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 Astronomy Colloquia at Caltech for 2011-12

Colloquia are held every Wednesday during the academic year at 4:00 pm in the Cahill Hameetman auditorium. Tea and cookies are served at 3:45 pm in the Ahmanson library located on the 1st floor of Cahill.





                                                   Talk Title



Mariska Kriek

Harvard-Smithsonian Center for Astrophysics/Berkeley
Host: Richard Ellis

Characterizing the distant galaxy population using pseudo-spectroscopy

With the recent large photometric and spectroscopic surveys and new
instrumentation on the Hubble Space Telescope, it is now finally
possible to study galaxies in a systematic way at earlier times and
directly witness how the relations between spatial structure, stellar
population, stellar mass, and environment change with redshift. Until
very recently, these studies were hampered by the small sizes of
spectroscopic galaxy samples, whereas much larger photometric samples lack the required spectroscopic information. I will discuss a novel approach, that makes use of medium-band photometry to perform detailed "spectroscopic'' studies of ~3500 galaxies at 0.5<z<2.0. By identifying analogous galaxies we construct composite spectral energy distributions, which are of spectroscopic quality. This composite spectrum collection opens up efficient studies of Halpha and other spectral features for large distant galaxy samples, which would otherwise require extensive near-infrared spectroscopic campaigns. I will show how we have used the composite spectra to study star formation histories of galaxies, constrain stellar population and dust models, and analyse the relation between structural and stellar population properties. Finally, I will present new stellar kinematic measurements of distant galaxies and discuss the implications for the structural evolution of galaxies.



Lisa Kewley


Host: John Johnson

Galaxy Formation and Evolution through Metals

Chemical abundances in galaxies provide a fossil record of previous generations of star formation, modulated by galactic-scale gas flows. I will present the latest results from our investigation into the chemical evolution of galaxies, both locally, and at high redshift.  Theory predicts that as a merger progresses, galaxy disks become disrupted by tidal effects, causing large radial gas flows toward the central regions where kpc-scale starbursts and AGN may be fueled. Isolated disk galaxies have strong chemical abundance gradients that may become disrupted during a merger.  We have conducted the first investigation into chemical abundance gradients across the merger sequence.  We show that abundance gradients evolve dramatically with merger progress, providing a smoking gun for galactic-scale gas flows in merging galaxies.  Moving out in redshift, I present recent results from our investigation into the cosmic chemical history of galaxies. We have measured the chemical abundances for an unprecedented number of galaxies to z~1, finding little evolution between z~1 and the present day.  At higher redshift, we exploit the power of gravitational lensing to investigate the chemical evolution in galaxies between 1<z<3. We have measured the first metallicity gradient in a normal spiral galaxy at z~2, showing a steeper gradient than observed in local spiral galaxies. I will discuss the implications of this result and the future of this field with the next generation of telescopes.


David Arnett

Kavli Institute for
Theoretical Physics, UCSB,
Steward Observatory, Arizona

Host: Christian Ott

Turbulence, Computers and Stars

It is now feasible to numerically simulate moderately turbulent flow in the stellar context. The impact of such simulations on astrophysical theory will be illustrated, as well as a connection to deterministic chaos. There have been a number of surprises, whose implications are only beginning to be appreciated. Applications to solar abundances and helioseismology, and to gravitational collapse and supernovae will be stressed.


Nitya Kallivayalil

Host: Samaya Nissanke

A 1% Proper Motion Measurement for the Large Magellanic Cloud

I present proper motions for the Large & Small Magellanic Clouds (LMC & SMC) based on three epochs of Hubble Space Telescope data, spanning a $\sim 7$ yr baseline, and centered on background QSOs. The first two epochs are provided by the ACS/HRC and were the subject of Kallivayalil et al. (2006a,b) but have been reanalyzed here. The third epoch is brand new data taken with the WFC3/UVIS, providing a completely independent check. Due to the longer timebaseline and the high quality of the WFC3 data we derive proper motions of high accuracy. We are therefore also able to derive a purely proper motion-based rotation curve for the LMC, which is in excellent agreement with the latest line-of-sight velocity-based studies, and for the first time, competitive with the kinds of accuracies typically quoted in such studies. We determine the rotation velocity at large radii a factor of 3 more accurately than previous work. I discuss the consequences of these new measurements for our understanding of the global dynamics of the Milky Way-LMC-SMC system. This work is part of a larger effort towards 6-D mapping of the Milky Way.


