2008 Hubble Fellows Symposium

Speaker: Sean Andrews (Smithsonian Astrophysical Observatory)
Title: Protoplanetary Disk Structure at High Resolution: A Glimpse at the Planet Formation Process
Abstract: With the growing number of planetary systems found around other stars, attention is increasingly focused on the origins of the Solar System and others like it. Observations of the reservoirs of planet-building material -- the disks around young stars -- play a critical role in understanding planet formation mechanisms and their efficiencies. Because of their sensitivity to the amount and structure of this raw material, resolved data at (sub-) millimeter wavelengths provide unique access to the physical conditions in these disks, including in particular the spatial distribution of mass. I will describe some state-of-the-art measurements of disk structure that can yield a glimpse at the initial conditions available for assembling a planetary system.

Speaker: Beth Biller (Institute for Astronomy, University of Hawaii)
Title: An Imaging Survey for Extrasolar Planets around 45 Close Young Stars with SDI at the VLT and MMT
Abstract: We present the results of a survey of young (<=300 Myr), close (<=50 pc) stars with the Simultaneous Differential Imager (SDI) implemented at the VLT and the MMT for the direct detection of extrasolar planets. Our SDI devices use a double Wollaston prism and a quad filter to take images simultaneously at 3 wavelengths surrounding the 1.62 um methane absorption bandhead found in the spectrum of cool brown dwarfs and gas giant planets. By performing a difference of adaptive optics corrected images in these filters, speckle noise from the primary star can be significantly attenuated, resulting in photon (and flat-field) noise limited data. In our VLT data, we achieved H band contrasts >= 10 mag (5 sigma) at a separation of 0.5 from the primary star on 45% of our targets and H band contrasts of <= 9 mag at a separation of 0.5'' on 80% of our targets. With this degree of attenuation, we should be able to image (5 sigma detection) a 5 MJup planet 15 AU from a 70 Myr K1 star at 15 pc. We have obtained datasets for 54 stars. 45 stars were observed in the southern sky at the VLT and 11 stars were observed in the northern sky at the MMT (2 stars were observed at both telescopes). We believe that our SDI images are the highest contrast astronomical images ever made from ground or space for methane rich companions. We detected no tentative candidates with S/N > 2 sigma. Follow-up observations were conducted on 8 < 2 sigma candidates (with separations of 3 - 15.5 AU and masses of 2-10 MJup, had they been real) -- none of which were detected at a second epoch. For the best 20 of our survey stars, we attained 50% completeness for 6-10 MJup planets at semi-major axes of 20-40 AU. Thus, our completeness levels are sufficient to significantly test theoretical planet distributions. We also discuss preliminary results of an experiment at the High Contrast Imaging Testbed at JPL using a similar SDI multiwavelength differential imaging scheme bracketing the Oxygen (A) telluric absorption feature at 0.762 um.

Speaker: Judd D. Bowman (California Institute of Technology)
Title: "First Light" from New Probes of the Dark Ages and Reionization
Abstract: The application of the 21 cm hyperfine transition line of neutral hydrogen in the high-redshift intergalactic medium (IGM) to probe cosmological reionization and the early universe is transitioning rapidly from the realm of theory to practice. The Murchison Widefield Array (MWA) and the Experiment to the Detect the Global EOR Signature (EDGES), among other projects, have recently passed important milestones and will soon open the door to new views of the Universe spanning virtually every moment of cosmological time from recombination to today. Along the way, they have the potential to provide rich new insights into inflationary physics, the Dark Ages and reionization (including the first stars and galaxies), large-scale structure, and even Dark Energy. In this talk, I will provide a status report on these experiments and a brief primer on what to expect from this new field in the coming decade and beyond.

