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Talks / Presentations

Talk abstracts are in cosmological order. Highlighted titles indicate that the presentation is available for download. (Warning, some presentations may be relatively large >5MB)

The Frontier of Reionization: Theory and Forthcoming Observations

Prof. Avi Loeb (Harvard University)

The re-ionization history of cosmic hydrogen, left over from the big bang, was shaped by the first stars and black holes to have formed in the infant universe. High-resolution hydrodynamic simulations with radiative transfer are just starting to make detailed quantitative predictions about this history. A large number of facilities are being designed to test these predictions over the next decade through observations of the Lyman-alpha spectra of galaxies, quasars and gamma-ray bursts, and most importantly the detection of 21 cm emission from diffuse hydrogen.

Large Scale Structure in the Next Decade

Prof. Daniel Eisenstein (University of Arizona)

The large-scale structure of the Universe provides powerful probes of the composition of the Universe, a window into the first second after the Big Bang, and an opportunity to study the evolution of galaxies. I will review these applications, recent results, and a sample of new projects. The last decade has realized tremendous advances on these topics, but the next decade will be an equally large step forward.

Mass Assembly of Galaxies

Dr. Mark Dickinson (Nat'l Optical Astronomy Observatory)

Abstract not available at this time.

Upcoming Observations of the Formation and Evolution of Galaxies

Dr. Alice Shapley (Princeton University)

The redshift range 1.5<3.5 is an important one for galaxy formation. A large fraction of the local stellar mass density is formed, star-formation and AGN activity are at their peak levels, and the Hubble morphological sequence is in the process of assembly. With both ground- and space-based facilities in the next decade, we will be able to address countless outstanding questions in this area. Detailed studies of the stellar populations, gas and heavy-element content, structure and dynamics of distant galaxies will be possible with seeing-limited, AO-assisted, and space-based imaging and spectroscopy. Furthermore, the gains in both resolution and sensitivity will illuminate the interaction between galaxies and the intergalactic medium (IGM). This ``feedback," in the form of galactic scale outflows of gas, heavy elements, energy, momentum, and leaking ionizing radiation, may play a crucial role in shaping today's galaxy population, as well as enriching and heating the IGM.

Embedded Clusters, Dark Nebular Cores and the Origin of Stellar Masses

Dr. Charles Lada (Smithsonian Astrophysical Observatory)

The theory of stellar structure and evolution prescribes that once formed the subsequent life history of a star is essentially predetermined by one parameter, its birth mass. Consequently detailed knowledge of the initial distribution of stellar masses at birth (the IMF) and how this quantity varies through space and time is necessary to predict the evolution of all stellar systems from star clusters to galaxies. Yet the origin of stellar masses remains one of the most fundamental unsolved problems of astrophysics. Stars form in the dense cores of dark nebulae, but little is understood about the detailed physical properties of these cores prior to star formation and even less is understood about their origin. Yet both these issues are critically linked to understanding the origin of stellar masses and the IMF. In this talk I will first review the current knowledge concerning functional form and universality of the IMF as derived from observations of field stars and extremely young clusters. I will then relate this knowledge to exciting new results concerning the physical nature of dense cores on the verge of star formation. I will argue that these results suggest that the distribution of initial stellar masses derives directly from the distribution of dense core masses which itself may have its origins in a process of simple thermal fragmentation in a pressurized medium. The initial distribution of stellar birth masses produced by star formation may therefore be the result of the interplay only a few very basic and measurable physical processes.

Accretion Disks During the Star Formation Phase: Exploring Early Evolution of Gas and Dust with JWST and Other Facilities

Prof. Carsten Dominik (University of Amsterdam)

The accretion disks that form during the star formation process transport most of the stellar mass from the infall region to the star. They also form the basic configuration of evolved disks in which planets will likely later form. In fact, the initial steps toward planets must already happen in these young disks. I will review the current view on the properties of these disks and try to show how the emerging facilities like HERSCHEL, ALMA, and in particular the JWST will allow to study the evolutionary status of gas and dust in disks using a variety of tracers. In particular I will focus on the status of dust grains in the disks in terms of size, crystallinity, and spacial distribution, and using atomic and molecular tracers to study gas and dynamics in disks.

The Intergalactic Medium at High Redshifts

Prof. Steven Furlanetto (Yale University)

At low and moderate redshifts, the "cosmic web" pervading the intergalactic medium (IGM) has proven instrumental in unraveling the mysteries of structure formation, especially as observed through the Lyman-alpha forest. At high redshifts, the IGM promises to be an even more dynamic environment, and only by understanding its evolution can we understand the formation of the first generations of galaxies and quasars. I will describe how the IGM evolves from cosmological recombination through reionization, as well as methods to observe this era. These include fluctuations in the 21 cm background (which trace the first stars and quasars), metal absorption lines in the IGM (which trace the transition from exotic Population III stars to more normal stars), and cooling radiation from the first object. I will also show how the era of helium reionization, which is already accessible with today's telescopes, can serve as an analog for understanding the transformation of the IGM during reionization itself.

