Astrophysics Seminars From 2016 - 2017
September 26, 2016
- NOTE: Dark Matter Network Seminar
Monday @ 4:00 in SERF 329
- NOTE: Dark Matter Network Seminar
- Professor, Department of Particle Physics & Astrophysics
- The Weizmann Institute, Israel
September 28, 2016
- "Puzzles in Galaxy Scaling Relations"
- Professor, Observatory Director and Graduate Chair
- Queen's University
Galaxies like our Milky Way can be described in terms of their structure, dynamics, and stellar populations. Some very robust correlations between galaxy structural properties, such as total luminosity, maximum circular velocity, and size display rather small scatter, hinting at well-regulated galaxy formation processes. A major challenge to understanding these scaling relations, their tight scatter, and ultimately galaxy formation and evolution, is the elusive interplay between visible and dark matter. I will present the latest constraints on galaxy scaling relations and their link with modern cosmological models.
October 5, 2016
- "Atmospheric retrieval analysis of cloudy atmospheres"
- Marie Curie Fellow
- NASA Ames Research Centre & University of Hertfordshire
One of the most pressing problems in exoplanetary science is the robust determination of atmospheric composition in the presence of clouds. As the number of directly imaged exoplanets grow over the coming years, having robust comparisons of stellar and planetary compositions will be crucial for advancing our understanding of giant planet formation. At present, most estimates of the properties of directly imaged explanets rely on comparison to brown dwarfs, or to evolutionary and atmospheric grid models originally developed for brown dwarfs. This approach is unsatisfactory for reasons I will discuss in detail. I will outline progress in developing an atmospheric retrieval code targeted at the (possibly) cloudy atmospheres of L type brown dwarfs and directly imaged exoplanets, highlighting the challenges posed by this regime, the first applications to real examples and future opportunities for exoplanet applications.
October 12, 2016
- "Magnetic Fields in Molecular Clouds: Observations with the
- Postdoctoral Scholar
Polarized thermal emission from interstellar dust grains can be used to map magnetic fields in star forming molecular clouds and the diffuse interstellar medium. The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry (BLASTPol) flew from Antarctica in 2012 and produced degree-scale polarization maps at arcminute resolution of the Vela C molecular cloud. Our observations have increased our understanding of magnetic field morphology in molecular clouds and the far infrared polarized dust spectra. I will present the primary results from this unique data set as well as introduce the next generation instrument, BLAST-TNG, which will build on the success of BLASTPol.
October 13, 2016
- NOTE: Special Joint Plasma Physics-Astrophysics Seminar
Thursday, October 13th @ 11:00AM in SERF 383
- NOTE: Special Joint Plasma Physics-Astrophysics Seminar
- "High energy neutrino astronomy: Where are we now, what did we learn?"
- Weizmann Institute of Science, Israel
The detection of high energy extra-terrestrial neutrinos by IceCube opens a new window for observations of the Universe. I will discuss the likely extra-Galactic origin of these neutrinos, the clues that their detection provides towards the solution of the long standing question of the origin of cosmic rays (CRs), and the prospects for identifying the CR sources and for studying open questions in particle physics and astrophysics using combined electromagnetic and neutrino observations.
October 19, 2016
- "Exploring galaxy evolution and star formation with Toltec, a millimeter-wave
imaging polarimeter on a 50 meter telescope"
- Professor, Physics Department
- Arizona State University
Half of the light emitted by stars is absorbed by interstellar dust and re-emitted at long wavelengths. Only in the last 20 years or so have we begun to detect and resolve this far-infrared and millimeter-wave dust emission from galaxies into individual objects. The HERSCHEL space telescope (and BLAST balloon-borne telescope) provided catalogs of large numbers of objects at wavelengths of 250, 350 and 500 um but was confusion limited due to its beam size of 17". Ground-based instruments on 10 meter-class telescopes such as BOLOCAM and SCUBA2 have carried out deep surveys detecting hundreds of galaxies at longer wavelengths with similar angular resolution to HERSCHEL. Resolving these sources and comparing them with galaxies detected in deep optical surveys would enable us to explore the evolution of star formation in the universe, especially at high redshifts, in more detail.
