinated by Steph Sallum (UCSC) and Brendan Bowler (UT Austin)

Characterizing a Gaia-selected sample of giant planets using the US ELTs will address several open questions about giant planet formation, migration, and atmospheric evolution.

ELT Contributions to Tidal Disruption Events

Additional Authors: J. Craig Wheeler (The University of Texas at Austin) Rafaella Margutti (Northwestern University) Ryan Chornock (Ohio University) Dan Milisavljevic (Purdue University) Maryam Modjaz (New York University) Sung-Chul Yoon (Seoul National University)

An ELT system with its large aperture and sensitive optical and near infrared imager spectrographs will make major contributions to the study of stars ripped apart by supermassive black holes.

This white paper has been submitted to the Astro 2020 Decadal Survey.

ELT Contributions to The First Explosions

Additional Authors: J. Craig Wheeler (The University of Texas at Austin) József Vinkó (Konkoly Observatory) Rafaella Margutti (Northwestern University) Dan Milisavljevic (Purdue University) Maryam Modjaz (New York University) Sung-Chul Yoon (Seoul National University)

The large aperture and sensitive optical and near infrared imager spectrographs will enable an ELT system to observe some supernovae at large distances, deep into cosmological history when supernovae first began to occur.

This white paper has already been submitted to the Astro 2020 Decadal Survey website.

Resolving Galaxy Formation at Cosmic Noon: Connecting 1 Mpc to 100 pc Scales with GMT & TMT

Additional Authors: Rachel Bezanson, Andrew Newman, Gwen Rudie, Sean Johnson, Cameron Hummels, Jenny Greene, Kevin Bundy, Mauro Giavalisco, Jeyhan Kartaltepe, Mariska Kriek, David Law, Marie Lemoine-Busserolle, Matt Malkan, Danilo Marchesini, Erica Nelson, Swara Ravindranath, Allison Strom

Cosmic Noon was the most active period in the history of the Universe. During this epoch, roughly 10 Gyr ago, star formation and black hole accretion were at their highest rates,
%The universe at Cosmic Noon (a lookback time of 10 Gyr) was a very active place. Star formation and black hole accretion were at their peaks,
fed by prodigious gas accretion. Key characteristics of today's galaxies -- such as regularly rotating disks, central bulges, a population of dead galaxies -- were just emerging. We propose a Key Science Program for GMT and TMT that would transform our view of galaxy evolution at this important epoch by resolving both early galaxies and their surrounding gaseous medium. With AO-assisted IFU observations using GMT and TMT, we propose to resolve 100 typical $zsim2$ galaxies with 100 pc resolution, a critical scale that will allow us to resolve individual star forming regions, dissect galactic substructures such as disks and bulges, connect winds to their launching sides, and identify supermassive black holes. Using the sensitivity and multiplexing power of the ELTs, we will observe faint galaxies behind the IFU targets to provide a dense set of sightlines probing their circumgalactic and intergalactic medium (CGM/IGM) in absorption. With 7-15 sightlines per galaxy, we will trace the distribution of gas and metals from 50 kpc to 1 Mpc scales. Collectively these data will provide an unprecendented density of information over a wide range of scales, ranging from inflow from the IGM on Mpc scales, through the CGM on 100 kpc scales, and ultimately into individual giant star formation regions on 100 pc scales. The program will therefore provide an ideal data set for understanding the flow of baryons through galaxies and their surrounding medium, the nature of feedback, and its role in shaping early galaxies' star formation and structures---all of which are fundamental for a complete picture of galaxy evolution.

Galactic Center: A laboratory for the study of the physics and astrophysics of supermassive black holes

Additional Authors: Andrea Ghez (UCLA), Jessica Lu (UC Berkeley), Matt Hosek (UCLA), Andrea Bellini (STScI), Sukanya Chakrabarti (RIT), Mark Morris (UCLA), Shoko Sakai (UCLA)

