| Date |
Speaker |
Title |
Host |
| August 27 |
Mike Boylan-Kolchin (MPA) |
Simulating the formation of
structure in the Universe Numerical simulations of structure formation have become essential tools for studying cosmology and galaxy formation. I will describe some of the newest, highest resolution cosmological simulations and discuss how they are influencing our understanding of the formation and evolution of dark matter halos. I will also focus on the Milky Way as a testing ground for models of cosmology and galaxy formation. The wealth of available and forthcoming observational data will provide strong constraints on both luminous and dark matter in the Galaxy. I will discuss how combining this data with the latest generation of numerical simulations is advancing our knowledge of how galaxies form. |
Ma |
| September 3 |
Everyone |
1 Minute Colloquium |
Bower |
| September 10 |
John Johnson (Caltech) |
The Golden Age of Exoplanet
Spin-Orbit Measurements The angular momentum of the Solar System planets is remarkably well aligned with the spin axis of the Sun. This arrangement supports the hypothesis that the planets and the Sun formed from the same spinning disk of gas and dust. Until very recently, measurement of the spin-orbit alignment of exoplanets had revealed that planets around other stars, most in very close-in orbits, also have well-aligned spin and orbit axes. However, our recent measurements from this past year have revealed that there may be a second class of exoplanets that inhabit very tilted orbits, and that some may even have retrograde configurations. I'll show how spin-orbit measurements are made, and discuss how the distribution of observed spin-orbit angles informs, and challenges, theories of planet migration. |
Marcy |
| September 17 |
Pasquale Blasi (Arcetri) |
Particle Acceleration in
Supernova Explosions and the Origin of Cosmic Rays The Galaxy is permeated by Cosmic Rays, a gas of charged particles whose energy spectrum extends from 10^8 eV to about 10^20 eV. Their origin is still matter of much debate but in the last few years we have moved some crucial steps forward toward understanding how these particles are accelerated, the primary candidate sources being supernova remnants. I will describe these recent developments focusing on non linear particle acceleration at collisionless shocks and the important connection between the microphysics of particle scattering and the overall appearance of supernova remnants in radio, X-rays and gamma rays. I will also discuss some implications of the emerging picture that could provide a clue to the origin of the highest energy part of the cosmic ray spectrum, believed to be of extragalactic origin. |
Seljak |
| September 24 |
Dave Jewitt (UCLA) |
PRIMORDIAL ICE RESERVOIRS OF THE
SOLAR SYSTEM We now know that primordial ice exists in at least three distinct Solar system reservoirs; the Oort cloud, the Kuiper belt and the asteroid main-belt. Continuing efforts to determine the nature of the ice and its distribution are important for several scientific reasons. First, the mere existence of the ice sets a limit to the degree of thermal processing of the objects in which it is found, and therefore constrains geophysical models of thermal evolution of ice rich bodies. Second, water ice, if in the amorphous form, can trap other volatiles from the protoplanetary disk of the Sun at high abundance. Their subsequent release upon crystallization can perhaps explain the anomalous activity observed in many comets and is a source of energy, since crystallization is exothermic. Third, water and other volatiles on the terrestrial planets seem likely to have been delivered, in part, from the ice reservoirs. The comets and ice-rich asteroids therefore may hold the key to understanding the origin of the oceans and atmosphere. In this talk, I will aim to provide a broad overview of our current knowledge (and lack of knowledge) of the primordial ice reservoirs. I will emphasize links to the formation epoch and draw connections for those interested in the origin of the oceans and the atmosphere and in the thermal evolution of asteroids and comets. I will try to do this in a way interesting to astronomers, Earth scientists and atmospheric scientists alike. |
de Pater |
| October 1 |
Moshe Elitzur (UKy) |
The AGN Torus --- a Paradigm
Change The variety of observations of Active Galactic Nuclei (AGN) show that the nuclear activity is powered by a central massive black hole that drives radio emitting jets and ionizes surrounding line-emitting clouds. This central engine is surrounded by an obscuring torus, comprised of optically thick dusty clouds in a rotating configuration. The torus dynamical origin, and especially its vertical support, present a serious challenge. We have recently developed the formalism for radiative transfer in clumpy media, and in this talk I show that past problems with modeling the AGN infrared emission find a natural explanation in clumpy torus models. Furthermore, the clumpy model may also provide the answer for the torus dynamical origin and solidify the case for a paradigm shift: the torus is apparently just the dusty region of wind outflow from the AGN accretion disk in which the clouds are optically thick. |
McKee |
| October 8 |
Chris Fassnacht (UC Davis) |
Galaxy Halos and Subhalos at
Moderate Redshifts Current simulations of galaxy formation make predictions about how mass will be distributed in galaxy halos. Using the technique of gravitational lensing, it is becoming possible to measure details of mass distributions in galaxies beyond the local Universe and, thus, to compare observations directly to simulations for samples of cosmologically distant objects. I will describe results from two ongoing projects that take advantage of high- resolution space- and ground-based imaging. The first combines strong and weak gravitational lensing to quantify the relative contributions of the dark and luminous matter in galaxies on scales from 10 kpc to nearly 1 Mpc. The second focuses on detecting the CDM subhalos predicted by simulations, via both direct imaging and gravitational lens modeling. |
Bower |
| October 15 |
Eve Ostriker (UMD) |