Most of the Baryons: Where, When, What and How

Prof. Xavier Prochaska (UCO/Lick Observtory)

Abstract not available at this time.

Origin and Evolution of ISM

Xander Tielens (Space Sciences Division)

Abstract not available at this time.

Astrochemistry in Dense, Protostellar Environments

Prof. Ewine Van Dishoeck (Leiden Observatory)

The earliest stages of the formation of new stars and planets occur deep inside interstellar clouds with huge extinctions requiring observations at long wavelengths. The rapid changes in temperature and density during solar system birth drive a rich chemistry with strong interactions between the gas and the grains. An overview of recent infrared and submillimeter spectroscopic observations of simple and complex gases, ices, silicates, and PAHs obtained with the Spitzer Space Telescope and ground-based submillimeter observatories will be presented, and the diagnostic values of the various lines and bands will be illustrated. Prospects for tracing the chemical complexity and changes during star- and planet formation with JWST and concurrent facilities will be discussed, and the need for complementary laboratory data emphasized.

Emerging Planetary Systems: Exploring their Diversity with JWST

Michael Meyer (The University of Arizona)

The formation and evolution of planetary systems will remain one of the key topics in astronomical research for the coming decades. Utilizing all instruments on JWST, astronomers will help provide answers to key questions such as: 1) How does the composition of gas and dust in disks influence planet formation? 2) When, where, and how frequently do gas and ice giants form? 3) How do remnant disks affect the dynamical history of emerging planetary systems? We will present examples of observations with JWST that can address these issues.

Identifying Habitable Exoplanets in the JWST ERA

Prof. Sara Seager (Massachusetts Institute of Technology)

For thousands of years people have wondered if we are alone. For the first time in history we are on the brink of answering this question. In the JWST ERA, several ground- and space-based facitilies will discover a pool of low-mass transiting exoplanets. JWST will be able to confirm the NASA/Kepler planet transit light curves as real, with high S/N, addressing the question about whether terrestrial planets exist and are common. For transiting low-mass exoplanets orbiting bright stars, JWST will be able to take transmission or emission spectra, searching for molecular absorption features indicative of habitability. While an Earth-twin is likely out of reach, super Earths orbiting M stars will certainly be accessible to JWST.

Theories for the First Stars and Clusters

Prof. Tom Abel (KIPAC/Stanford University)

Abstract not available at this time.

Observations Constraints of Reionization History in the JWST Era

Xiaohui Fan (University of Arizona)

Current observations place the end of reionization at z>=6 with the peak of reionization activity at z~10. Determining the history and sources of reionization is one of the main science goals of the JWST. I will first review the current status of reionization observations, then discuss three main issues regarding using high-redshift quasars and galaxies to probe the reionization history in the near future: prospects of finding sources at z~10 or beyond, observational tests for a mostly neutral IGM, and theoretical issues affecting these reionization tests. I will conclude by suggesting two critical tasks: wide-field IR surveys that provide luminous z>8 AGNs to be observed with JWST spectroscopically, and synergetic surveys using JWST, ALMA and ELT to map high-z Ly alpha galaxy population at the peak of reionization era.

The Co-Evolution of Black Holes and Galaxies

Prof. Timothy Heckman (Johns Hopkins University)

One of the most remarkable discoveries over the past decade has been the close link between the formation and evolution of supermassive black holes and the galaxies in which they live. There is surprisingly strong two-way communication between supermassive black holes and their host galaxy: 1) The growth of black holes and of the bulge component of galaxies is well coupled, implying some common fueling mechanism. 2) Feedback from supermassive black holes in the form of kinetic energy is believed to play a crucial role in supressing the conversion of gas into stars in massive galaxies. In my talk I will summarize what we currently know about these two key problems and then forecast what we may learn in the next decade with facilities like JWST, ALMA, and the GSMT.

Stellar Evolution and Death

Prof. Mike Barlow (UCL)

One focus of this review will be on the dust mass budgets of galaxies and how future facilities, including JWST, ALMA and Herschel, can help to pin down the relative contributions made to ISM dust enrichment by low and intermediate mass stars (AGB, post-AGB and PN phases) and by massive stars (M supergiants, LBVs, WRs, SNIb,c or SNII), including which dust species these different objects produce. Their effects on galaxy gas mass budgets will also be covered, including how future observations can help determine whether high mass stars, versus low and intermediate mass stars, dominate carbon and nitrogen production; stellar evolution's `missing mass' problem for intermediate mass stars; and the nature of the progenitors of Type Ib and Ic supernovae.