As the closest example of a galactic nucleus, the Galactic center (GC) presents an exquisite laboratory for learning about supermassive black holes (SMBH) and their environment.
We describe how the high sensitivity, angular resolution, and astrometric precision offered by the combination of the TMT and GMT observatories will open many exciting directions for future research.
First, it will be possible to obtain precision measurements of the Galaxy's central potential, providing both a unique test of General Relativity (GR) in the unexplored regime near a SMBH and a detection of the extended dark matter distribution that is predicted to exist at the GC. The orbits of these stars will also allow us to measure the spin of the SMBH.
Second, we will probe the stellar populations at the GC to significantly lower masses than is possible today, down to the brown dwarf limit. Their structure and dynamics will provide an unprecedented view of the stellar cusp around the SMBH and distinguish between possible star formation scenarios to describe the young stars.
And third, the uncertainties on the SMBH mass and distance can be improved by a factor of $sim$20. The distance to the Galactic center is a fundamental Galactic parameter that will be important to many other scientific areas. We can also study the near-infrared accretion onto the black hole at unprecedented sensitivity and time resolution.
The instruments available from TMT and GMT provide a unique combination of capabilities for these science goals. Using realistic estimates of instrument performance, we predict that we will be able to measure the GR precession signal (which is not yet detectable today) to $>$10$sigma$, improve limits on extended mass by a factor of 100, black hole mass by a factor of 20, and uncertainty in the distance to the GC by a factor of 10 with 3 years of monitoring stellar orbits with TMT/GMT, assuming Keck continues observations up to the start of TMT/GMT operations.

Exploring active supermassive black holes at 100 micro-arcseconds

Additional Authors: Theo ten Brummelaar (The CHARA Array), Douglas Gies (CHARA, Georgia State University)

Super high spatial resolution observations in the infrared are now enabling big advancements of our understanding of supermassive black hole systems at the center of galaxies. Infrared interferometry, reaching resolutions of milli-arcseconds to sub-milli-arcseconds, is changing our view of the central structure from a static to a very dynamic one by spatially resolving pc-scale structure. Soon we might be able to directly observe the exact interaction site between the central supermassive black hole system and its host galaxy, and quantify the effect of such interaction processes. Further down the spatial scale, less than a light year, we are starting to measure the dynamical structure of the region of the fast moving gas clouds around active supermassive black holes. Near-future high angular resolution studies will definitely advance our ways of weighing these black holes, and we might even see the existence of binary black hole systems at the center of galaxies.

The origin and fate of the Universe from 2<z<5 spectroscopy

Inflation and Dark Energy science from Lyman-break galaxies and Lyman-alpha emitters at 2<z<5 with multi-object spectroscopy on >4m telescopes.

Link to draft or additional information: www.overleaf.com/read/jrtycmwtfryq.

Empirically Constraining Galaxy Evolution

Additional Authors: Charlie Conroy (Harvard University), Alexie Leauthaud (UCSC), Andrew Hearin (Argonne), Matt Becker (Argonne), Dennis Zaritsky (University of Arizona)

Over the past decade, empirical constraints on the galaxy—dark matter halo connection have facilitated enormous progress in understanding galaxy evolution. Past techniques have focused on connections between halo properties and galaxy stellar mass and/or star formation rates; techniques in the next decade will be able to empirically link halo properties and assembly histories with galaxies’ circumgalactic media, supermassive black holes, morphologies, kinematics, sizes, colors, metallicities, and transient rates. Uncovering these links will resolve many key uncertainties in our theoretical understanding of galaxy formation and will also enable much higher fidelity of mock catalogs essential for interpreting observations. To achieve these results, key goals include broader and deeper spectroscopic coverage of galaxies and their circumgalactic media; survey teams should also meet several criteria (cross-comparisons, public access, and covariance matrices) to enable combining their data with those from other teams. Acting on these recommendations will continue enabling dramatic progress in both empirical modeling and galaxy evolution for the next decade.

Link to draft or additional information: https://docs.google.com/document/d/1ZjDuIH6VDbVjDz6YcEsc4aoI5fHne3612kgclyxU1bE/edit?usp=sharing.

LSST: the Dark Matter Telescope

Additional Authors: Large effort of more than 100 coauthors and endorsers. Contacts are Keith Bechtol, Alex Drlica-Wagner, and Yao-Yuan Mao.

Astrophysical observations currently provide the only robust, empirical measurements of dark matter. Future observations with the Large Synoptic Survey Telescope (LSST) will provide necessary guidance for the experimental dark matter program. This white paper represents a community effort to summarize the science case for studying the fundamental physics of dark matter with LSST. We discuss how LSST will inform our understanding of the fundamental properties of dark matter, such as particle mass, self-interaction strength, non-gravitational couplings to the Standard Model, and compact object abundances. Additionally, we discuss the ways that LSST will complement other experiments and facilities to strengthen our understanding of the fundamental characteristics of dark matter. More information on the LSST dark matter effort can be found at https://lsstdarkmatter.github.io/.

