January 8, 2014 | 3:00 PM | BSLC 115 | Astronomy Colloquium Dwarf Galaxies: The Nexus of Dark Matter and Chemical Evolution Evan Kirby, University of California, Irvine
The Local Group's dwarf galaxies are near enough for exquisitely detailed, resolved stellar spectroscopy and diverse enough to conduct experiments on dark matter and chemical evolution. I have collected medium-resolution spectra for thousands of stars in many dwarf galaxies in the Local Group. Innovative techniques applied to these spectra recover velocities precise to a few km/s and detailed abundances precise to 0.1 dex. Although Milky Way satellites and field dwarf galaxies are different in many ways, their velocity dispersions show that both types of galaxy pose a serious challenge to cold dark matter. Both types also obey the same mass-metallicity relation despite the large diversity of star formation histories and detailed abundance ratios.
January 15, 2014 | 3:00 PM | BSLC 115 | Astronomy Colloquium From Reionization to Dark Matter with the Lyman-alpha Forest George Becker, Institute of Astronomy, University of Cambridge
Absorption lines in the spectra of distant quasars offer one of the most powerful probes of cosmic structure. The Lyman-alpha forest traces the baryons in the intergalactic medium (IGM) over several decades in scale. The properties of the baryons, in turn, reflect the ongoing interaction between luminous objects and the IGM, as well as the nature of dark matter itself. I will present recent results from a suite of projects focused on determining some of the most basic properties of the high-redshift IGM, including its temperature, ionization state, and small-scale density structure. These measurements are providing new insights into when and how the IGM was reionized, the properties of high-redshift galaxies, as well as the viability of warm dark matter. I will also discuss how upcoming IGM studies with current and next-generation facilities will advance our understanding of these and other topics.
January 22, 2014 | 3:00 PM | BSLC 115 | Astronomy Colloquium To Build an Elliptical Galaxy Jenny Greene, Princeton University
PDF I will discuss two essential aspects of elliptical galaxy formation: how they get their stars, and how they lose their gas. For the former, I use integral-field observations of local massive galaxies to study the stellar populations and kinematics of stars at large radius, to understand the origin of the size growth of elliptical galaxies. Then I focus on black hole feedback as a means of clearing gas from massive galaxies. I show that luminous obscured quasars have ubiquitous, round ionized outflows with very high gas dispersions of nearly 1000 km/s out to 20 kpc. Finally, if time permits I will combine these two themes and present our recent search for sub-pc supermassive black hole binaries.
January 29, 2014 | 3:00 PM | BSLC 115 | Astronomy Colloquium Direct Imaging of Extrasolar Planets Bruce Macintosh, LLNL
With current technology, young (<100 Myr) planets can be directly imaged - resolved from their parent star - in the near-infrared with adaptive optics. I will discuss the first system of extrasolar planets to be imaged - the four planets orbiting the young F0 star HR8799. The outer two planets have been characterized spectroscopically using adaptive optics on the Keck telescope, showing non-equilibrium chemistry as well as evidence of composition enhanced in C/O from the original stellar nebula. The supply of young stars in the solar neighborhood suitable for such searches has been essentially exhausted. Providing a statistically significant sample of planets, and accessing Jupiter-like masses and separations, will require dedicated instruments. The Gemini Planet Imager is one such facility, combining advanced adaptive optics with a coronagraph and near-infrared integral field spectrosgraph. Designed to be an order of magnitude more sensitive than current instruments, GPI had first light in November 2013. I will present results here.
February 5, 2014 | 3:00 PM | BSLC 115 | Astronomy Colloquium The role of ultra-luminous galaxies in galaxy formation and evolution Scott Chapman, Dalhousie University (Canada)
PDF I will provide an overview of ultra-luminous galaxies (L_IR>10^12 Lsun) at high redshift, and the different roles and properties they appear to exhibit as a function of their luminosity. I will focus on the molecular gas properties of the galaxies as the crucial fuel available for star formation, emphasizing our recent work with ALMA and the IRAM Plateau-de-Bure, where we have studied galaxies preselected at various wavelengths, and conducted blind surveys for CO gas. I will conclude with wide field surveys that are uncovering the most extreme specimens of star forming galaxies in the universe, and point to future facilities which will push the field to a new level of understanding.
