UC Berkeley Astronomy Colloquium Series

Spring 2010

Colloquiua are Thursdays @ 4pm.

Organizer:  Geoff Bower (gbower@astro.berkeley.edu)

21 January
Doug Lin (UCSC)
Origin of Super Earths:

A rich population of super-Earths are being discovered by both radial
velocity surveys and transit searches.  Based on a sequential accretion
scenario, we construct population synthesis models for these exo-planets.
Some important theoretical issues include: 1) what physical processes
determine their mass-period and size-period distribution? 2) how do
dynamical architecture emerge around any host star? 3) Why is
there no super-Earth in the solar system?  Based on these models,
we extrapolate predictions which may soon be tested and calibrated by
ongoing observations.
28 January
Shelley Wright (UCB)
High-Spatial Resolution Observations of z~1-2 Star Forming Galaxies:  Discovering Galactic Disks, Mergers, and Weak AGN

Studies of galaxies in the early universe (z > 1) have greatly benefited from recent advances in diffraction-limited techniques on 8-10m telescopes using adaptive optics and integral field spectroscopy.  I will present results from an on-going survey using Keck's latest instrument OSIRIS and adaptive optics to study the dynamics and chemical abundances of z~1.5 star forming galaxies.  Current challenges in using integral field spectrographs and adaptive optics observations will be described.  I will present H-alpha kinematics for merger and disk candidates at z~1.5.  All disk candidates' plateau velocities and radii are consistent with rotational properties of local spiral galaxies.  I will discuss their mass distributions and significance in the galaxy formation framework.  A few of these systems have [N II] and [O III] emission that is more concentrated than H-alpha emission, and peak emission line ratios are best explained by the presence of a weak AGN.  These are among the weakest known AGN at this epoch, and I will discuss their potential impact on metallicity studies and explore the high redshift AGN luminosity function. Lastly, I will discuss the future of AO instrumentation on 8-10m telescopes and extremely large telescopes (30m), and the benefits these instruments offer for studying galaxy formation and evolution.
4 February
Alice Shapley (UCLA)
The ISM in Star-forming Galaxies at z~2-3: Surprising New Insights

There has been a veritable explosion of surveys of z>1.5
galaxies within the few years. Much of this work has focused on the global
properties of distant galaxy populations, rather than the detailed
physical properties of individual objects. Indeed, given the faint
apparent magnitudes and small angular sizes of typical star-forming
galaxies in the distant universe, such detailed studies are challenging.
However, aided by gravitational lensing and a wide array of
multi-wavelength observations, we present some new results that provide
insight into the detailed physical conditions in HII regions of
star-forming galaxies at z~2-3, the nature of dust extinction in such
systems, and the structure of their large-scale outflows -- all crucial
ingredients in models of early star formation and its resulting feedback.
11 February
Jay Melosh (Arizona) - CIPS
Results from NASA’s Deep Impact Mission to Comet Tempel 1

 In the early hours of July 4, 2005, one of the two of NASA’s Deep Impact spacecraft splashed down on the surface of Comet Tempel 1 at 10.2 km/sec, creating an impact crater about 100 m in diameter and 30 m deep.  The second spacecraft, passing by at the safe distance of 500 km, sent images of the event back to the Earth.  The object of this interplanetary kamikaze mission was to dig deep beneath the surface dust deposits and expose the pristine interior 1 to 10 m below the surface. The mission succeeded spectacularly:  The impact threw out about 10 million kilograms of fine dust, tarry organic material, frozen water and CO2, after creating an initial jet of melted silicates and vaporized ices.  Analysis of more than 4,000 images and spectra returned from the two spacecraft, revealed that old ideas about the structure of comets must be substantially revised.  On November 4 of this year, the Deep Impact team is returning to Tempel 1 via the Stardust spacecraft to examine the consequences of the impact in more detail and complete our survey of the comet’s surface.
de Pater
18 February
Lori Lubin (UC Davis)
Understanding Cluster Formation and Galaxy Evolution...ORELSE

