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Astrophysics Seminars From 2010 - 2011


Fall 2010

August 31, 2010

 "Galaxy Mergers: Metals, Morphologies and
Environmental Dependence"

Sara Ellison, Associate Professor and Canada Research Chair, University of Victoria, Dept. Phys & Astr.

 The Sloan Digital Sky Survey presents an unparalled opportunity to study trends of galaxy properties and their environments at low redshifts, ranging from the effects of individual mergers to the importance of cluster membership. We have assembled the largest ever sample of close galaxy pairs from the SDSS DR7, and also used metrics of local density and cluster membership to study the hierarchical impact of environment. By combining spectroscopic measurements of mass, metallicity and SFR with image decomposition, we can establish a panoramic overview of interaction-driven galaxy evolution. Our careful treatment of crowding in the photometry of close pairs (where the SDSS reductions can yield spurious results) make this the most robust study of its kind, erent results from previous studies of galaxy pairs. In this talk I will discuss the environmental dependence of merger-triggered star formation and the subsequent impact on galaxy colours, morphologies and the mass-metallicity relation.

September 29, 2010

 "The Role of Gas in the Evolution of Disk Galaxies"

Alyson Brooks, Fairchild Postdoctoral Fellow, Caltech

 A realistic model for the formation of galaxy disks depends on a proper treatment of the gas in galaxies. Historically, cosmological simulations of disk galaxy formation have suffered from a lack of resolution and a physically motivated feedback prescription. Recent computational progress has allowed for unprecedented resolution, which in turn allows for a more realistic treatment of feedback. These advances have led to a new examination of gas accretion, evolution, and loss in the formation of galaxy disks. Here I highlight the role that gas outflows, inflows, and the regulation of gas by feedback play in achieving simulated disk galaxies that better match observational results as a function of redshift.

October 13, 2010

 "Dark Matters"

Annika Peter, Postdoctoral Researcher, Caltech

 Dark matter, constituting a fifth of the mass-energy in the Universe today, is one of the major "known unknowns" in physics. While the nature of dark matter is unknown, there are a number of potential candidates. The particle candidates for dark matter can be grossly categorized as "weakly-interacting massive particles" ("WIMPs") and "everything else", with WIMPs having long been considered aesthetically pleasing candidates by both the particle-physics and astrophysics communities. In this talk, I will review some techniques that may be used to distinguish among dark-matter candidates, and in the case that WIMPs dominate the dark-matter budget of the Universe, techniques to infer its properties. In particular, I will focus on detection of WIMP dark matter via its annihilation products, and on distinguishing WIMP dark matter from other types of dark matter using properties of dark-matter halos.

October 14, 2010

 "Empirical Constraints on the Formation and Evolution of Low-Mass Stars and Brown Dwarfs: A Data-Intensive Approach"

Keivan Stassun, Assoc Professor, Vanderbilt University

 Recent and ongoing large surveys, both from the ground and from space, are enabling new data-intensive approaches to a variety of problems in stellar astrophysics. This talk describes three such projects, each serving as a vignette of a different but complementary mode of data-intensive research into low-mass star formation and evolution. The X10000 Project takes a panchromatic, time-domain approach to study the structures of young stellar coronae in order to understand the role of extreme coronal mass ejections in the angular momentum evolution of young stars. SLoWPoKES takes an ensemble, data-mining approach to extract from the Sloan Digital Sky Survey the largest sample of wide low-mass binaries ever assembled, which can be used to constrain binary formation theory and for refining the fundamental mass-age-activity-rotation-metallicity relations for low-mass stars. The EB Factory project takes a time-domain, data-mining approach to identify rare, but astrophysically very interesting, case studies from among the large numbers of eclipsing binaries being harvested by surveys for transiting exoplanets. We will highlight recent discoveries from this work, and will draw these results together to elucidate the physical interrelationships between stellar rotation, magnetic field generation, and stellar structure during the star-formation process.