Toltec is a wide-field imaging polarimeter for the Large Millimeter-wave Telescope (LMT) in Mexico that has been recently selected for funding by the NSF MSIP. The LMT has been constructed through a collaboration between the national institute of astrophysics, optics and electronics (INAOE) in Mexico and the University of Massachusetts in the US. The Toltec instrument will observe simultaneously in three millimeter-wave bands from 1.1 - 2.1 mm wavelength with an instantaneous field of view of 4 arcminutes in diameter and an angular resolution from 5" (1.1 mm) - 9" (2.1 mm). Toltec will be constructed over the next 2.5 years and then spend 2.5 years carrying out three large scientific surveys. The details of the surveys are going to be worked out in consultation with the US and international scientific community and the survey data products will be made public as soon as they are produced. I will describe the Toltec instrument and some of the possible science that can be done with it on the LMT including: detecting and resolving the highest redshift dusty galaxies, measuring the profiles of hot gas in galaxy halos as a function of redshift and finding direct evidence for the feedback mechanism for quenching star formation and measuring the magnetic fields in star forming regions in our own galaxy through high andgular resolution dust polarization maps.
October 26, 2016
- "FIREBall-2: upcoming UV observations of the circumgalactic medium"
- NSF & Millikan Prize Postdoctoral Fellow
The Faint Intergalactic medium Redshifted Emission Balloon (FIREBall-2) is a balloon-born UV multi-object spectrograph designed to detect lyman-alpha emission from the circumgalactic medium (CGM) around low-z galaxies. I will discuss the science goals we hope to achieve, informed by recent exciting discoveries at higher redshifts. I will also discuss the final flight design, results from integration and testing, and the ongoing preparations for flight from Fort Sumner, NM in 2017. In addition to groundbreaking science, FIREBall-2 will flight test several new technologies in a balloon setting, including photon counting, high efficiency UV detectors. I will discuss these technologies in the context of their impact on future space missions.
November 2, 2016
- "Relatively Bright Supernovae"
- Associate Professor of Astronomy and Director, Mount Laguna Observatory
- San Diego State University
A small fraction of supernovae appear much brighter for their distance than normal. Included amoung these are so called "superluminous supernovae" (SLSNe) which have intrinsically high luminosities, but there are also normal luminosity supernovae that appear anomalously bright due to magnification by gravitational lenses. Both of these phenomena can be used to probe the distant universe, and they are, of course, of interest in their own right. In this talk I will first introduce SLSNe and discuss how searches for these objects serendipitously led to the first discovery of a gravitationally lensed supernova. Finally, I will discuss current searches for these rare objects including projects based at the Mount Laguna Observatory.
November 8, 2016
- NOTE: Special Astro Seminar
Tuesday @ 2:00 in SERF 383
- NOTE: Special Astro Seminar
- "Large-scale environment and the CGM: the hidden variables of
- PhD Candidate & Research Assistant, Department of Astronomy
- University of Massachusetts-Amherst
While the environments in which galaxies live have long been known to correlate with their star formation activity and morphology, the mechanisms inducing these effects, particularly at low environmental densities, are not well understood. I will present results leveraging the HST/COS archive, SDSS, and my own observational campaign showing that properties of the circumgalactic medium (CGM) strongly correlate with galaxy environment across a wide range of densities, from voids to clusters. Because these effects are evident on scales of even moderately populated groups, the implications are quite profound: Environmental processes are first detectable in the galaxies' halo gas, well before effects arise in their stellar or neutral gas components. In turn, UV absorption line spectroscopy provides detailed thermal, chemical, and kinematic information about this intervening medium and offers key insight to previously 'hidden variables' in phenomena such as galactic conformity and strangulation.