Krzysztof Gorski

Host: Sterl Phinney

Early Astrophysics Results from Planck

Planck has been measuring the sky at nine frequencies from 30 to 857 GHz since August 2009.  Designed to extract almost all of the information contained in temperature anisotropies of the cosmic microwave background and to improve significantly our knowledge of CMB polarization, Planck can also address a large range of Galactic and extragalactic astrophysics.  I will describe some early astrophysics results from Planck, and discuss Planck's promise and schedule for cosmology.



Boaz Katz

Host: Ott/Phinney

High energy emission from SNe and super-eccentric hot Jupiters

They are out there, they are detectable and they are crucial theoretically. Detection of early high energy emission (soft X-ray to gamma-rays) at the onset of SNe will allow us to measure the radius of the progenitor, the velocity of the blast wave and signify the presence of a dense stellar wind. Detection of highly eccentric (e>~ 0.99) extra-solar gas-giants with periastron of a few stellar radii may answer the question of how hot Jupiters get so close to their host star.


Paul Groot

Radboud University
Host: Christian Ott

Ultracompact white dwarf binaries; a fresh look


The evolution of ultracompact white dwarf binaries is set by the loss of angular momentum by the emission of gravitational waves. The discovery of detached and accreting systems with orbital periods as short as 5 minutes opens the possibility to test evolutionary theories, spin-orbit couplings of angular momentum, hot-slow merger events. Transient surveys such as the Palomar Transient factory are ideal to detect these systems in the Milky Way and Local Universe as they are are the (possible) sites of supernovae Type Ia, Type .Ia, helium novae and helium dwarf novae outbursts. The PTF has already discovered 6 of the 32 known interacting white dwarf ultracompact binaries and is set to revolutionize the field.


Enrico Ramirez-Ruiz


Host: Stefanie Wachter

Tidal Disruption of Stars by Massive Black Holes

A star interacting with a massive black hole cannot be treated as a point mass if it gets too close to the black hole that it becomes vulnerable to tidal distortions and even disruption. When a rapidly changing tidal force starts to compete with a star’s self-gravity, the material of the star responds on a complicated way, being stretched along the orbital direction, squeezed at right angles to the orbit and strongly shocked. This phenomenon poses an as yet unmet challenge to computer simulations. The art of modeling tidal disruption of stars, especially those entering the strong relativistic regime, forms the main theme of my talk. Detailed simulations should tell us what happen when stars of different types get tidally disrupted, and what radiation a distant observer might detect as the observational signature of such events.






  Debora Sijacki

  Host: Ott/Phinney
Moving mesh cosmology: the hydrodynamics of galaxy formation

As already established in Frenk et al. 1999, entropy profiles of galaxy clusters are systematically different when simulated with SPH versus Eulerian mesh codes. This systematic difference has persisted until now, casting doubts on the ability of hydrodynamical schemes to follow complex hydrodynamical flows in full cosmological settings reliably. I will present a detailed comparison between the well-known SPH code GADGET and the new moving-mesh code AREPO on a number of hydrodynamical test problems. Through a variety of numerical experiments with increasing complexity I will establish a clear link between simple test problems with known analytic solutions and systematic numerical effects seen in cosmological simulations of galaxy formation. These tests demonstrate deficiencies of the SPH method in several sectors. An inadequate treatment of fluid instabilities in GADGET suppresses entropy generation by mixing, underestimates vorticity generation in curved shocks and prevents efficient gas stripping from infalling substructures. These accuracy problems not only manifest themselves in idealized hydrodynamical tests, but
also propagate to more realistic simulation setups of galaxy formation, ultimately affecting local and global gas properties in the full cosmological framework.



Scott Gaudi

Ohio State

Host: John Johnson

The Demographics of Exoplanets with Gravitational Microlensing

I review the landscape of microlensing searches for exoplanets, beginning with an outline of the method itself, and continuing with a review of the results that have been obtained to date. Thirteen planets have been detected with microlensing; I discuss what these detections have taught us about the frequency of cold 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 such as Kepler, next generation microlensing surveys will yield a complete picture of the demographics of planetary systems throughout the Galaxy.




