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Staff Research
2013 Fall Series

All talks are held on Wednesdays in the STScI John N. Bahcall Auditorium at 3:30 p.m. preceded by tea at 3:15 p.m.

Please direct questions or comments to the colloquium committee. The 2013-14 committee members are Susan Kassin, Janice Lee, Mario Livio, and Jackie Radigan.

STScI presents live and archived webcasting of talks and Colloquium Series.

Date Speaker/Title
Sept. 11 Fabio Governato (University of Washington)
Title: Baryons over Dark Matter: interactions at the center of cosmic structures
Abstract: I will show results from cosmological simulations of galaxy formation where repeated gas outflows remove low angular momentum gas and transfer energy to the DM. This process solves three long lasting problems in galaxy formation: the substructure overabundance, the existence of bulgeless galaxies, and the presence of ubiquitous DM 'cores' at the center of dwarf field galaxies. I will then discuss the existing challenges to CDM in the context of alternative models to Cold Dark Matter as WDM and SIDM.
Host: Sussan Kassin
Sept. 16 Special Talk Markus Kissler-Patig (Gemini Observatory)
Title: New Opportunities with the Gemini Observatory
Abstract: Gemini Observatory's Director, Markus Kissler-Patig, will present an update of the facility and introduce some new opportunities for astronomers at Gemini. Gemini operates twin 8-m telescopes, one in Hawaii and the other in Chile. The departure of the UK from Gemini's international partnership at the end of 2012 provided the chance to re-evaluate the services offered to Gemini users and opened new opportunities in two domains. First, Gemini will welcome discussions with groups wanting to bring their own instruments for campaigns. This visiting instrument program will complement the suite of workhorse instruments offered by the Observatory, and will allow scientific breakthroughs not possible with the regular suite of instruments. Second, the Gemini Observatory will be offering cross-partnership large or long programs. Gemini is considering dedicating 20% of Gemini time to high-impact large or long collaborative programs selected through a yearly call. In addition to these two major initiatives, several new instruments are expected in 2013: Flamingos-2, the Gemini Multi-conjugate adaptive optics System (GeMS), and the Gemini Planet Imager (GPI). Gemini is also looking at the possibility of offering some fraction of time in a fast turn-around mode, as well as "eavesdropping" for remote observing. We remain very interested in having astronomers visit the telescopes. We encourage all astronomers to attend this presentation to learn about these new opportunities, and to provide feedback how Gemini Observatory can optimally support your research.
Host: Matt Mountain
Sept. 18 Jane R. Rigby (NASA/Goddard Space Flight Center)
Title: Galaxy Evolution in High Definition, Via Gravitational Lensing
Abstract: In hundreds of known cases, "gravitational lenses" have deflected, distorted, and amplified images of galaxies or quasars behind them. As such, gravitational lensing is a way to "cheat" at studying how galaxies evolve: lensing can magnify galaxies by factors of 10--100 times, transforming them from objects we can barely detect to bright objects we can study in detail. I'll summarize new results from a comprehensive program, using imaging from Hubble and Spitzer, and high-quality spectroscopy from Keck and Magellan, to study how galaxies formed stars at redshifts of 1--3, the epoch when most of the Universe's stars were formed. These results give insight into the process by which galaxies form elements and stars.
Host: David Soderblom
Sept. 25 Jenny Green (Princeton University)
Title: To Build an Elliptical Galaxy
Abstract: I discuss two essential aspects of elliptical galaxy formation: how they get their stars, and how they lose their gas. For the former, I use integral-field observations of local massive galaxies to study the stellar populations and kinematics of stars at large radius, to understand the origin of the size growth of elliptical galaxies. Then I focus on black hole feedback as a means of clearing gas from massive galaxies. I show that luminous obscured quasars have ubiquitous, round ionized outflows with very high gas dispersions of nearly 1000 km/s out to 20 kpc. Finally, if time permits I will combine these two themes and present our recent search for sub-pc supermassive black hole binaries.
Host: Paul Goudfrooij
Oct. 02 Genevieve Graves (Princeton University)
Title: Observing the Unobservable: Tracing Dark Matter Haloes and Galaxy Assembly
Abstract: A fundamental challenge in cosmology and galaxy evolution is to understand how dark matter (DM) haloes influence the galaxies that form inside them. Unfortunately, the parts of this process that we can simulate well—the growth of DM structures under the influence of gravity— cannot be observed directly, while the observable stars and gas are difficult to simulate over large scales because of the complicated physics involved. My past research has focused on connecting the star formation histories of passive galaxies to their observed dynamical structure. Here, I will present two projects that tackle different aspects of the larger problem of galaxy evolution. The first is a new method for measuring weak gravitational lensing. This method uses a photometry-only analog to the Fundamental Plane of early type galaxies in order to measure magnification due to weak lensing. Combined with existing techniques based on gravitational shear, this method will produce the most direct measurements of dark matter haloes around ordinary galaxies, allowing us to connect observed galaxies with the dark matter haloes that host them. The second project uses detailed, resolved galaxy kinematics and stellar population gradients in local massive galaxies to trace their assembly history. The goal is to isolate contributions from in situ star formation, major versus minor mergers, and the possible large-scale stripping of globular clusters. I will present a pilot study of M87, which is the first of several dozen local galaxies we ultimately aim to analyze.
Host: Susan Duestua
Oct. 09 Yuexing Li (Pennsylvannia State University)
Title: Observational Signatures of the First Galaxies and Quasars