November 9, 2016
- "On the Dynamics of Planets, Stars and Black Holes - New Insights from Triples"
- Assistant Professor, Department of Physics & Astronomy
Many observed triple systems in our Universe are in a hierarchical configuration: two objects orbit each other in a relatively tight inner binary while the third object is on a much wider orbit. Furthermore, the secular approximation for the evolution of hierarchical triple body systems has been proven to be very useful in many astrophysical contexts, from planetary to triple-star systems and even black holes. In this approximation the orbits may change shape and orientation, on timescales longer than the orbital periods, but the semi-major axes are constant. In early studies of hierarchical secular three-body systems (Kozai 1962; Lidov 1962), the wider orbit was set to be circular and one of the tight binary members was assumed to be a test (massless) particle. In this situation, the component of the tight orbit’s angular momentum along the total angular momentum is conserved, and the lowest order of the approximation (i.e., the quadrupole approximation) is valid. I will discussed recent developments that showed that considering systems beyond the test particle approximation, or circular orbits, requires the next level of approximation for a correct representation of the physics, called the octupole-level. This leads to qualitative different behavior of the system. In this case, the angular momenta component of the tight and wide orbits along the total angular momentum is not conserved. Most interestingly, at this level of approximation, for an eccentric wide orbit, the tight orbit can reach extremely high eccentricities and undergo chaotic flips of its orientation. This behavior has important implications to the evolution of many systems, and I will present some nominal examples, such as retrograde hot Jupiters, blue stragglers and low-mass X-ray binaries.
November 16, 2016
- “Exploring Nuclear and Particle Astrophysics with COSI, NuSTAR and GAPS”
- Incoming Dean of Physical Sciences, UCSD (currently at UCB)
- UC Berkeley
High energy astrophysics encompasses the study of some of nature’s most exotic creations such as black holes, neutron stars, and supernovae; as well as utilizing those systems to address fundamental physical questions. In this talk, I will survey my work with three different high energy astrophysics experiments. The Compton Spectrometer and Imager (COSI) wide-field gamma-ray telescope (0.2-5 MeV) is designed to probe the origins of Galactic positrons, uncover sites of nucleosynthesis in the Galaxy, and perform pioneering studies of gamma-ray polarization. The Nuclear Spectroscopic Telescope Array (NuSTAR) is a novel focusing hard X-ray telescope (3-78 keV), which has enabled major advances in our understanding of nuclear astrophysics. The General Anti-Particle Spectrometer (GAPS) s a wide-field charged particle telescope, designed to search for low-energy cosmic anti-deuterons as a unique signature of dark matter annihilations. The experiments have in common the novel application of gamma-ray spectroscopy to explore fundamental questions of nuclear and particle physics in our cosmos.
November 23, 2016
- "An X-ray View of the Dusty Universe"
- Postdoctoral Fellow
- University of Wisconsin-Madison
A significant fraction of the heavy elements produced by stars spend some time in the interstellar medium as dust grains. These heavy metal transporters influence gas cooling during star formation, eventually becoming the seeds for planet formation. Much like quasar spectra are used to probe intergalactic gas, observations of X-ray bright Galactic compact objects can yield key insights to the mineralogy and evolution of dust grains in the Milky Way. With high resolution X-ray spectroscopy, we can directly measure the state of metals and the mineral composition of dust in the interstellar medium. In addition, dust scattering produces a diffuse halo image around bright X-ray objects, revealing information about dust grain sizes and their spatial distribution. I will review the most recent exciting dust scattering discoveries, which draw on multi-wavelength observations. Finally, I will discuss future space based missions that will provide critical insights for astro-mineralogy and the life cycle of interstellar dust.
November 30, 2016
- "Dark Earthshine"
- Assistant Professor of Physics
- UC Riverside
I propose a search for dark matter annihilating into dark photons at the center of the Earth, focusing on the present and future reach of IceCube and space-based telescopes. I highlight the effect of low-velocity enhancements to dark matter capture and kinematic features that offer an opportunity for a smoking-gun signal. I also present prospects for an analogous search for dark photons from the center of the sun which may be detected by AMS-02, extending earlier work by modeling the effect of the solar wind.
December 7, 2016
- NOTE: Change in venue: SERF 329
- NOTE: Change in venue: SERF 329
- "Dwarfs and their tiny satellites as extreme probes to the LCDM model"
- Assistant Professor, Physics & Astronomy Department
- UC Riverside
Dwarfs come in all forms, from rotationally-supported star-forming disks to spheroidal stellar systems with no star-formation and negligible rotation. We use cosmological hydrodynamical simulations to show that environment plays a significant role on the assembly history, star formation and globular cluster population of these dwarfs, solving a long-standing issue on the origin of dwarf ellipticals in galaxy clusters. But as observations push deeper into fainter and fainter galaxies, the theoretical predictions become most extreme. LCDM makes two clear predictions: i) fainter objects should become increasingly more dark-matter dominated as we move to lower masses and ii) galaxies of any size should be surrounded by a wealth of dark-matter subhalos, many of them massive enough to host their own stars. I will use cosmological simulations to address these predictions and compare them to available observational constraints for the Baryonic Tully-Fisher relation and distribution of dwarfs in the Local Volume. The recent detection of several potential dwarfs associated to the Large Magellanic Cloud by the DES survey is an exciting discovery that cries for new observational campaigns able push the detection of very faint galaxies beyond the limits of our own backyard.