Link to draft or additional information: https://lsstdarkmatter.github.io/.

US ELT Program: Detecting and Characterizing Small Planets

Additional Authors: This effort is being coordinated by Ji Wang (OSU) and Michael Meyer (University of Michigan) and includes dozens of co-authors from around the community.

As part of the US ELT Program, several of us have been developing a "Key Science Program" on detection and characterization of "small planets" (namely <-= 4 R_earth) in both reflected light and thermal emission with ELTs. This KSP is being turned into a white paper.

The Seeds of Supermassive Black Holes

Additional Authors: Aaron Barth, UC Irvine \ Andrea Bellini, STScI \ Tuan Do, UCLA \ Karl Gebhardt, UT Austin \ Kayhan Gultekin, U Michigan \ Matthew Hosek Jr., UCLA \ Dongwon Kim, UC Berkeley \ Mattia Libralato, STScI \ Jessica Lu, UC Berkeley \ Matthew Malkan, UCLA \ Jonelle Walsh, Texas A & M \

We have compelling evidence for ``stellar-mass'' black holes (BHs) of $5-30$~msun. These are BHs that form through the death of massive stars. We also have compelling evidence for so-called supermassive BHs ($10^5-10^{10}$~msun) that are predominantly found in the centers of galaxies. To date we know of no BHs with masses between these two limits ($100-10^4$~msun). However, we have very good reason to believe there must be BHs in this gap, because the first $sim 10^9$~msun BHs are observed only hundreds of millions of years after the Big Bang. All theoretically viable paths to making supermassive BHs will leave remnants of ``intermediate'' mass. However, {it no BHs have yet been reliably detected in this mass range}. Uncovering these intermediate-mass BHs is within reach in the coming decade, with the advent of thirty-meter telescopes.

Link to draft or additional information: https://www.overleaf.com/read/jmkcxgtvpsnb.

Radial metallicity gradients in star-forming galaxies

Additional Authors: Danielle Berg (CCAPP, Ohio State University) Fabio Bresolin (Institute for Astronomy, University of Hawaii) Katia Cunha (Steward Observatory, University of Arizona) Laura Magrini (Osservatorio Astrofisico di Arcetri, INAF Italy)

Spiral star-forming galaxies are complex astrophysical objects whose baryonic component is dominated by the disk, where most of the star formation resides. The metallicity in the disk is not uniform, and it usually decreases with the distance to the galaxy center, in the so-called radial metallicity gradient. Radial metallicity gradients have been successfully used to set important constraints on galaxy formation and their chemical evolution. This paper focuses on the implications of radial metallicity gradients for a variety of galaxies and stellar populations, and on the foreseen advances in this field in the astronomical landscape of the 2020s.

Identification and characterization of the host stars in planetary microlensing

Additional Authors: Rachel Street (LCOGT), Kailash Sahu (STScI), Eliad Peretz (NASA/GSFC)

Microlensing offers a uniquie opportunity to probe exoplanets that are temperate and beyond the snow line, as small as Jovian satellites, at extragalactic distance, and even free floating exoplanets, which are not detected by other methods. This is because the microlensing does not depend on the brightness of the host star of the planets. Here we propose to robustly and routinely measure the mass of exoplanets beyond 1 AU from their host stars with the microlensing method; our experiment relies on directly imaging and resolving the host star (namely the lens) from the background source of the microlensing events, which requires high spatial resolution delivered by the ELTs. An immediate result from this project will be planet occurrence rate beyond the snow line, which will enable us to discern different planet formation mechanisms.

Link to draft or additional information: https://www.overleaf.com/read/zrmcxtncmdjc.

Cosmological Constraints from Strong Gravitational Lensing

Additional Authors: Ian Dell'antonio (Brown University) Adam Myers (University of Wyoming)

The current tension between the best-fit cosmological models from measurements of the cosmic expansion history (Type Ia supernovae (SN) and Baryon Acoustic Oscillations (BAO) combined with the CMB) and local measurements of Ho has reached the point where a consideration of non-standard cosmographic techniques seems prudent. The geometrical nature of strong lensing can provide an independent constraint, specifically through the modeling of multiple-arc systems where the details of a specific lens model may be minimized (e.g., Link & Pierce 1998, Julio et al. 2010, Magana et al. 2018). Furthermore, over the next decade, high resolution imaging via interferometers, such as ALMA, and the next generation of large ground-based telescopes will provide the capability to measure transverse co-moving distances, for strongly lensed systems that results from our secular motion with respect to the CMB (this is the "Cosmological Parallax"). This measurement is interesting in that it is: independent of both SN and BAO, is geometrical, and the secular signal increases with time. A focused effort to model both known multiple arc systems and to investigate the possibility of measuring secular, cosmological parallaxes is proposed.