October 20, 2010

 "Constraints on the Type Ia Supernova Progenitors from Hubble Space Telescope Treasury Surveys"

Louis-Gregory Strolger, Assoc Professor, Western Kentucky University

 I will present the state of the current observational constraints on SN Ia progenitors, based on volumetric rate measures (to z = 2) and host galaxy demographics. At present, SNe Ia in high and low redshift galaxies show inconsistent results on the implied progenitors responsible for these important cosmological tools. At its heart, the debate now hinges on two important factors: (1) the metallicity of the progenitor and its impact on event luminosity and production efficiency; and (2) the time required for a SN~Ia progenitor system to develop to an explosion from an episode of star-formation (commonly called the "delay time"). While these are conceptually measurable factors in low redshift (z < 0.1) galaxies, attempts to do so have been muddled by two degenerate effects: (1) population age, which steadily increases the range of metallicity within a given environment, and (2) rate of active star formation, which mix-up the incubation time between SN events and progenitor formation. Results from high redshift (z > 1) surveys, which by the nature of being age-limited surveys should elucidate the nature of SNe Ia, have instead implied very long (3 to 4 Gyr) delay times that are largely inconsistent with the relatively short (< 1 Gyr) times predicted from binary star evolutionary models and low-z observations.

October 27, 2010

 "The Fermionic Dark Condensate as the Culprit behind Dark Energy"

Stephon Alexander, Assoc Professor, Haverford College

 One of the most perplexing problems facing cosmology is the speed up of the universe’s expansion rate. The cause of this cosmic acceleration is unknown and seems to require new physics. A confluence of astrophysical data reveal that this dark energy is gravitationally self repulsive and makes up roughly two thirds of the energy in the universe. Some viable candidates are a cosmological constant, a light fundamental scalar field(quintessence) or a modification of general relativity. In this talk, I present a minimalist approach to the dark energy problem by exploiting an overlooked fact when fermions interact covariantly with the gravitational field. I will show that, instead of proposing new physics, fermions can consistently interact with the gravitational field to form a cosmic-BCS like condensate that behaves like dark energy at late times. I give a pedagogical account of the mechanism and discuss possible ways to probe the Fermioinc Dark Condensate with observations.

November 3, 2010

 "Probing the Helium Reionization Epoch with the HeII Lyman Alpha Forest in the HST/COS Era"

Gabor Worseck, Postdoctoral Researcher, UC Santa Cruz

 Like hydrogen, intergalactic singly ionized helium can be probed by Lyman alpha forest spectroscopy of quasars. However, the far UV flux of most high-z quasars is extinguished by intervening HI Lyman limit systems, so that only a handful of HeII sightlines have been studied in detail with HST. So far, the strongly evolving HeII absorption in these few sightlines provides the most direct evidence that HeII reionization ended at z~3. We correlated all known z>2.7 quasars with GALEX UV source lists to select new promising sightlines to detect intergalactic HeII. So far, our ongoing HST/COS follow-up program has revealed HeII absorption towards 3 of 8 UV-bright z~3 quasars we selected. This first comprehensive sample of new HeII spectra at COS resolution will enable a systematic investigation of the HeII reionization epoch. It is complemented by optical spectroscopy of the co-spatial HI Lyman alpha forest and a deep imaging survey to find the sources responsible for HeII reionization. With efficient pre-selection of dozens of promising quasar sightlines from GALEX photometry, the unique UV sensitivity of HST/COS offers unprecedented opportunities to observationally constrain the 2nd epoch of reionization.

November 10, 2010

 "Star Formation in Dwarf Galaxies"

Janice Lee, Postdoctoral Researcher, Carnegie Observatories

 Do cycles of violent, intense, but short-lived global bursts constitute a significant mode of star formation in low-mass galaxies? Such events have a profound impact on galaxies, particularly those with shallow potential wells, and observational measures of their prevalence inform our understanding of a wide range of issues in galaxy evolution. In this talk, I will discuss how my work with the Local Volume Legacy Survey has built a generally consistent picture of the average strengths, durations and frequencies of starbursts in low-mass systems. The inconsistencies that remain, however, are challenging our understanding of star formation in low-density environments. I will also share recent results on this puzzle involving the systematic underestimation of star formation rates in dwarf galaxies as traced by H-alpha emission, and ways toward clarifying the potentially serious implications of this systematic.