February 12, 2014 | 3:00 PM | BSLC 115 | Wednesday colloquium LSST Steve Kahn, Stanford National Accelerator Laboratory
February 19, 2014 | 3:00 PM | BSLC 115 | Astronomy Colloquium Rest-frame Optical Spectra: A Window into Galaxy Formation at z~2 Alice Shapley, UCLA
PDF Rest-frame optical spectroscopy provides basic insight into the stellar and gaseous contents of galaxies. Until now, our knowledge of the rest-frame optical spectroscopic properties of galaxies at 1.5<=z<=3.5 has been extremely limited, despite the critical importance of this cosmic epoch for the assembly of galaxies and the growth of black holes. The recent commissioning of the MOSFIRE spectrograph on the Keck I telescope represents a major development for the study of the rest-frame optical properties of high-redshift galaxies. The MOSFIRE Deep Evolution Field (MOSDEF) Survey fully exploits the new capabilities of MOSFIRE, charting the evolution of the rest-frame optical spectra for ~2000 galaxies in three distinct redshift intervals spanning 1.5<=z<=3.5 -- more than an order of magnitude improvement over existing surveys. With MOSDEF, we address key questions including: What are the physical processes driving star formation in individual galaxies? How do galaxies exchange gas and heavy elements with the intergalactic medium? How are stellar mass and structure assembled in galaxies (in situ star formation vs. mergers)? What is the nature of the co-evolution of black holes and stellar populations? In this talk I will present early science results from the MOSDEF survey.
February 26, 2014 | 3:00 PM | BSLC 115 | Wednesday colloquium Dark Energy Survey: Early Results Brian D Nord, Fermilab
PDF The expansion of the universe is accelerating, a discovery that earned the 2011 Nobel Prize in physics. Is cosmic acceleration due to "dark energy," or do we need to modify Einstein's General Relativity? If it is a new form of energy, is it constant or changing in time? Addressing these questions is the primary goal of the Dark Energy Survey (DES). After achieving first light in 2012, followed by months of commissioning and science verification, DES has just completed its first season of science observations at the Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory in Chile. The DES Collaboration built a new 570-megapixel digital imager, the Dark Energy Camera (DECam), to carry out a deep, wide survey over the course of five (5) years---observing thousands of Type-Ia supernovae and hundreds of millions of galaxies. The thick, red-sensitive imager will allow us to see more supernovae and galaxies at higher redshift than previous surveys, like the Sloan Digital Sky Survey (SDSS). These observations will provide a suite of cosmological signatures: the Supernova Hubble diagram, galaxy cluster number counts, large-scale galaxy clustering and weak gravitational lensing. With this data, we will probe both the cosmic expansion history and the growth of large-scale structures, and thus explore the nature of dark energy. I will discuss the motivation for DES, the first years of operation and early results.
March 5, 2014 | 3:00 PM | BSLC 115 | Wednesday colloquium News from the Extreme Energy Cliff Angela Olinto, The University of Chicago
PDF Thanks to giant extensive air-showers observatories, such as the Pierre Auger Observatory and the Telescope Array, we now know that the sources of ultrahigh energy cosmic rays (UHECRs) are extragalactic. We also know that either they interact with the CMB as predicted or they run out of energy at the same energy scale of the CMB interactions! Their composition is either surprising (dominated by heavier nuclei at the highest energies) or the hadronic interactions at 100 TeV are not a standard extrapolation of LHC interaction energies. Hints of anisotropies begin to appear as energies reach 60 EeV, just when statistics become very limited. Basic questions remain unanswered: What generates such extremely energetic particles that reach above 10^20 eV (100 EeV)? Where do they come from? How do they reach these energies? What are they? How do they interact on their way to Earth and with the Earth's atmosphere? To answer these questions larger statistics at the highest energies is necessary. Space-based observatories can significantly improve the exposure to these extremely energetic particles. The first step to answer these questions is to place a wide field UV telescope at the International State Station to monitor the Earth's atmosphere from above. This is the goal of the JEM-EUSO mission: the Extreme Universe Space Observatory (EUSO) at the Japanese Experiment Module (JEM).
March 12, 2014 | 3:00 PM | BSLC 115 | Wednesday colloquium Taking the Measure of Dark Energy with DESI Natalie Roe, LBNL
January 10, 2014 | 12:00 PM | LASR Conference Room | Friday noon seminar First WIMP search results from the Large Underground Xenon experiment Blair NV Edwards, Yale University
The Large Underground Xenon (LUX) experiment, a dual-phase xenon time-projection chamber operating at the Sanford Underground Research Facility (Lead, South Dakota), was cooled and filled in February 2013. An overview of the experiment and detection techniques will be provided followed by results of the first WIMP search dataset, taken during the period April to August 2013, presenting the analysis of 85.3 live-days of data with a fiducial volume of 118 kg, demonstrating the path to the world-leading sensitivity of the LUX experiment.