Speaker: Marusa Bradac (University of California at Santa Barbara)
Title: Dark Matter and Highest Redshift Galaxies: Revealing the Invisible with the "Bullet Cluster"
Abstract: The cluster of galaxies 1E0657-56 has been the subject of intense ongoing research in the last few years. This system is remarkably well-suited to addressing outstanding issues in both cosmology and fundamental physics. It is one of the hottest and most luminous X-ray clusters known and is unique in being a major supersonic cluster merger occurring nearly in the plane of the sky, earning it the nickname "the Bullet Cluster". In this talk I will present our measurements of the composition of this system, show the evidence for existence of dark matter, and describe limits that can be placed on the intrinsic properties of dark matter particles. I will conclude without lining the plans on using the bullet cluster as cosmic telescope to explore the Universe in its infancy and if time allows with recent results on another merging cluster RX J1347-1145.

Speaker: Niccolo Bucciantini (University of California at Berkeley)
Title: Long Duration GRBs and the Birth of Magnetars
Abstract: GRBs are burst of gamma-ray energy coming from cosmological distances. Recent observational results, while shedding light on their origin, have also challenged the standard accepted scenario, triggering a renewed interest in the investigation of the engine causing the release of such vast amount of energy. I will review the present knowledge of their properties showing that there is compelling evidence linking them to the death of massive stars. I will then discuss the central engine models that have been proposed, and in particular I will focus on the Magnetar model. I will show recent numerical results suggesting that, indeed, a GRB might be a natural outcome following the formation of a rapidly rotating magnetized neutron star.

Speaker: Alison Coil (University of Arizona)
Title: PRIMUS: A Prism Redshift Survey to z=1
Abstract: I will discuss a large new prism redshift survey that I have begun with collaborators at the University of Arizona and NYU. The PRIsmMUlti-object Survey (PRIMUS), is the largest redshift survey at z>0,with >300,000 spectroscopic galaxy redshifts over >13 square degrees of the sky. PRIMUS uses a revolutionary technique to measure galaxy redshifts: a very low-dispersion prism (R~40) in combination with multi-object slitmasks on the Magellan/IMACS spectrograph. We observe over 3000 galaxies at once, an order of magnitude larger than can be achieved with traditional high-resolution spectroscopy, and obtain 1% redshifts from the low-dispersion spectra. We are observing fields with IR (Spitzer/SWIRE), UV (GALEX), and X-ray data (XMM and Chandra),resulting in the largest multi-wavelength survey with spectroscopic redshifts at z>0. I will discuss the survey motivation, design, and technique and show preliminary data.

Speaker: Jürg Diemand (University of California at Santa Cruz)
Title: Formation of Cold Dark Matter Halos and Stellar Halos
Abstract: The largest cosmological simulations are now able to follow the formation and evolution of cold dark matter structures reliably and with considerable detail. Recent results about the structure and formation of cold dark matter halos will be presented. Since stars behave like collision-less dark matter particles, it is possible to paint mock stellar halos into dark matter simulations. Hierarchical structure formation predicts stellar halos full of structures, like stellar steams and satellite galaxies, in qualitative agreement with observations. We are now building models which will allow for a more quantitative comparison. They will be useful for near field cosmology, i.e. to constrain early galaxy formation by observing old stars in the halo of the Galaxy.

Speaker: Jason Kalirai (University of California at Santa Cruz)
Title: Stellar Remnants as Cosmological Probes
Abstract: White dwarfs represent the eventual end products of 98% of all stars. As such, their luminosity and mass distributions can be used to understand the properties of their progenitor populations (e.g., the initial mass function of stars). In this talk, I will summarize recent results from a large imaging and spectroscopic survey aimed at characterizing samples of white dwarfs in rich star clusters of different ages and metallicities. These data have now provided constraints on the initial-to-final mass relation (i.e., what mass main-sequence star maps to white dwarf mass) over a large mass range (M_initial = 1 -- 7 Msun), and therefore are a powerful input to chemical evolution models of galaxies including enrichment in the interstellar medium. I will also highlight how these results can be used to measure the age of the Galactic disk and halo. Finally, I will discuss direct empirical evidence that stellar mass loss is much more efficient in high metallicity environments. This result that may be critical in interpreting the UV upturn in elliptical galaxies, the dearth of planets around white dwarfs, and the different rates (and properties) of type Ia SNe in elliptical vs spiral galaxies.

