2020
Tuesday Lunch Seminar: Ani Chiti (MIT), "An extended halo around an ancient dwarf galaxy"
12:00–1:00 pm Zoom
The Milky Way is surrounded by dozens of ultra-faint dwarf galaxies. These systems are the remnants of some of the earliest galaxies as suggested by their ancient (~13 Gyr) and chemically primitive stellar populations. In this talk, I will present the detection of extremely metal-poor stars ([Fe/H] < -3.0) out to 9 half-light radii in one such galaxy, Tucana II. This is the first detection of a population of stars outside the core region (~4 half-light radii) of any ultra-faint dwarf galaxy. These distant stars are, on average, more metal-poor than the central population (<[Fe/H]>=-3.0 vs. <[Fe/H]>=-2.6) and suppress the mean metallicity to <[Fe/H]> ~ -2.77. This difference is the first evidence of a metallicity gradient in an early galaxy remnant and suggests Tucana II, and perhaps other ultra-faints, plausibly were influenced by early, strong feedback episodes or a galactic merger. Such distant stars also imply that Tucana II harbors a massive, spatially extended dark matter halo (> 10^7 solar masses out to 1 kpc). Collectively, these results suggest that key factors needed for understanding early galaxy formation and chemical evolution lie in the outskirts of these small, relic galaxies and may have been missed by previous observational studies. I will thereby also present an upcoming photometric survey of all southern-hemisphere ultra-faint dwarf galaxies that will reveal any spatially extended stellar populations, which our results suggest is necessary to understand the early evolution of these relic systems.
KICP Seminar: Brittany Kamai (University of California Santa Cruz and Caltech)
12:00–1:00 pm Zoom Room
Brittany Kamai, University of California Santa Cruz and Caltech, “Envisioning and Creating the Future of Gravitational-wave Astrophysics”
A&A Colloquium: Tonia Venters (Goddard)
3:30–4:30 pm Zoom - for link, please contact, Laticia Rebeles, lrebeles@oddjob.uchicago.edu
“Multimessenger Astronomy with POEMMA”
Abstract: The highest energy cosmic rays are the messengers of the most extreme physics in the cosmos; however, efforts to identify their origins have thus far been thwarted by the fact that they don’t point back to their sources. On the other hand, interactions between ultra-high energy cosmic rays (UHECR) and the lower energy particles that they encounter either within their sources or over the course of their cosmic journey will give rise to high-energy neutrinos. The Probe of Extreme Multi-Messenger Astrophysics (POEMMA) is a space-based probe-class mission concept for measuring ultra-high energy cosmic rays (UHECRs) and detecting high-energy cosmic neutrinos via fluorescence and optical Cherenkov signals from their extensive air showers. Using a stereo configuration of two satellites, POEMMA will perform precision measurements for UHECRs above 20 EeV, providing a significant increase in statistics at the highest energies and exposure over the entire celestial sky. POEMMA will also search for Cherenkov signals from tau neutrinos above 20 PeV converting in the Earth near the limb. POEMMA’s design will also feature the capability to slew by as much as 90 degrees in 500 s, allowing for rapid response to target-of-opportunity alerts. We discuss the prospects for multimessenger astronomy with POEMMA, including cross-correlation UHECR anisotropy searches, the detection of the diffuse astrophysical neutrino flux at greater than PeV energies, and the search for high-energy neutrinos associated with transient astrophysical phenomena.
Open Group Seminar: Chun-Hao To (Stanford University)
1:30–2:30 pm Zoom Room (online)
Chun-Hao To, Stanford University, “Cosmological constraints from a joint analysis of cluster abundances, galaxy correlations, and weak gravitational lensing in the Dark Energy Survey”
KICP Seminar: Brandon Hensley (Princeton)
12:00–1:00 pm
Brandon Hensley, Princeton, “New Perspectives on Polarized Dust Foregrounds for CMB Science”
KICP Colloquium: Anthony Pullen (NYU)
3:30–4:30 pm Zoom Room (online)
Anthony Pullen, NYU, “Line Intensity Mapping: Modeling & Analysis in the Precision Era”
Tuesday Lunch Seminar: Jose Maria Ezquiaga and Zhouwen Zhang (UChicago)
12:00–1:00 pm Zoom
Jose Maria Ezquiaga (UChicago), “The relevance of gravitational wave lensing phase shifts”
Zhuowen Zhang (UChicago), “Effects of Cluster Triaxiality on Stacked Weak Lensing Analysis”
KICP Seminar: Nicholas Rodd (UC Berkeley)
12:00–1:00 pm Zoom Room
Nicholas Rodd, UC Berkeley, “Evidence the 3.5 keV line is not from dark matter decay”
A&A Colloquium: Sarah Vigeland (University of Wisconsin at Milwaukee)
3:30–4:30 pm Zoom - TBA
“Supermassive Black Holes and Merging Galaxies: Low-Frequency Gravitational Wave Detection with Pulsar Timing Arrays”
Observations have shown that nearly all galaxies harbor massive or supermassive black holes at their centers. Gravitational wave (GW) observations of these black holes will shed light on their growth and evolution, and the merger histories of galaxies. Pulsar timing arrays (PTAs) use observations of millisecond pulsars to detect low-frequency GWs with frequencies ~1-100 nHz, and can detect GWs emitted by supermassive black hole binaries, which form when two galaxies merge. In this talk, I will discuss the current status of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) PTA, with an emphasis on results from our most recent search for the GW background. I will also discuss future prospects for detecting and characterizing GWs from individual supermassive binary black holes with PTAs.
Open Group Seminar: Yi-Kuan Chiang (Ohio State University)
1:30–2:30 pm Zoom Room
Yi-Kuan Chiang, Ohio State University, “Probing The Cosmic Energy Density Inventory With Tomographic Intensity Mapping”