Astronomy Colloquium

Colloquium meetings are held in the Bryant Space Science Center Building (BRT) in Room 217 from 12:45–1:45 pm every Thursday of the Fall and Spring semesters.

Refreshments will be served after the talk in Room 311

Coordinators: Elizabeth Lada, Anthony Gonzalez, Rafael Guzman, Desika Narayanan


Colloquium on Thursday, November 9, 2017 will take place at the New Physics Building, NPB 1002, at 4:05 pm


Fall 2017 Schedule

AUGUST 31HOST: Department
Speaker
Title
Welcome Back: Total Solar Eclipse 2017 Recap

SEPTEMBER 21HOST: Elizabeth Lada
Speaker
Andrew Mann,
University of Texas
Title
Observing Planetary Evolution from Formation to Maturity

Abstract

Planets are not born in their final state; before reaching a more mature and stable phase, young planets are significantly altered and reshaped by their environment. The first few hundred million years are thought to be the most formative, but planets in this age range are also the most difficult to identify and characterize. Instead, research has focused on inferring the history of exoplanets through patterns in the population of older systems. I will discuss how this paradigm is shifting, as novel search techniques and new missions have enabled our discovery of Earth- to Neptune-size transiting planets as young as 10 Myr. These discoveries have enabled new constraints on how close-in exoplanets form and migrate, and provided unique insight into how planets lose atmosphere. However, the current sample of young, transiting planets is too small to make conclusions about the bulk properties of their structures and atmospheres. The upcoming TESS mission, however, is expected to discover dozens or hundreds more young planets, including analogues of a young Earth, and planets orbiting bright stars ideal for detailed study. In the long term, JWST and 30m-class telescopes can eventually be used to probe the atmospheres of young, rocky planets, providing direct information on the history precursor of potentially habitable planets.

SEPTEMBER 22HOST: Department
Speaker
Graduate Students
Title
Grad Student Jamboree

SEPTEMBER 28HOST: Stephen Eikenberry
Speaker
Saida Caballero,
Florida Institute of Technology
Title
The Young and the Massive: Stars at the upper end of the IMF

Abstract

The upper mass limit of stars remains an open question in astrophysics. We will discuss observations of the most massive stars (greater than 100 solar masses) in the local universe and how the observations fit in with theoretical predictions. In particular, the Large Magellanic Cloud plays host to numerous very massive stars, making it an ideal template to study the roles that environment, metallicity, and multiplicity play in the formation and evolution of the most massive stars. We will discuss the work that is instrumental in laying the groundwork for interpreting future observations by James Webb of starburst regions in the high redshift universe.

OCTOBER 5HOST: Desika Narayanan
Speaker
Paul Torrey,
Massachusetts Institute of Technology
Title
Probing Galaxy Formation with Modern Cosmological Simulations

Abstract

Cosmological simulations are among the most powerful tools available to probe the non-linear regime of cosmic structure formation. They also provide a clear test-bed for understanding the impact that hydrodynamics and feedback processes have on the evolution of galaxies. I will present an overview of modern galaxy formation simulations that couple a novel moving mesh computational method with explicit baryon feedback prescriptions. This approach results in detailed galaxy formation models that reproduce fundamental observations such as the galaxy stellar mass function, cosmic star formation rate density, and galaxy morphological diversity. In turn, we are able to leverage these simulations to derive physical knowledge on a wide range of science questions, including the importance of supernova and black hole feedback on galaxy growth, the impact of environment on galaxy properties, the origin of diverse morphological types, and much more. I will discuss some of the most interesting insights gained from these simulations as well as ongoing efforts to improve the physical fidelity of our models.

