Berkeley Astronomy Department Colloquium

Spring 2011

 

All colloquia on Thursdays at 4 pm (except where noted)

Contact:  Geoff Bower (gbower@astro.berkeley.edu)

 

Date

Speaker

Title & Abstract

Host

20 January

Charles Conroy (CfA)

 

Quataert

27

Tomasso True (UCSB)

 

Chiang

3 February

Dominik Riechers (Caltech)

Fueling Cosmic Star Formation: High Redshift Star-Forming Galaxies and

The Molecular Gas Mass Density of the Universe

 

Virtually all major advances in extragalactic astronomy and our

understanding of galaxy formation and evolution over the past decade

are based on the constraints we obtained on the star formation history

and stellar mass density of the universe. These investigations are

greatly successful in explaining a range of galaxy properties

throughout cosmic times, yet are lacking one fundamental link: a

systematic study of the fuel for star formation, the cause for the

buildup of stellar mass - i.e., constraints on the molecular gas mass

density. I will review the current status of observations of molecular

gas in galaxies back to within a few hundred million years after the

Big Bang. Based on pathfinder studies with the (Expanded) Very Large

Array and the CARMA millimeter array, I will outline the prospects for

the upcoming new generation of large observatories (in particular the

Atacama Large sub/Millimeter Array) to provide the first solid

constraints on the gas mass density of the universe. In synergy with

large optical/infrared facilities such as Keck (and in the future, the

Thirty Meter Telescope, and the James Webb Space Telescope), this will

enable simultaneous studies of the past, present, and future star

formation in galaxies throughout cosmic times.

Bower

7 (Monday, 1pm,

544 Campbell)

Phil Hopkins (UCB)

Gas, Mergers, and Feedback: Driving an Evolving Hubble Sequence

 

I'll review how the combination of models that include realistic gas supplies in galaxies, and

feedback from massive stars and AGN to maintain those gas reservoirs, have led to huge shifts

in our understanding of galaxy formation. In particular, gas-richness may represent the most

important determining factor in galaxy evolution through hierarchical mergers, and may resolve a

number of decades-old outstanding mysteries. The degree of gas-richness in mergers has dramatic

effects on bulge structural properties, stellar populations, mass profiles, and kinematics; models

with the appropriate gas content have finally begun to produce realistic galaxies that resolve a

number of discrepancies with observations. Evolution in the gas properties of the Universe naturally

predicts evolution in the Hubble sequence, giving rise to many of the unique properties of

high-redshift galaxies and starbursts. In very gas-rich mergers, expected to occur more and more

frequently at high redshifts, gas can qualitatively change the character of mergers, making disks

robust to destruction in mergers and explaining the abundance of disks in a Lambda-CDM Universe.

Gas-rich mergers also link the brightest starburst and quasar populations with massive galaxies

today. I'll close by discussing the next generation of models at the interface between the fields of

star formation, AGN, and galaxy formation.

Marcy

10

Doug Finkbeiner (CfA)

Galactic structure: from Fermi to SDSS and Pan-STARRs

 

The Milky Way is full of surprises.  Our discovery last year of the "Fermi bubbles" is one of the most intriguing results the Fermi Gamma-ray Space Telescope.  This bilobular structure shines in 1-50 GeV gamma rays and spans 100 degrees on the sky.  We are following up with X-ray observations and refining our models, and expect to learn more about energetic events in the inner Galaxy.

 

Meanwhile, my group is studying the distribution of dust and stars in the Milky Way using millions of stars from the SDSS and Pan-STARRs surveys.  I will present a careful measurement of the dust reddening law in the diffuse ISM using SDSS data, which has led us to recalibrate the SFD dust map.  I will also describe future work with Pan-STARRs to explore Galactic structure, including dwarf galaxies and tidal streams.

Davis

14 (Monday, 1pm,

544 Campbell)

Mark Krumholz (UCSC)

Understanding the Star Formation Rate

 

Stars are the engines of the Universe: nuclear reactions within them are the only significant source of non-gravitational power in the cosmos and the source of most heavy elements. However, the process by which stars form remains poorly understood, and one mystery in particular stands out: why is star formation so slow? In many galaxies the bulk of the interstellar medium does not participate in star formation, and in all galaxies even those clouds that are active form stars at a rate of only ~1% of their mass per dynamical time. Any successful theory of cosmic evolution must be able to explain these facts, and be able to predict how the star formation process changes with galactic environment and over cosmological time. In this talk I discuss progress toward a physical theory of star formation capable of meeting these requirements.

