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Events on Thursday, April 1st, 2021

Cosmology Journal Club
Time: 12:00 pm
Abstract: Each week, we start with a couple scheduled 15-20 minute talks about one's research, or an arXiv paper. The last part will typically be open to the group for anyone to discuss an arXiv paper.

All are welcome and all fields of cosmology are appropriate.

Contact Ross Cawthon, cawthon@wisc, for more information.

Zoom info
Meeting ID: 93592708053, passcode: cmbadger

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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
New results from the Hydrogen Epoch of Reionization Array
Time: 2:30 pm
Speaker: Danny Jacobs, Arizona State University
Abstract: Observations of the 21cm hydrogen line in the early universe (redshifts 25 to 5) are expected to shed light on the origins of stars, inflation, and dark matter. First generation interferometers have placed ever-lower limits on the fluctuation power spectrum and the EDGES experiment has reported a potential global absorption trough at redshift 18. The Hydrogen Epoch of Reionization Array (HERA) is a second generation instrument which aims for a high significance power spectrum measurement between redshifts 5.5 and 12 and experimental observations to redshift 18. In 2016 HERA was operated with 20% of its collecting area. This data has been used to develop a pipeline which has produced what is currently the lowest power spectrum upper limit. I will report on these results and describe our upgrade campaign for the full array aimed at lowering systematic floors and expanding the redshift range to 25.

The speaker will be available for one-on-one meetings on Monday April 5 - Weds April 7. If you would like to meet with the speaker, please contact Peter Timbie to set up an appointment.
Host: Peter Timbie
Presentation: zoom_20210401.txt
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Astronomy Colloquium
How do galaxies in the nearby Universe grow?
Time: 3:30 pm
Place: Zoom meeting(see Abstract ) Coffee and tea 3:30pm, Talk 3:45pm
Speaker: Sanchayeeta Borthakur,, Arizona State
Abstract: Galaxy growth is a slow but continuous process. The observed properties of galaxies suggest that accretion must continue to support star formation. However, direct observational evidence of gas flows into galaxies have been extremely hard to come by. One of the most promising regions in our search has been the disk-halo interface, where we are uncovering signs of gas condensation.

In this talk, I will discuss the results from our ongoing DIISC (Deciphering the Interplay between the ISM, Stars, and the CGM) survey, which probes the disk-halo interface. I'll discuss our findings in terms of the signpost of gas accretion and galactic feedback. I'll also show evidence that structures such as high-velocity clouds and extra-planar gas seen in the Milky Way and a few other galaxies are indeed prevalent in most galaxies. These gaseous structures represent a pathway for gas accretion into galaxies and can be one of the primary ways how galaxies accrete gas in the nearby Universe.
Zoom Link
Host: Professor Amy Barger UW Astronomy
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Thesis Defense
Exploring the Use of Signal Envelopes for Neutrino Detection with In-Ice Radio Arrays
Time: 4:00 pm
Speaker: Benjamin Hokanson-Fasig, Physics PhD Graduate Student
Abstract: Neutrinos are unique cosmic messengers that can be used to probe the universe for sources of ultra-high energy cosmic rays. In order to detect the highest energy neutrinos, which are expected to interact very rarely, a large detector volume is necessary. The Askaryan Radio Array (ARA) and similar neutrino detectors use the Antarctic ice as their detector volume, searching for radio signals from neutrino-induced particle showers in the ice. This detection technique results in radio neutrino detectors that are highly sensitive to neutrinos with energies above 10 PeV. This thesis explores the possibility of using envelopes of the voltage signals from antennas in ARA to perform neutrino searches. A detector making use of signal envelopes could have a significantly lower power consumption, making it an attractive option in power-limited regions like Antarctica. By reproducing the reconstruction method used in previous ARA analyses, a reconstruction using signal envelopes is shown to be able to reconstruct the location of a neutrino event in the ice with an error of 1--2 degrees. However, since the ARA stations are not optimized for this method, the use of signal envelopes for a complete analysis of ARA data is ultimately found to be unrealistic. In the absence of a direct comparison between the previous ARA analysis and a signal-envelope analysis, further applications of the signal envelope are proposed, including detector geometries that are more optimized for envelope analysis as well as options for using signal envelopes to lower the trigger threshold of radio neutrino detectors.
Host: Kael Hanson, Faculty Advisor
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