November 17, 2010

 "Kinetic luminosity of quasar outflows and its implications to AGN Feedback"

Nahum Arav, Assoc Professor, Virginia Tech

 Sub-relativistic outflows are seen as blueshifted absorption troughs in the spectra of roughly one third of all quasars. I will describe how we determine the mass flux and kinetic luminosity of these outflows and show that the derived values suggest that absorption outflows may be a main agent of AGN feedback scenarios.

December 1, 2010

 "Insights into galaxy formation and cosmology from weak lensing"

Rachel Mandelbaum, Assoc Research Scholar, Princeton University

 Gravitational lensing is a convenient tool for observing the total matter content of the universe, including dark matter. Given the claim of modern cosmology that the majority of the matter in the universe is dark, lensing will be a critical part of future observational and theoretical efforts in cosmology. I will begin with an introduction to statistical weak lensing observations, including the role they currently play in galaxy formation and cosmology research, and what they may eventually contribute in the future. Then, I will describe an application of lensing combined with other probes of large-scale structure that may be used to constrain cosmological model parameters, while also learning about the galaxy population used for the study. This application is useful already in existing large surveys such as the Sloan Digital Sky Survey (SDSS), and should also play an important role in planned future surveys such as the Large Synoptic Survey Telescope (LSST).

December 6, 2010

 "Gas in the Vicinity of Star-Forming Galaxies at z~2-2.5"

Olivera Rakic, Grad Student, Leiden Observatory, The Netherlands

 We study the intergalactic medium around star-forming galaxies by analyzing high resolution spectra of 15 QSOs with ~700 foreground galaxies with spectroscopic redshifts at z~2-2.5, using pixel optical depth techniques. All the galaxies are within 2 Mpc (proper) from the lines of sight to the QSOs. We measure the distribution of HI, CIV, and OVI absorption as a function of separation from galaxies and of galaxy properties. We find many strong correlations that give us insight into the physical state of the intergalactic medium in the vicinity of starburst galaxies. Finally, we compare our findings with the results from the cosmological smoothed particle hydrodynamics simulations (OWLS).

December 8, 2010

 "A Direct Measurement of the Intergalactic Medium Opacity to H I Ionizing Photons"

Jason X. Prochaska, Assoc Professor, UCO/Lick Observatory, UC Santa Cruz


Winter 2011

January 12, 2011

 "Metal Transport to the Gaseous Outskirts of Galaxies"

Jessica Werk,
IMPS Postdoctoral Fellow,

 Neutral hydrogen gas often extends far beyond the stellar component of galaxies in forms ranging from relatively quiescent extended disks to tidally stripped tails. Despite its ubiquity, knowledge of gas enrichment levels outside the stellar components of galaxies has remained somewhat limited. In this talk, I will describe a search for outlying HII regions in the gaseous outskirts of extended, disturbed, and/or interacting gas-rich galaxies, and subsequent Gemini Telescope multi-slit spectroscopy from which I obtain the nebular oxygen abundances of numerous outlying and centrally-located HII regions. Then, I will present oxygen abundance gradients out to 2.5 times the optical radius for 13 gas-rich galaxies that span a range of morphologies and masses. By analyzing the underlying stellar and neutral HI gas distributions in the vicinity of the HII regions, I attempt to identify the physical processes that could give rise to the observed metal distributions in galaxies. These measurements, for the first time, convincingly show flat abundance gradients at large radii in a wide variety of systems, and have important implications on the efficiency of metal transport in galaxies, the star-formation history of outer-disk material, and the potential expulsion of metals into the intergalactic medium.

January 19, 2011

 "Black Hole Growth and Star Formation in the Local Universe"

Aleksandar Diamond-Stanic,
CGE Postdoctoral Fellow,

 I will present results regarding black hole accretion rates and star-formation rates in galaxies hosting active galactic nuclei (AGNs). I will use these results to identify biases in our census of black hole growth, to probe fundamental differences between obscured and unobscured AGNs, and to explore the connection between black hole growth and galaxy evolution.