I present the motivation, design, and latest results of the
Observations of Redshift Evolution in Large Scale Environments
(ORELSE) Survey, a systematic search for structure on scales greater
than 10 Mpc around 20 known galaxy clusters at redshifts of z >
0.6. The survey covers nearly 5 square degrees, all targeted at
high-density regions, making it complementary and comparable to field
surveys such as DEEP2 and COSMOS. I describe the large scale
structures that have been photometrically and spectroscopically
confirmed so far through this program. In particular, I focus on the
multi-wavelength studies of the Cl 1604 supercluster at z = 0.9, which
contains at least eight clusters and spans 10 Mpc by 100 Mpc. I will
describe the filamentary structure of this supercluster, the galaxy
properties as a function of environment, and the large population of
(optically-innocuous) active galaxies detected through radio, mid-IR,
and X-ray observations. The physical processes responsible for
star-formation, starbursts, and nuclear activity in these
intermediate-density regimes and the implications for galaxy evolution
will be discussed.
25 February
Dennis Zaritsky (Arizona)  --cosmology group colloquium A Revised Perspective on Galactic Structure

Unlike the theory of stellar structure, which has a simple and intuitive outline, that of galactic structure is piecemeal and ad hoc. In fact, it has been difficult even to determine whether or not one should expect there to be such an analog. Numerical modeling of the problem grows ever more sophisticated and detailed in its efforts to match observations, suggesting that perhaps the problem is beyond any simple description. However, I will, using simple and general arguments, demonstrate that the global structure of galaxies of all sizes, masses, and morphological types can be described to a high degree using only two observational parameters. I will then explore the nature of those two parameters and ultimately present an attempt to tie those to basic physical parameters, thereby providing (perhaps) a simple and intuitive outline of galactic structure.
4 March
Bart de Pontieu (Lockheed Martin)
Energizing the low solar atmosphere: recent results from Hinode

The Sun's corona is millions of degrees hotter than the photosphere, which is at about 5,000 K. This is the so-called "coronal heating problem"; an enigma that is typically addressed by invoking the deposition at coronal heights of non-thermal energy that is generated by the interplay between convection and magnetic field near the photosphere. However, many unresolved issues remain regarding the nature, location and detailed mechanism filling the corona with hot plasma. I will focus on the role of the chromosphere, the layer sandwiched between the solar surface (photosphere) and corona, in energizing the solar atmosphere. The chromosphere has its own heating problem: while it is only 10,000 K, it is much more dense than the corona and requires over 30 times more energy than the corona. The recent advent of advanced numerical simulations and high resolution observations with the Hinode satellite and ground-based telescopes have allowed significant advances in our understanding of this highly dynamic layer in the solar atmosphere, which has long been ignored because of its complexity. I will review recent results about the role of high-frequency acoustic waves in heating the quiescent chromosphere, and the formation of jet-like features called chromospheric spicules. I will focus on observations and 3d MHD modeling that indicate these jet-like features may provide large amounts of hot plasma to the corona, suggesting that some of the coronal heating may actually occur at very low heights in the solar atmosphere. I will also review the first observations of Alfven waves in the chromosphere, which show that these jets carry Alfven waves with enough energy flux to help accelerate the solar wind.
11 March
James Bullock (UC Irvine)

Dwarf Galaxies, Dark Matter, and the Threshold of Galaxy Formation

Over the past five years, searches in Sloan Digital Sky Survey data have more than doubled the number of known satellite galaxies orbiting around the Milky Way disk, revealing a population of ultra-faint systems with total light output barely reaching ~1000 times that of the Sun. These newly-doscovered dwarf galaxies represent galaxy formation in the extreme. They are not only the faintest galactic systems known but they are also the most dark matter dominated and most metal poor galaxies in the universe. Completeness corrections suggest that we are poised on the edge of a vast discovery space in galaxy phenomenology, with hundreds more ultra-faint galaxies to be discovered as future instruments hunt for the low-luminosity threshold of galaxy formation. I discuss how dark matter dominated dwarfs of this kind probe the small-scale power-spectrum and offer a particularly useful target for dark matter indirect detection experiments.
18 March
James Farquhar (UMD) - CIPS
A look into Earth's early environments

