Berkeley Astronomy Department Colloquium

Spring 2009

Jan 22
Andy Lawrence (Edinburgh)

UKIDSS is a suite of IR surveys being carried out using the UKIRT Wide Field Camera, starting in 2005 and expected to complete around 2011. Three wide area surveys cover the Galactic Plane and the high latitude sky to K=18.5, totalling seven thousand square degrees, with smaller deeper surveys reaching to K=23. These surveys are making an impact on studies of high-z quasars, very cool brown dwarfs, galaxy clustering, high redshift galaxy formation, and many other areas.  Data are immediately public to European astronomers and world-public eighteen months later. Data are made available through a queryable database system similar to that used by SDSS, but are also now available through VO tools in conjunction with many other resources. I will summarise the status of UKIDSS, show some science highlights, and give a live demo of data access and VO tools.
Avishai Dekel
The Main Mode of Galaxy Formation:  Cold Streams, Clumpy Disks and Compact Spheroids

Many of the massive galaxies in the young universe formed stars at surprising
intensities.  While this was commonly attributed to violent mergers, most of
these galaxies are incompatible with mergers, showing clumpy, extended rotating
disks. In parallel, a large fraction of the z~2 galaxies are compact spheroids
with suppressed star-formation rates (SFR), too abundant to be explained by
major mergers.  Hydro cosmological simulations reveal that most of the star
formers are Stream-Fed Galaxies, growing via steady, narrow, cold gas streams
that penetrate through the shock-heated media of massive dark-matter halos, and
rapidly turn into stars. On average, one third of the stream mass is in gas
clumps leading to mergers and the rest is in smoother flows.
A simple theoretical analysis reveals that the evolution of high-redshift disks
is governed by the interplay between fueling by smooth and clumpy streams and
stabilization by a spheroid of dark matter and stars, leading to a bimodality
in galaxy type by z~3. Disks of giant clumps and high SFR form when the streams
are relatively smooth.  The streams maintain a dense disk that undergoes
gravitational fragmentation into giant clumps, whose mutual encounters
self-regulate the instability with a high velocity dispersion.  Encounters and
dynamical friction induce rapid inward clump migration while the disk expands
in response.  The streams replenish the draining disk and extend the duration
of the clumpy phase to several Gyr in a steady state.  The clumps form stars at
the accretion rate and each turns into stars in several dynamical times. The
migrating clumps coalesce dissipatively into a compact bulge.
Passive spheroid-dominated galaxies form when the incoming streams are more
clumpy.  These external clumps stir up turbulence in the disk and grow a
dominant bulge; together they stabilize the disk and suppress in-situ clump and
star formation.  This scenario explains the bimodality observed at z~2, of
clumpy star-forming extended disks alongside with compact spheroids of
suppressed SFR.  High-resolution cosmological simulations reveal clumpy disks
consistent with this analysis.
Feb 5
Martha Haynes (Cornell)
HI Cosmology in the Local Universe with ALFALFA

The Arecibo Legacy Fast ALFA (ALFALFA) survey is an
on-going second generation blind extragalactic HI survey
exploiting Arecibo's superior sensitivity, angular
resolution and digital technology to conduct a census
of the local HI universe over a cosmologically significant
volume. When complete in 2-3 years, ALFALFA will detect
more than 25,000 extragalactic HI line sources out
to z~0.06, and its catalog will be especially useful
in synergy with wide area surveys conducted at other
wavelengths. ALFALFA is detecting HI masses as low as
10**6 solar masses and as high as 10**10.8 solar masses
with positional accuracies typically better than 20 arcsec,
allowing immediate identification of the most probable
optical counterpart to each HI detection. In the region
of the Virgo cluster of galaxies, a number of optically
dark HI sources have been found. These all lie in the
outskirts of the cluster and could be a mixture of
"harassment" debris and ram-pressure stripping events.
First ALFALFA results already indicate, in agreement with
the suggestions of previous, more limited studies, that
there is not a cosmologically significant population
of optically dark but HI rich galaxies. However, the majority
of ALFALFA detections are too optically faint or of low surface
brightness to have been included in previous targeted HI
surveys. ALFALFA promises a wealthy dataset for the exploration
of many issues in near-field cosmology and galaxy evolution studies,
setting the stage for future extension of these investigations
to higher redshifts with the Square Kilometer Array.
Nate Smith (UCB)
Eruptive mass loss in massive stars and immediate precursors to supernova