January 26, 2011

 "The Synoptic All Sky InfraRed Survey (SASIR): a bi-national astrophysics project"

William Lee,
Instituto de Astronomia, UNAM

 The SASIR project aims at a deep, multi-color all sky survey in the near IR (YJHK) with a wide-field, 6.5m Magellan-class telescope to be constructed at the site of the Observatorio Astronomico Nacional in San Pedro Martir, Baja California. SASIR would repeatedly image the sky every 3 months during the nominal survey duration of at least 4 years, providing an unprecedented view of the transient sky and identifying objects suitable for follow-up on 10m-class facilities with spectroscopic capability. The science case of SASIR touches upon practically all areas of astronomy, and ranges from the study of nearby brown dwarfs to the high-redshift Universe, and the connection to the neutrino and gravitational wave skies. The project is a bi-national collaboration between the major astronomical institutions in Mexico, and the Universities of California and Arizona in the US. Besides giving an overview of the current state of affairs regarding the science case, I will touch on technical issues related to the site, telescope and camera, as well as on partnership and development issues.

February 4, 2011

 "The Role of Gas in the Evolution of Disk Galaxies"

Allyson Brooks,
Fairchild Postdoctoral Fellow,

 A realistic model for the formation of galaxy disks depends on a proper treatment of the gas in galaxies. Historically, cosmological simulations of disk galaxy formation have suffered from a lack of resolution and a physically motivated feedback prescription. Recent computational progress has allowed for unprecedented resolution, which in turn allows for a more realistic treatment of feedback. These advances have led to a new examination of gas accretion, evolution, and loss in the formation of galaxy disks. Here I highlight the role that gas outflows, inflows, and the regulation of gas by feedback play in achieving simulated disk galaxies that better match observational results as a function of redshift.

February 7, 2011

 "Galaxy Formation: Science at the Intersection of Diverse Physics"

Brant Robertson,
Hubble Postdoctoral Fellow,

 Understanding galaxy formation requires a wide-ranging array of physics including dark matter, cosmology, gas dissipation, radiative transfer, chemical enrichment, and hydrodynamics. While this scientific breadth makes for a challenging problem, the large range of astrophysics involved also makes galaxy formation a fun and promising field for long-term research. In this talk, I will present an overview of selected outstanding theoretical problems in early galaxies, star formation on galactic scales, and the formation of dark matter halos, along with some recent successes that have inevitably posed further questions about how galaxies form and evolve.

February 9, 2011

 "Runaway Growth and the Late Stages of Planet Formation: Explaining the Kuiper belt Size Distribution"

Hilke Schlichting,
Hubble Postdoctoral Fellow,

 The Kuiper belt, located at the outskirts of our planetary system, is a remnant of the primordial Solar system where planet formation never reached completion. It provides a snapshot of earlier stages of planet formation that were erased elsewhere in the Solar system and it is therefore an ideal laboratory for testing planet formation theories. In my talk, I will focus on the size distribution of Kuiper belt objects, which contains many important clues concerning their formation, their effective strength and their collisional evolution. I will present recent analytic and numerical results of the runaway growth phase during planet formation that successfully explain the size distribution of large Kuiper belt objects and I will discuss recent results from our HST survey, which probes the size distribution of small Kuiper belt objects by stellar occultations.

February 16, 2011

 "The Quest to Measure the Reionization History"

Matt McQuinn,
Einstein Postdoctoral Fellow,

 One of the missing chapters in our cosmological narrative involves how most of the gas in the Universe, which we know was neutral a few hundred thousand years after the Big Bang, eventually became highly ionized. First, I will discuss models for, and observational diagnostics of, the reionization of the second electron of helium by quasars. I will argue that the evidence is now fairly convincing that this process was ending at z~3 and discuss the implications. In contrast, the exact redshifts and sources of hydrogen reionization remain uncertain. I will review our current state of knowledge regarding this epoch. I will discuss attempts to model hydrogen reionization, highlighting the successes and shortcomings of present day numerical models, and conclude by stressing the potential richness of forthcoming observations of this epoch.

February 18, 2011

 "Radiative Transfer Modeling of Lyman Alpha Emitters and New Effects in Galaxy Clustering"

Zheng Zheng,
Postdoctoral Fellow
Yale Center for Astronomy & Astrophysics, Yale University.

