Cosmology Lunchtime Seminar

All future


Monday, September 24th 2018
12:15 pm:
Speaker: Joshua A. Frieman, Fermilab
Subject: Probing Cosmology with the Dark Energy Survey

I will overview the Dark Energy Survey (DES) project and highlight its early science results, focusing on cosmology results from the first year of the survey. The DES collaboration built and is using the 570-megapixel Dark Energy Camera on the Blanco 4-meter telescope at NOAO's Cerro Tololo Inter-American Observatory in Chile to carry out a deep, wide-area, multi-band optical survey of several hundred million galaxies and a time-domain survey that has discovered several thousand supernovae. The survey started in Aug. 2013 and will finish early next year. DES was designed to address the questions: why is the expansion of the Universe speeding up? Is cosmic acceleration due to dark energy or does it require a modification of General Relativity? DES is addressing these questions by measuring the history of cosmic expansion and the growth of structure through multiple complementary techniques: galaxy clusters, the large-scale galaxy distribution, weak and strong gravitational lensing, and supernova distances, as well as through cross-correlation with other data sets, particularly the cosmic microwave background. I will also briefly discuss how the DES data are being used in unexpected ways, from probing dark matter with newly discovered ultra-faint dwarf galaxies to a new probe of the Hubble constant using the kilonova counterpart of a binary neutron star gravitational-wave source.

Faculty Host: Vuk Mandic

Monday, October 1st 2018
12:15 pm:
Speaker: Iary Davidzon, IPAC/Caltech
Subject: Probing the early universe *without* JWST

The James Webb Space Telescope (JWST) will not be the only breakthrough for high redshift (z>~3) studies. Exquisite data are coming from Subaru and Spitzer telescopes, eventually covering a large area of the sky (~25 sq deg) at an unprecedented depth. Probing such a large cosmic volume will allow to collect a statistically significant sample of rare, massive galaxies still undetected in pencil-beam HST surveys. In this talk I present "pathfinder results" from the COSMOS field, showing the importance of rare massive objects to constrain star formation efficiency and stellar-to-halo mass relationship at z>3. In the same context, I also discuss present limitations from an observational point of view and how they affect our understanding of galaxy evolution (e.g. the so-called "Eddington bias").

Faculty Host: M. Claudia Scarlata

Monday, October 8th 2018
12:15 pm:
Speaker: Ali Kheirandish, UW - Madison
Subject: The first evidence for the origin of high-energy cosmic neutrinos: multimessenger observation of a flaring blazar

For the first time since the discovery of high-energy cosmic neutrinos in IceCube, a distant gamma ray blazar was identified as a high-energy neutrino source. This represents the first evidence for the origin of very high energy cosmic rays. In this talk, I will review the status of high-energy cosmic neutrino flux measurements and how a multimessenger campaign led to the identification of blazar TXS 0506+056 as the origin of a high energy neutrino. Furthermore, I will discuss how archival data searches showed that the high-energy neutrino flux from the source is dominated by a neutrino burst, which implies flaring sources strongly contribute to the cosmic ray flux. I investigate the contribution of a subclass of flaring blazars to the high-energy neutrino flux and speculate on its connection to the very high-energy cosmic ray observations.

Faculty Host: Vuk Mandic

Monday, October 15th 2018
12:15 pm:
Speaker: Chris Pankow, Northwestern
Subject: TBD (LIGO)
Faculty Host: Vuk Mandic

Monday, October 22nd 2018
12:15 pm:
Speaker: Wenlei Chen, Washington University
Subject: Novel search for TeV-initiated pair cascades in the intergalactic medium

The observed magnetic fields in galaxies and galaxy clusters are believed to result from dynamo amplification of weak magnetic field seeds whose origin remains a long-standing open question. Beams of TeV gamma-rays from blazar jets can be used to infer the intensity, coherence length, and helicity of the intergalactic magnetic field. Intergalactic magnetic fields deflect the electron-positron pairs produced by TeV gamma-rays from blazars, resulting in broadened beams of secondary GeV gamma-rays known as pair halos. Such pair-cascades develop along the projected direction of the blazar jet, which is known from imaging radio observations. We searched for GeV pair halos in Fermi-LAT data around 12 high-synchrotron-peaked BL Lacs with well-determined jet orientation from VLBA radio observations. Our study exploits the expected asymmetry of blazar pair halos and uses advanced simulations of the pair cascades to improve the sensitivity of previous studies and increase the signal to noise. Although we find no significant detection, a 2-sigma hint for an extended pair halo along the direction of the jet appears in the stacked LAT data in the 30-300 GeV energy range, corresponding to an intergalactic magnetic field with strength of about 1E-15 Gauss. This magnetic field value is consistent with similar hints from independent studies using LAT data. We will present the results of our analysis and discuss the limitations of pair-halo searches due to astrophysical uncertainties. Finally, assuming that the apparent convergence on B ~ 1E-15 G is not coincidental, we will outline a clear path towards a positive detection of blazar pair halos with future space-borne and ground-based gamma-ray observatories.

Faculty Host: Patrick Kelly

Monday, October 29th 2018
12:15 pm:
Speaker: Clem Pryke, UMN
Subject: New BICEP/Keck Results
Faculty Host: Vuk Mandic

Monday, November 5th 2018
12:15 pm:
Speaker: Guillermo Fernandez Moroni, Fermilab
Subject: TBD (CCD Detectors)
Faculty Host: Vuk Mandic

Monday, November 12th 2018
12:15 pm:
Speaker: TBD
Subject: TBD
Faculty Host: Vuk Mandic

Monday, November 19th 2018
12:15 pm:
Speaker: Soumyajit Mandal, Case Western Reserve University
Subject: Ultra-steep-spectrum Sources in Galaxy Clusters
Faculty Host: Thomas W. Jones

Monday, November 26th 2018
12:15 pm:
Speaker: Sharan Banagiri, UMN
Subject: TBD (long duration transient searches with LIGO/Virgo)
Faculty Host: Vuk Mandic

Monday, December 3rd 2018
12:15 pm:
Speaker: Karl Young, UMN
Subject: TBD
Faculty Host: Shaul Hanany

Monday, December 10th 2018
12:15 pm:
Speaker: Rich Ormiston, UMN
Subject: TBD (Machine Learning and LIGO)
Faculty Host: Vuk Mandic

The weekly calendar is also available via subscription to the physics-announce mailing list, and by RSS feed.