January 11, 2017
- "Cosmic connections: from cosmic rays to gamma rays, to neutrinos
and magnetic fields"
- Professor, Department of Physics & Astronomy
Combined data from gamma-ray telescopes, cosmic-ray detectors, and neutrino detectors have produced some surprising new insights regarding the most powerful sources in the universe, as well as intergalactic and galactic magnetic fields and extragalactic background light. I will discuss how a unified treatment of gamma rays, cosmic rays, and neutrinos reveals some intriguing connections between some seemingly unrelated phenomena.
January 18, 2017
- "The Polarization of the CMB with Planck"
- Research Scientist
In this talk I will give an overview of Planck data and Cosmological results focusing on the analysis of polarized data. I will present new insights into the polarization of foregrounds rendered by the Planck satellite and an account of current constraints on the optical depth due to reionization, \tau, and the scalar to tensor ratio, r.
January 25, 2017
- "Earth-size Exoplanets"
- Professor of Astronomy
Earth-size exoplanets and their slightly larger ‘super-Earth’ cousins are the most abundant planets orbiting close to Sun-like stars. These planets have diverse physical compositions, unusual atmospheres, and poorly understood origins. My talk will trace the discovery and early characterization of these small worlds through Doppler and transit surveys, and look forward to future discoveries with instruments such as SHREK.
February 3, 2017
- NOTE: Special Astro Seminar in lieu of Journal Club @ Noon
(Pizza & soda provided)
- NOTE: Special Astro Seminar in lieu of Journal Club @ Noon
- "Unraveling LISA and her Secrets: A Quest for Human-Robot Cohabitation"
- Professor of Electrical and Computer Engineering
LISA turned sixteen and is the oldest one of her kind in the world. Long before evangelists of industry and media made us humans start feeling like vestigial parts in the grand evolution of smart driverless vehicles, LISA, your neighbor on the first floor, has pursued a sustained, systematic, and a multidisciplinary research agenda on the development of Intelligent and Safe Automobiles in a “human-centered” framework. In this presentation we will give an overview the major research activities and accomplishment of the LISA team.
With recent advances in embedded sensing, computing, machine perception, learning, planning and control, intelligent vehicle technology is moving tantalizingly closer to a future with large-scale deployment of self-driving automobiles on roadways. However, we are also realizing that many important issues need deeper examination so that the safety, reliability and robustness of these highly complex systems can be assured. Toward this end, we highlight research issues as they relate to the understanding of human agents interacting with the automated vehicle, who are either occupants of such vehicles, or who are in the near vicinity of the vehicles. A human-centered framework for a distributed intelligent system includes the driver, vehicle and environment as three key components. The main idea is to develop an approach to properly design, implement and evaluate methods and computational frameworks for distributed systems where intelligent robots and humans cohabit, with proper understanding of mutual goals, plans, intentions, risks and safety parameters. We emphasize the need and the implications of utilizing a holistic approach, where driving in a naturalistic context is observed over sustained periods of time to learn driving behaviors and to predict intentions and interactivity patterns of intelligent agents. Moving toward vehicles with higher autonomy opens new research avenues in dealing with learning, modeling, active control, perception of dynamic events, and novel architectures for distributed cognitive systems. This presentation will give examples of some of the accomplishments in the design of such systems and also highlight important research challenges yet to be overcome.