 Lyman Alpha Emitters (LAEs), galaxies selected by their Lya emission, are becoming an important probe of galaxy formation, cosmic reionization, and cosmology. Correct interpretations of the growing observations of LAEs require us to take into full consideration the radiative transfer (resonant scattering) of Lya photons. For this purpose, a Monte Carlo Lya radiative transfer code is applied to a state-of-the-art cosmological reionization simulation to study z~5.7 LAEs. It is the first time that realistic radiative transfer modeling of LAEs is performed in a cosmological volume. The study reveals a coupling between the observed Lya emission and the circumgalactic and intergalactic environments induced by the resonant scattering of Lya photons. Such an environment-dependent radiative transfer effect alone is able to explain an array of observed properties of LAEs. In addition, it gives rise to interesting new features in the clustering of LAEs. The study leads to a completely new framework for understanding LAEs, with important implications for using LAEs to study reionization and cosmology.

February 23, 2011

 “How do galaxies get their gas?”

Dusan Keres
Hubble Postdoctoral Fellow

 Most galaxies are actively star forming at all epochs. However, there is not enough gas in galaxies to support evolution of star formation activity over time. This suggests that galactic gas is being replenished from the intergalactic medium. I use cosmological hydrodynamic simulations to study the physics of gas supply into galactic component. At high redshift infall of cold filamentary gas dominates accretion rates of all galaxies. This cold mode accretion differs from the standard model of galaxy formation in which cooling of the hot halo atmospheres is a source of galactic gas. Cold mode accretion is a major driver of active star formation of high-z galaxies enabling such activity to proceed for a significant fraction of the Hubble time. At low redshift hot virialized gas can cool in some of the halos, but gaseous clouds that form in infalling filaments bring the cold gas into galaxies such as Milky Way. In this talk I will describe properties, physics and consequences of gas accretion processes as well as predictions for a variety of observational probes of cold halo gas that can provide strong constraints on the models. I will also discuss remaining open questions and future directions in the studies of galactic gas accretion, including new computational methods and observations with upcoming facilities.

March 16, 2011

 "Gravitational Wave Detection through Pulsar Timing"

Joris Verbiest,
Marie Curie Fellow,
Max-Planck-Institut für Radioastronomie,
Bonn, Germany

 Radio timing of millisecond pulsars (MSPs) has allowed some of the most precise tests in astrophysics to date, including the first indirect detection of gravitational waves, in 1982. Almost 30 years later, the direct detection of gravitational waves - and the birth of gravitational wave science - is predicted to be achieved by the same means. Specifically, simulations of hierarchical galaxy formation models predict a population of supermassive black-hole binaries in the nearby (z<2) Universe. These binaries would emit gravitational waves that would affect pulsar timing at the 10 to 100 ns level, over timescales of years to decades. In this talk I present results from the first sizeable long-term MSP timing campaign, confirming that the timing precision required for gravitational wave detection is achievable within the next decade. I further comment on how this gravitational wave sensitivity can be improved through ongoing pulsar surveys, detailed studies of the ISM, accurate pulsar distance estimates and the next generation of radio telescopes.

Spring 2011

March 30, 2011

 "Phases, Morphologies, and Magnetic Fields in the Diffuse Interstellar Medium"

Carl Heiles
Astronomy Professor
UC Berkeley

 In this broad-based talk, we describe some aspects of the diffuse interstellar medium (ISM) as revealed by actual data--old and new,radio to X ray. Page 6 of a new book by Bruce Draine entitled Physics of the Interstellar and Intergalactic Medium, lists the four basic phases of the ISM. How about the fifth phase--which seems to be best revealed by interstellar magnetic fields? His Chapter 29 is entitled HI Clouds: Observations. What do HI Clouds look like? Can gravity ever be important for diffuse atomic structures in interstellar space? His page 104 mentions the Local Hot Bubble, revealed long ago by the first soft X-Ray emission maps and, also, by the more complete ROSAT maps. But not so fast--it might not be so hot! Everybody hates magnetic fields--they are hard to observe and hard to treat theoretically. Does the magnetic field really matter at all?

