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 talk in Room 311

Coordinator: Elizabeth Lada


Spring 2017 Schedule

JANUARY 12HOST: Desika Narayanan
Speaker
Charley Conroy,
Harvard University
Title
Unraveling Galaxy Formation Histories with Semi-Resolved Stellar Populations

Abstract

The analysis of stellar populations has traditionally been pursued in two limiting cases: spatially-resolved stellar populations in the color-magnitude diagram, and integrated light observations of distant systems. In between these two extremes lies a rich and relatively unexplored realm of observational phenomena. In this talk I will describe our efforts to develop techniques and analyze datasets exploiting the “semi-resolved” stellar population regime, both spatially and temporally. We have used these techniques to unravel the stellar populations of nearby galaxies, which has offered new insights into their formation histories. These new tools will play an important role in maximizing the science returns from next generation ground and space-based facilities.

JANUARY 19
JANUARY 26
FEBRUARY 2HOST: Charlie Telesco
Speaker
Jamie Foster,
University of Florida
Title
Stromatolites: Windows into the Ancient Earth

Abstract

Stromatolites are the oldest known ecosystems on Earth, with fossils that date back more then 3700 million years. These ancient ecosystems once dominated the planet and dramatically changed the Earth’s atmosphere and landscape. In this seminar, Dr. Jamie Foster of the University of Florida will talk about the formation of these ancient ecosystems and how the study of modern stromatolites, with state-of-the-art molecular biology tools, can help inform us about how the microbial world adapts to a continuously changing environment.

FEBRUARY 9HOST: Charlie Telesco
Speaker
Marcia Rieke,
University of Arizona
Title
NIRCam for JWST: Your Next Near–Infrared Camera in Space

Abstract

The combination of NIRCam and The James Webb Space Telescope will provide astronomers with another huge leap in sensitivity and spatial resolution. NIRCam's characteristics, operating modes, and performance predictions will be reviewed both in the context of deep field extragalactic surveys and in the context of exoplanet observations. The design drivers for JWST and NIRCam will be examined and how these performance requirements have driven the NIRCam design will be presented. Sample observing programs in the guise of the NIRCam Instrument Team GTO program will also be presented.

FEBRUARY 16HOST: Robert Wilson
Speaker
Ed Sion,
Villanova University
Title
Recurrent Novae as Progenitors of Type Ia Supernovae

FEBRUARY 23HOST: Elizabeth Lada
Speaker
Uma Gorti,
SETI
Title
The Evolution of Gas and Dust in Protoplanetary Disk

Abstract

Protoplanetary disks, as the name implies, form planetary systems within their short lifetimes of a few million years. Understanding how the disk material evolves in time and space is central to our understanding of planetary system formation, with the physical and chemical conditions in the protoplanetary disk affecting not only formation processes, but also planetary compositions and dynamical evolution. In this talk, I will discuss disk evolution mainly from a theoretical perspective. I will describe recent models that consider photoevaporation, or the driving of thermal winds due to stellar heating, as the chief agent of disk dispersal. I will also discuss observational constraints on some of the key physical processes, including gas and dust diagnostics from optical to sub-millimeter wavelengths.

MARCH 2HOST: Elizabeth Lada
Speaker
Sean Andrews,
CFA
Title
Observing the Evolution of Solids in Protoplanetary Disks

Abstract

The canonical model for the formation of terrestrial planets and giant planet cores relies on an early and very efficient phase of planetesimal growth in a gas-rich circumstellar disk. But, as theorists have known for decades now, there are some formidable obstacles to meeting that requirement. Many of these problems, and potentially their solutions, are associated with the growth and migration of "pebbles" (mm/cm-sized particles) in the first few million years of a disk's lifetime. That is fortuitous, since the continuum emission from these particles in nearby disks can be readily detected and resolved with long-baseline radio interferometers (e.g., ALMA, VLA). In this talk, I will describe what we are learning about the evolution of solids from such data, including: (1) the signatures of particle growth and migration; and (2) the mounting evidence that small-scale substructures in the (gas) disk play fundamental - and perhaps mandatory - roles in the planet formation process.

