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Astrophysics Seminars From 2017 - 2018


Fall 2017

September 19, 2017

NOTE: Special Talk
on Sexual Harassment
Tuesday @ 1:00 in the Qualcomm Room, Jacobs Hall - 1st floor (EBU1)

Joan Schmelz
Arecibo Observatory Deputy Director
Universities Space Research Association (USRA)

 With the issue of sexual harassment repeatedly in the news, one hopes that student groups, academic departments, and university admini- strators are discussing what can be done to eliminate this plague from our community. There are fundamental flaws in the current system where the pressure for righting these wrongs is often placed on the shoulders of young women who can be in the most vulnerable stages of their careers, and where such harassing behavior can remain an “open secret” for years. We have to change the system – to train those with privilege to become not only allies but advocates who will add their voices and prestige to fight for right, to create a “safe space” where anyone facing sexual harassment can get help and advice, and to shine a light on the harassers who still operate in the shadows. Universities and their senior staff can do more to deter, detect, and effectively address inappropriate behavior. This talk gives advice and suggestions on how to change the system and is intended for students, faculty, and administrators.

This event is sponsored by the Division of Physical Sciences and the Office of the Vice Chancellor for Equity, Diversity, and Inclusion at UCSD.

September 20, 2017

 "History, Science & Discovery at the Arecibo Observatory"

Joan Schmelz
Arecibo Observatory Deputy Director
Universities Space Research Association (USRA)

 The Arecibo Observatory celebrated its 50th anniversary in 2013 and continues to do cutting-edge research in radio astronomy, planetary radar, and atmospheric science. Early discoveries include the 33-ms period of the pulsar in the Crab Nebula supernova remnant and the 59-day rotation rate of the planet Mercury. Later discoveries include the first binary pulsar, the first radar maps of Venus, the first megamaser galaxy, the first millisecond pulsar, and the first extrasolar planet. Arecibo’s legacy of great discoveries continues unbroken to the this day with the new detection of the first repeating Fast Radio Burst, which rules out an entire class of models requiring catastrophic explosions. Arecibo’s planetary radar observations provides information on the orbit and physical properties of the Near-Earth Asteroid, Bennu, paving the way for NASA’s OSIRIS-REx mission, which will travel Bennu and return a sample to Earth in 2023. The atmospheric radar has recently discovered the unexpected large amount of helium in the upper reaches of the ionosphere, forcing us to revise our understanding of the coupling between the ionosphere and the plasmasphere. High priority science investigations now include using pulsars to search for gravitational waves, characterizing near-Earth objects that threaten civilization, and heating the ionosphere to perform controlled plasma experiments. This talk will discuss 50 years of science at the Arecibo Observatory, from the early construction to the latest discoveries.

Bio: Joan Schmelz works for Universities Space Research Association (USRA) and currently serves as the deputy director of the Arecibo Observatory in Puerto Rico. She was honored in 2015 as one of Nature’s top ten people who made a difference in science for her work fighting sexual harassment. She is a former program officer for the National Science Foundation's Division of Astronomical Sciences and the former chair of the American Astronomical Society's Committee on the Status of Women in Astronomy. She was a professor at University of Memphis for over 20 years where she recently resigned her tenured position. During that time, she was a regular visitor to the Harvard-Smithsonian Center for Astrophysics, where she worked with multiple colleagues developing observational constraints to test models of solar coronal heating. Schmelz has published papers on a variety of astronomical topics including stars, galaxies, interstellar matter, the cosmic microwave background, and the Sun using data from ground- and space-based telescopes at every band of the electromagnetic spectrum (except gamma rays). She also writes regular posts for the Women in Astronomy BlogSpot on topics such as unconscious bias, stereotype threat, and the gender gap.

