Astronomy Colloquia

January 16, 2013 | 15:30, BSLC 115 | Host: Angela V. Olinto
Imaging instruments for the cosmic frontier
Juan Estrada, Fermilab
Note: Refreshments served at 3PM, TAAC 71
This talk reviews the current technology used for wide field optical imaging in astronomy, with emphasis in the recently commissioned Dark Energy Camera. This technology has enabled new experiments in the cosmic frontier that are starting to produce results now. Finally, during this talk, I discuss how this field is transforming to allow future astronomical instruments with unprecedented scientific potential.

January 30, 2013 | 15:30, BSLC 115 | Host: Angela V. Olinto
Neutron Star Radii and Masses
Feryal Ozel, University of Arizona
Note: Refreshments served at 3PM, TAAC 71
Neutron stars offer the unique possibility of probing the equation of state of cold, ultradense matter. Understanding the properties of the neutron star interior is also important for predicting the observational appearance of short gamma-ray bursts, the end stages of neutron star coalescence, and the outcomes of supernova explosions. I will present the recent measurements of neutron star radii and masses. I will show how the combination of the tightly constrained radii and the discovery of a 2 solar mass pulsar allows for the first astrophysical inference of the pressure of cold matter above nuclear saturation density. I will discuss the implications of this measurement for nuclear theory and astrophysics.

February 6, 2013 | 15:30, BSLC 115 | Host: Angela V. Olinto
Towards ab initio simulations of star formation in turbulent molecular clouds
Alexei Kritsuk, University of California, San Diego
Note: Refreshments served at 3PM, TAAC 71
Understanding how molecular clouds form in the interstellar medium and how they evolve to produce dense cores that eventually give birth to stars is an important unsolved problem in star formation. From a theoretical perspective, star formation is a challenging multi-scale problem that involves complex nonlinear interactions of gravity, turbulence, magnetic fields, radiation and feedback processes. I shall describe a self-consistent computational framework for modeling molecular cloud formation in the multiphase ISM as a first step to generate realistic initial conditions for star formation. Our approach is based on self-organization in the turbulent ISM and, with only a few control parameters, numerical experiments successfully reproduce the observed probability distributions of the molecular gas density, thermal pressure, magnetic field strength, as well as the core mass function. I shall briefly discuss the origin of Larson's scaling relations that naturally emerge in the model.

February 20, 2013 | 15:30, BSLC 115 | Host: Angela V. Olinto
Gamma-ray detections of cosmic-ray acceleration by supernova remnants
Elizabeth Hays, NASA
Note: Refreshments served at 3PM, TAAC 71
Supernova remnants have been considered prime suspects as accelerators of cosmic rays within our Galaxy for a long time. Gamma-ray observations have offered the promise of turning that suspicion into certainty for almost as long, but only recently high-energy gamma-ray telescopes, both the Fermi Large Area Telescope and AGILE, have provided data that can be used to look for direct evidence of protons in these sources. I will present the new results from Fermi that reveal the proton signature in two supernova remnants and put this in context with the growing catalog of GeV remnants detected by LAT and the remaining questions to be answered about Galactic cosmic rays.

March 13, 2013 | 15:30, BSLC 115 | Host: Angela V. Olinto
The Road to 100 Earths
Debra Fischer, Yale University
Note: Refreshments served at 3PM, TAAC 71
The search for planets orbiting nearby stars has been one of the greatest success stories of the past decade, with hundreds of discoveries being made using Doppler, transit, microlensing, and direct imaging techniques. More than 2300 candidates have been detected with NASA's Kepler mission. Exoplanet detections have launched a subfield of astronomy that includes host star characterizations, measurements of planet radii and density, studies of atmospheres, interior structure, formation theory, and orbital evolution. The search for exoplanets is motivated by the question of whether life exists elsewhere. This drives our interest in the detection of planets that are similar to our own world: rocky planets with the potential for liquid surface water and plate tectonics; worlds that might harbor life that we can recognize. Importantly, we will need to discover not just a few, but hundreds of these worlds to eventually gain a statistical understanding of whether life is rare, common, or ubiquitous and ground-based telescopes offer an ideal platform for carrying out decade-long surveys. It is critical for follow-up studies (imaging, atmospheric studies) that these planets orbit nearby stars rather than stars at distances of the typical Kepler field star. In this talk, I will discuss how we plan to take what we've learned and push on to the next frontier: a search 100 Earths.

April 24, 2013 | 15:00, BSLC 115
High redshift starburst galaxies revealed by SPT, ALMA, and gravitational lensing
Joaquin D. Vieira, California Institute of Technology
The South Pole Telescope (SPT) has systematically identified a large number of high-redshift strongly gravitationally lensed starburst galaxies in a 2500 square degree cosmological survey of the millimeter (mm) sky. These sources are selected by their extreme mm flux, which is largely independent of redshift and lensing configuration. The flux magnification provided by the gravitational lensing enabled us to perform a spectroscopic redshift survey with the recently commissioned Atacama Large Millimeter Array (ALMA). We targeted 26 SPT sources and obtained redshifts via molecular carbon monoxide (CO) lines. We determine that roughly 40% of these sources lie at z>4, indicating the fraction of dusty starburst galaxies at high-redshift is far higher than previously thought. Two sources are at z=5.7, placing them among the highest redshift starbursts known, and demonstrating that large reservoirs of molecular gas and dust can be present in massive galaxies near the end of the epoch of cosmic reionization. These sources were additionally targeted with high resolution imaging with ALMA, unambiguously demonstrating them to be strongly gravitationally lensed by foreground structure. We are undertaking a comprehensive and systematic followup campaign to use these "cosmic magnifying glasses" to study the infrared background in unprecedented detail, inform the condition of the interstellar medium in starburst galaxies at high redshift, and place limits on dark matter substructure. I will discuss the scientific context and potential for these strongly lensed starburst galaxies, give an overview of our team's extensive followup efforts, and describe our latest science results.

May 8, 2013 | 15:00, KPTC 106 | Host: Michael Gladders
Infalling groups and galaxy evolution in the IMACS Cluster Building Survey
Alan Dressler, Carnegie Institution of Washington Observatories
Note: Refreshments will be served at 4:00 in LASR.
From a photometric/spectroscopic study of galaxy clusters at z~0.4, using the wide field of the IMACS instrument on the Magellan-Baade telescope, we have studied infalling galaxies that were building typical rich clusters 4 billion years ago, and compared them to field galaxies at that epoch over the full range of galaxy environment. The results emphasize the important role of infalling groups of galaxies in building a cluster, and provide evidence that significant quenching of starforming galaxies occurs in such groups --- in both the cluster and field environment. Our study also suggests a new interpretation of the role that starbursts play in galaxy evolution.