The first two billion years of Earth's history are thought to have been characterized by an atmosphere and oceans with low to no free molecular oxygen, and this condition is thought to have changed about two and a half billion years ago. Our understanding of the nature of these environments draws on a variety of geological and geochemical lines of evidence, and a significant part of this evidence is linked to sulfur chemistry and sulfur isotopic compositions preserved in the rock record. In my talk, I will discuss the record of oxygen in Earth's early history and focus on aspects of the sulfur isotopic record that tell us about oxygen in Earth's early environments. We will examine issues related to links between sulfur and oxygen as well as possible links with biology and metabolism.
1 April
Shri Kulkarni (Caltech)
Charting the Transient Sky:
The Palomar Transient Factory

During most of the last century, the study of explosive transient
sources and variable stars was a major focus of astronomy. The
physical scale of the Galaxy and Universe and the build up of
elements were revolutionized by these studies.  This field is once
again undergoing a renaissance due to wide field optical surveys.
The Palomar Transient Factory (PTF) was designed to explicitly to
chart the transient sky with a  particular focus on events which lie
in the nova-supernova gap.. With its innovative two-telescope
architecture it achieves both high cadence and large areal rate of
coverage. PTF was commissioned during the summer of 2009.  PTF is
now finding an extragalactic transient every 20 minutes and a
Galactic (strong) variable every 10 minutes.  Our first two major
accomplishments are the discovery of a new class of ultra-bright
supernovae (dubbed spasmanova) and UV spectroscopy of a large sample
of local Ia supernovae (of considerable importance to the use of
Ia supernovae for cosmography). The large rate of SN discovery is
allowing us to sort the mystery of various supernovae sub-classes
(and in some cases radically altered our view of their origin).

8 April
Jim Stone (Princeton)
Gas and Dust Dynamics in Protoplanetary Disks.

As dust grains coagulate and grow into "pebble"- and "boulder"-sized
particles in a protoplanetary disk, they are subject to a dynamical
instability, driven by aerodynamic drag forces, that produces strong
clumping in the particle density and waves and/or turbulence in the gas.
I will present results from new hydrodynamical simulations of the
nonlinear regime of this "streaming instability" in vertically stratified
disks that investigate the settling and clumping of particles with a
range of sizes.  The upper layers of protoplanetary disks may also be
unstable to the MRI, and I will discuss the interplay of the streaming
instability and turbulence driven by the MRI, and how this might influence
planetesimal formation.
15 April
Bill Borucki (NASA Ames)
Status of Kepler Mission and Early Discoveries

Kepler is a Discovery-class mission designed to determine the frequency of Earth-size planets in and near the habitable zone of solar-like stars. The instrument consists of a 0.95 m aperture photometer designed to obtain high precision photometric measurement of > 100,000 stars to search for patterns of transits. The focal plane of the Schmidt-type telescope contains 42 CCDs with at total of 95 megapixels that cover 115 square degrees of sky. The photometer was launched into an Earth-trailing heliocentric orbit on March 6, 2009, finished its commissioning on May 12, and is now in the science operations mode. During the commissioning, data were obtained at a 30 minute cadence for 53,000 stars for 9.7 days. During the first 33.5 days of science-mode operation, 156,000 stars have been observed.  Discoveries based on these data are presented.  Although the data have not yet been corrected for the presence of systematic errors and artifacts, the data show the presence of hundreds of eclipsing binary stars and variable stars of amazing variety.  Analysis of the commissioning data also show transits, occultations and light emitted from the known exoplanet HAT-P7b. The depth of the occultation is similar in amplitude to that expected from a transiting Earth-size planet and demonstrates that the Mission has the precision necessary to detect such planets. Several new exoplanets discovered by Kepler are discussed and compared with known exoplanets with respect to mass, size, density, and orbital period. Detections of stellar oscillations and unusual objects are also presented.
22 April
Kevin Bundy (UCB)
Galaxy Metamorphosis: Quenching, Downsizing, and the Rise of Spheroidals