September 27, 2017

 "Formation of Close-in Super-Earths, Super-puffs and Ultra-Short Period Planets"

Eve Lee
Sherman Fairchild Postdoctoral Scholar in Theoretical Physics

 The riddle posed by super-Earths is that they are not Jupiters: their core masses are large enough to trigger runaway gas accretion, yet somehow super-Earths accreted atmospheres that weigh only a few percent of their total mass. In this talk, I will demonstrate that this puzzle is solved if super-Earths formed late, in environments akin to the inner cavities of transitional disks. Super-puffs present the inverse problem of being too voluminous for their small masses. I will show that super-puffs most easily acquire their thick atmospheres as dust-free, rapidly cooling worlds outside 1 AU, and then migrate in just after super-Earths appear. Super-Earths and Earth-sized planets around FGKM dwarfs are evenly distributed in log orbital period down to ~10 days, but dwindle in number at shorter periods. I will demonstrate that both the break at ~10 days and the slope of the occurrence rate down to ~1 day can be reproduced if planets form in disks that are truncated by their host star magnetospheres at co-rotation. Planets can be brought from disk edges to ultra-short (<1 day) periods by asynchronous equilibrium tides raised on their stars.

October 4, 2017

 "Secondary astrophysical production of anti-deuteron and anti-Helium3
cosmic ray"

Ryosuke Sato
Postdoctoral Fellow
Weizmann Institute

 Cosmic-ray anti-deuterium and anti-helium have long been suggested as probes of dark matter, as their secondary astrophysical production was thought extremely scarce.

But how does one actually predict the secondary flux? Anti-nuclei are dominantly produced in pp collisions, where laboratory cross section data is lacking.

We make a new attempt at tackling this problem by appealing to a scaling law of nuclear coalescence with the physical volume of the hadronic emission region. The same volume is probed by Hanbury Brown-Twiss (HBT) two-particle correlations.

We demonstrate the consistency of the scaling law with systems ranging from central and off-axis AA collisions to pA collisions, spanning 3 orders of magnitude in coalescence yield. Extending the volume scaling to the pp system, HBT data allows us to make a new estimate of coalescence, that we test against preliminary ALICE pp data.

For anti-helium the resulting cross section is 1-2 orders of magnitude higher than earlier estimates. The astrophysical secondary flux of anti-helium could be within reach of a five-year exposure of AMS02.

October 11, 2017

 "Dwarf galaxy formation and the nature of dark matter"

Anna Nierenberg
UC Chancellor Postdoc
UC Irvine

 The abundance of low mass dark matter halos (M_vir <10^9 M_sun) provides key insight into the nature of dark matter, as this abundance depends on the free-streaming length of dark matter at early times and thus its particle properties. Measuring the abundance of low mass halos is difficult as stars become increasingly poor tracers of structure on these scales owing to the complex and not yet well understood physics of star formation in these systems. I will present two complementary approaches to resolving these issues. First I will present measurements of the properties of faint satellite galaxies at a range of redshifts and around a variety of host types and demonstrate how these place strong new constraints on theoretical models of star formation in low mass halos. Secondly, I will present a novel approach to gravitational lensing which makes it possible directly measure the subhalo mass function to masses well below the mass scale of the missing satellite problem in a much larger sample of systems than previously possible. I will conclude by discussing future prospects for these programs given the next generation of ground and space based facilities.

October 18, 2017

 "Outflows in active galactic nuclei"

Sibasish Laha
Postdoctoral Scholar

 The last couple of decades have seen the most crucial developments in the understanding of AGN winds. This can be attributed mostly to the advent of great observatories like ALMA (Molecular outflows), Hubble space Telescope (UV outflows), XMM-Newton and Chandra (X-ray outflows). Coupled with advancement in theories, our understanding about AGN outflows in different wavelength bands (Radio, Infra-red, Optical, UV and X-rays) has never been better, yet there are many outstanding questions which we still need to answer. We present here the results from a comprehensive study of the warm absorbers (WA) in X-ray in a flux limited complete sample of Seyfert galaxies (WAX-I, Laha et. al. 2014, MNRAS 441, 2613), using high resolution XMM-Newton data. We found that the WA clouds are present in around 65% of the sources. We also found a gap in the ionization parameter distribution of the WA, pointing to thermal instability. We have found evidences of WA being radiatively driven and they originate from the dusty torus (WAX-II, Laha et al. 2016, MNRAS 457, 3896L). The dust opacity can also play a leading role in driving these clouds. These WA clouds can sometimes give “effective feedback” to the host galaxies. In another extensive sample study of AGN exhibiting molecular outflows (to be submitted), we find that the AGN plays the most important role in driving these large kpc scale outflows. However, we are still uncertain how the AGN interacts with these large scale molecular clouds.

