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