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Colloquium Series

All talks are held on Wednesdays in the STScI John N. Bahcall Auditorium at 3:30 p.m. preceded by tea at 3:15 p.m.

Please direct questions or comments to the colloquium committee . The 2015-16 committee members are Peter McCullough (chair), Jennifer Lotz, and Laura Watkins.

STScI presents live and archived webcasting of talks and Colloquium Series.

Date Speaker/Title
Sept. 02 Casey Papovich (Texas A&M)
Title: Witnessing Galaxy Formation from Modern Infrared Surveys
Abstract: One of the great triumphs of astrophysics is that we are able to predict the growth of dark-matter structures in our Universe with high accuracy. I will discuss how we use observations of galaxies to trace these dark matter structures, and how we use observations of some of the most distant galaxies to measure directly the properties of galaxies as they evolve. I will focus on results from two modern surveys using near-Infrared (IR) imaging (beyond 1 micron): the FourStar Galaxy Evolution (ZFOURGE) survey and the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS), which use very deep imaging from the Magellan Observatory in Chile and observations from the Hubble Space Telescope. Combined with observations at far-IR wavelengths from the Spitzer Space Telescope and the Herschel Observatory, I will show the typical (median) star-formation history, stellar-mass assembly history, and structural formation history of galaxies like the Milky Way and Andromeda galaxies over the past 10 billion years. I will also discuss evidence that galaxies depart widely from this "typical" evolution, and that the Milky Way and Andromeda themselves may be examples of such "atypical" evolution for galaxies of their size. I will discuss ongoing and future research to understand the formation epochs of galaxies, where the ultimate goal is to form a coherent physical theory for galaxy formation.
Host: Harry Ferguson
Sept. 09 Mark Reid (Harvard–Smithsonian Center for Astrophysics)
Title: Mapping the Milky Way: The BeSSeL Survey
Abstract: Over 2000 years ago, Hipparcus measured the distance to the Moon by triangulating from two locations across the Mediterranean Sea. However, determining distances to stars proved much more difficult. Many of the best scientists of the 16th through 18th centuries attempted to measure stellar parallax, not only to determine the scale of the cosmos but also to test Heliocentric cosmologies. While these efforts failed, along the way they lead to many discoveries, including atmospheric refraction, precession, and aberration of light. It was not until the 19th century that Bessel measured the first stellar parallax.
Distance measurement in astronomy remained a difficult problem even into the early 20th century, when the nature of "spiral nebulae" was still debated. While we now know the distances of galaxies at the edge of the Universe, we have only just begun to measure distances accurately throughout the Milky Way. Using the Very Long Baseline Array, we now can achieve parallax accuracies of 10 micro-arcseconds! I will present new results on parallaxes and motions of star forming regions from the BeSSeL Survey. These measurements address the nature of the spiral structure, size, rotation speed, and mass of the Milky Way.
Host: Johannes Sahlmann
Sept. 16 Zeljko Ivezic (University of Washington)
Title: What Did We Learn about the Milky Way during the Last Decade, and What Shall We Learn Using Gaia and LSST?
Abstract: Studies of stellar populations, understood to mean collections of stars with common spatial, kinematic, chemical, and/or age distributions, have been reinvigorated during the last decade by the advent of large-area sky surveys such as SDSS, 2MASS, RAVE, and others. These data, together with theoretical and modeling advances, are revolutionizing our understanding of the nature of the Milky Way, and galaxy formation and evolution in general. I will briefly review the progress over the last decade, including the mapping of stellar counts, metallicity and kinematics distributions, interstellar dust using extinction of stars, and dark matter halo using Jeans equations. I will discuss in more detail new breakthroughs expected from Gaia and LSST surveys, which will improve measurement precision manyfold, and comprise billions of individual stars.
Host: Annalisa Calamida
Sept. 23 (No Colloquium)
Sept. 30 Frank van den Bosch (Yale University)
Title: The Substructure of Dark Matter Halos Revisited
Abstract: The Cold Dark Matter paradigm predicts that dark matter haloes are abound with substructure. A detailed characterization of dark matter subhalos is important for understanding the evolution of satellite galaxies, for modeling time-delays and flux-ratio anomalies in gravitational lensing, for boosting the dark matter annihilation signal and for the survivability of fragile structures such as streams and disks. I discuss the abundance and evolution of dark matter subhalos based on a new analytical model, use the model to revisit the Too-Big-To-Fail problem, demonstrate important shortcomings in the studies of substructure based on numerical simulations, and present a comprehensive analysis of the segregation of dark matter subhalos within their host halos.
Host: Dan Coe and Armin Rest
Oct. 07 Remy Indebetouw (University of Viriginia/NRAO)
Title: Star Formation and Feedback in the LMC: ALMA and HST Analysis of the Evolution and Destruction of GMCs
Abstract: TBS.
Host: Margaret Meixner
Oct. 14 Marc Pinsonneault (Ohio State University)
Title: Asteroseismology and the Time Domain Revolution in Stellar Astrophysics
Abstract: TBD.
Host: Molly Peeples
Oct. 21 Caryl Gronwall (Pennsylvania State University)
Title: HETDEX and Star-Forming Galaxies of the z ~ 2 Universe
Abstract: TBD.
Host: Stefano Casertano
Oct. 28 Meg Urry (Yale University); Caroline Hershel Speaker
Title: Supermassive Black Hole Growth and Galaxy Evolution
Abstract: Using multi-wavelength surveys like GOODS, COSMOS, and Stripe 82X, we measure the growth of supermassive black holes at the centers of galaxies over the last ~12 billion years. Most actively growing black holes are heavily obscured and thus are not seen in large optical surveys, like the Sloan Digital Sky Survey; at the same time, the deep multi-wavelength surveys are too small to find rare objects like luminous SDSS quasars. So completing the census of black hole growth will require a large-volume X-ray survey, to explore obscured growth at high luminosity and/or high redshift. Theorists have suggested that mergers trigger Active Galactic Nuclei (AGN), whose radiation and/or outflows may quench star formation and strongly affect galaxy evolution (“feedback”). But our morphological analyses showed that most moderate luminosity AGN at redshifts z ~1-2 have not undergone a recent major merger. Finally, using morphological classifications in the local universe from Galaxy Zoo, we identify two distinct modes of galaxy evolution in the local universe, with mergers and AGN feedback affecting only a minority.
Host: Susan Kassin, Gerard Kriss, and Marco Chiaberge
Nov. 04 Veselin Kostov (Goddard Space Flight Center)
Title: Planets with Two Suns
Abstract: TBD.
Host: Peter McCullough
Nov. 11 Christopher Johns-Krull (Rice University)
Title: Searching for Planets Around the Youngest Stars
Abstract: TBD.
Host: Andrea Banzatti
Nov 18 Mercedes Lopez-Morales (Harvard–Smithsonian Center for Astrophysics)
Title: Exoplanet Atmosphere Observations Spinoffs
Abstract: TBD.
Host: Marie Ygouf
Nov. 25 (No Colloquium)
Dec 02 Karin Sandstrom (Arizona/UCSD)
Title: Dust and Gas in Nearby Galaxies
Abstract: TBD.
Host: Karl Gordon
Dec 09 Daryl Haggard (McGill University)
Title: Interpreting Sgr A*'s Most Luminous X-ray Flares
Abstract: TBD.
Host: Laura Watkins
Dec 16 Robert Mathieu (University of Wisconsin-Madison)
Title: Alternative Pathways of Normal Stellar Evolution
Abstract: TBD.
Host: David Soderblom