October 25, 2017

 "What matter(s) around galaxies? Shining a bright light on the cold phase of the
Circum Galactic Medium"

Sebastiano Cantalupo
Assistant Professor
Institute for Astronomy, ETH Zurich

 I will present the results of a new program to directly detect and study high-redshift cosmic gas in emission using bright quasars and galaxies as external "sources of illumination’. By looking in emission rather than in absorption, this program provides new and unique information on the morphology and physical properties of the cold phase of the Circum Galactic Medium (CGM) on both large and small scales. In particular, I will show results from ultra-deep narrow-band imaging and recent integral-field-spectroscopy as a part of the MUSE Guaranteed Time of Observation program that revealed numerous giant Lyman-alpha emitting filaments extending up to several hundred kpc around quasars and bright galaxies. I will discuss how the unexpectedly high luminosities of these systems, together with the constraints from Helium and metal extended emission, represent a challenge for our current understanding of cosmological structure formation. In particular, I will show that current observations suggest that a large amount of “cold" and dense gaseous “clumps" should be present around high-redshift galaxies and I will present our first attempts to understand the origin and nature of these structures in the Early Universe. At the same time, current galaxy formation models lack an efficient mechanism to prevent too much cooling of the CGM onto galaxies at later epochs and rely on very strong “ejective" feedback. In the second part of the talk, I will show how the interaction between high-energy radiation from star-forming galaxies and the CGM - still ignored by almost all galaxy formation models - provides a natural way to prevent excessive CGM cooling onto galaxies (“preventive” feedback). Finally, I will mention recent COS observations that provide support for the importance of this “preventive” feedback mechanism and, at the same time, can give vital constraints on the SED of star-forming galaxies in the FUV range.

November 1, 2017

 "The Development of the Next Generation Instrumentation for the Compton
Spectrometer and Imager"

Jarred Roberts
Postdoctoral Scholar

 The Compton Spectrometer and Imager (COSI) is a balloon-borne, soft-gamma ray imager, spectrometer, and polarimeter with sensitivity from 0.2 to 5 MeV. Utilizing a compact Compton telescope design with twelve cross-strip, high-purity germanium detectors, COSI has three main science goals: to study the 511 keV positron annihilation line from the Galactic plane, to image diffuse emission from stellar nuclear lines, and to perform polarization studies of gamma-ray bursts and other extreme astrophysical environments. The COSI experiment is currently undergoing a significant instrumentation development that aims to improve the energy and angular resolution of the instrument. This talk will focus on the current status of these developments and the scientific motivation for making these improvements to the instrument.

November 8, 2017

 "Revolutionizing our Understanding of Galaxy Evolution using the Circumgalactic

Cameron Hummels
NSF Postdoctoral Fellow, Department of Astronomy

 Cosmological hydrodynamics simulations are increasingly able to reproduce galaxies like those we observe in nature. However, the detailed structure of the circumgalactic medium (CGM), the tenuous gas around galaxies, remains an unresolved challenge. As the interface between star formation, feedback, galactic gas accretion, and acting as a reservoir hosting half the baryons in a galaxy, the CGM is the key to understanding what drives galactic evolution. I will discuss my recent work at modeling the circumgalactic medium with a focus on the absorber sizes and phase structure of the halo gas as probed through the FIRE and the Tempest simulations, the two highest resolution zoom hydro simulations of the CGM produced to date. Lastly, I will present Trident, an open-source code for generating synthetic spectra to compare simulations with observations.

November 15, 2017

 "Clouds in the Galactic Sky - The Gaseous Halos of Galaxies from the synergy of Observation and Theory"

Cameron Liang
Graduate Student, Department of Astronomy and Astrophysics
University of Chicago

 Undoubtedly, the Earth's atmosphere is an integral part of its ecosystem. Everyday weather and long-term climate of the atmosphere are directly linked to activities on the surface of the Earth and vice versa. Gaseous halos, known as the circumgalactic medium (CGM), are the equivalent atmosphere of galaxies. The galactic climate arises from infalling gas from intergalactic space, enriched materials launched from the interstellar medium and more. The CGM is one of the largest gas reservoirs with complex baryonic cycles. It is paramount to improve our understanding of the CGM to achieve a complete picture of galaxy formation and evolution.

