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Astrophysics Seminars From 2013 - 2014


Summer 2013

June 26, 2013

NOTE: Special Astro Seminar
12:00-1:00pm - SERF 383
(Pizza/soda served)
 "Multi-chroic dual-polarization bolometric detector for studies of the
Cosmic Microwave Background"
Aritoki Suzuki

Physics Graduate Student
UC Berkeley
Host: Brian Keating

 Abstract: Characterization of the Cosmic Microwave Background (CMB) B-mode polarization signal will test models of inflationary cosmology, as well as constrain the sum of the neutrino masses and other cosmological parameters. The low intensity of the B-mode signal combined with the need to remove polarized galactic foregrounds requires an extremely sensitive millimeter receiver and effective methods of foreground removal. Current bolometric detector technology is reaching the limit set by the CMB photon noise. Thus, we need to increase the optical throughput to increase an experiment's sensitivity.

Our group is developing next generation multi-chroic antenna-coupled TES detector. In each pixel, a dual polarizedbroadband antenna collects light over two octaves of frequency band. Each antenna couples to the telescope with a contacting silicon lens. The antenna couples the broadband RF signal to microstrip transmission lines, and then filter banks split the broadband signal into several frequency bands. A TES bolometer detects the power in each frequency band and linear polarization. I will describe the design of this device and demonstrate its performance with optical data taken from prototype pixels. I will also describe an upgrade of the POLARBEAR CMB ground based experiment and installation for the Simons Array, South Pole Telescope-Third Generation and LiteBIRD CMB satellite experiment with focal planes of these detectors to increase mapping speed and provide greater discrimination of polarized galactic foregrounds.

July 30, 2013

NOTE: Special Astro Seminar 12:00-1:00pm - SERF 383
            (Pizza/soda served)
 "Cosmological and supernova neutrinos"
Toshitaka "Taka" Kajino

NAO of Japan, Department of Astronomy at the University of Tokyo, and Graduate University for Advanced Studies
Host: George Fuller

 Abstract: Still unknown mass and oscillation properties of neutrinos take the important keys to solve fundamental questions such as why we need unified theory of elementary particles beyond the standard model, why baryon- and lepton-symmetries were broken in the early universe, which particle the neutrino is, Dirac or Majorana particle, why core-collapse supernovae explode, etc. Core-collapse supernovae are the unique sources in nature, except for cosmological background neutrinos, that provide three flavors of energetic neutrinos that play the significant roles in explosive nucleosynthesis like r-process and neutrino-processes. We here discuss how to determine the neutrino mass and oscillation parameters from the studies of the cosmic microwave background (CMB) anisotropies, supernova nucleosynthesis, and galactic chemical evolution (GCE).

References: Suzuki and Kajino, J. Phys. G40 (2013), 083101. Mathews, Kajino, Aoki, Fujiya, PR D85 (2012), 105023. Yamazaki, Kajino, Mathews, Ichiki, Phys. Rep. 517 (2012), 141. Kojima et al., PR D78 (2008), 045010.

August 7, 2013

NOTE: Special Astro Seminar 12:00-1:00pm - SERF 383
            (Pizza/soda served)
 "The CMB as a Backlight: Cosmology from Secondary Anisotropies
of the Microwave Background"
Blake Sherwin

Physics Department, Princeton University
Host: Brian Keating

 Abstract: Short abstract: Gravitational lensing and the Sunyaev-Zel'dovich (SZ) effect introduce new intensity fluctuations, known as secondary anisotropies, into the cosmic microwave background radiation (CMB). These secondary anisotropies directly probe the projected distribution of dark matter and baryons out to high redshifts. In this talk, I will discuss recent studies of lensing and the SZ effect with high resolution CMB experiments. In particular, I will describe the first detection of the power spectrum of CMB lensing with the Atacama Cosmology Telescope (ACT) and its cosmological implications, and will show results from cross-correlations of CMB lensing maps with quasars, galaxies and other tracers of dark matter. I will then explain the great scientific potential of CMB polarization lensing measurements and will discuss ongoing work on early measurements of polarization lensing with the POLARBEAR experiment.

August 26, 2013

NOTE: Special Astro Seminar 12:00-1:00pm - SERF 383
            (Pizza/soda served)
 "Search for planets around ultracool dwarfs with astrometry"
Johannes Sahlmann

Observatory of Geneva, Switzerland
Host: Adam Burgasser

 Abstract: Ultracool dwarfs are very low-mass stars and brown dwarfs and because of their faintness they are difficult targets for radial velocity and transit planet searches. I will present results from our planet search survey of ultracool dwarfs using ground-based imaging astrometry with the Very Large Telescope. The realised accuracy of 100 micro-arcseconds allows us to set stringent constraints on the presence of planets and to measure parallaxes with unprecedented precision. I will present preliminary survey results and our first discovery, a L1.5 dwarf with a low mass-ratio companion in a tight orbit.

Fall 2013

October 2, 2013

 "The Dynamic Circum-galactic Medium"
Amanda Brady Ford

Graduate Student in Astronomy
University of Arizona
Host: Dusan Keres

 Abstract: Recent pioneering COS observations have allowed for detailed studies of the circum-galactic medium (CGM) around galaxies at low redshift. However, due to the complexity of including the necessary physics in simulations, a solid theoretical foundation for understanding the intricate interplay between gaseous inflows from the IGM, galactic winds, and gas recycling has been lacking. In this talk, I will present results from cosmological hydrodynamic simulations that include these physical processes in order to develop a model for this baryon cycle of gas around galaxies. I discuss the extent and strength of HI and metals in the neighborhood of galaxies, as well as the typical temperatures, densities, and ionization conditions of the gas that gives rise to absorption features. I additionally demonstrate the sensitivity of these observables to the details of how galactic super-winds are modeled, and how different feedback prescriptions leave unique, observable signatures within the CGM. Finally, I will discuss observable diagnostics of inflows and outflows, key to our understanding of galaxy evolution.