McKee

17

Anna Frebel (CfA)

Near-Field Cosmology with the Oldest, Most Metal-Poor Stars

 

One of the most important topics in modern astrophysics is

understanding the formation and evolution of stars and

galaxies. Recent works on the oldest, most metal-poor stars in the

Galactic halo and satellite dwarf galaxies have shown that these and

many topics, ranging from nuclear astrophysics to cosmology, can be

studied with stellar chemical abundances ("stellar archaeology").  I

will present plans to overcome current bottlenecks in the field:

Through the discovery and analysis of new metal-poor stars,

theoretical modeling of early Universe science can be significantly

constrained. In particular, any primitive objects with [Fe/H]<-4.0

will provide missing critical information on the details of element

nucleosynthesis that started the chemical evolution of the

Universe. Knowing the details of the chemical evolution of faint dwarf

galaxies will enable us to investigate the link between halo and dwarf

galaxy stars to find out whether those old halo stars once came from

earlier, analogous galaxies ("dwarf archaeology"). Finally, based on

results from state-of-the-art LCDM cosmological simulations, the

chemical nature of the first galaxies can be established for an

understanding of their relation to the surviving dwarfs, and the

"building blocks" of the Milky Way's halo ("near-field cosmology").

 

To achieve these goals it is essential to produce cosmologically

motivated abundance interpretations by combining the necessary

observational and theoretical ingredients for a comprehensive study of

the Milky Way's halo and its metal-poor constituents.  This provides

prime motivation and stepping stones for the development of concrete,

testable ideas about early Universe science that will be addressed

with theoretical modeling over the next decade. This unique "hybrid"

approach will significantly advance the fields of galaxy formation and

the early Universe by closely connecting stellar archaeology with the

respective theoretical subfields for a "whole that is greater than the

sum of its parts".

Quataert

22 (Tuesday, 1pm,

544 Campbell)

Shelley Wright (UCB)

Observing Galaxy Evolution: The Exciting Promise of Adaptive Optics Instrumentation

 

Adaptive optics (AO) with integral field spectroscopy on 8-10m telescopes has recently become a powerful observational tool for studying galaxies in the early universe (z > 1) at sub-kiloparsec scales. These innovative spectrographs have led to significant scientific achievements and are stimulating the design of future near-infrared instrumentation. I will discuss the development and use of both the latest instruments behind Keck Observatory's AO system and future AO instrumentation on the Thirty Meter Telescope (TMT). In particular, I will present the latest results from Keck OSIRIS observations of spatially resolved optical emission lines (e.g., Hα, and [N II]) from high-redshift (1 < z < 3) star forming galaxies. These results are part of an ongoing survey to study the dynamics, chemical abundances, and active galactic nuclei (AGN) in early galaxies. The high spatial resolution afforded by AO and the 2D capability of an integral field spectrograph have allowed the discovery of some of the lowest luminosity AGN known at this epoch, and I will discuss their potential impact on high-redshift metallicity studies and galaxy formation. Lastly, I will discuss future AO instrumentation for Keck and the TMT project. I will present sensitivities achievable for AO science with TMT, and highlight TMT's extraordinary potential to probe the dynamics, assembly, and abundances of galaxies in the early universe.  

Filippenko

24

Aaron Parsons (UCB)

21cm Cosmology: Probing the Epoch of Reionization

 

The Epoch of Reionization (EoR)--the rapid ionization of the majority

of the hydrogen

in the universe by the light of the first stars and supermassive black

holes--is perhaps the last major phase transition of our universe that remains

unexplored.  First-generation experiments aiming to measure

the 3-dimensional power spectrum of reionization fluctuations via redshifted

21cm emission are currently underway.  While calibration, foreground removal,

and obtaining the requisite sensitivity are all challenging aspects of

these efforts,

early results suggest that there may imminently be a detection that

significantly

impacts our understanding of the dominant processes at work during this era.

 

I will discuss current prospects for detecting the 21cm EoR signal in

the context

of our recent progress with 16- and 32-antenna deployments

of the Precision Array for Probing the Epoch of Reionziation (PAPER)

in Green Bank, West Virginia, and the Karoo Desert of South Africa.

I will also discuss a novel technique for accessing the 3-dimensional power

spectrum of reionization, and the impacts of systematics and foregrounds on

recent measurements.  Finally, I will present our current plans for the

Hydrogen Epoch of Reionization Array (HERA) that will supersede all current

efforts and enable the direct imaging of reionization structures.

 

Heiles

28 (Monday, 1pm,

544 Campbell)

Daniel Stark (Cambridge)

 

Bloom

3 March

Mariska Kriek (CfA)

 The Diverse yet Orderly Lives of Galaxies

 

At first glance the galaxy population today and even more so at

earlier times exhibits a huge diversity. However, the well-known

correlations between different galaxy properties, such as spatial

structure, stellar population, stellar mass, stellar dynamics, and

environment suggest that galaxy formation is actually an orderly

process. With the recent large photometric and spectroscopic surveys

and new instrumentation on the Hubble Space Telescope, it is now

finally possible to study galaxies in a systematic way at earlier

times, so that we can see directly how these relations changed over

cosmic time and what the physical processes are that drive them.