Related Publications (accessible on http://cvrr.ucsd.edu/publications/): E. Ohn-Bar, M. Trivedi, "Looking at Humans in the Age of Self-Driving and Highly Automated Vehicles", IEEE Transactions on Intelligent Vehicles, 2016. A. Tawari, S. Sivaraman, M. Trivedi, T. Shanon, M. Tippelhofer, "Looking-in and Looking-out Vision for Urban Intelligent Assistance,” IEEE Intelligent Vehicles, 2014. E. Ohn-Bar, A. Tawari, S. Martin, M. Trivedi, "On Surveillance for Safety Critical Events: In-Vehicle Video Networks for Predictive Driver Assistance Systems,” Computer Vision and Image Understanding, 2015 A. Rangesh, K. Yuen, E. Ohn-Bar, M. Trivedi, “Pedestrians and their Phones, Detecting Phone Use Activities of Pedestrians for Autonomous Vehicles, IEEE Intelligent Transportation Systems Conference, 2016.
Mohan Trivedi is a Distinguished Professor of Electrical and Computer Engineering and founding director of the Computer Vision and Robotics Research Laboratory, as well as the Laboratory for Intelligent and Safe Automobiles (LISA) at the University of California San Diego. Currently, Trivedi and his team are pursuing research in autonomous driving, intelligent vehicles, machine perception, machine learning, human-robot interactivity, driver assistance, active safety and intelligent transportation systems. The team has won over 20 best paper or “finalist” awards and Trivedi has received the IEEE ITS Society’s Outstanding Research Award, IEEE LEAD Institution Award, Pioneer (Technical Activities) and Meritorious Service Award of the IEEE Computer Society. Trivedi was a charter member of the Cal-IT2 Executive Committee and also of the UC System wide Digital Media Innovation-UC Discovery Program. He serves regularly as a consultant to industry and government agencies in the USA and abroad. He is a Fellow of IEEE, SPIE, and IAPR.
February 8, 2017
- "Precision chemical evolution of galaxies across cosmic time"
- Assistant Professor, Department of Physics
- UC Davis
Chemical evolution is a powerful probe of galaxy assembly and the cycle of baryons between galaxies and the intergalactic medium. Significant observational efforts have been invested to measure chemical evolution out to redshifts z=3.5 with samples now reaching thousands of galaxies. However, these efforts rely on indirect "strong-line" metallicity estimates which are known to cause significant systematic errors at high redshifts. I will present direct measurements of metallicity which show that appropriate strong-line diagnostics can be used to reliably estimate metallicity at z~1, and likely at much higher redshifts. I will also discuss measurements of chemical abundance ratios in high redshift galaxies which provide additional information on the dust and gas content, star formation timescale, and the buildup of disks and bulges.
February 15, 2017
- "Extending our Vision to a Galaxy of Planets"
- Chief Scientist
- NASA Exoplanet Exploration Program, JPL-Caltech
The most obvious method of studying extrasolar planets - directly imaging them alongside their parent star - is also the most difficult. Image contrasts exceeding a billion to one, at subarcsecond separations, are required to detect an analog of our solar system in reflected starlight. Following the charge of the Astro2010 decadal survey, the NASA Exoplanet Exploration Program (ExEP) is tasked with developing the technology and precursor science needed to realize the goals of directly imaging Earth analogs and characterizing their atmospheres for habitability and the presence of life. In this talk, I will review the history of efforts to image extrasolar planets; the methods that can be used, and technical challenges that must be met to image and characterize Earth analogs; the role of exoplanet imaging on the WFIRST mission; and how ExEP and the broader community are working to make a "New Worlds" space telescope into a ready option for our community in the 2020s.
Short bio sketch: Karl Stapelfeldt is Chief Scientist of the NASA Exoplanet Exploration Program at NASA's Jet Propulsion Laboratory in Pasadena CA. He is an observational astronomer specializing in studying circumstellar disks, exoplanets, and planet formation at optical, infrared, and millimeter wavelengths. He has a B.S.E. in Engineering Physics from Princeton University and a Ph.D. in Astrophysics from Caltech. From 1993-1998 he was a member of the HST/WFPC2 instrument science team that restored Hubble's vision, followed by more than a decade in Project Science Office for the Spitzer Space Telescope. He has extensive experience in studies of future space missions for exoplanet direct imaging. From 2011-2016 he was Chief of the Exoplanets and Stellar Astrophysics Laboratory at NASA Goddard Space Flight Center.