October 9, 2013

 "Why So Few? The Dearth of Women in Physics and Astronomy"
Meg Urry

Israel Munson Prof Physics & Astronomy, Dir Yale Center Astronomy & Astrophysics; Chn Physics
Yale University
Host: Alison Coil

 Abstract: Women continue to be underrepresented in STEM fields (Science, Technology, Engineering, and Mathematics), and the gender imbalance is particularly large in physics, where fewer than 20% of college physics majors are women and only 10% of physics faculty are women. Interestingly, astronomy requires more or less the same skills as physics but has roughly double the percentages of women at all levels, indicating the influence of factors beyond scientific/quantitative talent. Decades of social science research suggest the dearth of women is due in large part to lower expectations and evaluations of women as leaders, thinkers, do-ers. I discuss the experimental data and outline steps that can be taken to mitigate obstacles to equal participation, full utilization of available talent being critical to the health of STEM professions.

October 16, 2013

 "The Formation of The First Stars, Galaxies, and Globular Clusters"
Sasha Muratov

Postdoctoral Scholar
Host: Dusan Keres

 Abstract: Understanding the origins of galaxies ab initio requires fully comprehensive cosmological modeling from the bottom up, starting with those galaxies that live in the least massive halos at the earliest cosmic times. Using high-resolution hydrodynamic simulations, I model the formation of the first galaxies, focusing on the effects of the massive Population III stars which may have dominated their internal dynamics and feedback. While these stars seed their host galaxies with metals, they cannot drive significant outflows to enrich the intergalactic medium in our simulations. Feedback from pair instability supernovae causes Pop III star formation to self-terminate within their host galaxies, but is not strong enough to suppress star formation in external galaxies. Within any individual galaxy, Pop II stars overtake Pop III stars within ~50-150 Myr. I also present semi-analytical model which traces the assembly of a Milky Way-like galaxy, and prescribes that massive globular star clusters form in the mergers of the low-mass protogalactic building block halos. Our model is the first that, using a single formation mechanism, successfully reproduces a system of massive star clusters with the bimodal metallicity distribution characteristic to the Milky Way's globular clusters.

October 23, 2013

 "Advances in galaxy-formation simulations: calculating mock observables
& using a more-accurate numerical technique"
Christopher Hayward

PostDoc in Theoretical Astrophysics
HITS, Heidelberg
Host: Dusan Keres

 Abstract: Galaxy formation has been studied using idealized numerical simulations of isolated disk galaxies and galaxy mergers for decades, but most simulations performed to date have suffered from two potentially significant limitations: First, when comparing simulations with observations, physical quantities -- rather than observables -- from the simulations are used. Second, the most-commonly used techniques, smoothed-particle hydrodynamics (SPH) and adaptive mesh refinement, suffer from numerical inaccuracies that can potentially jeopardize the results of simulations performed with those techniques.

I will discuss methods for solving both of these limitations. I address the first limitation by performing 3-D dust radiative transfer on hydrodynamical simulations to calculate spatially resolved UV-mm spectral energy distributions of simulated galaxies. I will present an application to submillimeter galaxies, for which a realistic comparison with observables yields results that are qualitatively different from those of more naive comparisons. I address the second limitation by using the more-accurate moving-mesh hydrodynamics code Arepo. I will discuss how merger simulations performed with the moving-mesh technique differ from otherwise identical simulations performed using SPH. Finally, based on this comparison and other work, I will outline the types of galaxy-formation simulations for which the traditional formulation of SPH is sufficiently accurate and describe when and why this is not the case.

October 29, 2013

NOTE: Special Astro Seminar @ Noon - SERF 383 (Pizza/soda served)
 "Quark Matter in Compact Stars"
Milva Orsaria

Postdoctoral Fellow, Department of Physics
San Diego State University
Host: Fridolin Weber

 Abstract: Massive neutron stars provide very important constraints on the high-density nuclear matter and its associated Equation of State (EoS), which is still essentially unknown. Depending on neutron star mass and rotational frequency, gravity may compress the matter in the core regions of such objects up to more than ten times the density of ordinary atomic nuclei, thus providing a high-pressure environment in which numerous subatomic particle processes are likely to compete each other and phase transitions to new states of matter may occur. In this seminar, we explore whether or not quark deconfinement may occur in high-mass neutron stars such as J1614-2230 (1.97 +/- 0.04 M_sun) and J0348+0432 (2.01 +/- 0.04 M_sun). Our study is based on a non-local extension of the SU(3) Nambu Jona-Lasinio (n3NJL) model with repulsive vector interactions among the quarks. By combining the quark matter EoS and a relativistic mean field hypernuclear EoS we find that the n3NJL model predicts the existence of an extended region of a mixed phase of quarks and hadrons (so-called quark-hybrid matter) in high-mass neutron stars. Extended central stellar cores made of pure quark matter are however not predicted by the model.

