MIT Astrophysics Colloquia - Fall 2010

Tuesdays at 4:00 PM in the Marlar Lounge, Room 37-252
MIT Kavli Institute for Astrophysics and Space Research
70 Vassar Street, Cambridge, MA
(unless location otherwise noted)
Refreshments are served at 3:45 PM.

Sponsored by
the Astrophysics Division of the MIT Department of Physics and
the MIT Kavli Institute for Astrophysics and Space Research.


Tuesday September 14:
Exoplanet Atmospheres: from Discovery to Characterization and Beyond
Sara Seager
MIT
Host:

Abstract:

Tuesday September 21:
Do we have a coherent picture for the formation of galaxies and supermassive black holes?
Rachel Somerville
STScI
Host: Rob Simcoe

Abstract: It has been shown recently that incorporating the energy feedback from growing supermassive black holes into models of galaxy formation set within the Cold Dark Matter framework can plausibly solve several of the most persistent problems that plagued these models for decades, such as the 'overcooling' and 'star formation quenching' problems. I will discuss whether these models can rise to the challenge of correctly predicting the observed "downsizing" in stellar mass and star formation rate with cosmic time, as seen in lookback studies and in "fossil" evidence in nearby galaxies. I will then show how a revision of the classical model for spheroid formation via galaxy mergers leads to improved predictions for the fraction of early type galaxies as a function of stellar mass. Finally, I will discuss whether these "unified" models can simultaneously reproduce the evolution of galaxies and AGN over cosmic history, and what lessons we can take away about the physics of black hole growth and galaxy formation.

Tuesday Spetember 28:
The Co-Evolution of Galaxies and Black Holes: Current Status and Future Prospects
Tim Heckman
JHU
Host: Rob Simcoe

Abstract: I will summarize the evidence that there is close relationship between the evolution of galaxies and supermassive black holes. I will review what we know about this co-evolution in the "modern universe" (z < 1). We now have a good documentation of the demographics of which black holes are growing and where. The challenge going forward is to understand the physical processes that drive the observed co-evolution. At high redshift (z > 2) the most massive black holes and the progenitors of the most massive galaxies are forming. We currently have a tantalizing but fragmented picture of these processes. The next steps will be to investigate large and complete samples in order to achieve a robust understanding.

Tuesday October 5:
A New View of the Solar Corona from the Solar Dynamics Observatory
Leon Golub
SAO
Host: Al Lazarus

Abstract: The SDO mission has an unprecedented ability to observe the magnetic and coronal origins of solar activity, especially coronal mass ejections and the conditions that lead to these eruptions. We will discuss the capabilities of SDO (mainly of the Atmospheric Imaging Assembly, AIA) for improving our understanding of coronal dynamics and of the drivers of CMEs as space weather phenomena.

Tuesday October 12:
Einstein@Home's first discoveries, and the search for new neutron stars
Bruce Allen
Max Planck Institute for Gravitational Physics / AEI
Host: Erik Katsavounidis

Abstract: Einstein@Home is a volunteer distributed computing project with more than a quarter-million participants from the general public. It uses donated computer cycles to search data from the LIGO gravitational wave observatories and from the Arecibo Radio Observatory, looking for signals from undiscovered rapidly-rotating neutron stars.

This talk is intended for several audiences. For the astrophysicists, we'll talk about Einstein@Home's first two discoveries, in data from Arecibo. The first appears to be the fastest-spinning disrupted recycled pulsar yet discovered; the second is a 48 Hz pulsar in a 9.4-hour binary system. We'll also talk about the methods Einstein@Home uses to search LIGO and radio data. For computer scientists, we'll talk about how volunteer distributed computing works, and the Berkeley Open Infrastructure for Network Computing (BOINC) infrastructure behind the project. For sociologists, we'll talk about why people volunteer their computers for projects like this (there are about 100 such projects world-wide). What motivates the volunteers? Why did some of them stick with the project for years, even though it didn't find anything?

For people who don't fall into any of the categories above, we'll talk about interesting things like

-- stars whose density exceeds that of an atomic nucleus
-- the most important untested prediction of Einstein's theory of relativity (which might be confirmed in the next decade)
-- how to combine the laptops and desktops of people from every country in the world, to beat the mightiest supercomputers
-- and how these volunteer computing systems might enable exciting new science in the future.


Tuesday October 19:
Strong Lensing Clusters: From Handfuls to Hundreds
Mike Gladders
University of Chicago
Host: Rob Simcoe

Abstract: A detailed and statistically robust visual inspection of the SDSS DR7 imaging footprint, and similarly the entire RCS-2 cluster catalog has produced hundreds of candidate cluster-scale strong lensing systems, over a volume of approximately 9 Gpc^3 out to a redshifts beyond z=1. An extensive multi-wavelength multi-telescope follow-up program has confirmed the lensing interpretation of several hundred of these lensing candidates, providing a dramatic increase the total number of known lenses from all previous samples. The resulting samples probe strong lensing from group mass scales all the way to the most massive clusters, covering two orders of magnitude in mass. These lenses inform our understanding of massive halos through studies both of the statistics of the source images and lenses, and detailed lensing studies of individual systems, as well as provide a unique view on the distant universe.