Speaker: David Kaplan (Massachusetts Institute of Technology)
Title: Nearby Thermally Emitting Neutron Stars
Abstract: Neutron stars are among the densest objects in the universe. The conditions in their centers are largely unconstrained by current theoretical physics or terrestrial laboratories, leaving a wide variety of compositions and structures possible. Observations of thermal emission from neutron stars -- specifically measurements of their sizes and cooling rates -- may therefore be the best way to constrain the behavior of matter in these extreme conditions. I will discuss a sample of nearby, cooling neutron stars that we are using for this purpose. We are attempting to pin down the basic parameters of these neutron stars with a variety of ground- and space-based observations, coupled with theoretical modeling. Along the way, we have encountered a number of interesting astrophysical puzzles that I will describe.

Speaker: Daniel Kasen (University of California at Santa Cruz)
Title: Modeling Core Collapse Supernovae as Cosmological Probes
Abstract: Massive stars which retain their hydrogen envelope until the onset of core collapse will explode as Type~II plateau supernovae (SNeIIP). Future observational surveys should discover 100,000's of them every year out to redshifts of a few, offering potentially interesting probes of the evolving universe. I present results from a grid of theoretical models which demonstrate how the light curves and spectra of SNeIIP depend upon the progenitor star mass, metallicity, explosion energy, and host dust properties. These models exhibit a tight relationship between luminosity and expansion velocity, similar to that noted in observations, which may be used to calibrate them as standardized candles.

Speaker: Juna Kollmeier (Carnegie Observatories)
Title: Where Are the Old Population Hypervelocity Stars?
Abstract: Hypervelocity stars (HVS) are a relatively new population of stars in the Galaxy. These stars have the potential to constrain the shape of the Milky Way's halo as well as the nature of star formation at the Galactic Center. To date, only young HVS have been found because the techniques currently being used to locate these rare stars have been focused on the blue for several reasons. However, finding the (potentially more numerous) old-population stars (or lack thereof) would be extremely important in order to exploit the HVS as multi-scale probes of the Galaxy. I'll discuss new frontiers in the search for old-population hypervelocity stars.

Speaker: Mark Krumholz (Princeton University)
Title: The Secret Lives of Molecular Clouds
Abstract: Giant molecular clouds are the basic units of star formation, and they constitute a significant fraction of the mass of the interstellar medium, but their properties have proven remarkably difficult to determine from observations within our own galaxy. In the last decade, however, high resolution, multi-wavelength, multiple-tracer surveys of nearby galactic disks have given us the first solid results on molecular cloud lifetimes, locations, dynamical states, and star formation properties. I will review these observational results and then describe a combination of analytic models and numerical simulations that have begun to provide significant insight into the physical mechanisms that control the behavior of molecular clouds. I will demonstrate how these models can explain a number of recent observations, and begin to sketch out a unified theory of molecular clouds and star formation across a wide range of galactic environments.

Speaker: Ivo Labbe (Carnegie Observatories)
Title: The Emergence of Massive Quiescent Galaxies Between 1 < z < 3
Abstract: The evolution of massive galaxies over time provide strong constraints on galaxy formation models and the physics of galactic scale star formation. Observations indicate that by z=1 the most massive galaxies are largely assembled and in-situ star formation has ceased, suggesting that studies at z>1 are necessary to determine how and when their stellar mass was assembled and to directly observe the quenching process. I will discuss recent results from deep multiwavelength surveys which are putting constraints on the number densities, stellar populations, specific star formation rates, sizes, and AGN activity of massive galaxies during their formation epoch. I will highlight systematic shortcomings in current analyses and discuss upcoming instruments and techniques which herald new breakthroughs in this rapidly evolving field.

