Talks & Events
KICP Friday Noon Seminars: 2014
First WIMP search results from the Large Underground Xenon experiment
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.
Star Formation in a Galactic Context
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.
The chemo-dynamical structure of the Milky Way
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.
Assessing the Role of Stellar Feedback from Small to Large Scales
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.
Very High Energy Photons from Distant Blazars and the Potential for Cosmological Insight
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.
Chasing the Cosmic Dawn with 21 cm Tomography
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.
Axions and Moduli in Cosmology: from the Primordial Epoch to Galaxy Formation
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.
Cosmology with the Cosmic Microwave Background: Past, Present and Future
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.
Cosmology with Lyman-alpha forest
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.
Excess of Diffuse Gamma-ray Emission from the Inner Galaxy: Bubbles, Jets, and Dark Matter
Our analysis of data from the Fermi Gamma-ray Space Telescope revealed a pair of large gamma-ray bubble structures, named the Fermi bubbles, each extending ~10 kpc above and below the Galactic center. I will present new results using five years Fermi-LAT data and multi-wavelength observations of the Fermi bubbles in X-ray, microwave, and radio, including updates from dedicated observations. New observations help us to distinguish hadronic from leptonic origin of the cosmic-ray electrons emitting gamma-ray/radio emission, and constrain the magnetic field within the Fermi bubbles. I will also show our numerical simulations which demonstrate that the bubble structure could be evidence for past accretion events and outflow from the central supermassive black hole. Furthermore, we recently found gamma-ray evidence for large-scale collimated jet-like structure penetrating through the bubbles from the Galactic center, which might provide further evidence of a past activity in the Galactic center. We have proposed to change the survey strategy of Fermi to increase the exposure at the inner Galaxy by more than a factor of 2. This new survey strategy has been initiated since December 2013 and will last for at least one year. I will end up with a discussion of future gamma-ray space missions.
Science with CMB Spectral Distortions: a New Window to Early-Universe Physics
Since COBE/FIRAS we know that the CMB spectrum is extremely close to a perfect blackbody. There are, however, a number of processes in the early Universe that should create spectral distortions at a level that is within reach of present day technology. I will give an overview of recent theoretical and experimental developments, explaining why future measurements of the CMB spectrum will open up an unexplored window to early-universe and particle physics, with possible non-standard surprises but also guaranteed signals awaiting us.
Measuring the Power Spectrum of Dark Matter Substructure with Gravitational Lensing
The abundance of substructure within dark matter halos surrounding galaxies has been an area of intensive study for over a decade. Quantifying the small-scale structure of dark matter halos, which is influenced by the spectrum of primordial density fluctuations and the micro-physics of dark matter, can allow us to probe multiple areas of fundamental physics. Observationally, however, very little is known about the true abundance and the structure of dark matter sub-halos. In this talk, I will discuss the promising prospects of using ALMA and the recently discovered populations of strong gravitational lenses in mm/submm-wave surveys (SPT, Herschel, ACT, Planck) for mapping the small-scale structure of galaxy halos. In particular, I will show that we can measure the power spectrum of dark matter substructure by analyzing the correlations in perturbations of strongly lensed images. I will show that the large number of discovered lenses and the spectacular power of ALMA paint a bright future for a robust characterization of the small-scale structure of dark matter halos.
The Weak Lensing Signal and Clustering of SDSS-III CMASS Galaxies
AMS-02 latest results
First measurement of pp neutrinos in real time in the Borexino detector
Neutrino astrophysics and the low and high energy frontier