October 30, 2013

 "CMB Lensing: reconstruction from polarisation & implications for cosmology
from cross correlation with galaxies"
Ruth Pearson

Associate Tutor, Physics and Astronomy / KIPAC visitor @ Stanford
University of Sussex / Stanford University
Host: Brian Keating

 Abstract: CMB Lensing is a probe of the matter distribution between the surface of last scattering and today, which has been measured using CMB temperature data. Signal to noise for lensing reconstruction from CMB polarisation data is expected to be much better, since B modes on small scales should vanish in the absence of lensing. An effect of having data from an incomplete sky is leakage of E mode power in to B mode power. Upcoming data analysis from ground based CMB polarisation instruments must account for this effect. In the first part of my talk I will show forecasts for CMB polarisation lensing reconstruction from small patches of sky, which incorporate the pure B mode estimator to clean up the E-B leakage problem. CMB lensing is also well correlated with the galaxy distribution, indeed CMB lensing was first detected via cross correlation with a radio survey. In the second part of my talk I will show results on cosmology (neutrino mass sum and tau parameters) and astrophysics (bias and redshift distribution parameters) from the joint analysis of CMB lensing and the 2D galaxy power spectrum. It remains to be seen what can be learned about cosmology and astrophysics from this correlation, and our forecasts begin to quantify this.

November 6, 2013

 "An Absence of Quenched Dwarf Galaxies in the Field"
Marla Geha

Associate Professor, Astronomy and Physics Departments
Yale University
Host: Adam Burgasser

 Abstract: Environment plays a major in role in the evolution of galaxies. This is particularly true of low mass dwarf galaxies where more massive galaxies dramatically affect the local gravitational potential. Isolated low mass galaxies offer a unique testbed for comparisons to theoretical models since they do not suffer as complex environmental effects which galaxies in more dense environments endure. We have shown that, for dwarf galaxies less massive than M_star < 10^9 M_sun, ending star-formation requires the presence of a more massive neighbor. I will discuss the implications of this result and described follow-up HI observations to study the gas components in these isolated systems.

November 13, 2013

 "Autonomous Spacecraft Navigation With Pulsars"
Werner Becker

Max Planck Institute of Extraterrestrial Physics (MPE), Garching, Germany
Host: Fridolin Weber

 Abstract: An external reference system suitable for deep space navigation can be defined by fast spinning and strongly magnetized neutron stars, called pulsars. Their beamed periodic signals have timing stabilities comparable to atomic clocks and provide characteristic temporal signatures that can be used as natural navigation beacons, quite similar to the use of GPS satellites for navigation on Earth. By comparing pulse arrival times measured on-board a spacecraft with predicted pulse arrivals at a reference location, the spacecraft position can be determined autonomously and with high accuracy everywhere in the solar system and beyond. The unique properties of pulsars make clear already today that such a navigation system will have its application in future astronautics. In my talk we will describe the basic principle of spacecraft navigation using pulsars and report on the current development status of this novel technology.

November 20, 2013

 "Mergers or not? A Submillimeter Perspective on Cosmic Star Formation"
Caitlin Casey

Postdoctoral Researcher
UC Irvine
Host: Alison Coil/Dusan Keres

 Abstract: Whether many of the Universe’s stars are formed in galaxy mergers or quiescent, secularly evolving disk galaxies is fiercely debated. Whatever the formation mechanism, about half of all star formation activity is emitted in the infrared by dusty galaxies. Locally, dusty infrared galaxies are merger-dominated, but their origin is less clear at high-redshift. Observing the most luminous star-forming galaxies -- galaxies which are rare but produce huge numbers of stars very rapidly -- provides an important method of studying galaxy evolution and the stellar mass assembly of the early Universe. Infrared observations are uniquely useful since they probe star formation directly, as seen from dust-reprocessed emission of ultraviolet light from young stars.

I will describe some of the latest research surrounding infrared-luminous starburst galaxies, from low to high redshift, and present some of the conundrums of the field (from sample selection biases, observational limitations, to disagreements over galaxies' evolution). With a plethora of new observational tools becoming available in the infrared and sub-millimeter (e.g. Herschel, SCUBA-2 and ALMA, and eventually CCAT), distant galaxies will soon be studied in exquisite detail in both dust and gas, filling in gaps of information which cannot be answered by detailed studies of their obscured stellar emission. Future observations with 30m-class telescopes like the TMT will dramatically improve observations of stellar continuum and nebular line emission in dusty galaxies to the necessary depth, so that stars, dust and gas can be studied in tandem. Our long-term goal is to understand the triggering mechanisms for star formation episodes in extreme, ultraluminous starburst environments, how they relate to star formation in more common "Milky Way" type galaxies at high-redshift, and what the implications are for galaxy evolution at very early times.

December 4, 2013

 "Cosmological Simulations: Now with Physics!"
Philip Hopkins

Assistant Professor of Theoretical Astrophysics (TAPIR)
Host: Dusan Keres

 Abstract: Many of the most fundamental unsolved questions in star and galaxy formation revolve around star formation and "feedback" from both massive stars and accretion onto super-massive black holes. This occurs in a chaotic, highly nonlinear system dominated by super-sonic turbulence and gravity. Yet, despite this complexity, there is remarkable regularity observed in many properties. I'll present new models which attempt to realistically model the diverse physics of the interstellar medium, star formation, and feedback from stellar radiation pressure, supernovae, and photo-ionization, and their interplay with feedback from luminous quasars. These mechanisms lead to 'self-regulated' galaxy and star formation, in which global correlations such as the Schmidt-Kennicutt law, the black hole-host galaxy correlations, and the global inefficiency of star formation emerge naturally. I'll discuss how, within galaxies, feedback regulates the structure of the interstellar medium, and how many observed properties of the ISM, star formation, and galaxies can be understood as a fundamental consequence of super-sonic turbulence in a rapidly cooling, self-gravitating medium. But feedback also produces galactic super-winds that can dramatically alter the cosmological evolution of galaxies, their behavior in galaxy mergers, and structure of the inter-galactic medium. I'll highlight how a combination of improved theoretical models and observations can elucidate the physics driving these winds and their role in phenomena on an enormous range of spatial scales.