January 17, 2014 | 12:00 PM | LASR Conference Room | Friday noon seminar Star Formation in a Galactic Context Adam Leroy, National Radio Astronomy Observatory
Gas accretion from the cosmic web and its transformation into stars drives the evolution of galaxies. Consequently, the formation of molecular clouds and then stars are significant steps in our cosmic origins. Understanding these processes in a galactic context represents a major, long-standing goal of astronomy. New facilities across the spectrum, including ALMA, at last give us the tools to identify the physical drivers of these processes across the galaxy population. I will discuss our current knowledge and future prospects focusing on three key steps: the emergence of a molecular interstellar medium, the formation of dense gas within this medium, and the formation of stars from this dense gas. Each of these processes represents a limiting step across a key part of the galaxy population, from dwarf galaxies to starbursts. In particular, I will show how an interplay of metallicity and gravity drives the molecular abundance and show how dense, turbulent superclouds drive the enhanced efficiency in starbursts. Finally, I will highlight the exciting prospects for rapid progress in this field using the awesome spatial resolution and sensitivity to physical conditions of the next generation of long wavelength instruments.
January 24, 2014 | 12:00 PM | LASR Conference Room | Friday noon seminar The chemo-dynamical structure of the Milky Way Jo Bovy, Institute for Advanced Study
Observations of the structure and dynamics of different stellar populations in the Milky Way's disk provide a unique perspective on disk formation, evolution, and dynamics. I will review our current knowledge of the chemo-orbital structure of the disk and its implications for our understanding of how the Milky Way formed and evolved. In particular, I will show recent results from a dissection into mono-abundance populations (MAPs) of the Galactic disk based on SDSS/SEGUE data. These results show that the individual components are simple, but exhibit very different spatial and kinematic structure, with important implications for the formation and evolution of the Milky Way's disk. I will further present a new dynamical measurement of the MW's surface density between 4 and 10 kpc, obtained by rigorous 3-integral modeling of the vertical kinematics of MAPs. Combined with the latest measurements of the MW's rotation curve, this allows us to separate the disk and halo contributions to the gravitational potential and to measure the mass of the MW's stellar disk.
January 31, 2014 | 12:00 PM | LASR Conference Room | Friday noon seminar Assessing the Role of Stellar Feedback from Small to Large Scales Laura Lopez, Massachusetts Institute of Technology
Stellar feedback has a profound influence in many astrophysical phenomena, yet it is often cited as one of the biggest uncertainties in galaxy formation models today. This uncertainty stems from a dearth of observational constraints as well as the great dynamic range between the small scales (<1 pc) where feedback occurs and the large scales (>1 kpc) of galaxies that are shaped by this feedback. In this talk, I will show how multiwavelength observations can be used to overcome these challenges and to assess the role of many stellar feedback mechanisms (e.g., radiation, photoionization, stellar winds, supernovae, protostellar outflows, and cosmic rays). I will present results from the application of this approach to a variety of sources and discuss the implications regarding the dynamics of star-forming regions. Finally, I will highlight the exciting prospects of using current and upcoming facilities to explore feedback in the diverse conditions of nearby galaxies and to probe the effect of feedback on molecular gas properties.
February 7, 2014 | 12:00 PM | LASR Conference Room | Friday noon seminar Very High Energy Photons from Distant Blazars and the Potential for Cosmological Insight Amy Furniss, Stanford University
Gamma-ray blazars are among the most extreme astrophysical sources, harboring energetic phenomena far beyond that attainable by terrestrial accelerators. These galaxies are understood to be active galactic nuclei that are powered by accretion onto supermassive black holes and have relativistic jets pointed along the Earth line of sight. The very high energy photons emitted by these extragalactic sources are detectable with ground based imaging atmospheric Cerenkov telescopes such as VERITAS. As these photons propogate extragalactic distances, the interaction with the diffuse starlight that pervades the entire Universe results in a distance and energy dependent gamma-ray opacity, offering a unique method for probing photon densities on cosmological scales. These galaxies have also been postulated to be potential sources of ultra-high-energy cosmic rays, a theory which can be examined through the deep gamma-ray observations of sources which probe moderate gamma-ray opacities.
February 21, 2014 | 12:00 PM | LASR Conference Room | Friday noon seminar Chasing the Cosmic Dawn with 21 cm Tomography Joshua S Dillon, MIT
Realizing the promise of 21 cm cosmology to provide an exquisite probe of astrophysics and cosmology during the cosmic dark ages and the epoch of reionization has proven extremely challenging. We're looking for a small signal buried under foregrounds orders of magnitude stronger. We know that we're going to need very sensitive, and thus very large, low frequency interferometers, which present their own set of difficulties. And, as I will explain, we're going to need a rigorous statistical analysis of the maps we make to extract interesting cosmological information. I will discuss the steps we've taken to overcome these obstacles with prototype data from the Murchison Widefield Array by isolating foregrounds to a region of Fourier space outside a clean ''epoch of reionization window.'' Additionally, I will present some of most recent and exciting predictions for what 21 cm cosmology can tell us as we move to larger telescopes and higher redshifts.