Abstract: A large number of galaxies and quasars at different redshift have been discovered from recent multi-wavelength surveys. However, despite the strong observational push, theoretical modeling has lagged behind in unraveling the physical processes that determine the properties of these objects. I will report some recent progress in bridging this gap. I will present state-of-the-art calculations that combine multi-scale cosmological simulations with multi-wavelength radiative transfer to follow the formation, evolution, and multi-band properties of galaxies. In particular, I will discuss the emergence of the first galaxies and their detectability with next generation instruments such as JWST and ALMA.
Host: Harry Ferguson
Oct. 16 Lee Hartmann (University of Michigan)
Title: What Do we Really Understand About Star Formation?
Abstract: Star formation is an exceedingly complex process. We can identify the main phases of star formation at "cartoon" level, but many aspects are yet to be understood. In this talk I will address the following questions: a) What is a molecular cloud, and what is the dynamical state(s) of these star-forming regions? b) What about magnetic fields? and c) where does the stellar initial mass function come from?
Host: James Muzerolle
Oct. 23 Amy Mainzer (NASA/Jet Propulsion Labratory)
Title: The Solar System According to NEOWISE
Abstract: NASA's Wide-field Infrared Survey Explorer (WISE) launched in December, 2009, and surveyed the entire sky in four infrared wavelengths (3.4, 4.6, 12 and 22 microns).  While its primary mission objectives were to discover the closest and coolest stars and the most luminous galaxies, it also proved to be an effective tool for the discovery and characterization of minor planets.  The NEOWISE project was responsible for archiving the mission's individual exposures as well as developing solar-system friendly query tools, in addition to creating a tool for independently discovery new asteroids and comets.  The primary WISE mission ended on October 1, 2010, and the mission was extended for an additional four months as NEOWISE in order to complete a survey of the inner solar system.  The spacecraft was placed into hibernation on February 1, 2011.  NEOWISE detected >158,000 asteroids and comets, including >34,000 new discoveries, among them the first known Earth Trojan asteroid.  Now, the mission has recently been reactivated to continue the search for near-Earth objects.
Host: Margaret Meixner
Oct. 30 David Hogg (New York University)
Title: Exoplanets, quasars, confusion: Hierarchical modeling in astrophysics
Abstract: Many measurements of individual objects (for example, the orbital parameters of an exoplanet, the SED of a quasar, or the parallax of a star) are made in order to inform distributions or population studies. The most general probabilistic method for propagation of information from object measurements up to population inferences is hierarchical modeling, which I will explain and demonstrate with a few examples. A key take-home message is that "building a histogram" of best-fit values (or worse, co-adding of likelihood functions) produces biased (often strongly biased) population estimates; hierarchical modeling is far preferable. Another is that hierarchical modeling is capable of deriving useful information from extremely low signal-to-noise data and non-detections.
Host: Lou Strolger
Nov. 06 Avi Loeb (Harvard University)
Title: A Closer Look at Black Holes
Abstract: Several new techniques are currently being employed to probe the strong gravitational field in the vicinity of supermassive black holes. Long baseline interferometry at sub-millimeter wavelengths sets constraints on the silhouette of the black holes in the Galactic center (SgrA*) and M87. Stars which get tidally disrupted as they orbit too close to a single black hole are being discovered at cosmological distances. Electromagnetic counterparts of black hole binaries in galaxy mergers are being identified, and can be used to calibrate the rate of gravitational wave sources. Most interestingly, the recoil induced by the anisotropic emission of gravitational waves in the final plunge of binaries leaves unusual imprints on their host galaxies.
Host: Mario Livio
Nov. 13 Roman Scoccimarro (New York University)
Title: Recent progress in Large-Scale Structure
Abstract: I will discuss recent progress in the understanding of how to model galaxy clustering. While recent analyses have focused on the baryon acoustic oscillations as a probe of cosmology, galaxy redshift surveys contain a lot more information than the acoustic scale. In extracting this additional information three main issues need to be well understood: nonlinear evolution of matter fluctuations, galaxy bias and redshift-space distortions. I will present recent progress in modeling these three effects that pave the way to constraining cosmology and galaxy formation with increased precision.
Host: Guantun (Ben) Zhu
Nov. 20 Dawn Erb (University of Wisconsin-Milwaukee)
Title: Feedback in Faint Galaxies at the Peak Epoch of Star Formation
Abstract: Because faint, low mass galaxies are numerous at high redshifts, their impact on the Universe is expected to be significant. They may host a substantial fraction of global star formation, provide many of the energetic photons needed to reionize the universe, and contribute to the enrichment of the intergalactic medium through the expulsion of metals in galactic outflows. Because of their faintness, however, the properties of these galaxies are difficult to determine. I will discuss a variety of observations aimed at characterizing the physical conditions in low mass galaxies at redshifts z~2-3, the peak epoch of star formation in the Universe, with particular emphasis on the study of galactic outflows in faint galaxies.
Host: Jen Lotz
Dec. 04 David Spergel, Caroline Herschel Speaker (Princeton University)
Title: Cosmology after Planck
Abstract: The Planck Telescope has made an accurate full-sky measurement of the cosmic microwave background (CMB) temperature, the leftover heat from the Big Bang. These measurements probe both the physics of the very early universe and the basic properties of the universe today. The Planck measurements confirm the earlier results from the WMAP telescope and rigorously test our standard cosmological model and provide an accurate determination of basic cosmological parameters (the shape of the universe, its age, and its composition). When combined with other astronomical measurements, the measurements constrain the properties of the dark energy and the nature of dark matter. The observations also directly probe the physics of first moments of the Big Bang: the current data are consistent with the idea that the early universe underwent a period of rapid expansion called inflation.