In this talk, I will first focus on the observational efforts to place empirical constraints on the spatial extent and the metallicity of the CGM. I will then present some theoretical work on the baryonic cycles in cosmological zoom-in simulations and show that the CGM provides orthogonal constraints to star formation and feedback processes. Finally, I will present a new high-resolution (< 1pc) simulation study to model the CGM more systematically with radiative cooling, thermal conduction, and magnetic fields.

November 29, 2017

 "Cosmology Results from the Dark Energy Survey Year 1"

Elisabeth Krause
Research Scientist

 This talk presents cosmology constraints from a combined analysis of galaxy clustering and weak gravitational lensing, using 1321 deg2 of griz imaging data from the first year of the Dark Energy Survey (DES Y1). The analysis combines (i) the cosmic shear correlation function of 26 million source galaxies in four redshift bins, (ii) the galaxy angular autocorrelation function of 650,000 luminous red galaxies in five redshift bins, and (iii) the galaxy-shear cross-correlation of luminous red galaxy positions and source galaxy shears. These three measurements yield consistent cosmological results, and provide constraints on the amplitude of density fluctuations (S8 = 0.794+0.029-0.027) and dark energy equation of state (w = -0.80+0.20-0.22) that are competitive with those from Planck cosmic microwave background measurements.

I will describe the validation of measurements and modeling from catalogs to cosmology, and highlight cosmology constraints from the combination of DES Y1 with external data sets.

Based on DES Collaboration 2017 (1708.01530) and supporting papers.

December 1, 2017

NOTE: Special Plasma-Astro Seminar @ 3:00 in SERF 329
 "Using properties of MHD turbulence to study B-fields and remove B-mode

Alex Lazarian
Professor of Astronomy
University of Wisconsin-Madison

 I shall discuss a new technique of tracing magnetic fields in the galaxy that uses the properties of MHD turbulence and show the advantages of this new technique compared to the traditional ways of magnetic field study. I shall also show that the observed properties of galactic CMB foreground, in particular the E/B mode ratio measured for the foreground polarized emission, is consistent with the expectations of the MHD theory.

December 5, 2017

NOTE: Joint Physics-CASS-CER Seminar @ 4:00 in SERF 383
 "Ultra-strong laser fields: from linear to nonlinear QED"

Felix Mackenroth
Distinguished Postdoctoral Fellow
Max-Planck-Institute for the Physics of Complex Systems, Dresden, Germany

 In the interaction of ultra-intense laser fields with matter the ever increasing peak laser intensities render relativistic quantum effects ever more prominent. Such effects are properly described in the framework of quantum electrodynamics and range from manifestations of the photons' particle nature to the famous production of matter from light. Furthermore, the unprecedentedly high photon densities reached at state-of-the-art laser facilities lead to nonlinearities in the interaction with the laser photons, requiring nonperturbative field theoretical methods. Nonlinear or strong-field QED, the proper framework to describe such phenomena, is still an area of intense research. In this talk we are going to discuss a recent proposal how the linear QED effect of producing matter from a two-photon collision could be observed for the first time. Then, we turn to the underlying principles of strong-field QED and how to compute nonperturbative scattering amplitudes. We present quantitative examples for typical nonlinear QED processes. The full result is then benchmarked against common approximations employed in large-scale numerical plasma simulations and it is demonstrated that these approximations have certain limitations. These limits are then discussed in light of upcoming experimental tests.

Author information:

The author received his undergraduate education in physics in Konstanz and Heidelberg, Germany, and did his PhD on quantum radiation in ultra-intense laser pulses under the supervision of PD Antonino Di Piazza in the quantum dynamics group of Prof. Keitel at the Max-Planck-Institute for Nuclear Physics in Heidelberg. For his PhD thesis he was awarded the Otto-Hahn medal of the Max-Planck-Society in 2013 and the thesis was selected to be published under the distinguished Springer Theses program. He then did a post-doc on relativistic plasma physics and laser-based ion acceleration at Chalmers Technical University in Gothenburg, Sweden, from 2014 to 2016. In late 2016 he moved back to Germany to join the Max-Planck-Institute for the Physics of Complex Systems in Dresden where he currently holds a position as Distinguished Postdoctoral Fellow.