We are arguably living through a transitional epoch in the evolution of galaxies. During the peak of galaxy growth and assembly at z~2, vigorously star-forming disk galaxies were abundant at all masses. Soon after, however, the most massive disks underwent a metamorphosis into spheroidals largely quenched of star formation. This transformation occurs in lower mass galaxies with time, and at present, the rising abundance of quenched spheroidals accounts for more than half of the global stellar mass density. Understanding what drives this metamorphosis remains a key challenge. I will discuss several observational tests enabled by recent galaxy surveys that are providing new insights on possible explanations, including galaxy mergers, AGN feedback, environmental effects, and secular processes. While a consistent picture seems to be emerging, several surprises have revealed unexpected complexity and highlight the notion that evolution likely proceeds in several stages.
29 April
Carey Lisse (JHU)
Mid-IR Spectroscopy of Comets & Dusty Disks : Mineralogical and Elemental Clues to the Formation and Evolution of Solar Systems

With observations made by the Spitzer Space Telescope, we are beginning to understand the details of how the composition and formation of our own Solar System compares to those of other stars in our Galaxy.  This is a major question in astronomy, and recent, detailed observations by Spitzer of comets (remnants of the solar systems proto-planetary disk), proto-planetary disks around Young Stellar Objects, debris disks around moderate-age stars, and dust rich DZ white dwarfs have given us a collection of detailed spectra containing clues about our Galactic context. In this talk I will discuss Spitzer and related ISO mid-infrared (5 to 40 micron) spectroscopy of 6 comets and the dusty systems SST-LUP3-1 (1My old BD), HD100546/HD163296 (Herbig Baby Vegas), HD113766 (F5 building a Mars/Earth), HD172555/HD145263/HD23514 (giant impact systems), HD69830 (mature Epsi Eri w/ hyperzody),and  G29-38/GD362 (WDs).  Using the results from the recent Deep Impact and STARDUST space missions as ground truth, we can now constrain the relative abundances of silicates, carbonates, water ice/gas, amorphous carbon, sulfides, and polycyclic aromatic hydrocarbons (PAHs) in dusty disks, and directly relate the temperature of the circumstellar dust to its location with respect to the system primary.  I will discuss the similarities and differences in the spectra, the amount, kind, and location of the dust and gas species detected, the primitive or advanced state of processing of the dust, compositional solar system analogues for the inferred source parent bodies, and their implications for our Solar System's origin and evolution.

6 May
Sukanya Chakrabarti (UCB) Deciphering the Dynamical Impact of CDM Sub-Structure

The Cold Dark Matter (CDM) paradigm is very successful at explaining the growth of structure on large scales. However, it predicts an excess of structure on sub-galactic scales. This over-abundance of CDM sub-structure in simulations relative to observations of Local Group dwarf galaxies is currently one of the most outstanding problems in astrophysics and cosmology. Motivated by this discrepancy, we ask the question if dark galaxies (or dim dwarf galaxies) can be discovered by their tidal gravitational effects on the gas disks of spiral galaxies. I will focus most of my talk on my recent work (Chakrabarti & Blitz 2009; Chakrabarti et al. 2010) where I analyze observed perturbations in the outskirts of the gas disk of the Milky Way to infer and characterize a dark sub-halo that tidally interacted with our galaxy. By comparing the Fourier amplitudes of a large set of high resolution SPH simulations of the Milky Way tidally interacting with perturbers, I show that the best fit to the simulations occurs for a 1:100 mass ratio perturber with a pericentric approach distance of ~5 kpc. I will also demonstrate a fundamental property of parabolic orbits that allows us to break the degeneracy between the mass of the perturber and the distance of closest approach in the evaluation of the tidal force. Next, I will show recent results that allow us to extend this tidal analysis method and apply it in generality. I will end by discussing results obtained using my radiative transfer code RADISHE to calculate emergent SEDs and images of simulated galaxies along the course of their time evolution that allow us to correlate multi-wavelength observables with dynamical tracers of tidal interactions.

Previous Colloquiua

Spring 2009
Fall 2008
Spring 2008