December 11, 2013

 "Dwarf Galaxies: The Nexus of Dark Matter and Chemical Evolution"
Evan Kirby

CGE Postdoctoral Fellow
UC Irvine
Host: Alison Coil

 Abstract: The Local Group's dwarf galaxies are near enough for exquisitely detailed, resolved stellar spectroscopy and diverse enough to conduct experiments on dark matter and chemical evolution. I have collected medium-resolution spectra for thousands of stars in many dwarf galaxies in the Local Group. Innovative techniques applied to these spectra recover velocities precise to a few km/s and detailed abundances precise to 0.1 dex. Although Milky Way satellites and field dwarf galaxies are different in many ways, their velocity dispersions show that both types of galaxy pose a serious challenge to cold dark matter. Both types also obey the same mass-metallicity relation despite the large diversity of star formation histories and detailed abundance ratios. Finally, I have begun the Stellar Isotope Survey at Lick Observatory (SISLO), which is an experiment not only in the most detailed spectroscopic analysis possible but also an experiment in bringing young women into cutting edge astronomical research.

Winter 2014

January 6, 2014

NOTE: Special Astro Seminar @ Noon - SERF 383 (Pizza/soda served)
 "The Connection between Star Formation and the Cold Interstellar Medium
in Nearby Galaxies"
Karin Sandstrom

Bart J. Bok Postdoctoral Fellow, Department of Astronomy and Steward Observatory
University of Arizona
Host: Alison Coil

 Abstract: The efficiency at which interstellar gas is converted into stars is one of the major factors governing the evolution and observable properties of galaxies at all redshifts. In the Milky Way we can study the star formation process in great detail, but only over a limited range of environmental conditions. We must move to nearby galaxies to expand this range. Over the last several years, multiwavelength surveys of nearby galaxies have provided key, new insights into the connection between star formation and the amount and properties of gas in the interstellar medium. I will present the results of recent work greatly improving the accuracy with which we trace molecular gas---a key ingredient for forming stars. Using our improved assessment of the molecular gas distributions in nearby galaxies, we can measure the gas reservoir and star formation efficiency under a variety of environmental conditions. I will show that while molecular gas is converted into stars with a constant efficiency in most regions of nearby galaxies, some central regions appear to have enhanced efficiency, similar to what has been observed in starbursts induced by galaxy mergers. I will also discuss the degree to which molecular gas is concentrated in the centers of several nearby barred galaxies. Finally, I will discuss the exciting prospects for studying molecular gas and star formation in galaxies, both nearby and high redshift, with the next generation of telescopes.

January 10, 2014

NOTE: Special Astro Seminar @ Noon - SERF 383 (Pizza/soda served)
 "Assessing the Role of Stellar Feedback from Small to Large Scales"
Laura Lopez

Pappalardo Postdoctoral Fellow and NASA Einstein Postdoctoral Fellow
MIT Kavli Institute
Host: Alison Coil

 Abstract: Stellar feedback has a profound influence in many astrophysical phenomena, yet it is often cited as one of the biggest uncertainties in galaxy formation models today. This uncertainty stems from a dearth of observational constraints as well as the great dynamic range between the small scales (<1 pc) where feedback occurs and the large scales (>1 kpc) of galaxies that are shaped by this feedback. In this talk, I will show how multiwavelength observations can be used to overcome these challenges and to assess the role of many stellar feedback mechanisms (e.g., radiation, photoionization, stellar winds, supernovae, protostellar outflows, and cosmic rays). I will present results from the application of this approach to a variety of sources and discuss the implications regarding the dynamics of star-forming regions. Finally, I will highlight the exciting prospects of using current and upcoming facilities (e.g., ALMA, Keck, and TMT) to explore feedback in the diverse conditions of Local Group galaxies and to probe the effect of feedback on molecular gas properties.

January 13, 2014

NOTE: Special Astro Seminar @ Noon - SERF 383 (Pizza/soda served)
 "Interdependent Enterprises: Dark Matter and Galaxy Evolution"
Sarah Miller

Chancellor’s ADVANCE Postdoctoral Fellow and McCue Fellow, Department of Physics & Astronomy
UC Irvine
Host: Alison Coil

 Abstract: The as-yet undiscovered dark matter particle(s)/field(s) has come to dominate our matter paradigm. Some of the earliest hints of dark matter were seen in the dynamics of galaxies and confirmed at the largest scales measurable, yet the foremost challenge to the favored cold dark matter model arises in the smallest scales of galaxy dynamics. While whole disciplines beyond astrophysics are now devoted to the search for dark matter candidates, I will highlight unique opportunities in galaxy evolution and other astrophysical signatures. Such studies can take advantage of a wide variety of existing and future observational facilities, including instruments which could be supported by new and enticing high-altitude airship and aerostat platforms that are in development.

January 15, 2014

 "Mapping the Cool Baryons: Toward a Physical Picture for Galaxy Evolution"
Kate Rubin

Postdoctoral Scholar
Harvard-Smithsonian Center for Astrophysics (CfA)
Host: Alison Coil

 Abstract: Current models of galaxy formation require that the buildup of galactic stellar mass proceeds at a rate much slower than the rate at which gas is accreted onto dark matter halos, with only ~6% of the cosmic energy density of baryons ending up in stars at z~0. These models typically invoke energetic feedback from star formation to suppress stellar mass growth; however, the mechanisms regulating this process remain poorly understood. I will discuss my efforts to constrain the physics of galaxy formation by developing a set of empirical measurements of the incidence, mass, energetics, and spatial distribution of outflowing and accreting gaseous material around galaxies. These experiments, conducted with the Keck, Gemini, and Magellan Telescopes, include analysis of the kinematics of cool, photoionized material along the line of sight to galaxies, as well as measurement of the surface density of neutral hydrogen and metals in the environments surrounding galaxies over the past 10 Gyr. I will also discuss the potential of upcoming spatially-resolved spectroscopic surveys using current and next-generation facilities to revolutionize our understanding of the processes regulating galaxy growth.