February 28, 2014 | 12:00 PM | LASR Conference Room | Friday noon seminar Axions and Moduli in Cosmology: from the Primordial Epoch to Galaxy Formation David J. E. Marsh, Perimeter Institute
Axions and Moduli are ubiquitous in theories of beyond the standard model particle physics, in particular those containing SUSY and/or extra dimensions. The mass scales of these particles are unknown and so priors are important and can be motivated by various considerations, including naturalness, least information, or even within string theory. When masses span a large range, so do the cosmological phenomena produced. In this talk I will explore two aspects of the physics of axions and moduli with relevance to cosmology and astrophysics. Firstly, I will discuss the generation of perturbations in dark matter and dark radiation during and following inflation, and how, using CMB data, these constrain the inflationary epoch and SUSY. In the second half of the talk I will discuss late time dark matter phenomenology of axions. Ultra-light axions can behave as "Fuzzy" dark matter, and imprint a characteristic scale on structure formation. For a particular range of masses this scale is relevant to the small-scale problems of cold dark matter, and can out-perform a warm dark matter solution. I will close with discussing future prospects from data and challenges for theoretical techniques.
March 7, 2014 | 12:00 PM | LASR Conference Room | Friday noon seminar Cosmology with the Cosmic Microwave Background John Carlstrom, The University of Chicago
From its discovery 50 years ago through recent measurements of its fine angular scale anisotropy, the study of the cosmic microwave background (CMB) has led to surprises and spectacular progress in our quest to understand the origin, make up and evolution of our universe. We now have a standard cosmological model, LCDM, that fits all cosmological data with only six parameters -- although tensions in the data are beginning to surface. Far from being the last word in cosmology, the model points to exciting times ahead using the CMB to explore new physics, i.e., inflation, dark matter, dark energy, neutrino masses and possibly extra relativistic species, or dark radiation. This talk will review the current status of CMB measurements, with an emphasis on recent results from the South Pole Telescope, and discuss ongoing work and future plans for increasingly sensitive polarization and fine angular scale anisotropy measurements.
March 14, 2014 | 12:00 PM | LASR Conference Room | Friday noon seminar Cosmology from the Lyman-alpha Forest Anze Slosar, Brookhaven National Laboratory
I will discuss recent results from measurements of the Lyman-alpha forest in the spectra of distant quasars by the Baryon Oscillation Spectroscopic Survey (BOSS), part of the Sloan Digital Sky Survey (SDSS-III). Our main success to date is detection of the baryon acoustic oscillation feature at z ~ 2.4 in the three-dimensional correlation function of the transmitted flux fraction. This result is derived from a sample of ~60k quasars in Data Release 9. In a striking confirmation of the standard cosmological model, the position of the baryonic peak is measured with 2% statistical and 1% systematic error and is consistent with the LCDM model. Pending permission from the collaboration, I will present results for the ~140k high redshift quasars in the Data Release 11. In addition and somewhat unexpectedly, we have also detected BAO in the cross-correlation between Lyman-alpha forest and quasar positions. Combination of low and high-redshift BAO measurements allow us to put non-trivial constraints on the cosmological model without inclusion of the CMB data. Finally, I will mention some of the other developments: measurement of the 1D power spectrum of flux fluctuations, first measurements of the Lyman-beta forest power spectrum and renewed efforts to simulate the intergalactic medium responsible for the forest.
February 10, 2014 | 11:00 AM | LASR Conference Room | Open Group seminar Ultra-Relativistic Soliton Collisions Mustafa Amin, University of Cambridge Institute of Astronomy
Solitons appear in many physical models, from scalar field theories in the early universe to optical fibres. What happens when solitons collide? I will show that these collisions simplify considerably when the collision happens at high velocities. For relativistic scalar field theories, I will discuss a perturbative framework based on the suppression of the space-time interaction area where the solitons overlap. Crucially, our perturbation series is controlled by a kinematic parameter, and hence not restricted to small deviations around integrable cases. Our method works best in the high velocity limit when simulations are most difficult. Based on our framework, I will present the nontrivial leading order results for collisions of (1+1) dimensional kinks in periodic potentials. In the end, I will discuss limitations of our technique as well as some applications.