Steve Furlanetto

Host: Ott/Phinney

Piecing Together the Epoch of Reionization

The era of the first galaxies and reionization is one of the final frontiers of observational cosmology.  At the moment, a wide range of observations provide tantalizing - but often confusing - clues.  I will summarize our current knowledge about this epoch and its low-redshift analog, when helium is fully ionized.  I will then describe how future observations can settle some of the important open questions that remain. When did reionization occur? What sources were responsible? How did the intergalactic medium affect the process?  And what did it do to future generations of sources?



Annika Peter

UC Irvine

Host: Samaya Nissanke

What the #*!$ is dark matter? One astrophysicist's perspective

The nature of dark matter is one of the major "known unknowns" of physics of the Universe.  From astronomical observations, we know that dark matter exists, makes up 23% of the mass budget of the Universe, clusters strongly to form the load-bearing frame of structure for galaxy formation, and hardly interacts with ordinary matter.  This information is not enough to identify the particle specie(s) that make up dark matter, though.  As such, the problem of determining the identity of dark matter has largely shifted from astronomy to the fields of astroparticle and particle physics.  In this talk, I will give an overview of the ecosystem of astroparticle and particle-physics searches for dark matter, and show what its prospects are for dark-matter detection in the next decade.  I will also highlight some of the pitfalls of this particle-physics-oriented search.  This will lead me to advocate a return of the problem of dark-matter identification to astronomy, and show what kinds of theoretical and observational work might be used to pin down the nature of dark matter once and for all.





Andrei Beloborodov

Columbia/Kingsley Visitor

Host: Sterl Phinney

Emission Mechanism of Gamma-Ray Bursts

Gamma-ray bursts are emitted by super-powerful ultra-relativistic jets from compact engines, most likely just born black holes or magnetars. A long debated problem is how the jet emits the observed gamma rays. A simplest model resembles the big bang: the opaque hot plasma expands to transparency and releases its thermal photons. The expected spectrum from a radiation-dominated jet is Planckian with a peak around 1 MeV. The observed burst spectra do peak around 1 MeV, however they have non-Plankian shapes, with extended high-energy tails. Physical processes generating non-Plankian radiation will be discussed. The old phenomenological model of synchrotron emission from internal shocks is currently experiencing a crisis -- it appears to contradict both shock physics and observations. I will describe a different emission mechanism: internal motions in the neutron-proton jet generate electron heat via nuclear and Coulomb collisions, and the electrons radiate the received energy. This mechanism invokes no phenomenological parameters, and the produced radiation can be calculated from first principles. Remarkably, the predicted spectra agree with observations. I will also discuss the central engine and the mechanism driving the jet. The jet may be a strongly magnetized outflow driven by rotation of the central object. Alternatively, the jet may be driven by thermal pressure due to neutrino heating around the central object. Both mechanisms can supply the observed luminosities, but require extreme rotation rates and magnetic fields.


Julianne Dalcanton

University of Washington

Host: Nick Scoville

Galaxies Viewed as Collections of Individual Stars

In extragalactic astronomy, we routinely observe galaxies in broad-band filters, and then interpret the resulting spectral energy distribution to learn about the galaxies' masses, star formation rates, ages, and metallicities.  The fidelity of this interpretation relies on having a detailed understanding of the stellar populations within the galaxy, and on accurately characterizing the luminosities and colors of the billions of stars which contribute to a galaxy's light.  In this talk I will discuss several large programs which use the Hubble Space Telescope to resolve millions of the most luminous stars in nearby galaxies.  I will highlight results using near infrared observations, focusing on implications for the evolution of stars, the integrated NIR light of distant galaxies, and the structure of the dusty interstellar medium.



Ruth Murray-Clay

Harvard CfA

Host: John Johnson

Planet Formation at Wide Separations

Several giant planets have now been directly imaged, offering the first view of extrasolar planets at wide separations from their host stars.  Formation of these objects, either by core accretion or gravitational instability, presents substantial theoretical difficulties.  In this talk, I will discuss the challenges and opportunities posed by wide-separation planets for theories of planet formation and orbital  evolution.  I will demonstrate how to use upcoming constraints from direct imaging to distinguish between theories of planet formation, and I will present a new theory of planetary core growth in the presence of gas that extends the reach of core accretion to large stellocentric distances.  Finally, I will briefly discuss how the atmospheres of planets at all stellocentric distances are shaped by their formation histories, including their protoplanetary disk environments and atmospheric escape.