February 22, 2017
- NOTE: Special Astro Seminar @ Noon (Pizza & soda provided)
- "Values Affirmation as a Buffer Against Impostor Syndrome"
- Torres Fellow in Exoplanetary Science
- MIT Kavli Institute for Astrophysics and Space Science
Physics is only one field of many in which Impostor Syndrome is rampant among students. The syndrome presents as a narrative about one's "impostor" status that resists evidence from achievements and praise, and is most common among underrepresented groups. It's challenging to address, since it reflects in part the internalization of stubborn cultural stereotypes. Values affirmation practices-- encouraging individuals to focus upon their personal worth independent of science entirely-- have emerged as effective intervention strategies. As two recent studies in Science demonstrate, individuals who've suffered most from negative internalized stereotypes stand the most to gain from values affirmation. I'll review the literature about values affirmation and describe not only how it improves student performance, but also bolsters findings about the value of empathy in scientific interactions.
February 22, 2017
- "The Puzzle of (Tabby) Boyajian's Star"
- Associate Professor of Astrophysics & Astronomy
- Penn State
I have been at the center of efforts to understand KIC 8462852, a strange star found during the Kepler mission. It exhibits deep, irregular "dips" or dimming events lasting days, up to 22% in depth, and appears to be dimming secularly on decadal timescales. As ever-more-contrived natural explanations are proposed and explored by my team and others, we continue to put together monitoring and target-of-opportunity programs to catch it "in the act" of dipping and determine the nature of the dips. In parallel, I have led an effort with the Berkeley SETI Research Center to use GBT to perform a SETI program, inspired by the similarity between the Kepler light curve and predictions by Luc Arnold and Freeman Dyson for observable effects of large alien civilizations.
March 8, 2017
- "A Cosmic Bell Test with Measurement Settings from Milky Way Stars"
- Assistant Research Scientist
I'll discuss a recently published experimental test of Bell's inequality, where, for the first time, our collaboration used real-time observations of astronomical sources (in our case, Hipparcos stars in our galaxy), to randomly choose measurement settings in an otherwise conventional entangled particle "Bell test". We sent polarization-entangled photons from a central source through free space to detectors located in two buildings in Vienna, Austria separated by a little over a kilometer. The goal is to put tension on one of the most subtle assumptions Bell used when deriving his inequality, namely, that the choices of measurement settings for each detector are completely free of any relevant hidden degrees of freedom in the past light cone of the experiment that are not part of the formalism of quantum theory. We observed statistically significant violation of Bell's inequality in each of our two experimental runs, which each took only ~3 minutes. Given our assumptions, we therefore relegate any non-quantum explanations for the measured entanglement correlations to have been in place no more recently than ~600 years ago, the time when the light from the nearest star was emitted in both experimental runs. This represents an improvement of ~16 orders of magnitude in time compared to previous experiments.
March 15, 2017
- "The ISM of spiral galaxies seen in the FIR [CI] lines"
- Assistant Professor
- Reed College
Neutral carbon exists sandwiched between the C+ and CO layers at a range of low extinctions heading into a molecular cloud. However, due to the inhomogeneous structure of turbulent molecular clouds, these low Av surfaces can exist nearly throughout a cloud, making it more likely that [CI] emission may be a good tracer of molecular gas within a cloud (Offner+ 14, Glover+ 15). I will discuss results on the observed [CI](1-0) and [CI](2-1) emission in 18 local spiral galaxies based on the Beyond the Peak survey using the Herschel SPIRE FTS spectrometer. The [CI](2-1) line is extremely well correlated with the CO(4-3) line, suggesting it traces more highly excited (warmer and/or denser) molecular gas than lower-J CO transitions. LVG modeling suggests this is a natural result from the similar excitation temperatures of the [CI](2-1) and CO(4-3) lines. I’ll finish by discussion the use of an “alpha-CI” factor to convert [CI] line emission to a molecular gas mass.