December 6, 2017

 "The Breakthrough Listen Search for Advanced Life Beyond Earth”

Andrew Siemion
Director, Berkeley SETI Research Center
UC Berkeley

 The Breakthrough Listen Initiative is an ambitious effort to conduct the most comprehensive and sensitive search for advanced extraterrestrial life in humanity’s history. Breakthrough Listen has secured approximately 20% of the time on two of the largest radio telescopes in the world, the 64m Parkes Telescope in NSW, Australia and the 100m Green Bank Telescope at Green Bank Observatory in West Virginia, along with 36 nights per year on the 2.4m Automated Planet Finder at Lick Observatory. Breakthrough Listen has also entered into an agreement with the National Astronomical Observatory of China to collaborate on the development of search techniques, software and observing procedures for the 500m FAST Telescope, and the Jodrell Bank Observatory / University of Manchester to work together in a similar fashion toward developing SETI capabilities on the 76m Lovell Telescope and the MERLIN network.

Breakthrough Listen observations at the APF employ the Levy Spectrometer to conduct ``spectroscopic optical SETI’’ observations, searching for artificially narrow spectral lines that are known only to arise from technological sources (lasers). At the GBT and Parkes, Breakthrough Listen is deploying state-of-the-art digital backends capable of searching for a wide variety of signals indicative of a technological source, across many GHz of instantaneous bandwidth. As of this writing, Breakthrough Listen has deployed a 6 GHz system at the Green Bank Telescope and a 5 GHz system at the Parkes Telescope.

The current Breakthrough Listen target list includes a spectral-type complete sample of nearby stars, 100 nearby galaxies spread over all morphological types, a complete survey of the galactic plane and exotic objects and targets of opportunity (e.g. KIC 8462852, FRB121102). The Breakthrough Listen team is currently exploring opportunities to engage in commensal SETI programs with the SKA and its precursors. These potential extensions to the Breakthrough Listen program would allow significant expansion of the Breakthrough Listen target list and would lay the groundwork for extremely high sensitivity observations with the full SKA. These latter observations would be the first SETI ever conducted that would be sensitive to Earth-level leakage radiation from nearby stars.

Here I will review the Breakthrough Listen program, current observational capabilities and latest results.

Winter 2018

January 10, 2018

NOTE: Seminar will be held in SERF 329
 "Cosmology Through the Dust: Mitigating Galactic Foregrounds with HI"

Brandon Hensley
Postdoctoral Fellow

 Whether galaxy surveys in the optical or polarized CMB measurements in the microwave, cosmological observations are sensitive to contamination from Galactic dust. I will first present new, large scale maps of interstellar reddening constructed from the fully-sky, spectroscopic HI observations of the HI4PI Survey. Using atomic hydrogen as a tracer of Galactic dust eliminates the need for dust temperature corrections and allows easy removal of extragalactic contamination, producing reddening maps of higher fidelity than those based on far-infrared dust emission, such as that of Schlegel, Finkbeiner, and Davis 1998 ("SFD"). Given the ability of HI to serve as a template for the dust column, I will describe a novel method for using HI to make Cosmic Infrared Background (CIB) maps with high fidelity on large angular scales. Finally, I will discuss some possibilities for using HI and other ancillary data to constrain dust physics and ISM structure, enabling more effective component separation in CMB experiments.

January 17, 2018

 "Analysis of dust emission in nearby galaxies - Implications of the modeling

Jérémy Chastenet
Postdoctoral Scholar

 My work focused on the implications of dust emission modelisation choices on its derived properties in nearby galaxies. A first approach showed that all models do not fit observations of two nearby galaxies adequately and similarly, although they all managed to fit the Milky Way infrared emission. It also highlighted that the dust composition is not the same between those two galaxies, and also with that of the Milky Way. The choice of the dust grains environment, through the incident radiation field, can significantly impact results like the total dust masses. A second project investigated the systematics errors due to the empirical laws used to describe theradiation field that heats the dust grains. I showed that some parameters can be over- or underestimated, while showing good fits to the observations. By getting rid of uncertainties due to dust composition, my results show that the current approach leads to discrepancies in the dust content in spite of a correct dust description.

