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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 2014-15 committee members are Rongmon Bordoloi, Susana Deustua, Peter McCullough and Eileen Meyer.

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

Date Speaker/Title
Sept. 10 Claude-Andre Faucher-Giguere (Northwestern University)
Title: Feedback-Regulated Star Formation on Galactic and Cosmological Scales
Abstract: A central problem in galaxy formation is to understand why star formation is so inefficient. Within individual galaxies, gas is converted into stars at a rate two orders of magnitude slower than unimpeded gravitational collapse predicts, a fact embodied in the low normalization of the observed Kennicutt-Schmidt (K-S) relationship between star formation rate surface density and gas surface density. Star formation in galaxies is also globally inefficient in the sense that the stellar mass in dark matter halos is a small fraction of the universal baryon fraction. I will show that these two facts can be explained by the self-regulation of star formation by feedback from massive stars. Within galaxies, stellar feedback drives turbulence that supports the interstellar medium against collapse and the K-S law is set by the low strength of gravity relative to stellar feedback. The energy input from the same stellar feedback processes drive powerful galactic outflows that remove most of the gas accreted from the intergalactic medium before it has time to turn into stars. Using cosmological hydrodynamical simulations from our FIRE project ("Feedback In Realistic Environments"), I will show that gas removal by star formation-driven galactic winds successfully explains the observed galaxy stellar mass function, at least for galaxies less massive than the Milky Way. I will also discuss the observational signatures of circum-galactic gas flows, focusing on predictions for HI around the peak of the cosmic star formation history. Feedback from massive black holes may be required to quench galaxies much more massive than the Milky Way.
Host: Jason Tumlinson
Sept. 17 Ray Jayawardhana (York University)
Title: Characterizing Exoplanets from the Ground and from Space
Abstract: On-going searches for extrasolar planets have revealed a remarkable diversity of worlds, from close-in super-Earths to far-out super-Jupiters, and challenged our preconceptions many times over. Meanwhile, comparative studies of exoplanet physical properties have begun in earnest: planets caught in transit and those imaged directly are best suited for detailed characterization, especially of their atmospheres. I will discuss recent results and future prospects for ground-based and space observations, including the possibility of extending these techniques to lower-mass planets.
Host: Hussein Jirdeh
Sept. 24 Alberto Bolatto (University of Maryland – College Park)
Title: The ALMA View of NGC253, One of the Nearest Nuclear Starbursts
Abstract: In the context of galaxy evolution it is particularly interesting to understand better the mechanisms that regulate star formation activity in galaxies. ALMA observed the prototypical nearby starburst galaxy NGC 253 in cycles 0 and 1 in the 3mm band that contains the ground rotational transitions of several key molecules. In this talk I will present an analysis of the molecular ISM properties in the nuclear starburst region derived from the ALMA data. I will show that the molecular superwind is very significant at determining the duration of the starburst phase, and I will discuss the possible gas entraining mechanisms. These data also allow us to obtain for the first time a detailed view of giant molecular clouds in a starburst environment. I will show that the clouds we are able to identify have very large surface and volume densities, and consequently short free-fall and sound crossing times, which are likely connected to the large star formation efficiencies found in these environments. Finally, I will present and discuss some of the chemical complexity we see in the data. The extremely rich spectroscopy, a common feature in many ALMA datasets, opens new windows for the study of physical conditions in extragalactic systems.
Host: Eileen Meyer
Oct. 01 Michael Cooper (University of California – Irvine)
Title: Expanding the Low-Mass Galaxy Frontier
Abstract: TBD.
Host: Molly Peeples
Oct. 08 Felix Mirabel ( CEA-Saclay-France & CONICET-Argentina)
Title: Stellar Black Holes at the Dawn of the Universe
Abstract: The end of the dark age of the universe is one of the major frontiers in cosmology. Until recently most models assumed that the ultraviolet radiation from the first generations of massive stars was the main (and in some models the only) cause of re-ionization of the intergalactic medium. Based on recent observational and theoretical results I will show that during the first billon years, sources of X-rays, such as accreting stellar black holes, determined the early thermal history of the universe, as well as the re-ionization of the intergalactic medium over large volumes of space. X-rays from the fossils of massive stars had a direct impact on the properties of the faintest galaxies at high redshifts and on the smallest dwarf galaxies in the local universe. In this context, feedback from compact high mass X-ray binaries can provide additional clues to understand the tension between the number of dwarf galaxies observed in the local universe and the number of those galaxies predicted by the cold dark matter model (lCDM) of the universe.
Host: Andy Fruchter
Oct. 15 Michael Boylan- Kolchin (University of Maryland – College Park)
Title: The Local Group as a Cosmological Laboratory
Abstract: The Local Group affords us the opportunity to study the low-mass extremes of galaxy formation and cosmology. In this capacity, it presents some of the most enduring challenges to the very successful LCDM cosmology. I will discuss to what degree standard theoretical models of the local Universe - including the idea that photoionization heating from cosmic reionization is crucial to suppressing galaxy formation in low mass halos - match the growing volume and diversity of observations in the Local Group and beyond. Since reionization is expected to be a dominant process in determining the abundance of low-mass galaxies around the Milky Way, observations hold the promise to understand aspects of the high-redshift Universe by studying its descendants locally. I will argue that, even in the JWST era, the local Universe may be our best probe of low-mass, currently unobservable galaxies at high redshift that are expected to be crucial for reionization.
Host: Molly Peeples
Oct. 22 Amy Barger (University of Wisconsin - Madison)
Title: New Insights on Star Formation in the Distant Universe
Abstract: TBD.
Host: TBD
Oct. 29 TBD
Title: TBD
Abstract: TBD.
Host: TBD
Nov. 05 Sarah Burke-Spolaor (California Institute of Technology)
Title: Fast Radio Bursts: Ere One Can Say ‘It Lightens’
Abstract: TBD.
Host: TBD
Nov. 12 Meredith Hughes (Wesleyan University)
Title: Planet Formation through Radio Eyes
Abstract: Circumstellar disks provide the raw material and initial conditions for planet formation. Millimeter-wavelength interferometry is a powerful tool for studying gas and dust in planet-forming regions, and it is undergoing a multiple-order-of-magnitude leap in sophistication with the advent of the ALMA interferometer that is now in the late stages of construction. I will discuss some ways in which millimeter-wavelength interferometry is being used to study the process of planet formation in circumstellar disks, with particular emphasis on the kinematics of turbulence in protoplanetary disks and the degree to which debris disk structure reflects the dynamics of embedded planetary systems.
Host: Susan Deutsua
Nov. 19 Richard Townsend (University of Wisconsin – Madison)
Title: Ghost Hunting at Five Hundred Parsecs: The Glowing Magnetospheres of Massive, Luminous Stars
Abstract: TBD.
Host: Nolan Walborn
Nov. 26 No Colloquium;
Dec. 03 Ryan Hickox (Dartmouth College)
Title: The SF-AGN Connection: Do All Star-Forming Galaxies Host an AGN?
Abstract: TBD.
Host: Eileen Meyer
Dec. 10 Sally Dodson-Robinson (University of Delaware)
Title: From Snowflakes to Snowballs: Bypassing the Bouncing Barrier in Icy Planetesimal Growth
Abstract: TBD.
Host: Karoline Gilbert
Dec. 17 Remi Soummer (Space Telescope Science Institute)
Title: Direct Imaging of Exoplanets and Disks
Abstract: TBD.
Host: Neill Reid