Speaker: Janice Lee (Carnegie Observatories)
Title: H-alpha Imaging Surveys of Galaxies Near and Far
Abstract: H-alpha nebular emission is one of the most direct tracers of star formation. As such, a great deal of our current understanding of star formation in local galaxies is based on a long and rich history of H-alpha observational studies. In this talk, I will highlight results from our H-alpha imaging census of galaxies in the local 11 Mpc volume, and describe the on-going GALEX ultraviolet and Spitzer infrared Legacy programs that have grown up around it. Moving into the more distant Universe, I will then introduce a new campaign to extend deep, wide H-alpha narrowband galaxy surveys to higher redshift (z~1-2) using the recently commissioned NOAO Extremely Wide-Field Infrared Imager (NEWFIRM).

Speaker: Mercedes Lopez-Morales (Carnegie Institution of Washington)
Title: Transit Timing: In Search for Earth-like Planets
Abstract: Transit timing is the most novel technique to detect extrasolar planets. This technique consists on measuring periodic changes in the mid-time of transit of known transiting planets. Those times can vary up to several minutes if there are additional small planets in the system perturbing the orbit of the transiting planet, making this technique sensitive to planets in the Earth-mass regime. I will present the status and prospects of the project currently underway at the 6.5-m Magellan telescopes in Chile to measure such transit timing variations.

Speaker: Rachel Mandelbaum (Institute for Advanced Study)
Title: Exploring The Dark Content of Galaxies with Weak Gravitational Lensing
Abstract: Gravitational lensing is a convenient tool for observing the total matter content of the universe, including the dark matter. Galaxy-galaxy lensing thus allows a measurement of the total matter content of galaxies and their environs, which may be compared against optical tracers of galaxy contents to learn about the way galaxies form and evolve, and about the nature of the dark matter halos in which they reside. After a basic introduction to lensing, I will describe some recent work on the relationship between stellar mass, luminosity, and dark matter halos, both for the general galaxy population and for special galaxy types such as active galactic nuclei (AGN). These results provide crucial constraints on theories of galaxy formation.

Speaker: Rachel Osten (University of Maryland/NASA GSFC)
Title: Multiwavelength Signatures of Magnetic Activity from Young Stellar Objects in the LkHalpha 101 cluster
Abstract: I describe the results of a multi-wavelength observing campaign on the young stellar objects in the LkH$\alpha$101 cluster. Simultaneous X-ray and multi-frequency radio observations are unique in providing simultaneous constraints on short-timescale variability at both wavelengths as well as constraints on the thermal or non-thermal nature of radio emission from young stars. Focusing in on radio-emitting objects and the multi-wavelength data obtained for them, multi-frequency radio data indicate non-thermal emission even in objects with infrared evidence for disks. We find radio variability on timescales of decades, days and hours: the fraction of objects considered radio-variable increases as the timescale decreases. About half of the objects with X-ray and radio detections were variable at X-ray wavelengths, despite lacking large-scale flares or large variations. Variability appears to be a bigger factor affecting radio emission than X-ray emission. A star with infrared evidence for a disk was observed in the decay phase of radio flare. In this object and another, we find an inverse correlation between radio flux and spectral index for two cluster members in contrast to behavior seen in the Sun and active stars. A radio and X-ray source lacking an infrared counterpart may be near the sub stellar limit; its radio properties are similar to other cluster members, but its much higher radio to X-ray luminosity ratio is reminiscent of behavior in nearby very low mass stars/brown dwarfs. We find no correspondence between signatures of particle acceleration and those of plasma heating, both time-averaged and time-variable. The multi-wavelength behavior suggests that the structures giving rise to the radio and X-ray emission on young stars are physically and/or energetically distinct.