Robert Williams

STScI/Kingsley Visitor

Host: Richard Ellis

The Nova Outburst:  An Evolving Paradigm?


Volker Bromm

University of Texas

Host: Samaya Nissanke

The First Stars and Galaxies

How and when did the cosmic dark ages end? I present simulations of the formation of the first stars and galaxies, discuss their feedback on the intergalactic medium, and describe ways to probe their signature with missions such as WMAP and the James Webb Space Telescope. The properties of the first stars are determined by the interplay between cold dark matter and the atomic and molecular physics of hydrogen. I will identify the key processes and outline the major remaining uncertainties.


Claude-André Faucher-Giguère         
UC Berkeley
Host: Sterl Phinney

Inflows, outflows, and the physics of galaxy formation

Galaxies must continuously accrete gas from the intergalactic medium in order to maintain their star formation rates. At the same time, star-forming galaxies and their black holes drive powerful winds that strongly affect their evolution. Inflows and outflows are thus among the key physical processes in galaxy formation, tying together the vastly different scales involved. I will first summarize the inflow predictions from cosmological simulations and show how they can be tested observationally. In doing so, I will address the physical nature of Ly-alpha blobs and Lyman limit absorbers. Motivated by breakthrough discoveries of massive, galaxy-scale outflows driven by active galactic nuclei in the last year, I will then address two puzzles raised by the data: the extreme multiphase structure traced by cool absorbers, and the origin of the large outflow momentum fluxes. The talk will conclude by outlining advances that will dramatically improve the realism and predictive power of theoretical studies of galaxy formation in the next few years.


 Risa Wechsler


 Host: Samaya Nissanke
The Galaxy-Halo Connection Across Mass and Time

Dark matter halos are the fundamental building blocks in the growth of structure and they provide the framework for our modern understanding of galaxy  formation.  I will discuss the current state of the art in our understanding of the connection between galaxy properties and their dark matter hosts over a range of masses and redshifts.  In the context of a given cosmological model, I will show how the galaxy-halo relation can be tightly constrained at low redshift, and how it can be used to infer the full star formation histories of galaxies.   This model for the co-evolution of galaxies and LCDM halos is in excellent agreement with a wide range of data, including the evolution of the stellar mass function, galaxy clustering statistics, and the statistics of satellites around Milky Way mass hosts.  The faintest dwarf galaxies still present challenges to this picture, and may hold the key to new insight into galaxy formation or the properties of dark matter on small scales.




Andreas Burkert

LMU Munich
Host: Nick Scoville
Watching a Little Gas Cloud on its Way into the Galactic Supermassive Black Hole

The Galactic center is one of the most fascinating and extreme places in the Galaxy. Harboring a supermassive black hole with a mass of order 4 million solar masses it experiences cycles of activity and star formation, separated by periods of quiescence that last of order a million years. The Milky Way's SMBH currently is inactive. However a small, diffuse gas cloud (G2) has recently been detected (Gillessen et al. 2012) on an orbit almost straight into the Galactic SMBH. Within the next 2 years, G2 will pass the SMBH at a small distance of just 3000 Schwarzschild radii, corresponding to 4e15 cm. Depending on its nature it might break up and feed the SMBH, triggering a phase of AGN activity. The next years will therefore provide a unique opportunity to investigate directly the processes that drive and regulate gas accretion onto the Galactic SMBH as well as the onset of activity cycles in the Galactic center.

This talk will summarize the observations of G2 and current models about its nature. The existence of such a tiny, cold gas cloud in the hostile vicinity of the SMBH raises numerous fascinating questions. Is G2 a diffuse gas clump that originates from winds of high-mass stars in the surrounding stellar disk or is it the atmosphere of an evaporating, invisible protostellar disk, planet or star? Or is it something completely different? Where did it come from and where will it go? Why is it on such a highly eccentric orbit? Which physical processes constrain its properties like its size, mass, density, temperature and geometrical shape? How many clouds like G2 are currently orbiting Sgr A* and how do they affect its activity and gas accretion rate? Like comet Shoemaker Levy's 1994 collision with Jupiter, the big challenge has started for astrophysicists to predict the outcome of G2's close encounter with the SMBH in the year 2013 and beyond. Their models will be validated directly by observations within the next couple of years.