Comments (1)

*willing to collaborate

Spectroscopic Probes of Galaxies at the Epoch of Reionization

Additional Authors: A. Hoag (UCLA), B. Lemaux (UCDavis), C. Mason (UC Davis), T. Treu (UCLA), V. Strait (UCDavis) et al.

The epoch of reionization, which signified the transformation of the universe from opaque to
transparent, is poorly understood. When did it start/end? Was it patchy or smooth? How did
galaxies reionize the universe (if they did)? What are the properties of the earliest galaxies? To
answer these questions, over the last decades, several surveys have explored the high redshift
universe at progressively increasing depth. However, they still either lack the sample size or depth (or both). What emerges from these surveys is that the answers to these questions are likely tied
to the properties of even fainter galaxies. Future large spectroscopic studies of a large sample of
previously unexplored faint galaxy populations at redshifts z > 6 is needed to answer these fundamental questions. This can be achieved by a concerted efforts of using galaxy clusters that
serve as cosmic telescopes and ground-based telescopes enabling high resolution follow up of
galaxies deep into the epoch of reionization.

First Stars and the Origin of the Elements

Additional Authors: D. Buzasi (FGCU), A. Ji (Carnegie Obs), G. Mace (McDonald Obs and U Texas), V. Placco (U Notre Dame), I. Roederer (U Michigan), J. Sobeck (U Washington)

Adaptation of a US-ELT program Key Science Program concept that focuses on detecting metal-free stars or excluding their existence, as well as characterizing the nature and end states of the first stars that produced metals.

URL for draft coming soon.

Comments (1)

Dynamical Processes in the Planet-Forming Environment

Metallic emission lines, along with the Balmer series of hydrogen, probe the chemistry and kinematics of gas within the planet-forming and central regions of circumstellar disks.
The transfer of circumstellar disk mass and momentum onto the protostar and out into the environment occurs via a variety of mechanisms including magnetospheric accretion, jets, outflows, and disk winds. The interplay of these processes determine both the conditions under which planet formation occurs and the lifetime of the disk. High-spectral resolution study of these emission lines provides critical information on
disk chemistry, mass and momentum loss, turbulence, and disk wind origins.

Comments (1)

*willing to collaborate

Solar system Deep Time-Surveys of atmospheres, surfaces, and rings

Additional Authors: (this initial list is comprised of participants from the US ELT KSP effort, Nov-Dec 2018) Michael H. Wong (UC Berkeley) Richard Cartwright (SETI Institute) Glenn Orton (JPL) Matthew Tiscareno (SETI Institute) Thomas Greathouse (SWRI) David Trilling (Northern Arizona Univeristy) Kunio Sayanagi (Hampton University) Nancy Chanover (NMSU) Al Conrad (LBTO) Imke de Pater (UC Berkeley) Eric Gaidos (University of Hawaii) Michael Lucas (UT Knoxville) Karen Meech (University of Hawaii) Noemi Pinilla-Alonso (University of Central Florida) Megan E. Schwamb (Gemini Observatory)

Observations at leading observatories reveal varying
environmental conditions in our dynamic solar system.
Observations conducted over decade-scale campaign durations
create a long-term legacy chronicling the evolution of dynamic
planetary atmospheres, surfaces, and rings, establishing a
permanent resource for comparison with other observations
conducted in past, contemporaneous, or future epochs.
Long-duration datasets address questions about potential
biosignatures, circulation and evolution of atmospheres from the
edge of the habitable zone to the ice giants, orbital dynamics
and planetary seismology with ring systems, exchange between
components in the planetary system, and the migration and
processing of volatiles on icy bodies, including Ocean Worlds.
The common factor uniting these scientifically diverse
investigations is the need for a very long campaign duration, and
temporal sampling at an annual cadence. The integrity of
long-duration programs requires an institutional-level commitment
beyond the scope of typical general observer cycles.