Until very recently, these studies were hampered by the small sizes of

spectroscopic galaxy samples, whereas much larger photometric samples

lack the required spectroscopic information. I will discuss a novel

approach, that makes use of medium-band photometry to perform detailed

spectroscopic studies of ~3500 galaxies at 0.5<z<2.0. By identifying

analogous galaxies we construct composite spectral energy

distributions, which are of spectroscopic quality. This composite

spectrum collection opens up the possibility to efficiently study

Halpha and other spectroscopic features for large distant galaxies

samples, which would otherwise require extensive near-infrared

spectroscopic campaigns. I will show how we have used the composite

spectra to study the dimensionality and star formation histories of

galaxies. Furthermore, I will discuss many other applications, among

which the relation to structural properties, AGN demographics, and

dust properties. I will close with an outlook on future spectroscopic

capabilities (e.g., MOSFIRE, NIRSPEC on the JWST, WFIRST) for large

surveys of distant galaxies, in order to understand their origin.

 

Ma

10

 

 

 

17

 

 

 

24

Spring Break

 

 

31

Andrea Ghez (UCLA)

Sackler Lecture

 Quataert

7 April

 Fred Adams (Michigan)

 Constraints on the Birth Environment of the Solar System

 

Most stars -- and hence most solar systems -- form within groups and

clusters.  The first objective of this talk is to explore how these

star forming environments affect solar systems forming within them.

The discussion starts with the dynamical evolution of young clusters

with N = 100 - 3000 members. We use N-body simulations to study how

evolution depends on system size and initial conditions.  Multiple

realizations of equivalent cases are used to build up a robust

statistical description of these systems, e.g., distributions of

closest approaches and radial locations.  These results provide a

framework from which to assess the effects of clusters on solar system

formation. Distributions of radial positions are used in conjunction

with UV luminosity distributions to estimate the radiation exposure of

circumstellar disks. Photoevaporation models determine the efficacy of

radiation in removing disk gas and compromising planet formation. The

distributions of closest approaches are used in conjunction with

scattering cross sections to determine probabilities for solar system

disruption. The result of this work is a quantitative determination of

the effects of clusters on forming solar systems. The second objective

of this talk is to use these results to place constraints on the

possible birth environments for our solar system.

 

 Blitz

14

Jonathan Mitchell (UCLA)

The tropical nature of Titan's climate and storms

 

Joint w/EPS

 

21

Matthew Bailes (Swinburne)

Pursuing Big Science from a no-name University

 

The University of California Berkeley is one of the world's great

research Institutions (currently #2 on the Shanghai-Jiaotong index).

The birthrate of Berkeley graduate students and Postdocs however

far exceeds the retirement rate of Faculty, and hence the vast majority

will either have to obtain positions at lower-ranked institutions, or

leave the field. This need not be the end of their careers.

 

Swinburne University of Technology in Melbourne Australia was a former

technical college with no tenured staff in Astronomy and Astrophysics until the

early 2000s.  It now has over 60 staff and postgraduate students actively engaged in

research, teaching and public outreach. The staff have guaranteed access to the

Keck telescopes, one of the largest supercomputers in Australia, and are members of many large and vibrant research programmes with colleagues around Australia and the world. In a recent government research quality measurement exercise, it

achieved the highest possible ranking.

 

In the first half of this talk I will explain how the Centre grew to

its current size against the backdrop of decreasing relative public sector income by pursuing online education, 3D virtual reality film production, external grants, and overseas student income. I will then focus on one of the Centre's larger observational programs, the Parkes Pulsar Timing Array for gravitational wave detection, and how supercomputers and large aperture telescopes are making progress in the search for gravitational waves at nanoHertz frequencies using millisecond pulsar timing. 

Bower

28

Lars Hernquist (CfA)

 "Collective Origin of Spiral Structure in Disk Galaxies"

 

 

It is now nearly 50 years since spiral structure in galaxies was

hypothesized to originate from density waves propagating through a

shearing disk.  However, the nature of this process remains uncertain.

Relevant theories range from interpreting spiral arms as long-lived

density waves to their being produced stochastically in response to

gravitational perturbations.  In this talk, I examine the latter

possibility, where spiral arms are seeded by density fluctuations

orbiting within a disk.  Using high-resolution simulations, I study

the response of a thin, differentially rotating disk of stars to a

population of perturbers.  Individually, each perturber excites a wake

locally in the distribution of stars around it.  When sufficient

numbers of these perturbers are present, they collectively amplify to

yield large-scale patterns that resemble those in flocculent and

intermediate spiral galaxies.  Combining the N-body experiments with

simple analytic arguments, I develop a theory for spiral structure

based on the collective effects of swing amplification.  The model

makes numerous testable predictions, making it possible to finally

test the theory that spiral arms are stochastic in nature.

 

Quataert

5 May

Steve Squyres

Science Results from the Mars Exploration Rover Mission

De Pater