January 19, 2018

NOTE: Special Lecture from 3:00-5:00PM in SERF 383
 "Dark Matter Decay According to Conformal Cyclic Cosmology: Does it Provide
Detectable Gravitational Signals?"

Sir Roger Penrose
Oxford/Penrose Institute

 In the cosmological scheme of conformal cyclic cosmology (CCC), the equations governing the crossover form each aeon to the next demand the creation of a dominant new scalar material, postulated to be dark matter. In order that this material does not build up from aeon to aeon, it is taken to decay away completely over the history of each aeon. The dark matter particles (erebons) may be expected to behave almost as classical particles, though with bosonic properties, being probably of about a Planck mass, and interacting only gravitationally. Their decay would be to gravitational signals, and responsible for the (~scale invariant) temperature fluctuations in the CMB of the succeeding aeon. In our own aeon, erebon decay might well show up in signals discernable by gravitational wave detectors.

January 24, 2018

Victor Robles
Postdoctoral Researcher
UC Irvine

January 31, 2018

 "Breaking the Habit - The peculiar 2016 eruption of the remarkable recurrent nova
in M31"

Martin Henze
San Diego State University

 Since its discovery in 2008, the Andromeda galaxy nova M31N 2008-12a has been observed in eruption every single year. This unprecedented frequency indicates an extreme object, with a massive white dwarf and a high accretion rate, which is the most promising candidate for the progenitor of a type-Ia supernova known to date. The previous three eruptions of M31N 2008-12a have displayed remarkably homogeneous multi-wavelength properties. In contrast, the delayed 2016 eruption (in December last year) showed significant deviations from this pattern. In this talk, I will discuss the 2016 observing campaign and its results, together with possible interpretations on the physics and evolution of this unique system in the context of extragalactic nova science.

February 7, 2018

NOTE: Joint Astro-Plasma Physics Seminar
 "The Basis for Cosmic Ray Feedback: Microscales to Macroscales"

Ellen Zweibel
W. L. Kraushaar Professor of Astronomy & Physics, Department of Astronomy
University of Wisconsin-Madison

 Cosmic rays, mostly relativistic protons, represent less than a billionth of interstellar particles, but comprise roughly the same energy density as the thermal gas. Their interaction with the thermal gas is primarily collisionless, mediated by the ambient magnetic field. I will discuss the plasma physics that underlies this interaction, and how it allows cosmic rays to sculpt, or feed back on, their environments.

February 14, 2018

Joy Didier
UC Santa Cruz

February 21, 2018

Rene Ong
Professor, Department of Physics and Astronomy

February 28, 2018

 "Closing in on Black Hole Spins"

John Tomsick
Researcher, Space Sciences Lab
UC Berkeley

 Determining how rapidly black holes (BHs) spin has been a key goal of astrophysics for decades. Knowing the spin rates of BHs is relevant to probing regions of strong gravity, understanding how relativistic jets are powered, and determining how BHs form and evolve. In this talk, I will discuss methods that have been developed for measuring the spins of accreting BHs with X-ray spectral and timing observations. This includes past X-ray timing and spectral measurements with RXTE, recent X-ray reflection measurements with the Nuclear Spectroscopic Telescope Array (NuSTAR), and future X-ray and soft gamma-ray polarization measurements with IXPE, XIPE, and COSI-X. Comparisons between spins of accreting stellar mass BHs and the constraints found by gravitational wave measurements for BH/BH merger events will also be presented.

March 7, 2018

Emily Pringle
Scripps Postdoctoral Fellow

March 14, 2018

Gina Panopoulou
Staff Scientist, Radio Astronomy

Spring 2018

April 25, 2018

Jorge Pineda
Research Scientist

May 9, 2018

Jessica Werk
Assistant Professor
University of Washington

May 23, 2018

Chung-Pei Ma
Professor of Astronomy and Physics
UC Berkeley

May 30, 2018

Ruth Murray-Clay
UC Santa Cruz