Talks & Events
Faculty Research Seminars
Faculty Research Seminars - This talk series is aimed at first-year students. These talks are designed to give an overview of research in the department.
Mondays, at 12 PM, in ERC 583. Bring your lunch!
Past Faculty Research Seminars
Modelling Galaxy Formation
Gravitational-Wave Astrophysics with LIGO
The era of gravitational-wave astrophysics has begun! We will give a brief overview of what LIGO is, what it is finding, and what this teaches us about the Universe.
The LSST project is constructing an 8.4 meter telescope at Cerro Pachon, Chile, which will be used to conduct a 10 year imaging survey in six bands over 18,000 square degrees of sky. Four major science goals include: the study of dark matter and dark energy, detect hazardous asteroids and other objects in the solar system, monitor the transient optical sky, and address questions regarding the formation and structure of the Milky Way. This talk will address how these science goals will be achieved, focusing particularly on dark energy. It will also examine some of the technical requirements driving the design, solutions that have been developed, and the impact of certain features of the hardware on the ability to extract science.
The Extreme Energy Frontier from Up, Up, and Away
Thanks to giant extensive air-showers observatories, such as the Pierre Auger Observatory and the Telescope Array (TA), we now know that the sources of ultrahigh energy cosmic rays (UHECRs) are extragalactic. We also know that either they interact with the CMB as predicted or sources run out of energy at the same primary energy scale that triggers pion production on the CMB! Their composition is either surprising (dominated by heavier nuclei at the highest energies) or the hadronic interactions at 100 TeV are not a standard extrapolation of LHC interaction energies. Hints of anisotropies begin to appear as energies above ~60 EeV, just when statistics become very limited. Basic questions remain unanswered: What cosmic objects generates such extremely energetic particles that reach above 10^20 eV (100 EeV)? What is this extreme acceleration mechanism(s)? What is the composition of these particles? How do they interact on their way to Earth and with the Earth's atmosphere? To resolve this mystery, we need to increase the statistics of UHECRs observations above 60 EeV. In addition neutrino and gamma-ray observations at ultra-high energies will be ground-breaking. An international collaboration built the Extreme Universe Space Observatory (EUSO) on a super pressure balloon (SPB) to be the first to detect UHECR fluorescence from above. EUSO-SPB will fly this Spring and inform future space missions designed to unveil the extreme energy cosmic frontier.
The Dark Energy Survey
I will overview the Dark Energy Survey (DES) project, highlight its early science results, and discuss its on-going activities and plans. The DES collaboration built the 570-megapixel Dark Energy Camera for the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory in Chile to carry out a 5-year, deep, multi-band, optical survey over one eighth of the sky and a time-domain survey that will discover several thousand supernovae. The survey started in Aug. 2013 and is now nearing completion of its fourth observing season. DES was designed to address the questions: why is the expansion of the Universe speeding up? Is cosmic acceleration due to dark energy or does it require a modification of General Relativity? If dark energy, is it the energy density of the vacuum (Einstein's cosmological constant) or something else? DES is addressing these questions by measuring the history of cosmic expansion and the growth of structure through four complementary techniques: galaxy clusters, the large-scale galaxy distribution, gravitational lensing, and supernovae, as well as through cross-correlation with other data sets. I will also discuss how the data are being used to make a variety of other astronomical discoveries, from our Solar System to the most distant quasars.
Cosmology at Argonne National Lab
In this FRS, we will give an overview to cosmological research at Argonne National Lab. At Argonne, we study the growth of large scale structure (LSS), the Cosmic Microwave Background, and research at the intersection of the two. For (LSS) we make extensive use of computing resources at the lab to perform computationally intensive simulations (large scale cosmological N-body and hydrodynamical simulations) and are actively involved in a number of optical-IR surveys including DES, DESI and LSST. Our CMB research centers around science with the South Pole Telescope where we are major partners in instrumentation, including fabricating and testing detectors using nanofacilities and cryogenic testbeds at the lab. Argonne is also naturally exploring science at the intersection of LSS and CMB including studies of galaxy clusters and gravitational lensing.
Order and Chaos in the Mergers of Galaxies
The virial equations and the virial theorem are well known tools of inquiry in dynamical astronomy. However, astronomers seldom appreciate the full power of the tensor virial equations in theoretical investigations of the dynamics of stars and stellar systems. After a brief review of the history of the virial equations and of conventional astronomical applications, we devote most of the seminar to an investigation of the dynamical behavior of a low-dimensional model of a merger of two galaxies. The governing equations of the model are the complete sets of moment equations of the first and second orders derived from the collisionless Boltzmann equations of the galaxies. The moment equations of the first order reduce to an equation governing the relative motion of the galaxies. The moment equations of the second order separate into the tensor virial equations of the galaxies and sets of equations governing the evolution of the kinetic energy tensors of the galaxies. In order to close the systems of moment equations, we represent the galaxies as heterogeneous spheroids with arbitrary stratifications of their density distributions, and we represent the mean motions of the stars in terms of velocity fields that sustain the adopted density distributions consistently with the equation of continuity. We reduce and approximate the governing equations in the case of a head-on encounter of a dwarf galaxy with a giant galaxy. That reduction includes the effect of dynamical friction on the relative motion of the galaxies as in earlier investigations by Tremaine and others. In a survey of mergers involving dwarf galaxies of different masses and sizes, relative to the giant, chaotic behavior of the system arises mainly in non-linear oscillations of the dwarf galaxy. An encounter either disrupts the dwarf, excites chaotic oscillations of the dwarf, or excites regular oscillations. Dynamical friction can drive a merger to completion within a Hubble time only if the dwarf is sufficiently massive.