Astronomy Colloquia at Caltech for 2014-15

Colloquia are held every Wednesday during the academic year at 4pm in the Cahill Hameetman auditorium.
Wine and cheese will be served in the Cahill Foyer from 5-6pm.

Month
Date
Speaker

Talk Title
OCTOBER
01


Nicholas Law
Univ North Carolina

Host: Shri Kukarni

The Evryscope: the first full-sky gigapixel-scale telescope

Current wide-field time-domain sky surveys generally operate with few-degree-sized fields and take many individual images to cover large sky areas each night. I will discuss the Evryscope (“wide-seer”), which takes a different approach: using an array of small telescopes to form a single image covering every part of the accessible sky simultaneously and continuously. The Evryscope is a low-cost gigapixel-scale imager with a 10,000 sq. deg. field of view, and has an etendue three times larger than the Pan-STARRS sky survey. The system will search for transiting exoplanets around nearby bright stars, M-dwarfs and white dwarfs, as well as obtain minute-by-minute  imaging of microlensing events, nearby supernovae, and gamma-ray burst afterglows as they happen. We plan to deploy the system at CTIO in early 2015. I will present the project status and plans for science operations, as well as an update on the Evryscope prototype telescopes which we are operating near the North Pole (the first High-Arctic astronomical survey).

08

Shane Davis
Virginia

Host: Phil Hopkins

How Black Holes Dine above the Eddington "Limit" without Overeating
or Excessive Belching

The study of super-Eddington accretion is essential to our understanding of the growth of super-massive black holes in the early universe, the accretion of tidally disrupted stars, and the nature of ultraluminous X-ray sources. Unfortunately, this mode of accretion is particularly difficult to model because of the multidimensionality of the flow, the importance magnetohydrodynamic turbulence, and the dominant dynamical role played by radiation forces. However, recent increases in computing power and advances in algorithms are facilitating major improvements in our ability to model the transport of radiation in numerical simulations of astrophysical plasmas.  I will briefly describe our new radiation transfer modules and discuss our efforts to model super-Eddington accretion flows.  I will focus on applications to ultraluminous X-ray sources, which must be radiating well above their Eddington luminosity unless they harbor intermediate mass black holes. I will argue that most of these sources can be (and likely are) "normal" ~10 solar mass black holes accreting and radiating with luminosities well above their Eddington "limit".

15

John Wise
Georgia Tech

Host: Christian Ott

The First Stars and Galaxies in the Universe
Cosmic structure forms hierarchically through smooth accretion and dark matter halo mergers.  As a consequence, all galaxies are the product of the dozens of mergers over billions of years.  However, one can ask, "What were the first stars and galaxies in the universe?"  I will review the current state-of-the-art simulations of early galaxy formation, starting with the formation of the first stars, which are initially devoid of elements heavier than lithium and are suggested to have a characteristic mass of tens of solar masses.  I will then present results from a suite of cosmological radiation hydrodynamics simulations that focus on the transition from the first stars to the first galaxies.  Each simulation captures the radiative and chemical
feedback from ~300 first stars, leading to the formation of a 10^9 solar mass dwarf galaxy 700 million years after the Big Bang.  I will show that momentum transfer from ionizing radiation plays an important role in providing turbulent support and mixing supernova ejecta, preventing the overproduction of stars and metals.  This results in a stellar population with a tight metallicity distribution function centered at 0.01 of solar metallicity, agreeing with the observed luminosity-metallicity relation in local dwarf galaxies.  I will also demonstrate that these faintest galaxies are the primary driver of the reionization of the universe, only to be suppressed by photo-heating at later times, perhaps evolving into a subset of dwarf galaxies in the local universe.

22

Todd Thompson
Ohio State

Host: Christian Ott

Preludes to a Theory and Phenomenology of Galactic Winds

Galactic winds are ubiquitous in rapidly star-forming galaxies at low and high redshift.  They shape the stellar mass function, enrich the IGM, and determine in part the evolution of the metal abundance of galaxies.  I will present new work constraining the physics of galactic outflows and feedback processes in these systems.   I will first focus on galactic superwinds driven by very hot gas generated by overlapping supernovae within the host galaxy, and argue that the X-ray observations strongly constrain the mass-loading efficiency, from dwarf starbursts to ultra-luminous infrared galaxies.  These constraints also limit the ability of a hot wind to accelerate cool gas clouds via ram pressure.  I will then show in what regimes hot winds become radiative on 1-100kpc scales and discuss the observational implications.  I will then focus on momentum injection by supernovae and radiation pressure of starlight on dust grains.  I will discuss new work on the phenomenology of high redshift galaxies and their generalized Eddington limit for expelling gas.  Finally, I will discuss a set of numerical experiments to understand the coupling between radiation and matter in highly optically-thick environments relevant for dense starburst nuclei and the self-gravitating disks that attend the fueling of active galactic nuclei.

29

Meredith Hughes
Wesleyan

Host: Jessie Christiansen

Planet Formation through Radio Eyes

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 an immense leap in sophistication with the advent of the ALMA  interferometer that is now beginning operations.  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.

NOVEMBER 5

Bekki Dawson
Berkeley

Host: Jessie Christiansen

Planetary Systems in 4D

Discoveries of exoplanets so different from those in our Solar System have called in question conventional theories for how planetary systems form and evolve. I will present recent progress in our understanding of the physical processes that drive the assembly of planetary systems and result in the surprising variety of orbital properties we observe today. I will focus on the orbital evolution of giant planets, including the origin of hot Jupiters and giant planets on elliptical and tilted orbits. I will conclude with pathways forward toward a blueprint for how planetary systems form and evolve, including connections between small and giant planets and the different initial conditions that lead to a diverse array of planetary orbits and compositions.

12

Amy Reines
Univ of Michigan

Host: Fiona Harrison

TBD

19

Jenny Greene
Princeton

Host: Judy Cohen

TBD

DECEMBER
3

Konstantin Batygin
GPS

Host: Jessie Christiansen

TBD

JANUARY
14

Eve Ostriker
Princeton

Host: Phil Hopkins

TBD

21

Joshua Frieman
Fermilab

Host: Richard Ellis

TBD

28

Kartik Sheth
NRAO

Host: Gregg Hallinan

TBD

FEBRUARY
4

Fabian Walter
MPIA

Host: Phil Hopkins

TBD

11

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18

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25

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MARCH
4

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11

Kathryn Johnston
Columbia

Host: Judy Cohen

TBD

APRIL
1

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8

David Hogg
NYU

Host: Phil Hopkins



15

Dave Alexander
Durham

Host: Fiona Harrison

TBD

22

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29

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MAY
6

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13

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20

Niel Brandt
Penn State

Host: Fiona Harrison

TBD

27

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Information for Speakers

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