April 6, 2011

 "The Contribution of Evolved Stars to the Near-IR Luminosities of Galaxies: Implications for Stellar Mass Estimates of High Redshift Galaxies"

Jason Melbourne,
Postdoctoral Scholar,

 Stellar mass estimate of galaxies are typically made by measuring the luminosity of a galaxy and modeling the mass/light ratio. Because near-IR (NIR) luminosities are less affected by dust obscuration and less driven by current star formation than optical wavelengths, they have been employed extensively to estimate the stellar masses of galaxies, especially at high redshift using Spitzer imaging. However, certain phases of late-stage stellar evolution have been shown to contribute dramatically to the NIR luminosity of galaxy while contributing negligible mass. Unless these phases are well calibrated, stellar mass estimates of galaxies can be systematically wrong by large fractions. Using resolved stellar populations of local galaxies from HST WFC3, we demonstrate that current stellar populations synthesis codes over-predict the numbers of asymptotic giant branch branch stars, for the measured star formation history. Simultaneously, these codes tend to under-predict the numbers and luminosities of luminous red helium burning stars. We explore the implications of these two results for stellar mass estimates of galaxies at high redshift.

April 13, 2011

 "What I cannot create, I do not understand": A galaxy builders toolkit

Andrew Benson,
Senior Research Fellow,

 Galaxy formation is an intricate process and observations of galaxies have complex relations to the underlying physical quantities. I will argue that to prove we have understood the physics of galaxy formation requires that we be able to create model universes which are indistinguishable from our observed Universe. I will describe a recently developed toolkit, Galacticus (, which aims to meet this challenge by providing a coherent framework within which to compute expectations about galaxies across all wavelengths, mass scales and redshifts. To demonstrate the flexibility and power of this approach I will highlight some of my recent work: I will explain how observations of Local Group galaxies can constrain the properties of decaying dark matter models, and describe the detectability of evolving hydrogen and helium ionization fronts around primordial galaxies. Additionally, I will present predictions for the evolution of dust-enshrouded star formation across cosmic history in advance of next generation sub-mm observatories. I will end by discussing the potential for future improvement of our galaxy formation theory.

April 20, 2011

 "Probing dark matter, reionization and the expansion history of the Universe with Lyman-alpha in absorption"

Martin Haehnelt,
Cambridge University

 The Lyman-alpha forest in QSO absorption spectra is a sensitive probe of the matter distribution as well as the physical state of the Intergalactic Medium. I will present constraints on the mass of (warm) dark matter particles and discuss the ionization state of the Intergalactic Medium at $z>5$. I will further discuss prospects of measuring the redshift drift and improving constraints on the variability of fundamental constants with the ultra-stable high-resolution spectrograph CODEX proposed for the E-ELT.

May 4, 2011

 "The ups and down of star formation: What regulates star-formation in galaxies?"

Nicolas Bouche,
Marie Curie Postdoctoral Fellow,
UC Santa Barbara

 Globally, the efficiency to form galaxies is low, only 5% of the baryons made it into stars. Moreover, this efficiency is a strong function of mass, and peaks at around 20% for halos similar to the Milky Way. What causes this efficiency to decline in low mass galaxies? Feedback is traditionally invoked for various reasons. Accretion, however, can have an big impact as well. We will address this central issue of galaxy formation efficiency and discuss the role of feedback and accretion in regulating the global properties of galaxies.

May 18, 2011

 "ALMA Science"

Jean Turner,
Professor of Astronomy,
UC Los Angeles

 Asteroids and moons, debris disks, star formation of all kinds and at all distances, dust and gas masses, gas dynamics of disks of many flavors, secular evolution of galaxies, galaxy interactions and mergers, cosmic pyrotechnics, and monster-feeding are among the many topics that can be studied with the Atacama Large Millimeter/Submillimeter Array, ALMA, now being constructed in the high, dry Atacama Desert. I will discuss the capabilities of this new instrument and describe many of the explorations of the extraterrestrial world that are possible with ALMA both in its Early Science incarnation, and in full ALMA, with a bias toward studies of extreme star formation in local galaxies.

June 1, 2011

 "Discovering Galactic Disks, Mergers, and Weak AGN in High-Redshift Star Forming Galaxies"

Shelley Wright,
Hubble Postdoctoral Fellow,
UC Berkeley

 Studies of galaxies in the early universe (z > 1) have greatly benefited from recent advances in diffraction-limited techniques on 8-10m telescopes using adaptive optics (AO) and integral field spectroscopy. These innovative spectrographs have led to significant scientific achievements and are stimulating the design of future instrumentation. My talk will focus on development and use of the latest near-infrared instruments behind Keck Observatory's AO system. I will present OSIRIS and Keck AO 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 and 2D capability of an integral field spectrograph has 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 on extremely large telescopes (30m), which will offer extraordinary potential to probe the dynamics, assembly, and abundances of galaxies in the early universe.