Link to draft or additional information: http://astro.berkeley.edu/~mikewong/papers/US_ELTP_KSP_SS01_cadence_20181218.pdf.

Tracing the AGN feeding and feedback

Additional Authors: Robert Nikutta (NOAO), Nancy Levenson (STScI), Chris Packham (UTSA), Erin Hicks (University of Alaska), Kohei Ichikawa (Tohoku University), Vivian U. (UC Irvine), Sibasish Laha (UC San Diego).

The relation between the masses of galaxies' central super massive black holes and their host galaxies implies an evolutionary connection. Thus, the buildup of the central black hole mass is a fundamental facet of galaxy growth and evolution, which occurs at least in part through accretion. However, the global physical processes by which this occurs is uncertain. For few decades, the best picture of the feeding material surrounding the super massive black hole in active galaxies has been a static structure re-processing the emission from the central engine (black hole and accretion disk). The cause of this picture is mainly due to the small physical scales, $le 10$ pc, of this structure and our limited instrumental capabilities to fully characterize it. Recent ALMA and IR interferometric observations using VLTI have provided new insights towards our understanding on this structure from a dynamical framework-- the feeding material is the central structure in a gas flow cycle in which gas is brought in from the host galaxy disk (inflow) and then driven out by the AGN in a wind (outflow) that can be explained by radiation-driven outflow models and/or magnetic disk-wind models. However, the limited sensitivity and the impossibility to obtain images using IR interferometry, and the limited AGN sample due to that both ALMA and VLTI are in the Southern hemisphere, make the dynamical framework unclear. This white paper discusses key open questions on our understanding about AGN feedback/feeding that can be addressed with a multiwavelength analysis using the next generation of extremely large telescopes, X-ray and radio facilities.

Comments (2)

*willing to collaborate

Protocluster Evolution

Additional Authors: Gregory Rudnick, University of Kansas Caitlin Casey, University of Texas Nimish Hathi, Space Telescope Science Institute Steve Finkelstein, University of Texas Jeff Newman, University of Pittsburgh Mark Dickinson, NOAO

This white paper will discuss key open questions that can be addressed by detailed study of protoclusters at at ”Cosmic noon“, the key redshift range of z∼2−3 where galaxies were at the peak of their star formation rates and black hole growth and where protoclusters were forming into the most massive structures in today’s universe. We will particularly focus on the vast improvements that can be made with targeted spectroscopic surveys with a range of depths and area coverage in order to provide unprecedented characterization of galaxies over the full dynamic range of environmental densities at cosmic noon across a wide-range in cluster progenitor mass. These open science questions include:

1) What governed the cessation of star formation in present-day massive cluster galaxies?

2) How did environment regulate or enhance star formation during the epoch when the first large (~Mpc scale) structures were collapsing?

3) How did gas flows in and out of galaxies proceed at these epochs?

4)Were galaxies in early structures merely “accelerated” in their evolution, or did the environment actively affect their evolution?

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*willing to collaborate

Investing for Discovery and Sustainability in Astronomy in the 2020s

As the next decade approaches, it is once again time for the US astronomical community to assess its investment priorities on the ground and in space in the coming decade. This report, created to aid NOAO in its planning for the 2020 Decadal Survey on Astronomy and Astrophysics, reviews the outcome of the previous Decadal Survey (Astro2010); describes the themes that emerged from the 2018 NOAO Community planning workshop "NOAO Community Needs for Science in the 2020s"; and based on the above, offers thoughts for the coming review. We find that a balanced set of investments in small- to large-scale initiatives is essential to a sustainable future, based on the experience of previous decades. While large facilities are the "value" investments that are guaranteed to produce compelling science and discoveries, smaller facilities are the "growth stocks" that are likely to deliver the biggest science bang per buck, sometimes with outsize returns. Investments in data-intensive missions also have benefits to society beyond the science they deliver. By training scientists who are well equipped to use their data science skills to solve problems in the public or private sector, astronomy can provide a valuable service to society by contributing to a data-capable workforce.

[Note: This white paper considers broad issues that are relevant for the 2020 Decadal Survey, rather than a focused science topic. It may be submitted in response to a future call for white papers on the state of the profession. In addition to the link below, it is also available at https://arxiv.org/abs/1901.08605]

Link to draft or additional information: https://noirlab.edu/science/documents/scidoc1167