January 21, 2014

NOTE: Special Astro Seminar @ Noon - SERF 383 (Pizza/soda served)
 "Inflation and Neutrinos: Testing New Physics with the Cosmic
Microwave Background"
Christian Reichardt

BCCP Postdoctoral Scholar
UC Berkeley
Host: Brian Keating

 Abstract: The cosmic microwave background (CMB) is revolutionizing our understanding of the Universe. The CMB is the strongest single piece of evidence that we live in a geometrically flat Universe, dominated by non-baryonic cold dark matter and dark energy. Many outstanding questions remain around this basic framework: Did inflation occur, and what physics was responsible for it? What is dark energy? What drove the reionization of neutral Hydrogen in the early Universe? What are the neutrino masses? Are there new particle species that we can detect cosmologically? Remarkably the CMB can shed light on all of these questions. I will present the latest results from the South Pole Telescope (SPT), which recently finished a millimeter-wave survey of 2500 square degrees of sky with unprecedented sensitivity and angular resolution. I will highlight the SPT measurements of the CMB power spectrum and the implications for inflation and neutrinos. I will also discuss two experiments that are being built to explore the next frontier in CMB science: using gravitational lensing to map the matter distribution in the Universe.

January 22, 2014

 "The Fine-Structure Constant Story: A Tale of Woe"
Jonathan Whitmore

Postdoctoral Research Associate in Extragalactic Physics, Centre for Astrophysics and Supercomputing
Swinburne University of Technology, Australia
Host: Kim Griest

 Abstract: The metal absorption lines found in high resolution QSO spectra have been at the forefront of measurements of several fundamental dimensionless constants of nature. These measurements are made by comparing the relative wavelength spacings of absorption lines found of QSO spectra. The fine-structure constant (alpha) and the mass ratio of the proton to electron (mu) are two fundamental constants that have been measured to a precision of a few parts per million in the redshift range ~0.5--4.0. They thus require careful wavelength calibration.

The high resolution echelle spectrographs UVES and HIRES on the telescopes VLT and Keck (respectively) have provided the measurements resulting in evidence of a change in the value of alpha over cosmological time. Measurements of alpha in hundreds of absorption systems in a study combining data (153 measurements on VLT and 141 measurements on Keck) that have led to a proposed spatial dipole across the sky (King, et al., 2012). My research has recently uncovered several long-range wavelength calibration distortions that have direct implications for alpha and mu measurements taken with each spectrograph. I will present some preliminary results that suggest disappointing implications for the dipole.

January 24, 2014

NOTE: Special Astro Seminar @ Noon - SERF 383 (Pizza/soda served)
 "Dark matter signals from the Inner Galaxy?"
Jennifer Siegal-Gaskins

Einstein Postdoctoral Scholar in Theoretical Astrophysics (TAPIR)
Host: Alison Coil

 Abstract: Dark matter makes up roughly 80% of the matter in the universe, yet the details of its particle nature remain unknown. Many particle dark matter candidates can pair annihilate or decay to produce Standard Model particles, including gamma rays, charged particles, and neutrinos. The detection of these indirect signals of the annihilation or decay of dark matter in our Galaxy and beyond is a promising method for identifying dark matter, understanding its intrinsic properties, and mapping its distribution in the universe. Recent indirect searches with gamma rays have yielded several tantalizing hints of dark matter signals from the Inner Galaxy, however a confident detection remains elusive. I will discuss these recent results and possible alternatives to the dark matter interpretation of the claimed signals, as well as new approaches and prospects for robustly identifying a dark matter signal from the Inner Galaxy with upcoming experiments.

January 29, 2014

 "Spatially Resolving Galaxies in the Early Universe: The Exciting Promise
of AO instrumentation"
Shelley Wright

Assistant Professor, Department of Astronomy & Astrophysics
and the Dunlap Institute for Astronomy & Astrophysics
University of Toronto
Host: Brian Keating

 Abstract: Recent advances in diffraction-limited techniques on 8-10m telescopes using adaptive optics (AO) and integral field spectrographs (IFS) have led to significant scientific achievements and are stimulating the design of future instrumentation. My talk will focus on development and use of current near-infrared AO instruments to study galaxies in the early universe, as well as the design and capabilities of AO instrumentation for the future Thirty Meter Telescope (TMT). I will present our team's work on the recent upgrade of OSIRIS at Keck Observatory, which has doubled the sensitivity of the IFS. With this gain in performance, I will present preliminary results of our spatially resolved observations of intermediate redshift (z~1) star forming galaxies. These results are part of an ongoing survey to study the dynamics, chemical abundances, and active galactic nuclei (AGN) in early galaxies. I will also present a powerful method that utilizes IFS and AO observations to reveal QSO host galaxies, which can provide important constraints on galaxy-black hole formation and evolution. Lastly, IRIS (InfraRed Imaging Spectrograph) is a near-infrared instrument being designed to sample the diffraction-limit of the Thirty Meter Telescope, which will yield revolutionary capabilities on a range of science cases. There are several instrumental and observational challenges that need to be overcome in order to exploit the diffraction-limit of a 30m telescope. I will discuss IRIS's instrument design, diverse science cases, and our current efforts in the laboratory to maximize the instrument's sensitivities.