The Large-Scale Regulation of
Star Formation in Disk Galaxies Star formation in disk galaxies takes place in cold, dense clouds containing millions of solar masses of molecular gas. These clouds are very dynamic, forming out of diffuse interstellar gas, undergoing local collapse to produce clusters of stars, and then dispersing due to energetic feedback from star formation. Recent numerical simulations have shown how self-gravitating ISM compression results in strings of HII regions that light up spiral arms, and creates interarm structures seen in high-resolution HST and Spitzer images of grand design spirals. Simulations including a multiphase ISM have been able to reproduce observed relationships between large-scale gas properties and star formation rates in nearby disk galaxies, and have demonstrated how feedback-driven turbulence and environment (including the rotation rate and the stellar disk's gravity) are crucial in setting these rates on ~kpc scales. These results help to explain why observed molecular-to-atomic mass ratios and star formation rates correlate with the mean midplane pressure. In addition, they suggest that empirical Kennicutt-Schmidt relations between star formation rate and gas surface density arise in part as a result of long-term galactic evolution toward Toomre parameters near unity. In discussing these recent results, I will also highlight the importance of resolving disks' vertical structure in numerical models, in order to obtain reliable measures of the star formation rate. |
Quataert |
| October 22 |
Laurent Loinard (UNAM) |
The space distribution of nearby star-formation |
Bower |
| October 29 |
Paul Ho (CfA/ASIAA) |
Preparing for ALMA First Science The Submillimeter Array has been in operations on Mauna Kea since 2004. Many interesting and important results have been obtained in that time including planetary studies, dusty circumstellar disks, extremely collimated molecular outflows, circumnuclear disks in nearby galaxies, magnetic fields via dust polarization studies, and dark submillimeter galaxies at high red shifts. These studies are paving the say for the first science projects to be attempted on ALMA, currently under construction in that Atacama Desert. I will show some of our latest results. |
Blitz |
| November 5 |
Lincoln Greenhill (CfA) |
Moving Images of Accretion and
Outflow in High-Mass Star Formation The details of how massive stars form are poorly understood. Testing the viability of disk-mediated accretion, and identifying the processes that extract angular momentum benefit from direct measurement of the dynamics of gas at small radii, where outflows are launched and collimated. Using the VLBA and VLA, and for the first time, we have traced gas structures and tracked 3-D motions within them, 10-1000 AU from a high-mass YSO. We resolve an edge-on disk about 50 AU across and measure its rotation. We also resolve a wide-angle outflow that collimates at radii beyond 100 AU. The implied dynamical mass is about 8 Msun. Close to the disk, curved streamlines suggest that magnetic fields may play a role in launching the outflow. The YSO is quite highly embedded, without known emission up to 20 um. This is consistent with the inferred edge-on disk orientation and high column density. I will discuss possible origins for this disk |
Backer |
| November 12 |
Mate Adamkovics (UCB) |
Using tropospheric methane and stratospheric aerosol to monitor |
Kalas |
| November 19 |
Norm Sleep (Stanford) |
The interaction of
photosynthesis with the crust and mantle and the effect of the moon-forming impact on the current Earth Photosynthesis evolved before 3.8 billion years ago. Rocks of that age include metamorphosed black shales with pyrite showing that sulfur based and iron based photosynthesis existed. A complete carbon cycle existed on land and at sea. The land biota needed FeO to dump oxygen. A consortium with efficient weathering evolved to obtain the FeO from exposed rocks. Weathering in turn led to wide-spread continents with Fe-poor sediments and Fe-poor granites. The presence of these rock types provided selective pressure to vent oxygen directly and the advent of cyanobacteria. The mantle as well as the crust sequesters biological information. The Earth became habitable after the moon-forming impact once its interior was cold enough for carbonate to subduct in very C-rich domains in the upper oceanic crust. This process continues today causing mantle carbon to exist within highly concentrated domains. The chemical and isotopic character of these domains survives subduction and even partial melting of kimberlites and their freezing within the lithosphere. The build up of oxygen in the Earth's atmosphere is evident in U/Th of zircons in kimberlites. Subduction of carbonate 4.26 billion years ago and its emplacement with the continental lithosphere at 3.6 billion years ago is indicated by study of a 1.48 suite of alkalic rocks in India. |
Millitzer |
| December 3 |
Maryam Modjaz (UCB) |
Elucidating the SN-GRB
Connection from the SN Perspective Massive stars die violently. Long-duration gamma-ray bursts (GRBs) and Type Ib/c Supernovae (SN Ib/c) are two of nature's magnificent explosions that can be seen over cosmological distances, and both are products of collapsing massive stars. However, we still do not fully understand the exact conditions that produce each kind of stellar explosion. While GRBs emit relativistic jets, SN Ib/c are core-collapse SN whose massive progenitors have been stripped of their hydrogen and helium envelopes. I will present a number of observational venues that probe the progenitor environments of SN with and without GRBs, the metallicities at their sites and their explosion geometries. Specifically, I will discuss SN 2008D, which was discovered serendipitously in January 2008 with the NASA Swift satellite via its X-ray emission and has generated great interest by astronomers (12 papers and counting). I will discuss the significance of this SN, whether it harbored a jet, and its implications for the SN-GRB connection. I will conclude with the most promising venues of upcoming research that can clarify how massive stars die. |
Bloom |