Many key cosmological questions remain unanswered: What happened during the first moments of the big bang? What is the dark energy? What were the properties of the first stars? I will discuss the role of ongoing and future CMB observations and describe how the combination of large-scale structure, supernova and CMB data can be used to address these key cosmological questions.
Host: Andy Fruchter
Dec. 11 Karl Gebhardt (University of Texas)
Title: Black Holes and Dark Matter in the Local Universe
Abstract: A galaxy's black hole mass and dark matter profile provide significant clues as to its evolution and formation, namely the mass accretion history. These essential components are difficult to measure robustly however. I will give a general overview of the observational results for measuring the masses of black holes and the dark matter profile in nearby galaxies, including discussion of their effects on the stellar orbital distribution. I will focus the talk on the two extreme mass ranges, from whether globular clusters contain black holes up to black holes in brightest cluster galaxies. The present results suggests that the black hole correlations span over seven orders of mass. I will show results from both new instrumentation and computational approaches that demonstrate we are obtaining robust measures of both the black hole mass and dark matter profile.
Host: Donghui Jeong
Dec. 18 Brian Metzger (Columbia University)
Title: Observable Signatures of Coalescing Compact Binaries
Abstract: Coalescing stellar mass compact objects (binary neutron stars and black holes) are the most promising sources for the direct detection of gravitational waves by Advanced LIGO and Virgo in the next few years. However, maximizing the scientific opportunities from such a discovery will require the identification of a coincident electromagnetic counterpart. One possible counterpart is a short duration gamma ray burst (GRB), powered by the accretion of a centrifugally supported torus onto the central black hole. Although observations of short GRBs are largely consistent with the merger model, many bursts are accompanied by delayed X-ray flaring, which does not fit current theory and may require variations on the standard model, such as the presence of a long-lived neutron star remnant. Binary NS mergers are also accompanied by a supernova-like optical/IR transient, powered by the radioactive decay of heavy neutron-rich elements synthesized in the merger ejecta (a 'kilonova'). I will describe the first calculations of kilonovae including realistic nuclear physics and radiative transport and will report on the first potential discovery of kilonova emission by Hubble following a short GRB earlier this year.
Host: Andy Fruchter