I will discuss the role of mass loss in the late evolution of massive
stars, with emphasis on observational clues concerning episodic
mass-loss properties of massive stars in the time shortly before the
final explosion.  Eruptive outbursts of luminous blue variables (LBVs)
are sometimes called supernova "impostors" when their outbursts are
seen in other galaxies, and I will discuss mounting evidence that some
LBVs and related massive stars may be supernova progenitors.  Although
they dominate the late evolution of the most massive stars, these
outbursts still lack a plausible physical explanation.  However, they
will be an increasingly important component of the transient sky as
deeper searches come online, providing hope that we may achieve a
statistical understanding of their influence.  Finally, I will
highlight evidence from observations of some recent extraordinary
supernovae suggesting that explosive or episodic mass loss (like the
19th century eruption of Eta Carinae) occurs in the 5-10 years
immediately preceding the supernova.  Collectively, these precursor
eruptions indicate that we are missing an important and dynamic aspect
of stellar interiors in the last burning phases of massive stars.  The
connection of LBV-like eruptions to supernovae challenges current
paradigms of massive-star evolution, and may have implications for
supernovae in the early Universe.

Peter Smith (Arizona)  -- Joint EPS
Phoenix in Wonderland

On May 25, 2008, the Phoenix team began operation of a robotic laboratory on the northern plains of Mars.  Inside the arctic circle at 68 degrees, the undulated terrain driven by the ice underneath formed polygons.  The robotic arm quickly dug a trench 5 cm deep and exposed the underlying ice table; samples of soil and ice were retrieved and analyzed in 3 instruments.  The results of those instruments reveal an alkaline environment buffered by Ca-carbonate with nutrients and potential chemical energy sources.  This may be a habitable environment for microbes if liquid water is periodically available.  The Phoenix weather station monitored atmospheric conditions as the sky turned from dusty to cloudy with ice snowing onto the surface.  We are investigating conditions in previous epochs to determine if water could wet the soil at times when the obliquity exceeds 30 degrees.

de Pater
Eiichiro Komatsu (Texas)
Testing Physics of the Early Universe Observationally: Are Primordial Fluctuations Gaussian, or Non-Gaussian?

How can we test competing theories about the origin and evolution of the universe? The most direct observational probes are the statistical properties of the primordial density fluctuations. Current evidence strongly suggests that they were generated as quantum fluctuations and that their probability distribution is very close to gaussian, consistent thus far with the simplest class of cosmic inflation models but also with alternatives that predict larger deviations from gaussianity. Improving constraints on non-gaussianity is now recognized as one of the most powerful and fundamental observational tools for understanding the physics of the early universe. In this talk, I will discuss how to search for primordial non-gaussianities in observational data, the current state of affairs and future prospects.