Katrien Kolenberg
Harvard CfA
Host: Ott/Cohen

 Kepler and the RR Lyrae stars  

The spectacular data delivered by NASA's Kepler mission not only boost the discoveries of planets orbiting other stars, but they also open a window on the inner workings of the stars themselves. Kepler has been a breakthrough for the study of RR Lyrae stars and the still mysterious Blazhko effect.  I will present some of the most interesting results obtained so far.

To date, over 40 RR Lyrae stars have been found in the Kepler field. The outstandingly high-precision data of these stars are investigated within the RR Lyrae working group as part of the Kepler Asteroseismic Science Consortium (KASC).










Christian Ott
Core-Collapse Supernova Theory 78 Years after Baade & Zwicky 1934 -- Where we stand and where we are heading.

Core-collapse supernovae from massive stars are among the most energetic events in the universe. They liberate a mass-energy equivalent of ~15% of a solar mass in the collapse of their progenitor star's core. The majority (~99%) of this energy is carried away by neutrinos, while (~1%) is transferred to the kinetic energy of the explosive outflow. A smaller, yet still tremendous amount of energy is emitted in electromagnetic and gravitational waves.
In 1934, Baade and Zwicky proposed that a "[...] super-nova represents the transition of an ordinary star into a neutron star". 78 years and one core-collapse supernova (SN 1987A) in the Large Magellanic Cloud later, our understanding of core-collapse supernovae is still very incomplete. In particular, the details of the physical process(es) responsible for converting the gravitational energy liberated in collapse into energy of the explosion are still uncertain. I review the current state of core-collapse supernova theory and discuss recent progress made and insights gained from new multi-dimensional computational models. These models are yielding new predictions for the signature of core-collapse supernovae in neutrinos and gravitational waves and I outline how their observation from the next nearby core collapse event can shed light on the supernova mechanism. While a key goal is to understand the mechanism driving regular supernova explosions, a core-collapse supernova is not always the outcome of collapse. I delineate the ensemble of alternative outcomes and present new results on stellar-mass black hole formation and on the core-collapse supernova -- long GRB connection.


Scott Ransom
Host: Christian Ott

Nuclear Physics at Two Kiloparsecs with Millisecond Pulsars

The central densities of neutron stars are the highest known in the
Universe, so measurements probing the interiors of radio pulsars, or
even their overall mass and radii, can give us unique insights into
the physics of matter at extreme densities.  The discovery of several
interesting new pulsars as well as improved instrumentation has
finally allowed us to start measuring the masses of the rapidly
spinning millisecond pulsars. These systems have had potentially
substantial amounts of mass accreted onto them in the past and are
likely more massive, on average, than "canonical" 1.4 Msun neutron
stars. Relativistic Shapiro Delay has been used to make very precise
measurements of 1.67 and 1.97 Msun neutron stars in the past two
years. These systems strongly constrain the equation of state of
nuclear matter and a variety of other topics in physics/astrophysics.
Finally, I'll show that there is good potential for more measurements
in the near future.


Beth Willman
Host: Samaya Nissanke

Ultra-faint Dwarfs, Dark Matter and Galaxy Formation

Over the last decade, Galactic science has been revolutionized by the
maps made possible by the Sloan Digital Sky Survey.  These maps
revealed a new population of ultra-faint dwarf galaxies orbiting the
Milky Way that are 100 times less luminous than any galaxy previously
known, a million times less luminous than the Milky Way itself, and
may be the most numerous type of galaxy in the universe.  The Milky
Way's ultra-faint dwarf population is currently our best tracer of
dark matter on sub-galactic scales, making a well-defined census and
careful studies of these objects essential tests for cold dark matter
models on such scales. This talk will highlight recent progress in and
current obstacles to our understanding of dark matter and galaxy
formation at the smallest scales, including: i. the results of recent
photometric and spectroscopic observations of the Milky Way's
ultra-faints, placing them in a cosmological context, ii. the results
of new N-body + SPH simulations that resolve possible tension between
observations and predictions, and iii. the role that current and future
wide-field surveys will play in this near-field cosmology.