February 5, 2014

 "Exploring Fundamental Physics through Measurements of the
Cosmic Microwave Background"
Bradford Benson

Associate Scientist, Kavli Institute for Cosmological Physics
University of Chicago
Host: Brian Keating

 Abstract: The cosmic microwave background (CMB) provides a unique window into the early universe and cosmology. The CMB is generated by well-understood dynamics, only ~400,000 years after the Big Bang, that enables precise calculation of its observable features and which directly connects new measurements to fundamental physics. I will discuss the latest measurements of the CMB by the South Pole Telescope (SPT), including the first detection of a curl-only component (B-modes) in the polarization of the CMB by SPTpol. I will describe the instrumentation and detector technology in development for next-generation experiments, including SPT's next camera, SPT-3G, and a future ground-based CMB experiment, CMB-S4. The science goals of these experiments aim to answer some of the most exciting questions in cosmology: to differentiate between dark energy and modified gravity to explain the origin of cosmic acceleration, to test and constrain physics at grand-unified theory energy scales (~1e16 GeV), to measure the sum of the neutrino masses at a sensitivity below the minimum mass expected from neutrino oscillations (<0.06 eV), and to precisely constrain the relativistic energy density of the universe and any "dark radiation" component.

February 12, 2014

 "Neutrinos from astrophysical sources with IceCube"
Naoko Kurahashi Neilson

IceCube Postdoc, WIPAC (Wisconsin IceCube Particle Astrophysics Center)
University of Wisconsin, Madison
Host: Brian Keating

 Abstract: High-energy neutrinos are thought to be emitted by astronomical objects such as active galactic nuclei, gamma-ray bursts, and supernova remnants. However, due to their small predicted flux and large backgrounds from neutrinos and muons created in the atmosphere, they had not been observed until now. The IceCube Neutrino Observatory instruments a cubic kilometer of ice at the South Pole to detect neutrinos mainly above 100GeV. In a high-energy (>20TeV) data set from the first couple of years of the completed detector, an excess above atmospheric backgrounds is observed. These neutrino events are also incompatible in energy spectrum and arrival direction, therefore they are the first observation of astrophysical neutrinos. Studies on the arrival direction are performed to determine the individual astronomical sources, signaling the birth of neutrino astronomy.

February 19, 2014

 "A glimpse of our universe’s origins through superconducting detectors"
Roger O'Brient

NASA Postdoctoral Scholar
Host: Brian Keating

 Abstract: Over the past decade, a technological revolution in the design of millimeter and submillimeter wavelength camera focal planes and detectors has driven a comparably exciting revolution in observational cosmology. In my talk, I will discuss how this game-changing technology is allowing the CMB polarimetry experiment BICEP-2/Keck Array to lead the field in limits on GUT-scale inflationary physics and how near-future extensions of this effort in SPIDER, BICEP-3, and T-REX will further inform our understanding of the ultra-early universe. Similar multi-chroic detector technology to be used in upgrades to Polarbear and South Pole Telescope (SPT) that will allow the neutrino mass hierarchy to be determined over the next half-decade. Finally, at NASA-JPL, we are actively extending the Polarbear and SPT-style multi-chroic detectors to include integrated spectrometers for the TIME experiment. TIME will tomographically map ionized carbon during the epoch of reionization. When cross-correlated with 21-cm experiments’ maps, TIME will allow us to construct a detailed history of reionization, tracing ionized bubble sizes as a function of red-shift.

February 26, 2014

 "Friends of Hot Jupiters: A Search for Massive, Long Period Companions
in Hot Jupiter Systems"
Heather Knutson

Assistant Professor, Division of Geological and Planetary Sciences
Host: Adam Burgasser

 Abstract: Since the discovery of the first extrasolar planet around a sun-like star nearly two decades ago, exoplanets have revolutionized our understanding of planet formation and migration. Although it was suspected at the time that the giant planets in our own solar system might have undergone some modest orbital evolution, the discovery of a class of short-period gas giant planets known as "hot Jupiters" conclusively demonstrated that planet migration can play a pivotal role in reshaping the architectures of planetary systems. In my talk I will focus on the question of what causes these hot Jupiters to migrate inward, creating a radical departure from the "standard" arrangement of the planets in our own solar system. In particular, I will examine the hypothesis that dynamical interactions between proto-hot Jupiters and a massive outer stellar or planetary mass companion can result in inward migration. Although most hot Jupiters appear to be lacking in nearby planetary companions, I will present the results of a combined Keck radial velocity and adaptive optics search of 50 hot Jupiter systems which indicates that these planets might not be that lonely after all.

March 5, 2014

 "The importance of evaporative fractionation of volatile stable isotopes
during planet formation"
James Day

Assistant Professor, Geosciences Research Division, SIO
UC San Diego
Host: Carl Melis

 Abstract: The Moon is depleted in volatile elements relative to Earth and Mars. Low abundances of volatile elements, fractionated stable isotope ratios of S, Cl, K, Zn, high-μ (238U/204Pb) and long-term Rb/Sr depletion are a distinguishing feature of the Moon, relative to Earth. These geochemical characteristics indicate both inheritance of volatile-depleted materials that formed the Moon and evaporative loss of volatile elements that occurred during a global-scale event associated with lunar formation. Models of volatile-loss through localised eruptive degassing are not consistent with the available S, Cl, Zn and K isotope and abundance data for the Moon. Instead, the most likely cause of lunar volatile depletion is during global-scale evaporation either during the giant impact or during a magma ocean phase where inefficient volatile loss during magmatic convection led to the present distribution of volatile elements within mantle and crustal reservoirs. Volatile loss also occurred on other airless bodies, such as the parent bodies of eucrite and angrite meteorites. In contrast, Earth and Mars have chondritic Zn isotope compositions and higher volatile contents providing evidence that parent body size and the existence of early atmospheres were fundamental controls on planetary volatile retention or loss. Volatile loss and atmospheric retention processes are likely a common feature in all planetary systems.