OCTOBER 12HOST: Desika Narayanan
Speaker
Karin Sandstrom,
University of California, San Diego
Title
Interstellar Dust at Low Metallicity

Abstract

Dust plays critical roles in many of the processes occurring in the interstellar medium and dust’s infrared emission serves as a tracer for the ISM and star formation from the nearby universe out to high redshift. While most of our knowledge of dust is built from observations of the local area of the Milky Way, it is clear that dust properties change dramatically in low metallicity conditions which may be prevalent at high redshift and in nearby dwarf galaxies. I will discuss what we know about how dust properties change with metallicity and how this can impact physical processes occurring in the ISM. I will also present new results from studying low-metallicity dust in the Small Magellanic Clouds and other nearby galaxies. Finally, I will describe the exciting prospects for learning more about low metallicity dust with new and upcoming observational facilities like the James Webb Space Telescope.

OCTOBER 19HOST: Stephen Eikenberry
Speaker
Jeremy Darling,
University of Colorado








Rescheduled to Spring 2018
Title
Real-Time Cosmology

Abstract

Ours is a dynamic universe, so most cosmological observables such as redshift, distance, or flux change over time: given enough time or enough precision, these quantities will be observed to drift. One can compensate for the short careers of astronomers by seeking high precision, but measurements of parts per billion to parts per trillion are required. Nevertheless, "real-time" cosmology is now possible with precise measurement and monitoring of the locations of objects in the sky. In an accelerating universe, cosmological redshifts of objects will drift. In an expanding universe, objects will appear to shrink as they recede, providing a geometrical distance measurement. Large-scale structures of galaxies can be observed to collapse in real time. The baryon acoustic oscillation will converge, primarily due to cosmic expansion. Gravitational waves will cause distant objects to appear to move in the sky. Anisotropy or violation of the Copernican Principle will manifest as cosmic shear. The acceleration of the Sun's orbit causes distant quasars to appear to stream toward the Galactic Center. The motion of the Sun with respect to the Cosmic Microwave Background provides a means to measure the parallax (and thus distance) of galaxies in the local universe. The proper rotation of other galaxies can be observed (the infamous van Maanen effect), also providing a geometric distance. I present the first theoretical predictions of -- and the first application ofobservations to -- many of these phenomena and demonstrate that we can expect to measure most of these effects within the next decade.

OCTOBER 26
Speaker
Amy Mainzer,
JPL/NASA
Title
Getting to Know Earth’s Neighbors: Asteroids and Comets

Abstract

Asteroids and comets have played a key role in the evolution of life on Earth. Over the last two decades, significant progress has been made in identifying and tracking the largest Earth-approaching objects, but more work remains to be done to discover a majority of smaller objects. Surveys offer a powerful means of discovering and providing basic physical characterization of minor planets throughout the solar system. One such survey is provided by NASA’s Wide-field Infrared Survey Explorer (WISE) mission, which has been repurposed for studying near-Earth objects (NEOs) and identifies large, low albedo NEOs. However, it was not originally designed for this purpose, and natural changes to its orbit will eventually bring an end to the mission. The Near-Earth Object Camera (NEOCam) has been proposed as a mission capable of carrying out a more comprehensive survey for NEOs using large-format infrared detectors that are passively cooled.

NOVEMBER 2HOST: Anthony Gonzalez
Speaker
Anja von der Linden,
SUNY Stony Brook
Title
Cosmology with Galaxy Clusters: from Weighing the Giants to LSST

Abstract

Surveys of galaxy clusters provide a sensitive probe of cosmology by measuring the evolution of the halo mass function. However, already current cluster surveys are systematically limited by uncertainties in the relation between cluster mass and observables (e.g. X-ray luminosity, cluster richness, SZ decrement). Cluster weak lensing is the most promising observational method to calibrate the mass scaling to the needed precision, but requires the control of systematic errors to a few percent each. I will discuss the "Weighing the Giants” (WtG) project, which carefully investigated and quantified all sources of systematic uncertainty, resulting in accurate weak lensing masses for 51 clusters. From a sample of ~200 clusters selected from the ROSAT All-Sky Survey, WtG places some of the tightest constraints on a number of cosmological parameters, including the dark energy equation of state, neutrino masses, and modified gravity. Furthermore, when adopting the WtG mass calibration, the results from Planck CMB temperature anisotropies and Planck cluster counts are consistent without invoking the need for new physics. These results bode extremely well for future cluster surveys which will be able to utilize LSST's weak lensing capabilities to anchor the cluster mass scale.

