Jump to: navigation, search

Astrophysics Seminars


The CASS Astrophysics Seminar features world-class astrophysicists from around the world speaking on current topics of research. Presentations are aimed at the graduate and post-graduate level, but are open to the general public. CASS seminars take place on Wednesdays from 3:00 - 4:00 p.m. in 383 SERF (Marlar Seminar Room), unless otherwise noted. You can watch a live stream of the talk or prior talks at the CASS Seminar YouTube Channel. The organizers are Prof. Quinn Konopacky and Dr. Alexei Kritsuk.

Upcoming Seminars

Winter 2019

January 23, 2019

 "Dark Matter, First Light"

Katie Mack
Assistant Professor
North Carolina State University

 Dark matter forms the foundation for all cosmic structure, and its fundamental nature is one of science's most pressing enigmas. As we search for the most distant galaxies in the universe with radio and infrared observations, we are in a position to explore the particle physics of dark matter — the possibility of annihilation, decay, or other particle interactions — through its effects on early stars and galaxies. I will give an update on the quest to identify dark matter both in the lab and in the sky, major unsolved problems in dark matter theory, and how upcoming observations of the epoch of the first cosmic structures can be used to open a new window on the dark universe.

January 30, 2019

 "The Relationship Between Galaxies and the Large-Scale Structure of the

Alison Coil
Professor of Physics

 I will describe our current understanding of the relationship between galaxies and the large-scale structure of the Universe, often called the galaxy-halo connection. Galaxies are thought to form and evolve in the centers of dark matter halos, which grow along with the galaxies they host. Large galaxy redshift surveys have revealed clear observational signatures of connections between galaxy properties and their clustering properties on large scales. For example, older, quiescent galaxies are known to cluster more strongly than younger, star-forming galaxies, which are more likely to be found in galactic voids and filaments rather than the centers of galaxy clusters. I will show how cosmological numerical simulations have aided our understanding of this galaxy-halo connection and what is known from a statistical point of view about how galaxies populate dark matter halos. This knowledge both helps us learn about galaxy evolution and is fundamental to our ability to use galaxy surveys to reveal cosmological information. I will talk briefly about some of the current open questions in the field, including galactic conformity and assembly bias. (Note that this is a plenary talk I gave at the June 2018 AAS meeting, and it is designed to be understood by graduate students.)

February 6, 2019

 "Fission and lanthanide production in r-process nucleosynthesis"

Nicole Vassh
Postdoctoral Research Associate, Department of Physics
Notre Dame University

 The observations of the GW170817 electromagnetic counterpart last year suggested lanthanides were produced in this neutron star merger event. Lanthanide production in heavy element nucleosynthesis is subject to large uncertainties from nuclear physics and astrophysics unknowns. Specifically, the rare-earth abundance peak, a feature of enhanced lanthanide production at A~164 seen in the solar r-process residuals, is not robustly produced in r-process calculations. The proposed dynamical mechanism of peak formation requires the presence of a nuclear physics feature in the rare-earth region which may be within reach of experiments performed at, for example, the CPT at CARIBU and the upcoming FRIB. To take full advantage of such measurements, we employ Markov Chain Monte Carlo to "reverse engineer" the nuclear masses capable of producing a peak compatible with the observed solar r-process abundances and compare directly with experimental mass data. Here I will present our latest results and demonstrate how the method may be used to the learn which astrophysical conditions are consistent with both observational and experimental data. Uncertainties in the astrophysical conditions also make it difficult to know if merger events are responsible for populating the heaviest observed nuclei, the actinides. Here I will discuss a potential direct signature of actinide production in merger environments. However, an r-process which reaches the actinides is also likely to host fission, which is largely experimentally uncharted for neutron-rich nuclei. The influence of fission on lanthanide abundances, and the potential for future experimental and theoretical efforts to refine our knowledge of fission in the r-process, will be discussed. The question of where nature primarily produces the heavy elements can only be answered through such collaborative efforts between experiment, theory, and observation.

February 13, 2019

 "The Circumgalactic Medium of Star-Forming Galaxies at 2<z<3"

Gwen Rudie
Staff Astronomer
Carnegie Observatories

 The exchange of baryons between galaxies and their surrounding intergalactic medium (IGM) is a crucial but poorly-constrained aspect of galaxy formation and evolution. I will present results from the Keck Baryonic Structure Survey (KBSS), a unique spectroscopic survey designed to explore both the physical properties of high-redshift galaxies and the connection between these galaxies and their surrounding intergalactic baryons. The KBSS is optimized to trace the cosmic peak of star formation (z~2-3), combining high-resolution spectra of hyperluminous QSOs with densely-sampled galaxy redshift surveys surrounding each QSO sightline. I will present new detailed studies of metal-enriched absorbing gas in the high-z CGM, highlighting the gas kinematics and the diversity of physical conditions found close to galaxies. I will also present new measurements of the evolution of hydrogen and carbon-bearing gas within the CGM from z~2.3 to z~0.2 which exhibit surprising trends. Collectively, these data constrain the nature and sphere of influence of galaxy-scale outflows, intergalactic accretion, and their evolution as a function of time.

February 20, 2019

 "The Wind of Change: create, move, and observe cold gas around galaxies"

Max Gronke
Postdoctoral Scholar
UC Santa Barbara

 Galactic winds are large-scale, multiphase outflows from galaxies and crucial for the galactic ecosystem. They are, thus, a potent probe for the underlying feedback mechanisms. The usual picture is that the cold gas has been accelerated by ram pressure forces due to the hot gas. However, reproducing this ubiquitous observation in hydrodynamical simulations has proven to be challenging - simply because the destruction time is shorter than the acceleration time. During my talk, I will show some analytical estimates and results from recent (magneto-)hydrodynamics simulations which suggest a solution to this classical "entrainment problem". I will conclude by discussing potential implications for larger scale galactic simulations, and observables of cold gas in the surroundings of galaxies. In particular, I want to show that the Lyman-alpha line is a powerful probe of the (small-scale) structure of neutral hydrogen.

February 27, 2019

NOTE: Hans Suess Memorial Lecture 4:00-5:00pm in NSB Auditorium
(Reception in NSB Atrium from 3:00-4:00pm)

Victoria Meadows
University of Washington

March 13, 2019

Fridolin Weber
Distinguished Professor of Physics / CASS Research Scientist
San Diego State University / UCSD

Spring 2019

March 27, 2019

NOTE: Spring Break - no seminar today

April 3, 2019

Dmitry Savranksy
Assistant Professor of Mechanical and Aerospace Engineering
Cornell University

June 5, 2019

Greg Mace
Research Associate
University of Texas, Austin