March 12, 2014

 "The Gould's Belt Distances Survey: mapping the distribution of star-forming
regions in the Milky Way"
Laurent Loinard

Professor of Astronomy, Center for Radio Astronomy & Astrophysics
UNAM, Mexico
Host: Carl Melis

 Abstract: In the last decade, it has become possible to routinely measure the distance and the velocity vector of young stars located within 500 pc of the Sun with an accuracy of order 1% using Very Long Baseline Interferometry (VLBI) techniques. This represents an improvement by more than 1 order of magnitude over what was previously possible, and opens the door to some extremely high accuracy astrophysics. In particular, theoretical pre-main sequence stellar evolutionary models can now be confronted with very accurate observational constraints. The space distribution, and the internal structure and kinematics of star-forming regions, can also be investigated in unprecedented detail. This has important consequences both for star formation and for Galactic structure studies. In this talk, I will review these recent results, and explore their consequences. In particular, I will focus on a legacy VLA/VLBA project that we have initiated in the last year, and that aims at mapping in three dimensions all the nearby regions of star-formation. Early results include the unexpected detection at radio wavelengths of very young brown dwarfs.

Spring 2014

April 2, 2014

 "Bigger and brighter: detailed properties of gravitationally lensed galaxies"
Tucker Jones

CGE Postdoctoral Fellow
UC Santa Barbara
Host: Dusan Keres

 Abstract: Gravitational lensing is a powerful tool for studying the formation of galaxies in the early universe. I will present spectroscopic observations of lensed galaxies at high redshift (z~2) for which lensing magnification by factors >10 enable high resolution measurements, revealing a wealth of information about their physical properties and evolution. Nebular emission lines show turbulent rotating kinematics, giant star forming regions, and steep gas-phase metallicity gradients in typical galaxies at z=2, as well as the integrated properties of fainter sources. Ultraviolet absorption lines provide complimentary information on the geometry, kinematics, and heavy element abundances in the interstellar and outflowing (circumgalactic) gas. Initial results from ALMA indicate that the distribution of molecular gas is similar to the star formation, in particular showing discrete knots of emission which are roughly co-spatial with the giant H II regions and clumps of young stars. I will also discuss new results from the GLASS survey which is providing high spatial resolution measurements of emission lines for ~100 lensed galaxies.

April 16, 2014

 "Eavesdropping on the Dark Sound of the Universe"
Francis-Yan Cyr-Racine

W. M. Keck Institute for Space Studies Postdoctoral Scholar
Host: George Fuller

 Abstract: Self-interacting dark matter (DM) has been put forward as a way to address potential problems with the Cold DM paradigm on sub-galactic scales. For a broad class of models the interactions between DM particles are mediated by a light force carrier. At temperatures above its mass, the force carrier effectively behaves as a dark radiation (DR) component that tightly couples to the DM, forming an almost perfect fluid. We expect this combined DM-DR system to give rise to sound waves propagating throughout the cosmos until DM kinematically decouples from the DR. Much like the standard baryon acoustic oscillations, these dark acoustic oscillations (DAO) imprint two characteristic scales, the sound horizon of dark matter and its Silk damping scale, in the matter density field. The presence of these two fundamental scales makes these DM theories distinct from warm DM models, which are uniquely characterized by their free-streaming length. We review how the microphysics of the DM-DR interaction affects the clustering of matter in the Universe and show that the DAO physics also gives rise to unique signatures in the temperature and polarization spectra of the cosmic microwave background (CMB). We find that linear cosmological data and CMB lensing put strong constraints on existence of DAO features in the CMB and the large-scale structure of the Universe. We also study, for the first time, the nonlinear evolution of cosmological structures in this type of theories by performing N-body simulations including both the modified matter power spectrum and the DM self-interactions. We find the resulting phenomenology to be far richer then in the cold or warm DM case.

April 30, 2014

 "The Outer Architecture of Planetary Systems"
Brendan Bowler

JCPA Postdoctoral Fellow
Host: Adam Burgasser

 Abstract: High-contrast imaging is a powerful tool to probe the outer architecture of planetary systems and directly study the atmospheres of extrasolar planets. Adaptive optics imaging surveys have so far primarily focused on intermediate- and high-mass stars, revealing a handful of self-luminous planets. Yet M dwarfs have largely been neglected, despite having more favorable planet-star contrasts and representing about 75% of all stars. I will discuss current constraints on planetary systems beyond ~10 AU, focusing in particular on discoveries and new statistical results from the Planets Around Low-Mass Stars (PALMS) high-contrast AO imaging survey at Keck and Subaru. With a sample size of over 120 young M dwarfs, PALMS is the largest direct imaging planet search in this stellar mass regime. Altogether, complementary planet-finding techniques sensitive to a broad range of separations are beginning to map the complete architecture of giant planets around the most common stars in our galaxy.