NOVEMBER 9HOST: Joint with Physics
Speaker
Shane Larson,
CIERA, Northwestern University





Taking place at New Physics Building, NPB 1002, at 4:05 pm
Title
Probing the Stellar Graveyard: Gravitational waves from ultra-compact binaries

Abstract

The population of ultra-compact binaries in the Milky Way encodes a fossil record of stellar evolution in the galaxy. Taken as a population, the distributions of stellar types, orbital parameters, and masses encodes the signatures of processes that drive the evolution of these systems, including common envelope phases and epochs of mass transfer.

LISA is a planned gravitational wave interferometer in space, a million times larger than their ground-based counterparts. The enormous size makes LISA sensitive to orbital periods in the range of hundreds to tens of thousands of seconds, a regime populated by binary systems comprised of white dwarfs, neutron stars, and black holes. All told, there should be some 10 million such systems in the Milky Way, providing an ample discovery space to map out and characterize these sources.

In this talk we'll discuss LISA observations of the ultra-compact binary population. We'll discuss current work that illustrates how to use population synthesis to model the galaxy, and examine recent work that shows how joint gravitational wave and electromagnetic observations can constrain mass transfer processes in these systems.

NOVEMBER 16HOST: Desika Narayanan
Speaker
Dan Marrone,
University of Arizona
Title
The Cosmic Abundance of Molecular Gas: Intensity Mapping the Faint Universe

Abstract

The cool, molecular phase of the interstellar medium is the fuel that enables the formation of new stars. In the early universe, large gas reservoirs dominated the baryonic mass of galaxies and enabled a cosmic star formation density that peaked at 10 times the current value. While the light from young stars has made it possible to trace the star formation itself, observing the molecular gas itself is much more difficult. This phase, typically traced by CO emission, has only been observed at high redshift in the most massive objects, while normal galaxies are nearly inaccessible to even the most sensitive radio telescopes. The technique of “intensity mapping,” which measures the aggregate molecular emission from the three-dimensional distribution of galaxies, provides a tool to detect the faint signal of the molecular ISM and chart its history across cosmic time. I will describe a staged program of intensity mapping that targets CO emission from the peak of cosmic star formation to the present. The first phase, the CO Power Spectrum Survey (COPSS), used archival and targeted observations with the CARMA interferometer to constrain the CO power spectrum at z~3 for the first time. I will review these measurements and their implications for the distribution of molecular gas in the universe. This work is now transitioning into new phases in which we use archival and new data from the most sensitive radio telescopes to further explore the growth of the ISM. Preparations are also underway to install a dedicated intensity mapping experiment (TIME) on the new ALMA prototype antenna of the Arizona Radio Observatory to survey the universe from z~0 to the epoch or reionization.

NOVEMBER 30HOST: Jian Ge
Speaker
Eric Lopez,
NASA Goddard Space Flight Center
Title
Understanding Planet Formation by Studying Photo-evaporation from Hot Neptunes

Abstract

One of the most significant advances by NASA’s Kepler Mission was the discovery of an abundant new population of highly irradiated planets with sizes between that of the Earth and Neptune, unlike anything found in our Solar System. Understanding these populations poses a fundamental test for models of planet formation and evolution, with important implications for habitability and the frequency of Earth-like planets. Using models of planet evolution and atmospheric evaporation, I will discuss recent papers that shed light on the on the compositions and possible origins and compositions of these new populations. In particular, I will show that the most highly irradiated planets likely formed without large amounts of material from beyond the snowlike and I will examine observational paths forward for distinguishing between rocky planet populations that formed through photo-evaporative stripping vs those that were born rocky like the Earth.

DECEMBER 5 (Tuesday)HOST: TBA
Speaker
Charles Steinhardt,
Cosmic DAWN Center; Niels Bohr Institute
Title
TBA

Abstract

TBA