Mar 5
Russ Howard -- Joint EPS
 The SECCHI Experiment on the STEREO Mission

The Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) on the NASA Solar Terrestrial Relations Observatory (STEREO) mission is a suite of remote sensing instruments consisting of an extreme ultraviolet (EUV) imager, two white light coronagraphs, and two telescopes that comprise the heliospheric imager. SECCHI observes coronal mass ejections (CMEs) from their birth at the sun, through the corona and inner heliosphere. A complete instrument suite is being carried on each of the two STEREO spacecraft, which will provide the first sampling of a CME from two vantage points. The spacecraft, launched 25 October 2006, are orbiting the Sun, one Ahead of the Earth and the other Behind, each separating from Earth at about 22 degrees per year, so that they are now separated by about 90 degrees. The primary science objectives are focused on understanding the physics of the CME process - their initiation, 3D morphology, propagation, interaction with the interplanetary medium and space weather effects. By observing the CME from multiple viewpoints with UV and coronagraphic telescopes and by combining these observations with radio and in_situ observations from the other instruments on STEREO as well as from other satellites and ground based observatories operating at the same time, answers to some of the outstanding questions will be obtained. All of the telescopes are working very well and have been producing spectacular images. The panoramic view of the inner solar system is unprecedented. Perhaps the most intriguing and perhaps surprising observations have been the ability to image the fluctuations of the solar wind, the interactions of the solar wind with comet tails and the imaging of the compression ahead of high speed streams which form the corotation interaction regions (CIRs). The STEREO mission is certainly providing a global view to what up to now has been based on/ in-situ/ measurements. We will show examples of some of the data and some of the results.
Michael Garcia (MIT)
International X-Ray Observatory

The International X-ray Observatory (IXO) promises to open a new
window on the universe by delivering on the promise of X-ray
spectroscopy.  Current observatories are able to obtain
high quality spectra on only the brightest x-ray sources.
For the vast majority of x-ray sources what pass for spectra
are more akin to UBV colors.  The IXO will allow routine spectroscopy
at R>1000 for typical sources, and provide a factor of 100 improvement
in effective area for high resolution x-ray spectroscopy.
The science questions that the IXO will address are very broad, and include:
How do super-massive Black Holes grow and evolve? Does matter orbiting close
to a Black Hole event horizon follow the predictions of General
Relativity?  What is the Equation of State of matter in Neutron Stars?
How does Cosmic Feedback work and influence galaxy formation? How does
galaxy cluster evolution constrain the nature of Dark Matter and Dark
Energy? Where are the missing baryons in the nearby Universe?  When
and how were the elements created and dispersed?  How do high energy
processes affect planetary formation and habitability?  How do
magnetic fields shape stellar exteriors and the surrounding
environment? How are particles accelerated to extreme energies
producing shocks, jets, and cosmic rays?
The IXO is ready to compliment the suite of new large ground and
space based observatories coming in the next decade.  This colloquium will discuss both the science
and the implementation of the IXO.
Crystal Brogan (NRAO)

Searching for the Secrets of Massive Star Birth

Massive stars are among the most important constituents of galaxies. They dominate the energetics of ``normal'' and starburst galaxies by driving winds, outflows, heating, and ultimately by producing supernovae. However, many of the fundamental questions regarding massive star formation are poorly understood, even in our own Galaxy. Among these are: where, how, and under what conditions do high mass stars form? Fortunately, we are entering a new era in the exploration of massive star formation using new mm/submillimeter arrays like the SMA and CARMA, new cm-wavelength capabilities on the EVLA, as well as high resolution and sensitivity mid-IR data from Spitzer. In this talk I will present results from recent high resolution mid-IR to centimeter wavelength studies of massive star forming regions and their precursors: infrared dark clouds (IRDCs). I will also discuss how the tremendous advances offered by ALMA at mm/submm wavelengths and the ATA, and EVLA at cm wavelengths at the beginning of the next decade will allow us to probe the secrets of massive star birth with unprecedented frequency coverage, sensitivity, and resolution.
Apr 2
Luis Lehner (LSU)
Recess is over! understanding gravity in strong regimes in time for observations

Understanding some of the most bizarre (aka exciting)
events require gravity in its strongest regimes to
``play along'' and help in inducing violent scenarios.
Recent theoretical developments are beginning to shed
light in a number of fronts which will hopefully soon
be put to the test. This talk will discuss some relevant
systems including black holes, neutron stars and possibly
higher dimensional black holes and connect with efforts to
directly probe this system through gravitational waves detection
and indirectly by understanding possible signatures in the
electromagnetic waveband.
Sara Seager (MIT)
Exoplanets: Interiors, Atmospheres, and the Search for Habitable Worlds