May 16, 2014

NOTE: Special Joint Astro-Plasma Physics Seminar @ 12:00 - SERF 383
           (in lieu of Journal Club) *Pizza/soda to be served*
 "Current Results and Prospects of Cosmic Ray Experiments"
Eun-Suk Seo

Professor, Department of Physics
University of Maryland
Host: Mikhail Malkov

 Abstract: Cosmic ray research lies at the intersection of particle physics, cosmology, and astronomy. It focuses on highly relativistic particles produced in the most extreme non-equilibrium environments in nature, e.g., supernova explosions, gamma-ray bursts, or active galactic nuclei. Direct measurements of cosmic rays with satellite or balloon-borne detectors are used for understanding cosmic ray origin, acceleration and propagation. They have also been used to search for exotic sources, such as dark matter and antimatter, and to explore a possible limit to particle acceleration in supernova. Recent results will be presented, and the outlook for existing and future experiments will be discussed.

May 21, 2014

 "Orbits and Atmospheres of Directly Imaged Exoplanets: Unveiling
Planet Formation"
Quinn Konopacky

Dunlap Fellow
University of Toronto
Host: Adam Burgasser

 Abstract: Directly imaged exoplanets offer a new window into the rapidly evolving field of planet formation and evolution. The ability to separate the light of widely separated planets (~5 - 100 AU) from their host stars is extremely advantageous for studying Jovian planets. The combination of dynamical and atmospheric characterization can give essential clues about how these planetary systems form. To demonstrate this new insight, I will discuss our team's results from an ongoing monitoring campaign of the HR 8799 directly imaged multi-planet system using the Keck Observatory adaptive optics system. High precision astrometry (~1 mas) has provided constraints on the orbital properties of the four HR8799 planets. Moderate resolution (R~4000) spectroscopy has given precise estimates of the planets' effective temperature, surface gravity, and chemical composition. By analyzing the implied atmospheric chemisty, we have found tantalizing clues about the possible formation pathway for this planetary system. I will also discuss the successful first light runs of the Gemini Planet Imager (GPI), an instrument specifically designed to image and characterize young, widely separated Jovian planets. I will highlight some early results with GPI and describe the upcoming GPI Exoplanet Survey (GPIES), a three year campaign that will revolutionize our understanding of this fascinating planet population. GPIES will also pave the wave for future ground and space-based experiments designed to directly image Jovian and Earth-like exoplanets.

May 28, 2014

 "Illuminating the Dark Universe with Quasar-induced Lyman-alpha Emission"
Sebastiano Cantalupo

MPS Postdoctoral Fellow
UCO/Lick, UC Santa Cruz
Host: Dusan Keres

 Abstract: Gravitational collapse during the Universe's first billion years transformed a nearly homogeneous matter distribution into a network of filaments - the Cosmic Web - where galaxies form and evolve and where the majority of baryons reside as rarefied gas. Because most of this material is too diffuse to form stars, its study has been limited so far to absorption probes against background sources. In this talk, I will present the results of a new, successful program to directly detect and study cosmic gas in the early Universe. This experiment uses an external "source of illumination’’, a bright quasar, to light up with fluorescent Lyα emission "dark" proto-galactic clouds: dense streams around galaxies and the Cosmic Web. I will describe our pilot project based on deep narrow-band imaging with VLT /FORS centered on a z=2.4 hyper-luminous quasar: how we identified and characterized the physical properties of the first 12 “dark” galaxy candidates detected in the early Universe. I will then present observations of fluorescent emission from the gas surrounding star-forming galaxies and very recent results obtained with Keck/LRIS of the detection of hundred-kpc scale filaments surrounding bright quasars: the first direct images of the Cosmic Web.

June 4, 2014

 "Answers from the void"
Paul Sutter

Postdoctoral Fellow
IAP Paris
Host: Alison Coil

 Abstract: Voids are the large, underdense regions in the cosmic web, and they are potentially powerful cosmological probes due to their intimate connection to the growth of structure, their domination by dark energy, and their relative lack of systematics. I will present our latest work to identify voids in galaxy redshift surveys, our efforts to understand their fundamental nature and their connection to dark matter underdensities, and an overview of many diverse cosmological applications, including gravitational lensing, the ISW effect, and the Alcock-Paczynski effect.

June 5, 2014

NOTE: Special Astro Seminar @ 4:00 - SERF 383
 "The Search for Gravitational Waves using Precision Pulsar Timing"
Richard "Dick" Manchester

Head of Pulsar Research Group and CSIRO Fellow in Astronomy and Space Science
Australia Telescope National Facility, Epping NSW Australia
Host: Barney Rickett

 Abstract: Pulsars are extraordinarily good clocks, a property that has been exploited in a wide range of applications from studying the interiors of neutron stars to testing relativistic theories of gravitation. Pulsar Timing Array (PTA) projects make precision timing measurements of many millisecond pulsars that are widely distributed across the sky. Such arrays can in principle give a direct detection of nanohertz gravitational waves. Methods and results for the existing PTAs and the astrophysical implications of these results will be described. Current and future developments, including formation of an International PTA, new receiving systems for existing telescopes and new telescopes including the Square Kilometre Array, will be discussed.

June 11, 2014

 "Lessons in Near-Field Cosmology from Simulating the Local Group"
Shea Garrison-Kimmel

Graduate Student, Center for Cosmology
UC Irvine
Host: Dusan Keres

 Abstract: Studies of the Milky Way (MW) and Andromeda (M31) galaxies, along with their associated satellites and nearby dwarf galaxies, have proven immensely useful for constraining the cosmology of the Universe, particularly on small scales. I will present a number of simulations, many of which are a part of the ELVIS Suite, cosmological zoom-in simulations of Local Group-like volumes of MW/M31 pairs. Using these, and other simulations, I will highlight existing tensions within the LCDM paradigm, as well as illustrate how simulations can provide links between near-field and deep-field observations.