Speaker: Nikhil Padmanabhan (Lawrence Berkeley National Laboratory)
Title: From Quasars to Dark Energy: Adventures with the Clustering of Luminous Red Galaxies
Abstract: I will discuss some of the cosmological applications of a survey of luminous red galaxies (LRGs), from constraining the clustering and properties of low redshift quasars to a new survey to measure the expansion rate of the Universe with baryon oscillations. Starting on small scales, I will discuss the clustering of LRGs around z< 0.6 quasars in the SDSS, and constraints this places on the environments of quasars. I will then switch to scales two orders of magnitudes larger, and discuss the Baryon Oscillation Spectroscopic Survey -- a next generation survey to measure baryon oscillations, yield 1% distance measures to z=0.35 and z=0.6.

Speaker: Klaus Pontoppidan (California Institute of Technology)
Title: Straddling The Snow Line: Planet-Forming Regions of Circumstellar Disks At Very High Spectral and Spatial Resolution
Abstract: The planet-forming zones (radii of 0.1-10 AU) of disks around young solar-type stars is an active environment characterized by a rich chemistry and a complex dynamical synergy between gas, dust and potentially proto-planets. I will discuss how very high-resolution infrared spectroscopy of warm molecular gas can provide unique tests for models of the evolution of such disks. I will also present the first results imaging molecular gas in planet-forming zones at milli-arcsec resolution (or ~0.1 AU) using spectro-astrometry. The technique is used to image the distribution and kinematics of gas inside the inner dust gaps of so-called 'transition' disks, some of which have been suggested to harbor newly formed planets. I will discuss how spectro-astrometry of molecular gas can be used to distinguish between various gap formation mechanisms.

Speaker: Jonathan Pritchard (Harvard College Observatory)
Title: Evolution And Application of the 21cm Signal Throughout Cosmic History
Abstract: Upcoming low-frequency radio arrays offer the possibility of observing the redshifted 21 cm line of neutral hydrogen during the epoch of reionization. Fluctuations in the 21 cm brightness temperature arise from variation in the gas density and temperature, the neutral fraction, and the Lyman-alpha flux. Unraveling these different sources of fluctuation will be challenging, but may provide new information on topics ranging from inflationary cosmology to the first luminous sources and reionization. In this talk, I will discuss the evolution of the 21 cm signal from z~300 to the present day, focusing on the challenges and opportunities ahead.

Speaker: Seth Redfield (University of Texas at Austin)
Title: Observing the Atmospheres of Transiting Exoplanets
Abstract: High signal-to-noise ratio (S/N) and high spectral resolution observations of transiting exoplanets provide an opportunity to measure the properties of exoplanet atmospheres and exospheres through transmission spectroscopy. I present the results of a large-scale program which led to the first ground-based detection of absorption due to an exoplanetary atmosphere. Observations were taken with the Hobby-Eberly Telescope (HET), which is well suited for this type of program given its large mirror, high resolution spectrograph, and queue scheduling. We observe significant additional absorption in the cores of the neutral sodium doublet relative to the continuum, when in-transit observations are compared to out-of-transit observations. Two tests are performed to confirm the detection: (1) analysis of a strong control line that is predicted to show no absorption, and (2) an empirical Monte Carlo analysis to quantify the impact of systematic errors. Observations of several other bright transiting systems are ongoing with the HET, making direct comparisons of the physical characteristics of exoplanet atmospheres possible, and enabling studies in comparative exoplanetology.

Speaker: Dominik A. Riechers (California Institute of Technology)
Title: Masses of the Highest Redshift Quasars and Their Host Galaxies
Abstract: Detailed studies of the molecular gas phase in the host galaxies of the highest redshift quasars are important for our understanding of the formation and evolution of quasars and their bulges, since it is the molecular gas out of which stars form. The galaxies in this study are the earliest known examples of composite AGN-starburst systems, and offer the unique opportunity to constrain the correlation between black hole mass and stellar bulge mass (M_BH-M_bulge) found in the local universe out to the epochs when galaxies first formed. I will discuss recent observations of the few such systems that can currently be studied in detail, placing an emphasis on the dynamical properties of the host galaxies as obtained from mapping of molecular ISM cooling lines. The derived dynamical masses show that the dominant fraction of the mass is likely in the form of gas rather than stellar. In particular, they do not leave sufficient room for a massive stellar bulge as predicted by the local M_BH-M_bulge relation. This suggests that the black holes in these massive systems are largely in place, while most of the stellar mas have yet to assemble.