  Ewine van Dishoeck
 Leiden Observatory,  
 The Netherlands &
 Max Planck Institute
 for Extraterrestrial
 Physics, Garching,
 Host: Lynne Hillenbrand  

  Water in space: from interstellar clouds to
 planet- forming disks. (14th annual Greenstein Lecturer)

  Water is one of the most important molecules in regions in which new
 stars and planets are born, and is clearly associated with our own
 origins. In this lecture, an overview will be presented of the wealth
 of water data obtained with new infrared and submillimeter
 observatories that allow us to peer deeply into these highly obscured
 regions. In particular, the 'Water in Star-forming Regions with
 Herschel' (WISH) Key Program has obtained a comprehensive set of
 gaseous water spectra toward a large sample of well-characterized
 protostars, from the lowest to the highest mass sources and from
 pre-stellar cores to disks around pre-main sequence stars.  The data
 elucidate the physical processes responsible for the warm gas, probe
 dynamical processes associated with forming stars and planets
 (outflow, infall, expansion), test basic gas-grain processes, and
 reveal the chemical evolution of water and the oxygen-reservoir into
 planet-forming disks, comets and eventually Earth's oceans. The
 importance of a close interplay between astronomy and laboratory
 astrophysics is emphasized.

 This talk is presented on behalf of the entire WISH team. More details
 can be found at http://www.strw.leidenuniv.nl/WISH.




John Johnson

Hot on the Trail of Warm Planets Around Cool Stars

During the past 17 years our knowledge of planetary systems has been
revolutionized by the discovery of a diverse sample of thousands of
planets orbiting other stars. These exoplanets provide us with clues
about the origins of our planet, and help us place our Solar System in a
broader Galactic perspective. One of the most remarkable results to
emerge from the sample of known exoplanets is that there are many more
small planets than large ones throughout the Galaxy, with as many as 1-3
planets per star with periods less than ~1 year. I will present the
Caltech Exolab’s two-pronged approach to finding and studying these
low-mass planetary systems in the immediate Solar neighborhood (< 25
parsecs). Our first strategy is to study the planets orbiting the least
massive and most proximate Kepler target stars: the M dwarfs. This study
is made possible by the new spectroscopic and photometric tools we have
developed to measure the fundamental characteristics of low-mass stars
and their planets. Our second thrust involves the development of a new
telescope facility at Palomar for the detection of low-mass planets in
the habitable zones of their stars. This program, called Project
Minerva, continues the use of small, robotic telescopes to do big
science atop Palomar Mountain.


Laurent Vigroux
IAP Director/
Kingsley Visitor
Host: Anneila Sargent

Herschel view on star formation: from local star forming regions to the most distant galaxies

With the advent of the Herschel Space Observatory, following Spitzer, ISO and ground based telescopes, the coverage of the far-infrared to sub-millimeter spectral range becomes extensive. We now routinely observe most astrophysical objects in this range, from cold molecular clouds in our Galaxy to active galactic nuclei in the distant universe, including galaxies of all star formation intensities. Thanks to its unprecedented sensitivity, wavelength coverage and spatial resolution, Herschel has been particularly helpful to reveal the star formation processes, maping for the first time the protostellar cores distribution in Galactic star forming region. Spatial resolution was the key parameter to get SED maps in nearby galaxies to perform detailed energy budget. Sensitivity is such that dusty galaxies can be detected at very high redshift, providing new clues on galaxy evolution. I will highlight some of the results obtained from Herschel observations of Galactic star forming regions, nearby galaxies, and galaxies at high z.