Over 300 exoplanets are known to orbit nearby stars. Now that their existence is firmly established, a new era of “exoplanet characterization” has begun. A subset of exoplanets—called transiting planets—pass in front of their stars as seen from Earth. Transiting planets have immeasurably changed the field of exoplanets because their physical properties, including average density and atmospheric thermal emission, can be now be routinely measured. I will summarize the observations and their interpretation of some of the 50 transiting exoplanets. I will discuss how the race to find habitable exoplanets has accelerated with the realization that “big Earths” transiting small stars can be both discovered and characterized with current technology. These ideas will lead us down a path to the ultimate goal of finding and identifying Earth analogs.

Scott Gaudi (OSU)
The Demographics of Extrasolar Planets with Gravitational Microlensing

Microlensing is unique among planet detection methods in that it is potentially sensitive to analogs of all the solar system planets except Mercury, as well as to free floating planets. I review the landscape of microlensing searches for extrasolar planets, beginning with an outline of the method itself, and continuing with a review of the results that have been obtained to date. Eight planets have been detected with microlensing so far; I discuss what these detections have taught us about the frequency of terrestrial planets, giant planets, and solar system analogs. I then speculate on the expected returns of next-generation microlensing experiments both from the ground and from space. When combined with the results from other complementary surveys, next generation microlensing surveys will yield a complete picture of the demographics of planetary systems throughout the Galaxy.
Jim Cordes (Cornell)
The Right Place and the Right Time: Pulsars, ALFA and Gravity

There is great interest in discovering new pulsars for use
as astrophysical tools while also surveying radio transient
sources.  I will discuss the program of pulsar science,
the motivations over the near and longer term,
and using existing telescopes and future ones, like the
Square Kilometer Array.  I will highlight results from
the current large-scale pulsar/transient survey at Arecibo
using the ALFA system  and the prospects for finding pulsars
near Sgr A*. The payoff from finding new relativistic
binary pulsars and highly spin stable millisecond pulsars
follows from their use for probing  gravity and the environs of
their companions and for detecting  nano-Hertz gravitational
waves.   Issues and prospects for
success in these areas will be discussed.
Roger Romani (Stanford)
Fermi Lat Gamma-Ray Pulsars:  Initial Results and Interpretation

The Fermi LAT has detected some 50 gamma-ray pulsars, including 7 millisecond pulsars and over a dozen discovered directly in the gamma-rays. Since the pulsed gamma-rays represent a substantial fraction of the spin-down power, this population gives us important new insights into the physics of the pulsar machine. I review the early pulsar sample, summarize patterns in the data and discuss prospects for additional pulsar discoveries.
May 7
Lisa Kewley (Hawaii)
The Cosmic Star Formation and Metallicity History of Galaxies

Observing the star formation rate and metallicity since the
earliest times in the universe is crucial to understanding galaxy
formation and evolution. Current cosmic star formation history studies
are plagued by significant discrepancies between star formation rate
estimates at different wavelengths. I apply the new generation of stellar
population synthesis and photoionization models and show that metallicity
is key to resolving the star formation rate discrepancies. Although the
cosmic star formation history has been studied extensively, our
understanding of the metallicity history of star-forming galaxies is still
largely theoretical. I present the results of our large ongoing
observational investigation into the metallicity history of star-forming
galaxies between 0<z<1, and initial results from our new program to use
gravitational lensing to probe metallicities in galaxies at z>1. I compare
our observed metallicity history with predictions from cosmological
hydrodynamic simulations, and discuss the future directions for our star
formation and metallicity history research. The goal of this research
program is to gain a simultaneous observational understanding of the
gas-phase metallicity and star formation history of galaxies between 0<z<3
to confront chemical evolution models.