Speaker: Alicia Soderberg (Princeton University)
Title: A Unique View of the GRB-SN Connection through Radio and X-Ray Observations
Abstract: Throughout history, observational supernova studies have focused almost exclusively on their strong optical emission powered by the radioactive decay of Nickel. Yet many of the leading breakthroughs in our understanding of supernovae and their progenitors have been enabled by observations at other wavelengths. In particular, radio and X-ray observations of young supernovae traces the properties of the very fastest ejecta. These observations lead to direct constraints on the temperature of the shock-heated material, the density of the circumstellar environment, and the velocity and kinetic energy of the fastest ejecta. As I will discuss, these observations can distinguish GRB-SNe from ordinary core-collapse SNe, and have the potential to reveal the illusive nature of their progenitors (single vs. binary). Finally, I will present an exciting new result, a serendipitous discovery, stemming from my Swift/XRT follow-up of nearby supernovae.

Speaker: Jay Strader (Harvard-Smithsonian Center for Astrophysics)
Title: Kinematics of Extragalactic Globular Cluster Systems
Abstract: I present Keck studies of the radial velocities of globular clusters in a wide range of galaxies, from dwarf to giant ellipticals. The cluster systems of low-mass galaxies are generally rotationally supported, and suggest the presence of dark matter in dwarf ellipticals. In the massive elliptical NGC 1407, concordance constraints from X-ray gas, globular clusters, and satellite galaxies yield unexpected results on the orbital anisotropy of metal-poor globular clusters.

Speaker: Christy Tremonti (University of Arizona)
Title: Galactic Winds in Normal Star Forming Galaxies and Low Luminosity Active Galactic Nuclei
Abstract: A central question in galaxy evolution is how the formation of stars is regulated. Several decades ago it was recognized that supernovae could provide a source of negative feedback by reheating and removing the cold dense gas necessary for further star formation. More recently, theorists have postulated that Active Galactic Nuclei (AGN) may provide an additional source of energy which could slow or shut down star formation. To provide observational constraints on the feedback process, I am studying galactic-scale gaseous outflows from galaxy disks ('galactic winds'). I have looked for evidence of galactic winds by measuring the velocity of the interstellar Na I D line relative to the stars in a sample of normal star forming galaxies and low luminosity AGN drawn from the Sloan Digital Sky Survey. I compare the results of this survey to studies of outflows in starburst galaxies and quasars, and I consider the role that galactic winds play in regulating star formation and galactic chemical evolution.

Speaker: Glenn van de Ven (Institute for Advanced Study)
Title: Triaxial Galaxy Models
Abstract: Various early-type galaxies have been modeled successfully with axisymmetric dynamical models. Many elliptical galaxies, however, show significant signatures of non-axisymmetry in their photometry (e.g. isophotal twist), as well as in their kinematics (e.g. kinematic misalignment and kinematically decoupled components), as clearly revealed by e.g. the integral-field spectrograph SAURON. Recently, we have extended Schwarzschild's orbit superposition method to triaxial geometry. This enables us to fit simultaneously the observed photometry and (two-dimensional) kinematics of these elliptical galaxies in detail. Besides the best-fit parameters, such as viewing direction, mass-to-light ratio and dark matter content, we also recover the intrinsic dynamical structure. Application to NGC4365 already revealed the surprising result that its 'proto-typical' kinematically decoupled core is most likely part of its single (weakly) triaxial structure.