David Sobral
Jean-Rene Gauthier

The 11 Gyr Evolution of Star-forming galaxies: the HiZELS/H-alpha view

I will present new deep and wide narrow-band surveys undertaken with UKIRT, Subaru and the VLT; a unique combined effort to select large, robust samples of H-alpha (Ha) emitters at z=0.40, 0.84, 1.47 and 2.23 (corresponding to look-back times of 4.2, 7.0, 9.2 and 10.6 Gyrs) in a uniform manner over ~2 sqdeg in the COSMOS and UDS fields. The deep multi-epoch Ha surveys are sensitive to Milky-Way SFRs out to z=2.2 for the first time, while the wide area and the coverage over two independent fields allows to greatly overcome cosmic variance. A total of over ~600 sources per epoch are homogeneously selected. Overall, the evolution seen in Ha is in good agreement with the evolution seen using inhomogeneous compilations of other tracers of star formation, such as FIR and UV, jointly pointing towards the bulk of the evolution in the last 11 Gyrs being driven by a strong luminosity/SFR increase from z~0 to z~2.2. Our uniform analysis allows to derive the Ha star formation history of the Universe, for which a simple time-parametrisation is a good approximation for the last 11Gyrs. Both the shape and normalisation of the Ha star formation history are consistent with the measurements of the stellar mass density growth, confirming that our Ha analysis traces the bulk of the formation of stars in the Universe up to z~2.2. We are also exploring the large, multi-epoch and homogeneously selected samples of Ha emitters to conduct detailed dynamics, dust, clustering, environment and mass studies which are providing us with a unique view on the evolution of star-forming galaxies and what has been driving it for the past 11 Gyrs.


 Marc Postman
Richard Ellis

Early Results from the Cluster Lensing And Supernova survey with Hubble (CLASH)

The Cluster Lensing And Supernova survey with Hubble (CLASH) is a 524-orbit Multi-Cycle Treasury Program to use the gravitational lensing properties of 25 galaxy clusters to address at least 4 key science objectives: (1) Map the dark matter distribution in clusters with unprecedented accuracy, (2) Detect type Ia supernova out to z~2 to constrain the time evolution of the dark energy equation of state and the evolution of SN Ia themselves, (3) Detect and characterize some of the most distant galaxies (z > 7), and (4) study the internal structure and evolution of the galaxies in and behind the clusters. The survey is obtaining broadband images of the clusters in 16 passbands, providing remarkable panchromatic coverage from 0.2 - 1.6 microns, all with HST-quality resolution. I will present highlights from each of the 4 main science objectives.

   30 Luc Dessart
Laboratoire d'Astrophysique de Marseille, France
Host: Christian Ott
Radiative-transfer Modeling of Supernova Spectra and Light Curves. Application to Massive-star Explosions.

Supernovae (SNe) play a critical role in modern astrophysics. Their extraordinary luminosity makes them prime beacons of the distant Universe and thus critical tools for cosmology. These catastrophic stellar death and explosion are a major contribution to the chemical enrichment of the Universe, from the first generation of stars to now. SNe come in different flavors, in association with white-dwarf thermonuclear explosions in the single- and double-degenerate scenarios (Type Ia), with the gravitational collapse of massive stars (Type II/Ib/Ic), with the interaction of ejected shells (Type IIn), or through the so-called pair-production instability. In this talk, I will summarize the fundamental properties of these various mechanisms and the stellar progenitors. I will then introduce a new approach to the radiative-transfer modeling of SN spectra and light curves which takes into account line blanketing and departures from Local Thermodynamic Equilibrium, as well as treats time dependent terms in the radiative-transfer, energy, and statistical-equilibrium equations. Combined with hydrodynamical inputs of SN ejecta produced from the explosion of white-dwarf, red-supergiant, blue-supergiant, or Wolf-Rayet stars, we simulate the photometric and spectroscopic evolution from early time until the nebular phase. I will describe the assets of this method, in particular the possibility of constraining the properties of the explosion and the progenitor from the combined analysis of spectra and light curves. I will also review the key radiative-transfer properties of SN ejecta. I will then illustrate with results from an on-going study of SNe IIb/Ib/Ic, of relevance to massive-star evolution and long-duration Gamma-ray bursts.


 Alicia Soderberg
 Host: John Johnson

"Supernova Forensics"

For several decades, observational studies of supernova explosions have focused almost exclusively on the optical emission that dominates their bolometric luminosity. Yet many of the leading breakthroughs in our understanding of supernovae have been enabled by observations at other wavelengths.  I will present new results on the nature of the progenitors, evolutionary histories, and explosion properties based on nontraditional supernova studies.  The unique combination of sensitive radio/mm-band arrays (EVLA, CARMA, ALMA), new wide-field optical surveys (PTF, Pan-STARRS, CSS, LSST), and gravitational wave facilities (aLIGO) mark this decade as opportune for the study of Supernova Forensics.

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