Summer 2011

June 22, 2011

NOTE: "Special Astrophysics Lecture, 12-1pm in SERF 329
 "New constraints on neutrino physics from the CMB"

Alessandro Melchiorri, Sapeinza University of Rome

June 29, 2011

 "Characterizing the Stellar/Substellar Boundary: An Overview of the HLIMIT Project at Georgia State University"

Sergio (Serge) Dieterich, Doctoral Student in Astronomy, Georgia State University - RECONS

 The last fifteen years have seen a revolution in stellar astronomy with the discovery and characterization of the substellar brown dwarfs and the creation of the spectral classes L and T. Despite considerable efforts from both an observational and theoretical perspective, the population properties of objects with masses close to the theoretical hydrogen burning limit are still poorly understood. In this talk I will outline a series of observational projects my collaborators and I are undertaking to better characterize this population. I will place special emphasis on our recent results regarding M dwarf multiplicity, and briefly discuss what we expect to learn from our other projects.

August 24, 2011

NOTE: "Special Astrophysics Seminar, 12-1pm in SERF 329"
 "Inflation, Reionization, and All That: The Primordial Inflation Explorer"

Al Kogut, NASA Goddard, WMAP Co Investigator

 The Primordial Inflation Explorer is an Explorer-class mission to measure the gravity-wave signature of primordial inflation through its distinctive imprint on the linear polarization of the cosmic microwave background. PIXIE uses an innovative optical design to achieve background-limited sensitivity in 400 spectral channels spanning 2.5 decades in frequency from 30 GHz to 6 THz (1 cm to 50 micron wavelength). The principal science goal is the detection and characterization of linear polarization from an inflationary epoch in the early universe, with tensor-to-scalar ratio r < 10^{-3) at 5 standard deviations. The rich PIXIE data set will also constrain physical processes ranging from Big Bang cosmology to the nature of the first stars to physical conditions within the interstellar medium of the Galaxy. I describe the PIXIE instrument and mission architecture needed to detect the inflationary signature using only 4 semiconductor bolometers.

August 25, 2011

NOTE: "Special Astrophysics Seminar, 4-5pm in SERF 329"
 "Current Status of ASIAA"

Paul Ho, Distinguished Research Fellow, Academia Sinica; Director of ASIAA; Lecturer, Harvard-Smithsonian Center for Astrophysics

August 31, 2011

NOTE: "Special Cosmology Seminar, 12-1pm in SERF 329"
 "Surfing effects in Cosmology"

Alex Polnarev, Queen Mary University of London

 When propagating in the vicinity of a single monochromatic Gravitational Wave (GW), an Electromagnetic Wave (EMW) experiences phase modulations (PMs). When calculating the PMs generated by the random GW background one should integrate the dispersion of the PMs generated by GWs over angles between the wave vectors of these GWs and line of sight. If these angles are small, the EMW and GW are nearly in-phase and their interaction looks like the propagation of EMW through a nearly constant gravitational field. In this case PMs are proportional to the distance passed by EMW through GW (a cumulative change in the phase of the EMW) and can give a considerable contribution to the dispersion of random PMs in the random field of cosmological GWs. Due to the transverse nature of both EMWs and GWs, the Surfing Effect leads to significant cumulative PM only if the phase velocity of GWs is smaller than the phase velocity of EMWs (for example, in the case of GWs and EMWs interaction in plasma). The PM analysis which takes into account the SE could be very important in application to cosmological birefringence (CB) due to parity violating Chern-Simons modifications of standard electromagnetism. Such modification results in ‘slow’ and‘fast’ modes of circularly-polarized light. The fast mode traveling with a phase speed larger than the speed of light in vacuum, can experience cumulative PMs due to the SE. This is a potentially observable effect which could modify the angular (multipole) dependence of CMB polarization and could be used for separation of instrumental systematics from CB. This could be considered as an essential observational application of Cosmology to the fundamental Physics of Fields.