Tuesday October 26:
The IMF, the UV bump, and AGB stars: New Insights From Stellar Population Synthesis
Charlie Conroy
Harvard Univeristy / Society of Fellows
Host: Paul Schechter

Abstract: Stellar population synthesis (SPS) combines stellar evolution and atmosphere calculations, an initial mass function, a dust model, and a star formation history in order to `predict' the emergent spectrum of a galaxy. SPS techniques have proliferated in the past decade, resulting in the routine estimation of stellar masses, star formation rates, and metallicities of large samples of galaxies. In this talk I will focus instead on the basic SPS ingredients, including the IMF, dust attenuation curve, and evolution of AGB stars, and demonstrate that these uncertain inputs can actually be constrained directly from the integrated light of galaxies. By confronting a flexible SPS model with a variety of data, I will show that the low-mass IMF is not universal, the 2175A dust feature seen in our Galaxy also exists in typical star-forming galaxies, and that AGB stars contribute substantially less light in the near-IR than state-of-the-art stellar evolution calculations predict. Implications of these results will also be highlighted.

Tuesday November 2:
Advancing tests of relativity via lunar laser ranging
Tom Murphy
UC San Diego
Host: R. Simcoe

Abstract: Laser range measurements between the earth and the moon have provided some of our best tests to date of general relativity and gravitational phenomenology--including the equivalence principle, the time-rate-of-change of the gravitational constant, the inverse square law, and gravitomagnetism. APOLLO (the Apache Point Observatory Lunar Laser-ranging Operation) is now collecting measurements at the unprecedented precision of one millimeter, which will produce order-of-magnitude improvements in a variety of gravitational tests. Experimental performance, evidence for degradation of the reflectors, finding the lost Soviet Lunokhod 1 reflector, project status and science outlook will be discussed.

Tuesday November 9:
The Atacama Cosmology Telescope: Galaxy Clusters and the CMB
Tobias Marriage
JHU
Host: R. Simcoe

Abstract: In this talk I'll review recent results from the Atacama Cosmology Telescope (ACT). ACT is a millimeter-wave telescope conducting a 1000 square-degree survey at arcminute resolution from 5200m in the Atacama desert of northern Chile. I will discuss our initial inventory of galaxy clusters discovered through the Sunyaev-Zel'dovich effect and highlight how a consistent picture emerges from the integrated-SZ contribution to the spatial power spectrum of the CMB sky.

Tuesday November 16:
Transit timing variations of Kepler planets
Matthew Holman
Harvard/SAO
Host: J. Winn

Abstract: For a transiting planet following a fixed Keplerian ellipse, observers would measure a constant interval between successive transits. Orbital precession induced by GR or stellar oblateness could result in a variation of the transit interval for a planet with an eccentric or inclined orbit. Furthermore, tidal dissipation should alter the orbital period of the planet. These slow effects can only be detected over several years. However, the gravitational influence of other planets in the system can yield a detectable change in the transit interval over much shorter time scales. With the precision and continuous monitoring provided by Kepler photometry, the presence of sub-Earth mass planets in resonance, as well as larger planets at a wide range of orbital periods could, in principle, be readily detected. With the detection of transit timing variations in systems with multiple transiting bodies, such as Kepler-9, it is possible to establish from the transit observations alone that these bodies have planetary masses. But the combination of Kepler photometry with high-precision radial velocity observations is particularly powerful in establishing the orbital and physical properties of such systems. I will present the results of the analyses of transit timing variations in exoplanet systems observed by Kepler to date.

Tuesday November 23:
Observational and Theoretical Studies of the Intergalactic Medium
Michael Shull
University of Colorado, Boulder
Host: Rob Simcoe

Abstract: The Cosmic Origins Spectrograph (COS) installed on the Hubble Space Telescope provides access to high-quality ultraviolet spectra of the intergalactic medium (IGM) and galactic halos. I will report on new COS results on the physical state, baryon content, and spatial distribution of the the IGM at redshifts z < 0.5. COS has also measured the epoch of reionization in helium (He II) at redshifts z < 3. This talk will also describe the Colorado group's numerical simulations of the IGM and dynamical and radiative feedback from galaxy formation, using the adaptive-mesh N-body hydrodynamic code Enzo. These simulations help us understand the effects of IGM shock-heating, metal-transport, radiative cooling, and photoionization of the complex structures in the "Cosmic Web" of matter.

Tuesday November 30:
Exploration of the Circum-Galactic Medium at High Redshifts
Charles Steidel
Caltech
Host: Rob Simcoe

Abstract: During the peak epoch of galaxy formation, the intergalactic medium is both the source of gas fueling star formation in forming galaxies, as well as the waste dump for the products of star formation and black hole accretion that are not retained by galaxies. By studying the "Circum-Galactic Medium", the region within a few hundred physical kpc of forming galaxies, one can begin to constrain the flow of baryons into and out of galaxies. At present, there is a puzzling discrepancy between observations and theoretical expectations whose resolution may be key to unraveling the aspects of galaxy formation that are least well-understood.

Tuesday December 7:
TBA
Heidi Hammel
Space Science Institute
Host: Jim Elliot

Abstract:

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