March 29, 2017
- "The Assembly of the First Galaxies: Insights from the Renaissance Simulations"
- Distinguished Professor of Physics, CASS; Director of San Diego Supercomputer Center
The Renaissance Simulations are a suite of high resolution multiphysics cosmological simulations to explore the assembly of the first generation of galaxies. Consuming some 60 million core-hours on the Blue Waters supercomputer over 3 calendar years, the Renaissance Simulations bridge the gap between the formation of Population III stars in minihalos at z ~ 20 and the formation of the first chemically enriched star-forming galaxies at z ~ 10. In this talk I describe how the simulations were performed, and what we have learned about the first generation of galaxies. Topics include the duration of the Pop III epoch as a function of environment; the preprocessing of the IGM by Pop III chemical and radiative feedback; properties of the first galaxies; and their contribution to reionization. The UV luminosity function of our simulated galaxies agree with HST observations over the narrow range of magnitudes where they overlap, giving us some confidence in the results. I present synthetic JWST observations, and conclude by describing our efforts to build a data access portal called the Renaissance Simulations Laboratory so that others may independently explore the first galaxies computationally.
April 12, 2017
- "Lightning and Its Effects"
- Professor Emeritus, Department of Hydrology & Atmospheric Sciences
- University of Arizona
April 19, 2017
- "Relativistic Reconnection, in the Crab Nebula and Beyond"
- Professor, JILA, Department of Astrophysical & Planetary Sciences
- University of Colorado, Boulder
Observations of fast gamma-ray flares from pulsar wind nebulae and relativistic jets have sparked new interest in the role played by magnetic reconnection in accelerating particles to extremely high energies. I will discuss our theoretical and computational efforts to characterize reconnection in plasmas where the magnetic energy approaches or exceeds the rest mass energy, and the resulting particle acceleration and radiation.
April 26, 2017
- "New Ways of Magnetic Field Tracing"
- University of Wisconsin-Madison
I shall introduce three new techniques of magnetic field tracing. The first two use Doppler-shifted emission lines and employs the gradients of velocity in order to trace magnetic fields in the diffuse interstellar media as well as to trace regions of star formation associated with the gravitational collapse. The differences between these techniques is that they use different observationally available measures, i.e. the first one uses the velocity centroids and the other uses velocity channel maps.
I shall provide the theoretical justification of the use of these measures, its numerical testing as well as the comparison of the directions obtained with the velocity centroid gradients using GALFA HI data and those of magnetic field as traced by Planck as well as 13CO data and far infrared polarimetry. I shall also discuss the third technique which employs the synchrotron intensity gradients that also trace magnetic field and, unlike synchrotron polarization, are insensitive to Faraday rotation. I shall also show its correspondence with the magnetic field tracing by Planck and discuss the synergy of using this technique with synchrotron polarization studies. I shall discuss the big promise of the new techniques both for the star formation and CMB foreground studies.
May 3, 2017
- "Young Galaxies Forming in the High-Redshift Universe"
- Associate Professor
- Leiden Observatories
Over the last few years, enormous progress has been made in studying galaxies in the first two billion years thanks to the incredible capabilities of the Hubble and Spitzer Space Telescopes. Already, more than 1500 probable galaxies are known at redshifts above z~6, and now the current frontier is at z~9-10, with 50 plausible galaxy identifications to date, and a spectroscopic redshift measurement to z=11.1. Noteworthy advances are also being made in characterizing the physical properties for these distant galaxies, with probes of the nebular emission lines and specific star formation rates to z~8.5 and new constraints on dust-enshrouded star formation at z>~2 from ALMA. One area where there has been particularly exciting activity is in the study of ultra-faint galaxies in the early universe with the Hubble Frontier Fields (HFF) program, combining the power of long exposures with Hubble and Spitzer with gravitational lensing by massive galaxy clusters. In this colloquium, I survey these and other highlights of current research on high redshift galaxies, while looking forward to future work with JWST.
May 10, 2017
- "Planet Signatures in Transition Disks"
- Assistant Professor, Department of Physics & Astronomy
- California State University at Northridge (CSUN)
During the first million years of evolution, nascent planetary systems are embedded in dense disk-shaped clouds of gas. These circumstellar disks are home to a myriad of hydrodynamical processes, which bring about turbulence and the emergence of viscous-like behavior, enabling accretion of gas onto the protostar. Meanwhile, micron-sized dust grains embedded in the disk are growing through coagulation onto pebbles and rocks. Turbulence has a positive effect on these small solids, concentrating them into transient high pressure regions for long enough to achieve gravitational collapse through pebble accretion into km-sized bodies, forming the first planetesimals. Giant storm systems in the disk, similar to Jupiter's Great Red Spot, may exist in quiescent zones of the disk. These are even more prone to collecting solid material, producing the first terrestrial planets and cores of giant planets. In this talk I will discuss the state of the art and recent advances in the field of planet formation, as well as pressing problems such as the structure observed in high resolution sub-millimeter images of circumstellar disks, and how to interpret them.