MARCH 16HOST: Jonathan Tan
Speaker
Peter Behroozi,
University of California, Berkeley
Title
The Connection between Galaxy Growth and Dark Matter Halo Assembly from z=0–10

Abstract

We present a short review of the connection between galaxies and dark matter halos, followed by a new method to flexibly and self-consistently infer individual galaxies' star formation rates as a function of their host halos' potential well depths, assembly histories, and redshifts. The method is able to match galaxies' observed stellar mass functions, star formation rates (specific and cosmic), quenched fractions, UV luminosity functions, autocorrelation functions and lensing shear (including for quenched and star-forming subsamples), and quenching dependence on environment; each observable is reproduced over the full redshift range available, up to 0<z<10. We discuss physical implications for galaxy quenching, the connection between halo and galaxy assembly, revised stellar mass-halo mass relations, and predictions for higher-redshift galaxy correlation functions and weak lensing signals.

MARCH 23HOST: Anthony Gonzalez
Speaker
Lou Strolger,
STScI
Title
High Redshift Supernovae: Beyond The Epoch of Dark Energy

Abstract

For nearly two decades the Hubble Space Telescope has been heavily used to locate supernovae in high redshift environments, with the primary goal of improving constraints on the nature of dark energy. Along the way we have made surprising observations on the nature of supernovae themselves, and clues to their elusive progenitor mechanisms, some of which are difficult to reconcile with observations at much lower redshift. From complete volumetric supernova rate histories, that for the first time extend to z > 2, we find type Ia supernova delay-time distributions are consistent with a power law of index -1, but with the fraction of prompt (t_d < 500 Myr) much less than expected from various ground-based surveys. Core collapse supernova rates trace the cosmic star formation rate history, but require stellar progenitors more massive than has been seen in deep studies of nearby events (M > 20 M_sol). I will also detail our current campaigns on clusters of galaxies (RELICS and the Frontier Fields), where gravitational lens magnification provides a real potential for locating the first, primordial supernovae, while also providing useful constraints on the mass models of the foreground gravitational lenses.

MARCH 30HOST: Anthony Gonzalez
Speaker
Allison Kirkpatrick,
Yale University
Title
Dusty Star Forming Galaxies in the Distant Universe

Abstract

At z = 1 − 3, the formation of new stars is dominated by massive, dusty galaxies, whose far-IR emission indicates they contain colder dust than their counterparts in the local Universe. I explore the reasons for the evolving IR emission of similar galaxies over cosmic time using three samples of dusty galaxies. Despite similar infrared luminosities, z > 0.5 dusty star forming galaxies have an order of magnitude higher dust masses and 5 K colder dust temperatures. The increase in dust mass is linked with an increase in the gas fractions of dusty star forming galaxies with redshift. I find that dusty star forming galaxies are predominantly located on the main sequence at z=1-2, and I explore whether an active galactic nucleus is linked with declining star formation in these galaxies. Finally, I make predictions for the demographics of dusty galaxies that we will be able to observe with the James Webb Space Telescope at z=1-2.

APRIL 6HOST: Anthony Gonzalez
Speaker
Greg Dobler,
NYU
Title
Better Cities through Imaging

Abstract

With millions of interacting people and hundreds of governing agencies, urban environments are the largest, most dynamic, and most complex macroscopic systems on Earth. The interaction between the three fundamental components of that system (human, natural, and built) can be studied much like any physical system, with observation and application of physical principles to the collection and analysis of that data. I will describe how persistent, synoptic imaging of an urban skyline can be used to better understand the urban system, in analogy to the way persistent, synoptic imaging of the sky can be used to better understand the heavens. At the newly created Urban Observatory at the Center for Urban Science and Progress (CUSP), we are combining techniques from the domains of astronomy, physics, computer vision, remote sensing, and machine learning to address a myriad of questions related to urban informatics. I will demonstrate the power of these techniques from the point of view of urban energy and environmental impact of a city, which can lead to improved city functioning and quality of life for its inhabitants.

APRIL 13HOST: Jian Ge
Speaker
Xiaohui Fan,
University of Arizona
Title
The Most Luminous Quasars in the Early Universe