The Future of Brown Dwarf Science with JWST

Dr. Mark Marley (NASA Ames Research Center)

The explosive growth of brown dwarf and ultracool dwarf discoveries over the past dozen years has been so extraordinary that it is a rare paper in the field that does not open by remarking upon it. Today over 600 warm (Teff ~ 2400 to 1400 K) L and cool (600 to 1400 K) T dwarfs are known and the quest for the elusive, cooler Y dwarfs is ongoing. Most of the scientific inquiry into these ultracool dwarfs has focused on their formation and youth, on the resultant initial mass function, and on the determination of their global properties, particularly mass, effective temperature, metallicity, and cloudiness. Our review will focus primarily on the latter areas, first examining what we know about the atmospheres of brown dwarfs and exploring the new science that will be enabled by JWST. We will discuss the role that clouds and atmospheric mixing play in controlling the emitted spectra of these objects and the enigmatic L- to T-type transition that occurs near 1400 K as these objects cools. We will then look forward to a selection of the opportunities afforded to brown dwarf science by JWST. By providing cluster color-magnitude diagrams to very low masses (a Jupiter-mass or less), for example, JWST will revolutionize our understanding of brown dwarf cooling in environments controlled for age and metallicity. Atmospheric mixing, long recognized in Jupiter�s atmosphere, is important for brown dwarfs, yet the most diagnostic spectral region for this process lies in a spectral blind spot for Spitzer and most groundbased observatories, but not JWST. Given these and many other possibilities for exciting new results, it seems certain that cool dwarfs will remain a hot topic for some time to come.

The Outer Solar System

Prof. David Jewitt (University of Hawaii)

Astronomical advances in the study of the Solar system have been dramatic following the discovery of the Kuiper belt about 15 years ago. The Kuiper belt is important on several levels. First, the distribution of the orbits of the 1000 known Kuiper belt objects provides a record of dynamical events in the early Solar system, probably associated with the end-phases of planet formation. Second, the Kuiper belt is the Solar system's deep-freeze: objects there preserve ices and other primitive materials from the epoch of formation. Third, the Kuiper belt is a huge reservoir from which a variety of small bodies (Centaurs, Jupiter family comets and others) are fed to the planetary region. The belt provides a scientific context within which these other bodies, previously studied in isolation, can be properly understood. Fourth, the Kuiper belt is a source of collisionally-produced dust. As such, it is the closest example of a debris disk and a bridge to understanding similar systems around other stars. In this talk I will try to provide a broad and accessible overview of some of the most exciting new work on the outer Solar system, with an emphasis on the epoch of planet formation.

Observing the First Stars and Black Holes

Zoltan Haiman (Columbia University)

The high sensitivity of JWST will open a new window on the end of the cosmological dark ages. Small (globular-cluster sized) star-clusters and low-mass (10^5 M_sun) black holes should be directly detectable out to z=10, and individual supernovae are bright enough to be visible beyond this redshift. Dense primordial gas collapsing onto protogalaxies on large scales may be possible to image through diffuse recombination line emission. In this talk, I will discuss (i) the key physical processes that are expected to have determined the sizes of the first star-clusters and black holes, and (ii) the prospect of studying these objects by direct detections with JWST and with other instruments.

Star Formation and IMF II: In Extreme Environments

Jean Turner (UCLA)

The astronomical instruments of the last two decades have revealed remarkably luminous episodes of intense star formation in the local universe and in our own Galactic Center. We are now able to resolve star forming regions and populous clusters in local galaxies and we can begin to study the star formation process in these objects. In populous clusters such as R136 in the Large Magellanic Cloud, a census of O stars has been made and the IMF has been measured to subsolar masses. Super star clusters, possible precursors to globular clusters, have been detected in nearby galaxies, first in NGC 1569, and then by the thousands in the Antennae system. Super star clusters have also been detected at very early, embedded stages in the radio and infrared. Arcsecond imaging of molecules with millimeter arrays show that gas dynamics probably plays an important role in the initiation of extreme star formation events, and that galactic environment is closely related to cloud properties and chemistry. The instruments of the next decade will give us a new view of extreme star formation, including the most massive stars, initial mass functions of cluster systems, stellar feedback, and the initiation and regulation of star formation. Understanding how the star formation process takes place, including extreme star formation, is crucial to our understanding of how galaxies evolve through time.