May 17, 2017
- "The Dynamics of the Local Group: Challenges to Convention in the Era
of Precision Astrometry"
- Assistant Professor
- University of Arizona
Our understanding of the dynamics of our Local Group of galaxies has changed dramatically over the past few years owing to significant advancements in astrometry and our theoretical understanding of galaxy structure. I will provide an overview of key contributions by the Hubble Space Telescope to this evolving picture. In particular, I will highlight the HSTPROMO team’s proper motion measurements of key players in the Local Group, such as the most massive satellites of the Milky Way (the Large and Small Magellanic Clouds), the first ever direct proper motion measurement of M31 and an implied new orbital history for M33. These results have met with controversy, challenging preconceptions of the orbital dynamics and evolution of key members of the Local Group. I will further highlight the importance of HST’s continued role in this field in the era of Gaia.
May 24, 2017
- "Characterizing ExoPlanetary Systems with Polarized Light"
- Millikan Postdoctoral Fellow
Polarimetry has proven itself as a powerful tool for the characterization of extrasolar planetary systems. In high-contrast observations of circumstellar disks, fainter disks can be imaged in polarized light, due to the fact that light scattered off small dust within the disks is inherently polarized, while the host star light is not. In addition, the measured polarization fraction of the scattered light is a diagnostic of grain scattering properties and depends on size, composition and porosity. Polarimetry can also be used to study the atmospheres of cloudy exoplanets and brown dwarfs to constrain rotationally-induced oblateness, cloud morphology and cloud height. In this talk I will first introduce the Gemini Planet Imager’s polarimetry mode and summarize recent disk results that show morphological signs of unseen planets and unexpected polarization characteristics. I will then introduce a new spectropolarimeter, called WIRC-POL, currently being commissioned on the 200-inch Hale telescope at Palomar observatory, that we will use for a spectropolarimetric survey of 100s of nearby brown dwarfs to search for patchy clouds. The results of this survey will elucidate cloud physics relevant not only for brown dwarfs, but for observations of exoplanet atmospheres as well.
May 31, 2017
- "Mapping dark matter in galaxies"
- NSF Astronomy & Astrophysics Postdoctoral Fellow
- TAPIR, Caltech / Columbia University Dept of Astronomy
Cosmological simulations can now make specific and detailed predictions for the shapes, masses, and substructure fractions in galactic dark matter halos that depend on the dark matter model assumed. Comparing these predictions to the observed mass distributions of galaxies should therefore lead to constraints on the nature of dark matter, but observable dynamical tracers can be scarce in regions where the dark matter distribution is best able to discriminate between models. One such region is the outskirts of galaxies, where the influence of baryonic matter on the dark matter halo is limited and the effect of dark substructures most prominent. New advances in instrumentation, and new surveys of Milky Way stars, are now making it possible to obtain accurate position and velocity information for the faint tidal streams, remnants of disrupted satellite galaxies, that trace out the mass distribution in the distant reaches of galaxy halos. I will demonstrate how this new information can be used to characterize the dark matter distribution in the Milky Way and in other galaxies, and thereby place constraints on the nature of dark matter.
June 14, 2017
- NOTE: Special Talk in lieu of Astro Seminar
- "Report from Women in Astronomy IV"
- Professor of Physics
The fourth Women in Astronomy conference was held this past weekend in Austin, TX, with 170 astronomers participating in workshops, panels, and small group discussions focusing on issues that affect women in astronomy, and identifying ways institutions can create welcoming, equitable workplaces. A major focus of the workshop was intersectionality, recognizing and addressing the greater disparities of and barriers faced by women of color, disabled women, people across the gender and sexual orientation spectra, and other marginalized identities. Outcomes of the meeting include the development of recommendations, tool kits and resource lists for participants to take back to their departments; and the preparation of white papers for the 2020 Decadal Survey. In this talk, I will summarize the highlights of this two-day event and facilitate a group discussion on what we can do in CASS, Physics and UCSD to improve the climate and create a more equitable workspace for the full spectrum of women in the physical sciences.